Materials doi: 10.3390/ma19102043

Authors: Qunjiao Wang Jiangong Zhou Dapeng Wang Jun Miao Chunming Liu

The effects of Ti/Nb microalloying-induced MC-type carbide precipitation and tempered microstructure evolution on the dry-sliding wear behavior of low-carbon martensitic wear-resistant steels were systematically investigated. Three experimental steels with different microalloying strategies (0.04Ti, 0.1Ti, and 0.04Ti/Nb) were subjected to quenching and subsequent tempering. Microstructural features, carbide characteristics, and mechanical properties were characterized using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), tensile testing, and impact testing, while wear performance was evaluated by pin-on-disk tests under dry-sliding conditions. The results indicate that wear resistance is governed by the combined effects of tempered martensite stability and MC-type carbide precipitation. Low-temperature tempering effectively reduces the wear mass loss of Ti-containing steels by enhancing their resistance to abrasive shear deformation while maintaining sufficient toughness. In contrast, the Nb-containing steel exhibits a stage-dependent wear response associated with the formation and destabilization of oxide-derived third-body debris during sliding. (Nb,Ti)C precipitates act as microscale load-bearing units, contributing to strength enhancement and subsurface damage suppression, but their influence on wear behavior strongly depends on tempering temperature. The dominant wear mechanism is abrasive micro-cutting, accompanied by fatigue-induced spalling and oxidation-assisted damage at later stages. These results demonstrate that wear performance cannot be correlated with hardness alone, but instead requires the coordinated optimization of carbide precipitation and tempered microstructural stability. This work provides microstructural guidance for the design of microalloyed martensitic wear-resistant steels.

Materials doi: 10.3390/ma19102044

Authors: Yucheng Liu Yunhai Ma

In the field of materials engineering, friction, wear, and corrosion are key factors that constrain the service performance and lifespan of materials, and have long been extensively studied by both academia and industry [...]

Materials doi: 10.3390/ma19102042

Authors: Jerzy Zgraja

The article concerns the issue of simultaneous determination of material parameters of electrical conductors. In reference to previous work on a non-contact measurement station enabling the simultaneous determination of electrical and thermal properties of conductive materials, the concept of its extension to include magnetic measurements was analyzed by adding a module for determining the magnetization characteristics of ferromagnetic conductors, integrated with the station. The accuracy of determining the magnetization characteristics of a flat sample closing a magnetic circuit based on a U-shaped ferrite core with using a triangular excitation signal with a frequency of several kilohertz was analyzed through simulation and initially verified experimentally. Based on the measurement systems used, relationships enabling estimation of the magnetization characteristics were developed, and the influence of the geometric parameters of the magnetic circuit and the excitation signal parameters on the magnitude of the measurement error was presented.

Materials doi: 10.3390/ma19102040

Authors: Jaroslaw Piatkowski Mateusz Wojciechowski Tomasz Matula Katarzyna Nowinska

This article presents preliminary research on the development of a cast iron–ceramic composite for modern braking systems, such as brake discs. The composite matrix is gray cast iron with flake graphite (EN-GJL-150). The reinforcing phase is a porous ceramic composed of SiC and Al2O3 particles introduced separately (10% each) and together (70% SiC + 30% Al2O3). These particles were applied as a suspension onto polyurethane foam, yielding a ceramic structure with a pore density of up to 10 ppi. The resulting insert was placed in a mold cavity, and cast iron was poured into it. The resulting samples were treated as brake disc material, with a pad made of the commercial friction material P50094 serving as the countersample. Tribological tests showed that the lowest sample wear (average 2.23 mg/5000 m) was achieved for the composite reinforced with SiC + Al2O3 particles. This is probably due to the synergy between the antifriction properties of these particles and the lower friction coefficient (µ = 0.180–0.22). Similar mass loss values and the smallest difference between the tested samples were observed for composites with SiC particles (3.01 mg/5000 m) and Al2O3 (3.30 mg/5000 m). The second part consisted of microstructural studies. Microstructural analysis of the EN-GJL-150 + SiC + Al2O3 composite revealed a previously unobserved nucleation phenomenon at the cast iron–ceramic interface. This confirmed the general assumptions of Riposan’s theory regarding the involvement of oxide microinclusions and complex manganese sulfides of the (Mn, X)S type in the nucleation and crystallization of graphite precipitates. It was also found that, in the case of “in situ” GJL-150 + SiC + Al2O3 composites, this theory should account for the beneficial role of ceramic particles in promoting the uniform distribution of type A graphite flakes, which nucleate on their surfaces in the transition zone. Thus, the nucleating role of oxide microinclusions (the first stage of Riposan’s theory) could be taken over by SiC and Al2O3 particles, constituting a substrate for the heterogeneous nucleation of (Mn, X)S sulfides.

Materials doi: 10.3390/ma19102041

Authors: Paola Leo Gilda Renna Andrea Amleto De Luca Riccardo Nobile Caterina Casavola Vincenzo Moramarco Simone Carone Michele Angelo Attolico

Additive manufacturing (AM) has revolutionized industrial production. However, the repair of AM components remains a critical challenge due to their unique microstructural features. While repair approaches for conventionally manufactured alloys are well established, their direct transferability to AM parts remains largely unexplored due to the unique thermal history and anisotropic microstructure of additive components. This study investigates a novel repair and improvement strategy for Powder Bed Fusion–Laser Beam/Metal (PBF-LB/M)-fabricated AlSi10Mg components, combining Electrospark Deposition (ESD) for dimensional restoration with subsequent Ultrasonic Peening Treatment (UPT) for surface enhancement. Microstructure, porosity, surface roughness, hardness profiles, residual stresses, and corrosion behaviour were systematically characterized using SEM, optical microscopy, profilometry, Vickers microhardness testing, XRD, and electrochemical polarization tests. The results show that the ESD process is capable of producing coatings with excellent interfacial adhesion to the substrate, with an initial porosity of 3.6 ± 0.5%. The subsequent UPT induces a significant densification effect on the deposited material, reducing porosity by approximately 50% and increasing surface hardness by up to 48% in the upper region of the coating. Furthermore, XRD analysis reveals that UPT completely reverses the residual stress state from tensile (typical of the ESD process) to compressive in all measured directions, thereby improving the overall structural integrity. Ultimately, the combined ESD + UPT alters the electrochemical response of AlSi10Mg deposits, resulting in a nobler corrosion potential, albeit with a slightly higher corrosion current density.

Materials doi: 10.3390/ma19102039

Authors: Shuaixu Chun Haifeng Nie Xiaoyang Guo Tihao Cao Quanxing Ren Qing Sun Zhengren Huang Qing Huang Yinsheng Li

Reaction-bonded SiC (RBSC) ceramics exhibit limited hydrothermal corrosion resistance due to the presence of residual silicon. This study presents a strategy to enhance the corrosion resistance of RBSC through homogeneous incorporation of MoSi2 and concurrent reduction in residual silicon content. Three material systems were fabricated via reactive melt infiltration: conventional RBSC with a SiC/C preform (SC), a SiC–MoSi2 composite incorporating commercial Mo2C powder via physical mixing (MC), and a SiC–MoSi2 composite derived from a Mo2C/C precursor synthesized by a molten salt method (MS). The Mo2C/C composite synthesized at 1150 °C exhibited fine, uniformly distributed Mo2C particles coated on carbon black, contrasting with the agglomerated distribution in commercial Mo2C mixtures. During reactive sintering at 1600 °C, Mo2C reacted with molten Si to form MoSi2, reducing residual Si content. Sample MS achieved the lowest residual Si (8.77 ± 0.45 vol.%), followed by MC (12.43 ± 0.86 vol.%) and SC (19.17 ± 1.01 vol.%). All samples achieved near-full densification (open porosity < 0.1%), with bulk densities of 2.96 ± 0.05, 3.03 ± 0.03, and 3.07 ± 0.03 g/cm3 for SC, MC, and MS, respectively. Microstructurally, MS displayed homogeneous MoSi2 dispersion, while MC showed partial MoSi2 aggregation, and SC contained continuous residual Si regions. Hydrothermal corrosion tests at 345 °C and 15 MPa for 9 days demonstrated that corrosion resistance followed the order MS > MC > SC. After 9 days, weight loss was 22.3970 ± 1.2059 mg/cm2 (SC), 17.6370 ± 0.8266 mg/cm2 (MC), and 15.4347 ± 0.7807 mg/cm2 (MS), with corrosion depths of 393.17 ± 27.46, 267.40 ± 24.44, and 224.60 ± 25.13 μm, respectively. The enhanced performance of MS arises from two synergistic factors: reduced residual Si minimizes large corrosion pores, while uniform distribution of MoSi2 facilitates the formation of a stable, dissolution-resistant composite oxide layer composed of MoO3 and SiO2, in which MoO3 restrains excessive dissolution of SiO2 through a pinning effect. These findings demonstrate that combining residual Si reduction with homogeneous MoSi2 incorporation via molten salt-synthesized precursors offers an effective strategy for improving hydrothermal corrosion resistance of reaction-bonded SiC-based materials for applications in high-temperature and high-pressure aqueous environments such as nuclear water reactors.

Materials doi: 10.3390/ma19102038

Authors: Liang Wang Wendi Li Yunfa Lu Sai Xu

Bacterial cellulose (BC) is a natural nanofibrous material, but its limited functional tunability restricts its use in moisture-management applications. In this study, BC/carboxymethyl cellulose (CMC) composite films were prepared by in situ fermentation using a kombucha-derived high-yield strain, followed by citric acid post-treatment. The films were characterized by FTIR, XPS, XRD, SEM, and physicochemical tests. CMC incorporation regulated the BC nanofibrous network while preserving cellulose I, and citric acid post-treatment promoted possible ester-linkage-assisted network stabilization. The modified films showed improved water-management behavior, water-vapor barrier performance, and mechanical response while maintaining high surface hydrophilicity; notably, BC/CMC-3 reduced the water vapor transmission rate from 106.13 ± 4.24 to 71.07 ± 2.46 g/(m2·24 h). These results suggest that CMC dosage is an effective strategy for tailoring BC-based films for moisture-management applications.

Materials doi: 10.3390/ma19102029

Authors: Changsheng Ye Xin Shan

Ionic thermoelectric (i-TE) materials have attracted increasing attention for low-grade heat harvesting owing to their high thermovoltage output under small temperature gradients. However, the development of n-type i-TE materials remains challenging. Electrode-enabled polarity regulation provides a promising alternative to material-design strategies for developing n-type i-TE devices. In this work, a poly(vinyl alcohol) (PVA)-based ionic hydrogel was prepared with dimethyl sulfoxide (DMSO) and potassium chloride (KCl) through a freeze–thaw process, and its thermoelectric behavior was regulated by electrodes. While the i-TE hydrogel device with typical Cu electrodes exhibited p-type behavior, replacing the electrodes with graphite paper (GP) electrodes converted the device response from p-type to n-type. Morphological and spectroscopic analyses suggest that the GP surface selectively adsorbed K+ ions through cation–π interactions, suppressing cation thermodiffusion and enabling Cl−-dominated ion migration under a temperature gradient. As a result, the PVA-GP device achieved a maximum Si of −4.36 ± 0.26 mV K−1. In addition, the device exhibited favorable thermoelectric output, with a maximum PFi of 57.668 μW m−1 K−2, a room-temperature ZT of 0.0864, and a peak transient power density of 2.33 mW m−2 during short-time discharge. Owing to the large interfacial area of the GP electrodes, the device could also function as an ionic thermoelectric supercapacitor with appreciable energy-storage capability. This work demonstrates an effective electrode-engineering strategy for constructing n-type i-TE devices and provides a feasible route for simultaneous low-grade heat harvesting and transient energy storage.

Materials doi: 10.3390/ma19102037

Authors: Lounis Djenaoucine Álvaro Picazo Miguel Angel de la Rubia Jaime C. Gálvez Amparo Moragues

This study examines the effects of graphene oxide (GO) on the hydration behaviour, microstructure, and mechanical properties of Portland cement-based materials. Cement pastes and mortars incorporating GO at dosages of 0.0005%, 0.005%, and 0.05% by weight of cement were analysed through thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), and mechanical strength testing. TGA results indicate that GO exerts a time-dependent influence on cement hydration. At early ages, GO slightly retards hydration, evidenced by lower C–S–H and CH content in GO-containing samples at 2 and 7 days, attributed to water adsorption by its oxygen-containing functional groups. At later curing ages (28–90 days), TGA results show greater C–S–H and CH weight losses in GO-modified samples compared to the reference, consistent with GO acting as a water reservoir and nucleation site. XRD and SEM results confirm that GO incorporation leads to a reduction in CH crystal size, a denser and more homogeneous microstructure, and fewer pores and microcracks. Mechanical tests revealed that GO contents of 0.0005% and 0.05% produced the most significant improvements, with increases of up to 9% in compressive strength and 16% in flexural strength at 90 days compared with the control specimens. In summary, the incorporation of low GO dosages effectively refines cement microstructure, enhances long-term hydration, and improves mechanical performance, demonstrating GO’s potential as a strength- and durability-enhancing nanomaterial for cementitious composites.

Materials doi: 10.3390/ma19102036

Authors: Małgorzata Maciejewska Grzegorz Wójcik

Porous glycidyl methacrylate-based copolymers crosslinked with ethylene glycol dimethacrylate (EGDMA) and trimethylolpropane trimethacrylate (TMPTMA) were synthesized via suspension–emulsion polymerization and subsequently functionalized with triethylenetetramine. The effect of the monomer composition on the epoxy group content and porous structure was systematically investigated by varying the GMA-to-crosslinker molar ratio from 1:1 to 5:1. Increasing the GMA fraction enhanced the epoxy group content (2.8–5.0 mmol/g) but significantly reduced the specific surface area (333–23 m2/g), indicating a trade-off between functionality and porosity. ATR-FTIR and elemental analysis confirmed successful amine functionalization while preserving a considerable degree of porosity. The modified copolymers were evaluated for Cr(VI) removal, showing strong pH dependence, with maximum efficiency at pH 3 due to electrostatic interactions between protonated amine groups and HCrO4− ions. Equilibrium studies revealed saturation-type behavior, with a maximum sorption capacity of 165.47 mg/g for TMPTMA-based copolymers. Despite the higher nitrogen content in EGDMA-based materials, TMPTMA-crosslinked copolymers exhibited a superior adsorption performance, demonstrating that pore accessibility, rather than functional group density alone, governs adsorption efficiency. These findings provide insight into the rational design of amine-functionalized porous polymer sorbents for efficient chromium(VI) removal.

Materials doi: 10.3390/ma19102031

Authors: Yaoting Zhu Qi Xiong Yuqi Liao Xin Yu Chunpeng Yan

Surface modification processes significantly influence the aggregate characteristics of steel slag and the road performance of asphalt mixtures. Therefore, this study employs four different substances to conduct surface modification treatment on aged steel slag with particle size ranges of 4.75–9.5 mm and 9.5–13.2 mm to determine the optimal surface modification process through macroscopic and microscopic analytical methods. Ultimately, a comparative analysis is performed on the pavement performance of asphalt mixtures incorporating aged steel slag and modified aged steel slag at different volume replacement ratios. Experimental results demonstrate that Epoxy Acrylate-Modified Organosilicon Resin (EAOR) significantly improved the aggregate properties of Aged Steel Slag (ASS), making it a viable alternative to natural stone; under identical conditions, the volume stability of modified aged steel slag (EAOR-ASS) was slightly superior to that of ASS, while the differences in high-temperature stability and low-temperature cracking resistance of the corresponding asphalt mixtures were minimal. Surface modification of ASS with EAOR significantly enhanced the water damage resistance of the asphalt mixture under freeze–thaw cycle conditions, thereby improving the utilization rate of steel slag. Both an increased volume replacement ratio of steel slag and surface modification with EAOR contributed to improved resistance to elastic deformation of the asphalt mixture.

Materials doi: 10.3390/ma19102035

Authors: Abdulwahab Ibrahim Paul Bishop Georges Kipouros

The growing emphasis on environmental sustainability and the need for advanced manufacturing methods have accelerated progress in material processing. Aluminum powder metallurgy (APM) is particularly promising due to aluminum’s low density, high strength-to-weight ratio, and the inherent benefits of the powder metallurgy (PM) process. However, the corrosion resistance of sintered aluminum components remains a significant concern. In this study, shot peening (SP) was employed as a surface modification technique to improve the corrosion behavior of Alumix 321 PM alloy. Samples of the as-sintered and shot-peened Alumix 321 PM alloy, together with the wrought alloy counterpart AA6061, were characterized using non-contact optical profilometry, optical microscopy (OM), and scanning electron microscopy (SEM). Corrosion performance was evaluated in 3.5 wt.% NaCl solution using Tafel extrapolation (TE), cyclic polarization (CP), stair step polarization (SSP), and electrochemical impedance spectroscopy (EIS). The results revealed that shot peening increased surface roughness and significantly reduced the corrosion rate from 0.079 mmpy to 0.004 mmpy for the unpeened and peened samples, respectively. While pitting was the dominant corrosion mechanism in the wrought alloy, the PM alloy exhibited a combination of pitting, crevice, and intergranular corrosion. These findings highlight the potential of SP in enhancing the durability of aluminum-based PM components, offering valuable insights for industrial applications.

Materials doi: 10.3390/ma19102030

Authors: Annie Cavalcante Jorge M. Martins Margarida Lopes de Almeida Cláudio Henrique Soares Del Menezzi Luísa Hora de Carvalho

The construction sector’s drive for sustainability has increased the use of Cross-Laminated Timber (CLT), yet its structural reliability is governed by the integrity of the adhesive bond line. This study evaluates the influence of three one-component polyurethane (PUR) formulations (R1, R2, R3) on the adhesion performance of maritime pine CLT. To isolate adhesive-related effects, lamellas were mechanically classified by modulus of elasticity (MOE) and randomly allocated within stiffness classes. Adhesive characterization through ABES, FTIR, and DSC revealed that R3 exhibited slower cure kinetics (t0 = 5482 s) but higher thermal stability. Mechanical testing showed that all formulations developed structurally effective dry bonds with shear strengths exceeding 7.1 MPa, with R3 achieving significantly higher dry shear and interlaminar strength. However, 24 h water immersion caused a catastrophic strength reduction exceeding 95% across all formulations, shifting the failure mode from the wood substrate to the adhesive layer. DSC analysis identified glass transition temperatures between 28 °C and 32 °C, which are consistent with the potential for moisture-induced plasticization near service temperatures. These results indicate that while slower-curing formulations like R3 enhance bond quality in dense softwoods due to improved interphase formation, all evaluated PUR systems showed significant vulnerability to saturated conditions, suggesting that adequate moisture protection is essential for maritime pine CLT applications.

Materials doi: 10.3390/ma19102034

Authors: Elena A. Vyaznikova Andrey N. Dmitriev Galina Yu. Vitkina Vladimir V. Katayev

The cohesion zone of a blast furnace is instrumental in determining the gas-dynamic regime and the efficiency of reducing gas utilization. The extent of this phenomenon is contingent upon the initial and final temperatures at which iron ore undergoes softening, which, in turn, are determined by the chemical and phase composition, as well as the degree of reduction of the charge. The present study investigated sinter with a basicity (CaO/SiO2) ranging from 1.2 to 3.0 using a combination of methods. The experimental program involved the use of X-ray diffraction (XRD) with refinement using the Rietveld method, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and load-dependent softening tests. It was established that as the basicity increased, the content of the calcium–aluminum silicoferrite (SFCA) binder phase increased from 6.2 to 17.5 wt.%, whilst the amount of hematite decreased from 12.6 to 2.3 wt.%. The softening onset temperature increases from 1185 to 1260 °C, the softening end temperature from 1345 to 1415 °C, and the softening interval narrows from 160 to 155 °C. The evolution of the phase composition of sinter during controlled reduction (0–95%) has been investigated for the first time. It has been demonstrated that the maximum accumulation of wustite (FeO) is attained at a reduction degree of 40–60%, irrespective of the basicity of the substance. It is precisely in this range that the minimum softening start (1040–1065 °C) and end (1170–1210 °C) temperatures are observed, which is associated with the formation of low-melting eutectics. The sinter belongs to the CaO–SiO2–FeO–Al2O3–MgO system, and the softening behavior is governed by the FeO–CaO–SiO2 system where low-melting eutectics form. When the reduction rate exceeds 60%, the metallic phase becomes dominant, leading to an increase in softening temperatures and a narrowing of the cohesion zone. It is evident from the data obtained that the optimal basicity range of the sinter is 2.0–2.5. Furthermore, it is recommended that a reduction degree of at least 60% is implemented in order to improve gas dynamics and increase blast furnace productivity. The findings can be utilized to enhance the efficiency of charge materials and refine mathematical models of the blast furnace process.

Materials doi: 10.3390/ma19102033

Authors: Wookyung Lee Jaeseung Choi Jungkeun Ahn Hanbyul Lee Byungwook Kim Youngsoo Seo Changbun Yoon

Solid-state electrolytes (SSEs) are essential for achieving long-term stability and fast-charging performance in secondary batteries. Although Li1.3Al0.3Ti1.7(PO4)3 (LATP) offers high ionic conductivity, its practical application is restricted by high-temperature sintering requirements and interfacial reduction at the lithium anode. In contrast, Li-based oxide electrolytes can be sintered below 600 °C, offering improved compatibility with conventional electrodes such as graphite and silicon. In this study, a Li2O–LiCl–B2O3–Al2O3 (LCBA)/LATP composite SSE was fabricated via hot-press co-sintering at 600 °C. Composites with LCBA:LATP weight ratios of 8:2, 7:3, 6:4, 5:5, 3:7, and 2:8 were prepared to identify the optimal composition. The 3:7 composite achieved a sintered density of 2.40 g/cm3 and an ionic conductivity of 2.5 × 10−4 S/cm. Phase evolution and sintering behavior were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Compared to single-phase LCBA or LATP, the composite electrolyte exhibited improved interfacial stability and lower interfacial resistance against lithium metal.

Materials doi: 10.3390/ma19102032

Authors: Sichen Guo Yijing Sun Shanxin Li Xuzhou Jiang Dongbai Sun

Developing lightweight materials that simultaneously achieve efficient electromagnetic wave absorption and robust corrosion resistance remains a significant challenge for marine stealth and electromagnetic protection applications. The main obstacle lies in the rational integration of electromagnetic attenuation capability, impedance matching, and corrosion protection. In this work, a multilayer carbon-structured BaTiO3@C nanocomposite (CSTB-x) was successfully fabricated via freeze-drying combined with in situ pyrolysis. During the carbonization process, chitosan (CS) was transformed into a nitrogen-doped multilayer porous carbon framework, while BaTiO3 particles were embedded into the carbon matrix to construct a BaTiO3@C heterostructure. Benefiting from optimized impedance matching and the synergistic contributions of conduction loss, dipolar polarization, and interfacial polarization, CSTB-1.0 delivered a minimum reflection loss (RLmin) of −48.07 dB at 6.16 GHz with a thickness of 3.32 mm, and achieved a maximum effective absorption bandwidth (EAB) of 7.04 GHz at a thickness of 1.88 mm. In addition, CSTB-1.0 exhibited a low corrosion current density (8.93 × 10−6 A/cm2) and a high polarization resistance (7.87 × 103 Ω∙cm2), indicating excellent corrosion protection performance. The enhanced corrosion resistance is mainly attributed to the barrier effect of the multilayer carbon framework and the tortuous diffusion pathways generated by the porous and core–shell structures. Moreover, the material showed a minimum radar cross-section (RCS) value of −41.25 dBsm, demonstrating remarkable electromagnetic scattering suppression capability. These results provide a feasible strategy for the design and fabrication of marine stealth materials with integrated microwave absorption and corrosion resistance.

Materials doi: 10.3390/ma19102025

Authors: Jianping Lai Xin Shen Xiaohu Yuan Zhiming Gao Xiufang Gong Yuhang Zhang Mengli Liu Jiaxin Yu Qiyuan Li Zhiyuan Wei Bingbing Liu

Residual grit particles introduced during grit blasting are important process-induced defects that can significantly affect the interfacial damage evolution of thermal barrier coatings (TBCs) under thermal cycling; however, the coupled effects of thermally grown oxide (TGO) amplitude, grit size, and grit position on crack propagation in the bond coat (BC) remain insufficiently understood. In this work, a two-dimensional finite element model containing residual alumina grit particles was established to investigate the influence of these three factors on the radial stress distribution and crack growth behavior in the BC, and their individual contributions and interaction effects were further quantified using response surface methodology. The results showed that TGO morphology and interfacial grit defects jointly controlled the stress concentration and crack propagation behavior in the BC. Increasing the TGO amplitude intensified the radial tensile stress concentration in the BC and gradually shifted the critical stress region during thermal cycling. Larger grit particles further aggravated the local stress concentration near the grit tips, while the movement of grit particles toward the TGO peak led to a more pronounced increase in stress concentration and crack propagation tendency. The crack growth behavior was found to be consistent with the corresponding stress evolution characteristics. Response surface analysis further revealed that grit size and grit position had much stronger effects on crack propagation than TGO amplitude, and their interaction was the most significant among all factor combinations. The minimum crack length in the BC layer was obtained at a TGO amplitude of 0.01 mm, a grit size of 20 μm, and a position parameter of 0.752, and the predicted value agreed well with the finite element result. This study provides a comparative basis for interfacial damage assessment and grit-blasting parameter optimization in TBCs containing residual grit defects.

Materials doi: 10.3390/ma19102028

Authors: Qingwen Zhang Xiang Yi Zhengxin Li Weixin Zhou Jingxi Liu

This study evaluates fatigue crack growth in marine high-manganese steel LNG (Liquefied Natural Gas) storage tanks under cryogenic conditions. A 3D simulation framework using the M-integral for stress intensity extraction and the VCTD (Vertical Crack Tip Displacement) criterion for path prediction was developed. Parametric simulations showed that crack propagation is strongly directional, with the surface growth rate exceeding the depthwise rate. Fatigue life decreased with increasing initial crack surface length and maximum load but increased with crack inclination angle. In addition, the Mode I stress intensity factor along the depthwise path converged during propagation and rose sharply when the crack depth approached 90% of the wall thickness. An XGBoost-based dual-target model further achieved accurate prediction of crack depth and residual life.

Materials doi: 10.3390/ma19102027

Authors: Shengbo Zhou Gengfei Li Jian Wang Kai Zhang Shengjie Liu

This study systematically investigated the alkali activation behavior of construction waste micro-powder (CWM) to develop a low-carbon, high-performance cementitious material. The activator formulation was optimized, the hydration thermodynamics were analyzed, and a kinetics model was constructed to reveal the reaction mechanism. The composite activator (sodium silicate and Portland cement) exhibited a significant synergistic effect, outperforming single activators. The optimal ratio was determined: 40% CWM, 60% Portland cement, and 8% water glass (modulus 1.0), which balances the system’s alkalinity and silicate modulus. Thermogravimetric analysis revealed a notable net weight gain at 3 days, indicating an ongoing secondary hydration reaction. By 7 days, the main hydration was complete, accompanied by microstructural densification, which confirmed the efficiency of the composite activator. A key contribution was the successful application of the Krstulović–Dabić (KD) model to quantify the hydration mechanism. The hydration process evolved sequentially through nucleation and growth (NG, dominant before 0.05~0.15 h), phase boundary reaction (I), and diffusion (D). The period of 0.21–50 h was governed by both I and D, after which D became the sole rate-limiting step. The model yielded the rate constants (KNG, KI, KD), Avrami exponent (n), and transition points (α1, α2), providing a kinetic explanation for the ‘early strength and rapid hardening’ characteristic. In conclusion, this work establishes a material design framework guided by activator optimization, supported by thermodynamics, and explained by kinetics. The KD model proves to be a powerful tool for deciphering the hydration behavior of alkali-activated CWM, offering theoretical guidance for developing sustainable cementitious materials with controllable performance.

Materials doi: 10.3390/ma19102026

Authors: Krzysztof Granatyr Małgorzata Franus Katarzyna Kalinowska-Wichrowska Adam Masłoń

This study examined alkali-activated granular aggregates produced from biomass fly ash, coal fly ash, and basalt dust. The work focused on multicomponent industrial waste mixtures activated with two sodium silicate-based systems and on the effect of carbonation curing on aggregate properties. Twelve designed mixtures and reference series were evaluated in terms of particle density, water absorption, and mechanical performance. The response to carbonation was also analysed to assess the potential for CO2 uptake. Mechanical performance ranged from low to moderate and depended on mixture composition, activator type, and carbonation treatment. In most cases, the blended activator produced higher strength before carbonation than sodium silicate alone, whereas carbonation frequently reduced strength. Mixtures containing more basalt dust and less biomass fly ash generally showed the most favourable combination of properties. The results indicate that these industrial mineral wastes can be used to produce alkali-activated granular aggregates with adjustable properties, while carbonation curing may additionally contribute to phase changes and limited CO2 binding.

Materials doi: 10.3390/ma19102023

Authors: Xiaohong Jian Haijie He Ji Yuan Haifei Lei Shifang Wang Yuhao Shang Hanying Shou Peixuan He Zihang Ding Ziyu Mao

In an effort to explore the influence mechanism of expanded polystyrene (EPS) foam particle content on the freeze–thaw resistance of geopolymer EPS concrete (GEPSC) and realize the synergistic optimization of freeze–thaw durability and low-carbon performance, systematic tests on the apparent morphology, mass loss rate, and relative dynamic elastic modulus (RDEM) of GEPSC with different EPS contents (30%, 35%, 40%, 45%, 50%, 55%) were conducted via freeze–thaw cycle tests. A parabolic damage model was established based on the theory of damage mechanics, and comparisons were made between GEPSC and conventional EPS concrete (EPSC) in terms of microstructure and carbon emission effect. Results indicate that the freeze–thaw resistance of GEPSC exhibits a nonlinear negative correlation with EPS content, which clarifies the applicable scope of GEPSC with different EPS dosages. The fitting correlation coefficient R2 of the established parabolic damage model is all higher than 0.98, which can accurately predict the evolution law of freeze–thaw damage of GEPSC. The interfacial transition zone of GEPSC is indistinct and the geopolymer matrix presents a denser structure. Compared with EPSC of the same density, the carbon emission of GEPSC is reduced by 45.3%, demonstrating that GEPSC integrates favorable freeze–thaw resistance with prominent environmental benefits. This study provides a scientific basis for the mixed proportion design and engineering application of low-carbon concrete materials in cold regions.

Materials doi: 10.3390/ma19102024

Authors: Anwei Wang Yang Wang Lei Hou Hanxiao Sun Xinyi Xie Jingbo Duan Chen Li Yansen Li

In this paper, the elastic precompression method is employed as a pretreatment technique to investigate the evolution and characteristics of the micro-mechanical properties of metallic glasses. Nanoindentation analysis indicates that pre-compression treatment leads to structural rearrangement within the material, which in turn influences the nucleation and propagation of shear bands, resulting in a transition of serrated flow from a step-like to a wave-like pattern under a 400 MPa load held for 75 min. Crucially, precompression triggers a unique “decoupling” response: hardening alongside elastic softening. Further, this structural evolution is evidenced by the shear transition zone volume calculated using the jump rate method. The shear transition zone volume exhibits a nonlinear trend, initially increasing and then decreasing with increasing compressive strength and holding time, which reflects the kinetic competition mechanism between local shear instability and coordinated atomic rearrangement that arises under precompression. This study elucidates the effect of elastic precompression treatment on the micromechanical properties of a Ti-based metallic glasses, providing a reference for the optimization of plasticity in metallic glasses.

Materials doi: 10.3390/ma19102022

Authors: Shilei Li Jing Liang Li Yu Weiwei Zhang Tian Chang Yu Xia Kai Chen Wen Zhang Yanchao Li Hailong Xu Jianfeng Li

In this study, a continuous coating with a thickness of 20 μm and intimate bonding to the substrate was in situ fabricated on the TZM alloy (Mo-0.6Ti-0.08Zr-0.04C) via high-temperature gas-phase carburization at 1200 °C combined with water quenching, using CO as the carbon transport carrier. The coating possesses a fine equiaxed grain structure with an average grain size of 1.48 μm, and its microhardness reaches 1479 ± 42 HV. This modification process does not sacrifice the inherent strength and ductility of the TZM alloy matrix, while it does reduce the wear volume of the alloy by 78.8% in comparison with the uncoated rolled TZM alloy.

Materials doi: 10.3390/ma19102021

Authors: Mustafa Batikha Adil Tamimi Samer Al Martini

Concrete is regarded as the second most widely used material after water due to its many advantages [...]

Materials doi: 10.3390/ma19102019

Authors: Jifeng Xue Mingyu Zhu Hongjun Liang Haoyu Li

This paper innovatively employs an epoxy-free composite layer with basalt fiber-reinforced polymer (BFRP) and engineered cementitious composite (ECC) to reinforce the two-way concrete slab structure. Five strengthened slabs and one reference slab were tested under biaxial bending moments with four-side simply supported conditions. The thickness of ECC (15, 25, 35 mm) and BFRP grid (1, 2, 3 mm) were selected as two main variables in the test program. The experimental results showed that the cracking and ultimate load of the strengthened slabs were substantially improved. Notably, the cracking pattern was shifted from diagonally concentrated cracks to discontinuous short cracks, with no apparent debonding of the composite layer. As the thickness of the BFRP grid and ECC increases, both the flexural capacity and stiffness improve, with decrease in the maximum deflection and effective utilization rate of steel reinforcement and BFRP grid at mid-span. Furthermore, a theoretical model considering different positional distribution of yield line was proposed to predict the bearing capacity of the strengthened slabs, with the calculated values aligned well with the experimental results. This research highlights the FRP–ECC composite as a robust reinforcement method for two-way slabs, and offers a good design-oriented reference basis in the field.

Materials doi: 10.3390/ma19102020

Authors: Stefano Bellucci

Carbon materials continue to occupy a singular place in materials science because they can be engineered across multiple length scales while retaining a rare combination of low density, high specific performance, chemical tunability, electrical functionality, and processing flexibility [...]

Materials doi: 10.3390/ma19102018

Authors: Guiqin Liang Jian Zhang

Halide double perovskite materials have been used for various applications; their bandgap (Eg) and heat of formation (ΔHf) are their key properties. They can be obtained through calculations based on high-throughput density functional theory (DFT), but such calculations are computationally expensive and time-consuming. Machine learning (ML) has proved to be an effective tool for screening potential materials. The prediction accuracy of ML models strongly depends on both input features and ML algorithms. However, there is no unified feature set with which ML models can effectively distinguish halide double perovskite materials. Although it has been proven that stacking ML models can achieve higher prediction accuracy than individual ML models, little attention has been paid to the optimization of stacking models. To solve these problems, we constructed a new feature set obtained from periodic tables for predicting the Eg and ΔHf of halide double perovskites, and we further proposed a method integrating the nondominated sorting genetic algorithm (NSGA-II) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) decision-making tool for stacking model optimization to predict the Eg and ΔHf of 540 compounds of halide double perovskites. Experimental results from 40 runs of 5-fold cross-validation demonstrate that our proposed new feature set enables ML models to achieve better performance than the original feature set. Moreover, the stacking model optimized by our proposed method yields better predicting performance than that of any individual single model and stacking regression models without optimization, with average improvements of 5.02%, 2.70%, 3.72% and 0.28% in MSE, RMSE, MAE and R2, respectively, in Eg prediction, thus providing more effective guidance for screening potential compounds for solar cells from a large quantity of materials.

Materials doi: 10.3390/ma19102017

Authors: Jianquan Li Xiang Li Ziyong Liang Huailin Fan Qingyu Ma

This study addresses the poor compatibility between resin and reinforcement and the weak interfacial bonding in poly(ether ether ketone) (PEEK)-based composites by preparing several macromolecular silane coupling agents. Three types of coupling agents with different structures were synthesized using hydroxyl-terminated PEEK oligomers, and their structures were confirmed by FT-IR, NMR, and XPS analyses. The molecular weights were determined by GPC, and TG analysis showed that all three coupling agents exhibited good thermal stability. Glass fibers and carbon fibers were surface-modified with these coupling agents. SEM and EDS analyses revealed uniform coatings on the fiber surfaces, accompanied by increases in the characteristic elements of the coupling agents. Mechanical tests showed that the tensile and flexural strengths of the treated composites were higher than those of the untreated ones. DSC and TG results indicated significant improvements in crystallinity and thermal properties. These enhancements are attributed to improved fiber–matrix compatibility and interfacial bonding. Overall, this work establishes a structure-tailored macromolecular silane coupling strategy, providing new insights into structure–property relationships and offering an effective approach to enhance the performance of PEEK-based composites.

Materials doi: 10.3390/ma19102016

Authors: Eva T. B. Smeets Calvin D. Rans René Alderliesten Irene Fernandez Villegas

To ensure safety in structural design, a method to quantify the damage in thermoplastic ultrasonic single-spot-welded Single-Lap Shear (SLS) joints is needed. This paper investigates whether detailed knowledge regarding the shape of the weld is required when using the global compliance to quantify damage. A finite element model using cohesive zone elements is developed in Abaqus to simulate single-spot SLS specimens with varying weld areas, aspect ratios, and damage growth directions, covering damage levels from 0 to 90% of the initial weld area. For each configuration, the relationship between intact weld area and global compliance is evaluated, and the numerical trends are compared to previously published experimental data from similar joints. The results show that weld size and damage growth direction have negligible influence on the relationship between global compliance and weld area, and that weld shape is also insignificant as long as the aspect ratio remains within a practical range; only very elongated welds with an aspect ratio over 4.4, which are unlikely in production, deviate significantly. Global compliance can be used as a reliable indicator of damage in single-spot ultrasonic welds that is insensitive to weld shape. This enables simplified in situ damage monitoring and reduces the need for detailed geometric characterisation during mechanical testing.

Materials doi: 10.3390/ma19102015

Authors: Wei Guo

The perpetual drive for enhanced performance, energy efficiency, and sustainability in sectors like aerospace, automotive, and electronics hinges on the development of advanced materials.[...]

Materials doi: 10.3390/ma19102013

Authors: Fausta Kavaliauskienė Vitoldas Vaitkevičius Karolina Butkutė Maris Sinka Aleksandrs Korjakins

This study investigates the feasibility of incorporating wood-based waste in cementitious composites for extrusion-based three-dimensional (3D) printing through the production of artificial aggregates. Because lignocellulosic residues can retard cement hydration, wood dust was chemically modified with a calcium nitrate-based accelerator and granulated into aggregates using disc granulation. The resulting aggregates were characterized for mechanical robustness, and their influence on cement hydration and microstructural development was evaluated using X-ray diffraction (XRD) and thermogravimetric/differential scanning calorimetry (TG/DSC). The modified aggregates were then incorporated into 3D printable cementitious mixtures to assess fresh-state properties, printability, and mechanical performance. The accelerator affected hydration by increasing bound water content and altering the development of hydration products. The produced aggregates exhibited sufficient crushing resistance for practical handling. The incorporation of artificial aggregates resulted in reduced compressive and flexural strengths compared to the reference mixture. However, the differences between mechanical properties measured in different loading directions were reduced, indicating a more uniform structural response in printed elements. The findings demonstrate that chemically treated wood-based aggregates can be successfully integrated into 3D printable cementitious systems, offering a promising pathway toward more sustainable construction materials.

Materials doi: 10.3390/ma19102014

Authors: Weilin Li Yuguo Fu Hanrui Wang Xingtao Zhang

To mitigate the spatiotemporal mismatch between renewable energy supply and building heating demand, this study proposes a novel non-pressurized shell-and-tube latent heat storage (NP-LHS) device coupled with an air-source heat pump (ASHP) system. To overcome the inherent low thermal conductivity of organic phase change materials (PCMs), the thermal performances of plain, corrugated, and finned tubes were systematically compared using both computational fluid dynamics (CFD) simulations and full-scale experiments. Numerical results indicate that the optimal tube spacing ratio ranges from 1.0 to 1.5. Among the evaluated geometries, the finned tube configuration exhibited superior comprehensive performance. It achieved an exceptionally high PCM volume fraction of 92.5% and dramatically reduced the complete melting time to 180 min—significantly faster than both corrugated (280 min) and bare tubes—while attaining a higher terminal temperature. Full-cycle dynamic experiments further demonstrated that integrating the finned tube NP-LHS into the ASHP system yielded a peak-shaving power reduction rate of 98.0%, effectively maintaining indoor thermal comfort. These findings conclude that expanding the conductive surface area via fins is practically more effective than inducing fluid turbulence for low-conductivity PCMs in non-pressurized storage applications.

Materials doi: 10.3390/ma19102012

Authors: Szabolcs Rosta László Gáspár

In Europe, bitumen classification has traditionally relied on empirical tests, namely penetration and the Ring and Ball softening point, originally developed for unmodified binders and considered insufficient for modern modified binders. As an alternative, a rheology-based method, the Bitumen Typisierungs Schnell Verfahren (BTSV) rapid bitumen categorization method, has been developed in Germany to characterize high service temperature performance, with performance requirements introduced in 2025 in the German specifications. In this study, the performance of five bitumen types commonly used in Hungarian road construction was investigated using the BTSV method. During testing, the softening temperature corresponding to a rheological threshold value of G* = 15.0 kPa (TBTSV) and the phase angle (δBTSV) were determined. TBTSV is defined as the temperature corresponding to G* = 15 kPa, representing the softening state, while δBTSV reflects the viscoelastic balance between elastic and viscous behaviour. The objective of this study is to evaluate the high-temperature performance of commonly used Hungarian bituminous binders using the BTSV method and to compare the results with traditional empirical parameters and German classification systems. A total of 137 binder samples from production control were tested and analysed, including paving-grade, SBS-modified, and chemically stabilized rubber-modified binders. Statistical evaluation included mean values and 95% confidence intervals. For rubber-modified bitumens, the recoverable, insoluble rubber content was determined using the Soxhlet extraction method. Based on the results, it can be concluded that with increasing rubber content, the TBTSV value shows an increasing trend, while the δBTSV value decreases. As discussed in the paper, a strong linear relationship was observed between the investigated parameters in the TBTSV–δBTSV diagram, with a coefficient of determination of R2 = 0.99.

Materials doi: 10.3390/ma19102011

Authors: Zhongfa Mao Zhancheng Gu Yufeng Xie Wei Guo Xiulin Ji

Selective laser melting (SLM) offers significant potential for fabricating lightweight 316L stainless steel lattice structures (LSs), while forming defects and microstructural heterogeneity remain challenging, especially in fine struts. In this study, response surface methodology (RSM) and analysis of variance (ANOVA) were employed to quantify the coupled effects of geometric parameters (forming angle, FA; rod diameter, RD) and processing parameters (laser power, LP; scanning speed, SS; hatch spacing, HS) on the mass deviation (MD) of fine struts. The results show that FA and RD are the dominant factors affecting MD within the investigated parameter range, whereas LP and SS exhibit comparatively weaker effects. Representative samples with different FA and RD were further characterized by SEM, XRD, and EBSD to examine the associated microstructural evolution. The observations indicate that changes in FA and RD are accompanied by variations in solidification morphology, defect distribution, crystallographic texture, and GND density. Higher FA is associated with lower MD and stronger texture alignment along the building direction, whereas larger RD tends to promote columnar growth and enhanced texture intensity. These results suggest that geometric parameters can serve as effective design variables for tailoring forming deviation and representative microstructural characteristics of fine struts in SLM-fabricated 316L lattice structures.

Materials doi: 10.3390/ma19102010

Authors: Xi He Jiangyong Pei Xiaocai He Ruidong Xu

Ultrafine spherical Ag powders with narrow particle size distribution, high tap density, and limited agglomeration are important conductive fillers for advanced photovoltaic paste formulation. Current liquid-phase reduction scale-up is limited by uncontrolled nucleation, secondary agglomeration, and precursor passivation. This study investigates a process-integrated synthesis chain from precursor preparation to pilot-scale powder production from precursor preparation to kilogram-scale production. A flow-field-enhanced dissolution process (70–80 °C, 30–40% HNO3) alleviates silver ingot passivation, while a multi-stage NaOH spray system reduces NOx emissions to 186 mg/m3, meeting GB31573-2015 standards. Ascorbic acid kinetically decouples nucleation and growth per the LaMer model. Molecular dynamics simulations and RDF analysis reveal a synergistic dispersion mechanism involving PVP and gum arabic. A purpose-built 20 L pilot reactor with optimized fluid dynamics and high-pressure cleaning eliminates supersaturation heterogeneity. Subsequent ethanol displacement and supersonic jet milling yield 1 kg-scale powder with D50 = 1.90 µm, tap density = 6.0 g/mL, specific surface area = 0.6 m2/g, and LOI (538 °C) = 0.98%. The obtained powder shows powder-level characteristics relevant to subsequent photovoltaic paste formulation, rather than direct device-level validation.

Materials doi: 10.3390/ma19102008

Authors: Gabriela Elena Badea Ioana Maior Anda Ioana Grațiela Petrehele Oana Delia Stănășel Alexandrina Fodor Mioara Sebeșan Simona Dzitac Camelia Daniela Ionaș

Plant-derived corrosion inhibitors are increasingly investigated due to their rich content of adsorption-active phytochemicals. Four extracts obtained from Achillea millefolium were biochemically characterized through spectrophotometric and chromatographic analyses, confirming a substantial polyphenolic content and associated antioxidant capacity. In addition, the hydroethanolic extract (1:1) was examined for its ability to inhibit the corrosion of S235 mild steel in 1 M HCl and neutral medium of 3.5% NaCl by gravimetry, potentiodynamic polarization, open-circuit potential, and electrochemical impedance spectroscopy methods, suggesting that its antioxidant molecules may contribute to the passivation of the metal surface, but in different mechanistic ways. The inhibitory efficiency determined by both the gravimetric method and the Taffel polarization curve method reaches values of 78.53% in HCl 1 M and of 79.65% in NaCl 3.5%, thus demonstrating the contribution of polyphenols from the Achillea millefolium extracts to the inhibition of corrosion.

Materials doi: 10.3390/ma19102009

Authors: Wiktoria Grzebieniarz Nikola Nowak-Nazarkiewicz Joanna Tkaczewska Agnieszka Cholewa-Wójcik Michał Kopeć Krzysztof Gondek Helena Duma Ewelina Jamróz

In the present study, innovative active gelatin–chitosan films enriched with blackberry (ACTIVE-BF) and sage flower (ACTIVE-SF) extracts were developed and comprehensively characterised with regard to their physicochemical, functional and environmental properties. The incorporation of phenolic compounds increased the film’s UV–Vis (ultraviolet–visible spectroscopy) absorbance, confirming the presence of chromophoric groups and the improvement of light-barrier properties. FTIR (Fourier Transform Infrared Spectroscopy) analysis revealed hydrogen bond formation and intermolecular interactions between polyphenols and the –OH/–NH groups of the biopolymer matrix, which enhanced the structural stability of the films. Adding blackberry and sage extracts slightly increased the hydrophilicity and solubility of the films (40–48%), without significantly affecting their water vapour transmission rate (531–547 g/m2·d). The obtained films exhibited strong antioxidant activity, with FRAP (Ferric Reducing Antioxidant Power) values ranging from 17.75 to 40.83 mM Trolox/mg, DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging capacity between 42.58 and 46.88%, and metal chelating ability up to 50.82%. During the nine-day storage of salmon fillets at 4 °C, the active films effectively inhibited microbial growth (reduction of 1.5–2.1 log CFU/g) while maintaining pH stability (6.2–6.4). Respiration activity confirmed environmental safety. The developed materials represent biodegradable, multifunctional films with high potential for application as sustainable active packaging for perishable food products.

Materials doi: 10.3390/ma19102007

Authors: Xixi Cao Xueying Zhang Jiangtao Li Jiachen Liu

Mullite fiber materials are widely used in high-temperature thermal insulation applications, especially in aerospace thermal protection systems, due to their excellent thermal stability and low thermal conductivity. However, the material exhibits poor resistance to infrared radiative heat transfer at elevated temperatures. Accordingly, a dual-opacifier system composed of TiO2 and K2Ti6O13 binary whiskers was proposed as an effective strategy for enhancing thermal insulation performance. MF/TiO2w and MF/TiO2w/K2Ti6O13w were fabricated in this study using a sol–gel method combined with in situ whisker growth. The results show that upright and interlaced K2Ti6O13 and TiO2 whiskers were uniformly grown on the fiber surface, contributing to a high infrared reflectance of 97.7% in the wavelength range of 2.5–10 μm. Under a front-side temperature of 1000 °C, the modified mullite fiber-based material exhibits a backside temperature of 177.8 °C, corresponding to a reduction of 71.8 °C compared with the original sample (249.6 °C), demonstrating significantly enhanced thermal insulation performance. In addition, the composite exhibits an ultralow density of less than 0.20 g/cm3. The as-prepared thermal insulation material shows a high rebound rate of 76.5% at a strain of 30%, indicating good elasticity. The results demonstrate that the developed composite exhibits excellent infrared shielding and structural stability, confirming that the binary whisker strategy effectively enhances the thermal insulation performance of the mullite fiber-based materials, highlighting its potential for high-temperature aerospace applications.

Materials doi: 10.3390/ma19102006

Authors: Wenchao Zhan Yuefeng Wang Xumin Wang Hao Yang Qianqian Feng Xianfen Wang

Thanks to their low cost and environmental sustainability, sodium-ion batteries have emerged as a highly attractive alternative to lithium-ion systems in the field of large-scale energy storage; however, issues such as insufficient energy density and poor cycle stability have hindered their widespread adoption. We have rationally designed a Mg/Li co-doped P2-type NLMMO (Na0.8Mg0.22Li0.08Mn0.7O2) cathode material that enables reversible anion redox reactions through synergistic interactions, enhancing the stability of the layered framework. The material exhibits an exceptional initial discharge capacity of 158 mAh g−1 at 2.0–4.4 V and retains 68% of its capacity after 400 cycles at 0.1 A g−1, surpassing the performance of both lithium-doped (Na0.8Li0.3Mn0.76O2, NLMO) and magnesium-doped (Na0.8Mg0.3Mn0.7O2, NMMO) materials. In situ XRD shows that NLMMO has structural stability, and the Mg doping modification strongly inhibits the phase transition and stabilizes the interlayer structure. Ex situ XPS analysis indicates that the lattice oxygen in the cathode material underwent changes. This study provides a new path for designing cathodes with synergistic anionic and cationic redox reactions.

Materials doi: 10.3390/ma19102005

Authors: Elijah Biggs Amelia Bogard Jacob Attebery Parker Auerweck Dakota Blaha Subin Antony Jose Pradeep L. Menezes

MXenes are an emerging class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides with a unique combination of mechanical, electrical, and thermal properties. While MXenes have been extensively studied in electrochemical and materials science contexts, their mechanical behavior and engineering relevance remain comparatively underexplored. This paper provides a mechanically focused synthesis of MXene research, connecting structure, synthesis, processing, mechanical properties, and functional performance to engineering applications. Emphasis is placed on the tunability of tensile, elastic, shear, and thermomechanical properties through controlled variation of composition, surface terminations, and defects. Comparisons with graphene are used to clarify performance trade-offs and application-specific advantages. Key challenges, including environmental stability, moisture sensitivity, durability, scalability, cost, and integration with conventional engineering materials, are critically examined alongside current mitigation strategies. Applications in structural composites, mechanical reinforcement, energy storage, electromechanical systems, and MXene-based sensors and actuators are discussed to demonstrate practical relevance. By framing MXenes as engineerable materials rather than isolated nanomaterials, this work serves as a technical reference and entry point for mechanical engineers and interdisciplinary researchers seeking to design and deploy MXenes in advanced engineering systems.

Materials doi: 10.3390/ma19102002

Authors: Xianhui Wu Hongbing Peng Jie Zhou Sheng Pang Minghui He Ruili Zheng Houyuan Zhang Dong Wang Guoyu Qian Zhi Wang

The rapid expansion of crystalline silicon photovoltaic (PV) modules has increased the demand for sustainable and high-value recycling strategies for end-of-life (EOL) modules. A significant challenge is the removal of impurities such as carbon, oxygen, and non-metallic inclusions introduced into silicon solar cells during the dissociation of PV laminates. To address this, we propose a non-consumable electrode electroslag remelting (NCE-ESR) process to effectively eliminate inclusions. In this process, the reverse flow of alloy droplets and the extensive contact area are crucial during the reverse flow slag washing. Initially, we studied the occurrence characteristics of inclusions in silicon solar cells obtained after pyrolysis from enterprises. Pyrolysis facilitated the formation of inclusions like Si-O, C-O, Al-O, and Si-N, particularly in the fine size range below 5 μm. To enhance impurity removal, the recycled Si was alloyed with Cu, which increased the melt density and impurity activity. Based on optimized thermodynamics and physical properties, we designed a novel electroslag composition of 40%CaO-40%SiO2-20%CaF2 suitable for silicon alloy refining. Notably, during the reverse flow slag washing of the Cu-Si alloy, the maximum removal rate of inclusions reached 77.42%. The average diameter of inclusions was reduced to below 6 μm, and the removal rates of impurity elements such as Al, O, and C exceeded 98.09%, 94.86%, and 86.08%, respectively. Finally, we independently developed the NCE-ESR equipment and conducted a kilogram-scale amplification test. The results indicated that the impurity removal rates of Al and O exceeded 97%, and the final inclusion size was less than 10 μm. This study demonstrates a scalable and environmentally friendly approach for the high-value recycling of silicon resources from decommissioned PV modules.

Materials doi: 10.3390/ma19102004

Authors: Pengchang Liang Lianyong Zhu Ruize Yin Renfei Gao

To promote the practical application of metakaolin-slag geopolymer materials in engineering repair, it is essential to clarify the influence of mix proportion parameters on macroscopic properties, given their inherent deficiencies of inferior toughness and volume stability. In this study, a five-factor and four-level orthogonal experimental design was adopted to systematically investigate the effects of slag content, water glass modulus, alkali equivalent, water–binder ratio, and sand–binder ratio on the fluidity, compressive strength, flexural strength, compressive-to-flexural strength ratio (toughness indicator), and drying shrinkage rate (volume stability indicator) of geopolymer mortar. Range analysis and variance analysis were conducted to clarify the primary and secondary order of influencing factors for each performance index, and the optimal mix proportion balancing multiple performance demands was determined. The results indicate that alkali equivalent is the core factor governing compressive and flexural strength, whereas slag content dominates the compressive-to-flexural ratio, fluidity and drying shrinkage. The geopolymer mortar achieves relatively optimal comprehensive performance when the slag content is 20%, the sodium silicate modulus is 1.6, the alkali equivalent is 12%, the water-to-binder ratio is 0.49, and the sand-to-binder ratio is 2:1, and all indicators meet the specification requirements for rigid repair mortar. Combined with SEM-EDS and XRD microstructural analysis, the main products of the metakaolin-slag system are amorphous N-A-S-H gel and C-(A)-S-H gel. Appropriate alkali equivalent and slag content can promote the dissolution of aluminosilicate raw materials and facilitate the formation of both gel products, providing microstructural support for the improvement of macroscopic performance.

Materials doi: 10.3390/ma19102003

Authors: Yong Jic Kim Sung-Rok Oh Myounghwi Kim Hyung-Suk Kim

This study experimentally evaluates the mechanical healing performance of precast concrete incorporating hybrid capsules under load reapplication conditions. Hybrid capsule systems are defined as self-healing systems that combine solid capsules (SCs) and liquid capsules (LCs), to enable multi-scale crack healing. In this study, four mix proportions (HC-0, HC-1, HC-3, and HC-5), corresponding to 0%, 1%, 3%, and 5% replacement of fine aggregate by volume with hybrid capsules, were prepared. The hybrid capsules consisted of SCs and LCs in a fixed ratio of 7:3. Among the mixtures, a representative intermediate content (3%) was selected to examine the feasibility of mechanical recovery compared to plain concrete, rather than to determine an optimal dosage. Mechanical recovery was evaluated through compressive and flexural strength tests after preloading and healing periods. The results confirm that the incorporation of hybrid capsules enables partial recovery of mechanical properties after damage. These findings provide preliminary experimental evidence of the feasibility of hybrid capsule systems in precast concrete. Further studies are required to investigate the influence of capsule content and to establish optimal mixture conditions.

Materials doi: 10.3390/ma19102001

Authors: Abdellah Bachiri Agnieszka Syntfeld-Każuch Vitalii Gorbenko Sandra Witkiewicz-Lukaszek Tetiana Zorenko Yurii Syrotych Lukasz Adamowski Lukasz Swiderski Vasyl Stasiv Yaroslav Zhydachevskyy Yuriy Zorenko

In this work, we report the fabrication and characterization of single-film and double-film composite epitaxial garnet structures based on single-crystalline films (SCFs) and bulk single-crystal (SC) scintillators for enhanced α–γ discrimination in mixed radiation fields. These composite scintillators consist of TbAG:Ce and YAG:Ce SCFs grown by liquid-phase epitaxy (LPE) on Czochralski-grown Gd3Ga2.5Al2.5O12 (GAGG:Ce) bulk SC substrates. Single- and double-film architectures were designed to optimize the energy absorption and pulse-shape discrimination (PSD) performance for low-penetrating α-particles and high-energy γ-rays. Energy calibration was performed using different γ-ray sources (57Co, 51Cr, and 137Cs), enabling the conversion of detector signals to a calibrated electron-equivalent energy scale (keVee). Integration gates were systematically optimized, yielding maximum figures of merit (FOM) of 1.4 for the GAGG:Ce SC substrate, 1.9 for the single-film composite, and 5.0 for the double-film composite, demonstrating a progressive improvement in α–γ discrimination with increasing structural complexity. Two-dimensional PSD density maps reveal well-separated α and γ events, with the highest separation observed for the double-film composite. These results indicate that the engineering of LPE-grown composites provides tunable scintillation decay profiles, enhanced temporal separation, and increased light yields, making them promising candidates for applications such as mixed radiation field detection, dosimetry, and radiation monitoring.

Materials doi: 10.3390/ma19102000

Authors: Zichen Kang Yingguang Zhao Haochen Zhao Yezhou Wang Gaoning Tian Cong Zhao Jiangkai Liang Xixing Qian Yanli Lin Zhubin He

In response to the growing demand for complex thin-walled lightweight alloy components in the automotive and aerospace industries, this study investigates the limitations of traditional gas pressure forming technologies. Using 2A12 aluminum alloy thin sheets as the research material, hot high-speed gas bulging experiments were conducted to study the effects of rapid inflation and rapid deflation processes on the forming accuracy, wall thickness, and strain distribution of bulged components. This aims to provide guidance for theoretical research and validate the superiority of the rapid deflation process. The results show that: (1) When forming cup-shaped components at 400 °C, the die-fitting degree of the component formed by the rapid deflation process reaches 89.5% and the minimum corner radius is 2.5 mm. Overall, the forming accuracy of this process is significantly superior to that of the rapid inflation process. (2) Within the temperature range of 400–450 °C, the rapid deflation process successfully formed a spherical-bottom component with a depth of 30 mm, overcoming the cracking defects induced by localized cooling and non-uniform temperature fields in the rapid inflation process, thereby improving the forming limit. (3) Under consistent conditions, the wall thickness uniformity of the sheet formed by the rapid deflation process is significantly higher than that of the sheet formed by rapid inflation, and the wall thickness uniformity improves with increasing temperature. Future work is expected to further enhance the repeatability and stability of forming accuracy and the forming limits of extreme geometries by further optimizing process parameters and expanding the material applicability range. This will provide practical technical support for the manufacturing of lightweight, high-performance aerospace equipment and automotive components.

Materials doi: 10.3390/ma19101998

Authors: Dingkai Wang Mingyu Cui Xutang Liu Meiling Liu Xiaopeng Han Xiaoming Xiong Shanglong Chen Shangshang Ma Qiqi Sun Lingfeng Jiao Wei Zhao

Lignin, a complex natural three-dimensional aromatic polymer, is prone to condensation during the separation process, owing to the diverse properties of its basic structural units, linkage types, and spatial configurations. These inherent structural complexities present significant challenges for its efficient isolation and precise transformation. Current separation techniques primarily include physical, chemical (such as acid hydrolysis, alkaline dissolution, organic solvents, and ionic liquids), and biological methods. Each approach offers distinct advantages and limitations in terms of yield, purity, cost, and impact on lignin structure. Studies have indicated that ionic liquids and organic solvent methods demonstrate considerable application potential owing to their mild reaction conditions and high selectivity. Future research should focus on developing green, efficient, and low-cost separation technologies, while also enhancing detailed structural characterization and targeted lignin conversion to facilitate its large-scale utilization in the production of value-added materials and chemicals.

Materials doi: 10.3390/ma19101999

Authors: Desheng Chu Yanhan Wang Fangrong Zhou Ronghai Liu Longchang Zhu Qingjun Peng

SiC fiber-reinforced aluminum matrix (SiCf/Al) composites have the potential to replace titanium alloys for fan/compressor blades due to their low density and favorable high-temperature performance. In this study, thermal exposure and thermal cycling tests were conducted to simulate service environments and to clarify their effects on the microstructure and interfacial properties of a SiCf/AlFe5Si2 composite. Thermal exposure was performed at 260–450 °C for 20–100 h, and thermal cycling was carried out between 300 or 350 °C (1 h dwell) and room temperature for 20–100 cycles. Interfacial shear strength was evaluated by push-out tests, while microstructural evolution was examined using SEM, TEM/EDS, and XRD. Three-dimensional finite element simulations were used to assess mismatch-driven residual-stress distributions during the cooling stage after thermal excursion. The results showed that interfacial shear strength decreased with increasing exposure temperature/time and degraded more severely under thermal cycling than under isothermal exposure at the same temperature. A rapid loss of interfacial strength occurred above ~400 °C, associated with significant interfacial-layer thickening and the formation of brittle AlxSiOy phases. The interfacial reaction layer followed parabolic growth kinetics, yielding a preliminary apparent activation energy of Q ≈ 150 kJ/mol estimated from two isothermal temperatures. The simulations indicated large opposing stresses between the matrix and the carbon-rich layer, supporting a mechanical driving force for interfacial debonding; however, heating/dwell time-dependent effects were not explicitly modeled and are discussed as limitations. These findings provide quantitative guidance for defining service-temperature limits and improving interfacial thermal stability in SiCf/AlFe5Si2 composites.

Materials doi: 10.3390/ma19101996

Authors: Sefa Talay Ahmet Ferhat Bingöl Dilek Okuyucu Burak Gedik Muhammet Şahin

This study examines how fly ash-modified self-compacting concrete (SCC) behaves during curing under real conditions, focusing on changes in temperature and heat during the first days. Unlike typical lab tests at steady temperatures, three settings were used to copy real-life conditions: summer, winter with heating, and winter without heating. Temperature changes were tracked with built-in temperature sensors. Concrete maturity was calculated using a standard method (the Freiesleben-Hansen and Pedersen approach in ASTM C1074). The results show that heat in the first 72 h affects the maturity and strength of the concrete. After 7 days, strengths were measured as 32.7 MPa in summer, 27.2 MPa in winter-heated, and 15.7 MPa in winter-unheated settings. Predictions of strength based on maturity closely matched the measured values, proving that this approach works well in real settings. Examining the concrete’s structure with SEM and XRD tools showed that fly ash alters how the concrete forms and becomes denser, while lower temperatures slow key reactions, making the material more porous. These results show why early heat control matters. The maturity approach helps reliably estimate in situ strength and guide mix design for real projects.

Materials doi: 10.3390/ma19101997

Authors: Qiyu Zhang Jingwei Gong Miaomiao Gong

Enhancing the freeze–thaw resistance of cement-based materials in a green and efficient manner is crucial for hydraulic structures in cold regions. This study investigated the effects of soybean antifreeze protein (AFP) on the freeze–thaw durability of cement mortar through mechanical testing, low-temperature microscopy, NMR analysis, and frost-heaving stress monitoring. The results show that AFP improves freeze–thaw durability, with 0.5% dosage outperforming 1.0%. Relative to the control, the relative ice content at −20 °C decreased from 62.81% to 40.01%, and frost-heaving stress declined from 321.15 kPa to 123.04 kPa. Microscopy and pore structure analyses revealed that AFP transforms ice crystals from needle-like to fine granular forms, inhibiting ordered growth and retarding pore coarsening. A frost-heaving stress model based on the Gibbs–Thomson effect and ice-crystal fractal characteristics indicated that AFP suppresses stress development by reducing effective ice formation, weakening stress transfer, and increasing ice-crystal boundary complexity. This study offers insights for developing green antifreeze admixtures for cement-based materials in cold regions.

Materials doi: 10.3390/ma19101995

Authors: Weizi Wang Lianyong Zhu Jingcheng Ju Xiaotong Gao Xi Chen

To investigate the influence of basalt fiber (BF) on the mechanical properties and crack evolution of coal gangue–slag geopolymer concrete, geopolymer concrete specimens were prepared using coal gangue powder calcined at 700 °C and slag as precursors, with BF contents ranging from 0 to 1.25%. Mechanical testing combined with digital image correlation (DIC), scanning electron microscopy (SEM), and X-ray diffraction (XRD) was conducted to evaluate the effects of BF on macroscopic mechanical behavior, crack evolution, and underlying microstructural mechanisms. The results demonstrate that BF effectively enhances both the mechanical performance and crack-control capacity of coal gangue–slag geopolymer concrete, exhibiting a clear content-dependent trend. Compressive strength initially increases and subsequently decreases with increasing BF content. The 28-day compressive strength reaches a maximum value of 84.05 MPa at a BF content of 0.5%, representing an 11.92% improvement compared with the control group. Splitting tensile strength and flexural strength attain their peak values at a BF content of 1%, increasing by 37.88% and 25.81%, respectively. DIC analysis indicates that BF delays strain localization and effectively restrains the propagation of dominant cracks. Specifically, the compressive strain field becomes more uniformly distributed at 0.5% BF content, while crack propagation during splitting failure is more stable at 1% BF content. SEM observations reveal that the primary strengthening mechanisms include crack bridging, interfacial load transfer, and energy dissipation associated with fiber pull-out. XRD analysis shows that BF incorporation does not significantly alter the phase composition of the coal gangue–slag geopolymer system; thus, performance enhancement mainly arises from fiber bridging and interfacial reinforcement rather than changes in primary reaction products.

Materials doi: 10.3390/ma19101994

Authors: Hao Wu Zhe Wang Pengfei Li Mingliang Li Jun Li Shuangfeng Guo

Coal liquefaction residues (CLRs), including both indirect (ICLR) and direct (DCLR) variants, represent industrial by-products whose conventional landfill disposal raises environmental concerns. This study comparatively analyzes ICLR and DCLR properties against limestone fine aggregates through physicochemical characterization. Results indicate that ICLR contains predominant SiO2 crystalline phases (50.05%) with trace Fe-Ti-Al-Mg oxides, demonstrating higher Vickers hardness (615 HV vs. 246 HV for limestone) and elastic modulus (98 GPa vs. 81 GPa for limestone), while its apparent relative density (2.612) closely matches that of limestone (2.783). Conversely, DCLR features abundant carbonaceous components (75.9% C) with olefinic/aromatic structures (asphaltene content 66.2%), exhibiting lower mechanical strength (Vickers hardness 21 HV) but enhanced asphalt affinity, as indicated by strong C=C (1591 cm−1) and aromatic C–H (744 cm−1) absorption peaks in FTIR. Both CLRs share comparable gradation curves and micromorphological characteristics with limestone aggregates, including uniform surface scaly textures. While pore-size distributions differ minimally between CLRs, both present finer porosity than limestone and show no leachate toxicity risks, confirming their viability as sustainable alternatives to asphalt fine aggregates.

Materials doi: 10.3390/ma19101993

Authors: Lingyi Mao Yanyao Li Kande Liu Naiwang Liu Li Shi Xuan Meng

Diphenylamine is an important organic chemical intermediate, and its industrial synthesis is mainly achieved through the continuous condensation of aniline. In this study, Hβ zeolite was modified with citric acid, and its catalytic performance in the aniline condensation reaction for diphenylamine synthesis was systematically investigated. The crystal structure, acidic characteristics, pore properties, and Si/Al composition of the catalysts were comprehensively characterized by means of XRD, SEM, BET, Py-IR, ICP, and 27Al MAS NMR. The catalytic activities of Hβ zeolites modified with different concentrations of citric acid were evaluated in a micro fixed-bed reactor, and the structure–activity relationship was systematically discussed in combination with the characterization results. The results demonstrate that the Hβ zeolite modified with 1.5 mol/L citric acid achieves precise matching with the aniline condensation reaction in terms of crystal structure integrity, pore channel parameters, acid property distribution, and Si/Al ratio regulation. Compared with the unmodified catalyst, its catalytic activity is improved by approximately 28%, with a diphenylamine selectivity of 100%. This study proposes a modification mechanism of Hβ zeolite by citric acid.

Materials doi: 10.3390/ma19101992

Authors: R. Murillo-Ortíz María de Jesús Martínez-Carreón A. Lobo Guerrero R. Herrera-Rivera Eduardo G. Pérez-Tijerina

This study investigates the removal of Cd2+ ions from aqueous solutions using hard magnetic strontium hexaferrite (SrFe12O19) nanoparticles synthesized via the Pechini method, with an average particle size of 116 nm. The material was successfully obtained at a relatively low calcination temperature of 900 °C. The crystalline structure of the hexaferrite particles was investigated by X-ray diffraction, confirming SrFe12O19 crystalline structure. The powder samples were also characterized by Fourier transform infrared spectroscopy (FTIR). The morphology and size distribution were studied using scanning electron microscopy (SEM). Furthermore, the magnetic properties of strontium hexaferrite contribute significantly to adsorption and removal processes, primarily by acting as a recoverable magnetic adsorbent. The ferromagnetic material, with its high saturation magnetization and coercivity, responds rapidly to external magnets, facilitating the removal of contaminants and maintaining its magnetic characteristics even in complex chemical environments. For this purpose, its magnetic behavior was also studied using vibrating sample magnetometry (VSM). The experimental adsorption results were successfully modeled using PFO (pseudo—first—order) and PSO (pseudo—second—order) along with Freundlich and Langmuir isotherms, to fit the experimental adsorption data of the Cd(II) salt from the 0.1 and 0.2 mg samples at room temperature for two quantities of strontium hexaferrite at times ranging from 2.5 to 60 min. The results indicate that the strontium hexaferrite nanoparticles exhibited a 90% removal efficiency, which was the highest value. Additionally, the strontium hexaferrite can be magnetically recovered along with the adsorbed cadmium, representing a more efficient way to remediate water.

Materials doi: 10.3390/ma19101991

Authors: Zhe Pang Yuxuan Wang Chong Peng Yingfei Liu Jiaqian Que Kefeiyang Hu Xingbo Huang Yong Liu

Organic–inorganic hybrid halide perovskites have attracted extensive attention due to their excellent optoelectronic properties and potential applications in field-effect transistors (FET), light-emitting diodes (LEDs), and photodetectors. However, conventional three-dimensional (3D) perovskites are limited by intrinsic instability and ion migration. Two-dimensional Ruddlesden-Popper (2D RP) perovskites offer improved structural stability, but many systems still suffer from modest photoluminescence efficiency and limited charge-transport performance. In this work, a novel 2D RP perovskite, (C6H5NH3)2CsPb2Cl7, was designed and synthesized, where the anilinium ion (C6H5NH3+) serves as the organic spacer. Structural characterization indicates that the material possesses high crystallinity and a smooth surface morphology. Optical measurements reveal a violet emission peak at 411 nm with a single-peak feature and a full width at half maximum (FWHM) of 10 nm. The bandgap is determined to be 3.1 eV. Time-resolved photoluminescence (TRPL) measurements show an average lifetime of 4 ns, and the photoluminescence quantum yield (PLQY) is 29.8%. Based on the measured PLQY and lifetime, the radiative and non-radiative recombination rates were estimated to be Kr ≈ 7.45 × 107 s−1 and Knr ≈ 1.76 × 108 s−1, respectively, suggesting that radiative recombination is appreciable although non-radiative pathways remain present. FET measurements demonstrate an on/off current ratio of 104 and a carrier mobility of 1.1 cm2 V−1 s−1. Without any systematic optimization, (C6H5NH3)2CsPb2Cl7 exhibits relatively favorable emissive behavior and measurable field-effect charge transport performance when compared with structurally similar 2D RP perovskites reported under comparable, non-optimized conditions. This study expands the family of chloride-based 2D perovskites and provides a basis for future improvements in their recombination and field-effect transport properties.

Materials doi: 10.3390/ma19101980

Authors: Cheng Xu Haiyan Xing Liwei Zhao Haibo Miu Hai Zhang

Metal magnetic memory (MMM) is a promising non-destructive evaluation method for ferromagnetic materials, allowing early detection of stress concentration and micro-defects under weak geomagnetic excitation. However, current magneto-mechanical coupling models are computationally complex and insufficient to characterize the full-cycle evolution of mesoscale physically short cracks. This work proposes a magnetic dipole model and its decomposed formulation for V-shaped cracks. Combined with theoretical derivation, finite element simulation, and in situ three-point bending tests on Q345 steel, the magneto-mechanical coupling mechanism and magnetic signal evolution during crack propagation are investigated. Results show that the MMM normal component exhibits obvious peak-peak features at the crack tip, while the tangential component shows a single-peak characteristic. Two critical signal mutations are observed at crack lengths of about 100 μm and 3000 μm, corresponding to micro-meso and meso-macro crack transitions, respectively. The model is verified with relative errors of 15.2% for Hx and 17.6% for Hy. This study reveals the quantitative correlation between MMM signals and full-lifecycle crack growth, supporting damage assessment and fatigue life prediction for ferromagnetic engineering structures.

Materials doi: 10.3390/ma19101981

Authors: Kaixuan Shao Feng Liu

Flat bands exhibit vanishing group velocity and marked sensitivity to lattice geometry, making them a useful setting for studying localization driven by destructive interference. In this work, electrical-circuit simulations are employed to investigate flat-band systems in one, two, and three dimensions. A one-dimensional two-band circuit is first considered, and its flat-band response is characterized through node-to-ground impedance spectra and steady-state voltage distributions. The analysis is then extended to two- and three-dimensional Lieb lattice circuits characterized by sublattice imbalance. In the two-dimensional Lieb circuit, the flat band touches the dispersive bands at a Dirac point, so hybridization with dispersive modes affects the observed localization. Under periodic boundary conditions, wave vector quantization also produces responses that depend on whether the number of unit cells is even or odd. By contrast, in the three-dimensional Lieb circuit, the flat band is spectrally isolated from the dispersive bands, allowing stronger spatial confinement and clearer sublattice selectivity. The one-dimensional, two-dimensional, and three-dimensional models therefore represent three different situations: a singular flat band, a flat band that touches dispersive bands, and a spectrally isolated flat band. Comparing these cases shows how different degeneracy conditions shape impedance responses and localization patterns in electrical circuit systems. At the flat band frequency, the localized voltage response can also be used to generate spatial patterns in both two-dimensional and three-dimensional circuits, pointing to a possible route for spatial mode control of compact localized states in electrical systems.

Materials doi: 10.3390/ma19101990

Authors: Hamida Gouadria Jesús Álvarez María José Capitán

This study investigates how structural dimensionality affects the optoelectronic behavior of organic lead–halide hybrid perovskites. Using the chiral cation R-1-phenylethylammonium (PEA), which is known to be able to form both one-dimensional (1D) and two-dimensional (2D) lead–iodide frameworks, we synthesize 1D (PEA)PbI3 and 2D (PEA)2PbI4 compounds through tailored crystallization and deposition routes. X ray diffraction confirms structural purity, while ultraviolet photoelectron spectroscopy (UPS) provides insight into the electronic structure and photoresponse. Both materials exhibit a surface photo-voltage (SPV) under visible illumination, reaching a maximum work function shift of 1.5 eV for the 2D phase and 0.4 eV for the 1D phase in the thin-film samples. These results suggest that the 1D phase exhibits a reduced tendency for iodide-vacancy formation, which may result in a more stable response under visible illumination, accompanied by faster relaxation dynamics and more anisotropic charge transport. Overall, our findings highlight the central role of electronic confinement in shaping photoinduced processes in hybrid perovskites and support the consideration of structural dimensionality as a key design parameter for the design of next-generation optoelectronic materials.

Materials doi: 10.3390/ma19101989

Authors: Kuiqing Guo Benjun Cheng Weibin Xu Xiaocheng Liang Liming Zou Wencheng Wang Guoqi Liu

The bottom brick is a critical component of float glass furnace tin baths, serving under harsh conditions including high temperature, tin penetration, hydrogen diffusion and alkali attack. Traditional flint clay-based bottom bricks suffer from high porosity and insufficient service performance. In this study, a high-performance low-cement castable was developed by introducing mullite aggregates to partially replace flint clay. The effects of mullite particle size and addition content on sintering behavior, mechanical properties, thermal shock resistance, refractoriness under load and hydrogen diffusion were systematically investigated. The results demonstrate that, compared with the existing tin bath bottom bricks applied in float glass furnaces, the introduction of 18 wt% mullite with a particle size of 5–3 mm can significantly increase the bulk density, reduce the apparent porosity, enhance the mechanical strength at both room temperature and high temperature, and achieve a higher refractoriness under load and lower hydrogen diffusion capacity. Accordingly, a novel tin bath bottom brick with excellent comprehensive properties for float glass furnaces was successfully developed.

Materials doi: 10.3390/ma19101988

Authors: Muwen Chen Liguo Zhu Dengjie Yan Lingxin Kong Bin Yang

In this study, first-principles molecular dynamics (FPMD) simulations were employed to systematically investigate the effects of temperature and composition on the microstructure and transport properties of CaCl2–CaI2 mixed molten salts at the atomic scale. Structural analysis shows that the system exhibits good relaxation behavior and thermodynamic stability, with coordination strength following Ca-Cl > Ca-I. The transport properties reveal a coupled dependence on temperature and composition: increasing CaI2 content enhances the diffusion of I− ions, whereas at 1173 K, a decrease in diffusion coefficients is observed for all ionic species. Arrhenius analysis indicates that increasing CaI2 content lowers the activation energy for ion migration. The shear viscosity follows the order η(Ca2+) > η(Cl−) ≥ η(I−), and decreases with increasing temperature and CaI2 concentration, indicating improved fluidity. Notably, the results reveal a competitive coordination mechanism between Cl− and I− around Ca2+, as well as a non-monotonic transport behavior at high temperatures, reflecting the complex coupling between composition and ionic dynamics in mixed halide melts. This study provides a theoretical basis for the optimization of molten salt electrolysis processes and nuclear energy materials, and offers insight for future multiscale simulations and experimental validation.

Materials doi: 10.3390/ma19101987

Authors: Yuejia Wang Di Wang Xinyu Chen Yishan Sun Guoguo Shi Jianfang Cao

This study is dedicated to the development of novel boron-dipyrromethene (BODIPY)-based photosensitizers, focusing on investigating the regulatory mechanism of introducing different electron-donating groups at the α-position on the photosensitizing performance of thieno-bis-BODIPY derivatives, aiming to provide a theoretical basis for cancer photodynamic therapy (PDT). Five thieno-bis-BODIPY molecules (FD1-FD5) were constructed by connecting two BODIPY units via a thiophene π-bridge and introducing various substituents at the α-position of their phenyl groups. Systematic theoretical studies revealed that unilaterally substituted molecules exhibit superior photophysical properties compared to their bilaterally substituted counterparts. The key mechanisms involve structural planarization, increased electrostatic potential difference, and the formation of hybrid LE/CT characteristics in the excited state, all of which collectively promote the intersystem crossing (ISC) process. Specifically, the pyrrole-substituted FD4 exhibits the highest ISC efficiency due to its stronger electron-donating ability and greater molecular planarity, and it is predicted to possess a stronger singlet oxygen generation capability than the methoxy-substituted FD2 while maintaining fluorescence emission. In contrast, bilateral substitution leads to structural distortion, which favors fluorescence emission, as seen in FD5 which exhibits the longest absorption wavelength. This research elucidates the key mechanisms for enhancing ISC and photosensitizing performance from the perspectives of electronic structure and excited-state characteristics, providing theoretical guidance for overcoming limitations such as insufficient tissue penetration in traditional BODIPY photosensitizers and clarifying structure–activity relationships.

Materials doi: 10.3390/ma19101986

Authors: Yanfeng Liang Benchang Liu Haoran Ma Lining Pan Aina He Yaqiang Dong Qikui Man Jiawei Li

We constructed a multi-layer composite magnetic shield composed of Fe-based nanocrystalline (FN) and Co-based amorphous (CA) ribbons, and focused on the influence of the number of layers and their arrangement on the shielding effectiveness (SE). Finite element analysis (FEA) and layer-by-layer inversion calculations were performed to analyze the attenuation process of the magnetic field between shield layers. Increasing the number of shield layers improves the maximum value of SE (SEmax) and significantly broadens the working range (WWR). In a weak magnetic field, CA exhibits higher shielding performance, whereas FN is better in a strong magnetic field. The FN/FN/CA combination (FN is closer to the field source) exhibits an SEmax of up to 51.7 dB within a WWR of 674.3 A/m, and demonstrates a 14.4% improvement in SE compared to FN/FN/FN combination across the entire tested magnetic field range. Finally, a gradient layering design is proposed that enables each layer to operate within its optimal permeability range, thereby improving the overall SE and broadening the effective working magnetic field range.

Materials doi: 10.3390/ma19101985

Authors: Yuanwei Ju Anming She Junyan Wang

Ultra-high-performance concrete (UHPC) matrix faces critical challenges of high carbon footprint and significant autogenous shrinkage. Supersulfated cement (SSC), a potentially lower-carbon binder comprising ground granulated blast-furnace slag and gypsum, offers a promising alternative. This study systematically investigated the effect of gypsum type—phosphogypsum (PG), dihydrate gypsum (DH), and anhydrite (AH)—on the early hydration and shrinkage behavior of UHPC matrix incorporating 30% SSC as Portland cement replacement. A multi-technique approach, including mechanical testing, isothermal calorimetry, XRD, TG-DSC, SEM, LF-NMR, and autogenous shrinkage measurements, was employed. Results demonstrate that gypsum type critically governs sulfate dissolution kinetics, thereby dictating phase assemblage and microstructural evolution. DH provides relatively rapid sulfate dissolution, promoting earlier AFt and gel formation, which is associated with the highest early strengths and a marked reduction in autogenous shrinkage. AH shows a slower but sustained sulfate supply, resulting in comparable 28-day strength with moderate shrinkage reduction. PG yielded the lowest autogenous shrinkage (374 μm/m at 7 d), but it also suffered from severe early-age retardation due to soluble phosphate impurities, as evidenced by the delayed hydration peak and lowest 3 d strength. This behavior is mainly related to strong early-age retardation, delayed hydration, delayed setting, and a prolonged low-stiffness state. These findings suggest that appropriate gypsum selection in SSC enables tailored early-age performance and improved volume stability in the UHPC matrix, offering guidance for utilizing industrial by-products such as phosphogypsum in sustainable high-performance concrete design.

Materials doi: 10.3390/ma19101982

Authors: Zhihua Zhang Fangcheng Zheng Guohua Fan Mingming Xu

Three-dimensional braided carbon-fiber-reinforced polymer (CFRP) composites are promising for lightweight aircraft propeller blades. Aircraft composite structures may approach temperatures of 80–90 °C under the combined effects of solar radiation, infrared heating, and ground reflection. Yet the thermo-mechanical failure mechanisms of low-braiding-angle architecture remain insufficiently understood. This study comparatively investigates the tensile behavior and damage evolution of low-angle four-directional (3D4A-20°) and five-directional (3D5A-20°) braided CFRP composites under axial tension at both room temperature and 90 °C. A multi-scale approach integrating in situ X-ray computed tomography, digital image correlation, digital volume correlation, and scanning electron microscopy was used to characterize strain localization, internal cracking, and fracture morphology. At room temperature, 3D5A-20° shows higher stiffness and strength than 3D4A-20° because additional axial yarns improve load-transfer and three-dimensional constraint. At 90 °C, matrix softening and interfacial degradation accelerate crack initiation, strain localization, and damage propagation in both architectures. Nevertheless, 3D5A-20° maintains more stable and progressive damage evolution, whereas 3D4A-20° exhibits earlier crack coalescence and greater mechanical degradation. Overall, elevated temperature accelerates damage evolution through matrix softening and interfacial degradation, whereas braided architecture determines load transfer and crack connectivity. These findings provide guidance for the design of low-angle braided composites for thermally exposed aircraft propeller blades.

Materials doi: 10.3390/ma19101983

Authors: Yingxin Zhao Qingyuan Zhao Fengyuan Li Haibo Zhang Fei Du Xiyue Yu Aiguo Zhao

In high-speed train traction power supply systems, compensation ropes serve as critical transmission components to ensure system stability. These ropes are specially designed as right-hand alternating lay wire ropes. During tension compensation of the contact wire, the compensation rope undergoes repeated bending around the ratchet device, making it susceptible to fatigue fracture. This study conducted bending fatigue tests on compensation ropes with complete structural configurations in accordance with GB/T 12347-2008. The stress distribution and deformation evolution induced by bending were simulated using the finite element method, enabling fatigue life prediction under cyclic bending conditions. Given the significant convergence difficulties encountered in large-deformation bending simulations of the full structural model, this study innovatively adopts Love’s elastic thin-rod theory as an alternative approach, which avoids the computational prohibitions of full-scale helical modeling while preserving critical bending stiffness characteristics. The results demonstrate that the equivalent elastic modulus derived from Love’s elastic thin-rod theory closely matches the modulus obtained through stress–strain curve fitting from strand tensile tests. Furthermore, under identical axial tensile loads, the equivalent diameter model and the full-structure finite element model exhibit nearly identical end elongations. The predicted bending fatigue life using the equivalent diameter model agrees well with experimental results, and the fatigue fracture mechanisms are further revealed through microscopic morphology analysis, collectively confirming that the proposed equivalent modeling strategy provides an efficient and reliable solution for fatigue life prediction of complex wire rope structures under coupled tension–bending conditions.

Materials doi: 10.3390/ma19101984

Authors: Zitao Jiang Zigeng Huang Gengsheng Chen Yunan Zhang Shimao Liu Ziru Chang Xinru Yang

The growing demand for long-distance green methanol transportation highlights the critical need to evaluate the safety and reliability of pipeline sealing materials. This study investigates the swelling mechanisms of fluorocarbon rubber (FKM), nitrile butadiene rubber (NBR), and polytetrafluoroethylene (PTFE) under simulated methanol pipeline conditions. Static immersion tests were conducted under simulated pipeline conditions with water contents of 0–20% and temperatures of 25–55 °C, supplemented by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and gas chromatography–mass spectrometry (GC–MS). FKM exhibited severe physical swelling, with the volume increase reaching up to 80% in pure methanol. Notably, the addition of 5% water markedly suppressed this swelling, reducing the volume change of FKM sealing rings to approximately 3% and the mass change to 1%. Conversely, NBR experienced volume shrinkage and mass loss due to the extraction of the plasticizer Bis(2-ethylhexyl) phthalate by methanol, a process also inhibited by water. PTFE demonstrated exceptional chemical stability and negligible dimensional changes owing to its high crystallinity and rigid structure. Consequently, PTFE is recommended as the optimal sealing material for pure methanol pipelines. When utilizing FKM or NBR, strict control over the fluid’s water content and operating temperature is essential to prevent degradation and ensure long-term pipeline integrity.

Materials doi: 10.3390/ma19101979

Authors: Cheng Zhang Jiaxin Yao Zhe Zhang

The 316L stainless steel is widely utilized as structural material in hydrogen production industry due to its excellent combination of corrosion resistance and mechanical properties. However, it remains susceptible to localized pitting corrosion in chloride-containing high-temperature environments. Especially, the main electrolysis byproduct sodium chlorate (NaClO3) also has complicated effect on pitting corrosion. Therefore, evaluating and predicting the pitting severity grades of 316L steel in NaClO3 and NaCl environment is essential for controlling operation risks. In recent years, machine learning (ML) methods have gained significant attention in the field of corrosion prediction; however, existing research has primarily focused on the regression prediction of continuous parameters, while studies dedicated to the classification and evaluation of pitting severity grades remain relatively limited. Furthermore, experimental datasets are commonly constrained by small sample sizes and imbalanced class distributions, which hinder the performance enhancement of classification models. Based on experimental pitting data of 316L stainless steel, this study employs ADASYN (Adaptive Synthetic Sampling) to mitigate data imbalance and develops a Feedforward Neural Network (FFNN) for pitting rate classification. The proposed model is compared and analyzed against several commonly used machine learning models. Through a comprehensive evaluation of predictive performance, the feasibility of the developed model in pitting severity grading is verified, thereby providing a novel approach for the predictive evaluation of the pitting corrosion of 316L stainless steel.

Materials doi: 10.3390/ma19101978

Authors: Yue Luo Xiangyu Zhang Guanghai Shi

Baltic amber exhibits a wide range of colors and has attracted considerable attention in materials science. Previous studies have mainly focused on the origin and formation characteristics of beeswax-amber, while the relationship between beeswax-amber color and the microstructural characteristics of internal bubbles remains poorly understood. Ten beeswax-amber specimens exhibiting a color gradient from yellow to white were selected. Scanning electron microscopy (SEM) was used to examine and analyze their internal structures, with a focus on documenting bubble size, number, and density characteristics. Ultraviolet (UV) illumination was employed for qualitative optical observation, and Fourier-transform infrared (FTIR) spectroscopy was conducted to identify component phase and spectra. The correlation between bubbles and color was analyzed to infer the origin of white beeswax-amber’s coloration and explore the mechanisms underlying beeswax-amber’s color variation. Results indicate that beeswax-amber coloration is closely linked to its microscopic bubble characteristics. The microstructure satisfies conditions for Mie scattering, some white beeswax-amber samples contain abundant nanoscale bubbles, triggering a combined effect of Rayleigh and Mie scattering. These results demonstrate that the color of Baltic amber is governed not only by its intrinsic body color but also by the synergistic optical effects arising from internal bubble microstructures, providing a physically grounded explanation for its diverse appearances.

Materials doi: 10.3390/ma19101977

Authors: Yasin Onuralp Özkılıç Ali İhsan Çelik Memduh Karalar Muhannad Riyadh Alasiri Sadik Alper Yildizel

Throughout their service life, concrete buildings are subjected to a number of significant degradation processes, one of which is exposure to high temperatures. This degradation degrades the mechanical and physical properties of concrete, resulting in a reduction in its strength. Consequently, it is essential to enhance the qualities of concrete at elevated temperatures. Therefore, this study examines the synergistic effects of WBA content and temperature on the mechanical properties of concrete, emphasizing sustainability and high-temperature durability. WBA substituted fine aggregate at 0–50% by mass, and specimens were subjected to ambient and elevated temperatures up to 800 °C prior to testing for compressive strength (CS), flexural strength (FS), and splitting tensile strength (STS). Two-way ANOVA established that both WBA and temperature had statistically significant effects (p < 0.05) on all strength measures, with WBA accounting for the bulk of the variation. At 24 °C, augmenting WBA from 0% to 50% enhanced CS, FS, and STS by 37.26%, 40.63%, and 32.86%, respectively. Elevated temperatures diminished all strengths, with STS exhibiting the most significant relative decline, especially beyond 400 °C. response surface methodology (RSM) models exhibited exceptional prediction accuracy (R2 > 0.97) and indicated that WBA mitigates strength loss due to elevated temperatures.

Materials doi: 10.3390/ma19101976

Authors: Xi Xiong Long Jin Shenglong Wang Tianpei Xu Jiabin Zhang Longchao Huang Yong Ao Weili Deng Weiqing Yang

Polyvinylidene fluoride (PVDF), one of the most promising flexible piezoelectric polymers bridging mechanical compliance and infrastructure-scale sensing, suffers from low intrinsic β-phase content that limits energy conversion efficiency. Two-dimensional MXene nanosheets offer a compelling solution, inducing β-phase crystallization through interfacial hydrogen bonding while preserving essential flexibility, yet conventional fabrication methods lack precise control over dipole alignment and suffer from percolation leakage at functional loadings. Herein, we report a process-structure synergistic strategy that combines EHD printing with an optimized serpentine structure to reconcile piezoelectric sensitivity with mechanical durability. By precisely tuning the MXene loading to 0.75 wt% (near but below the percolation threshold), the composite achieves a β-phase content of 71.91% and a piezoelectric sensitivity of 18.09 mV/kPa, while the serpentine design delivers a tensile strength of 21.97 MPa and 17.46% elongation at break. As a proof-of-concept, the sensor is deployed in a vehicle-responsive tunnel lighting system, withstanding cyclic heavy loads and achieving a 95.04% energy-saving rate compared to continuous operation. This work advances high-performance flexible piezoelectric composites for intelligent infrastructure applications.

Materials doi: 10.3390/ma19101975

Authors: Huize Cui Han Wang Wenwen Gu Chumeng Luo Yan Zhang Chuang Zhang Shengtao Li

Epoxy/BaTiO3 nanocomposites with varying filler contents of BaTiO3 were prepared and characterized for flexible DC insulation applications such as IGBT. Their breakdown strength under DC, AC, and 10 kHz voltage, tensile properties, dielectric response, surface potential decay, temperature-/electric field-dependent conductance, and field grading capability were investigated. Results show that loading BaTiO3 increases the dielectric constant and alters loss behavior due to enhanced interfacial polarization and modified charge transport. However, breakdown and tensile strengths decrease monotonically with filler content, which is attributed to interfacial heterogeneity and local field distortion. Shallow-trap density rises while trap energy level declines with higher BaTiO3 loading, promoting charge trapping–detrapping. Electrical conductivity of epoxy/BaTiO3 nanocomposites increases with both electric field and temperature, while simulation of electric field distribution in the triple point of IGBT encapsulation reveals that the increased permittivity and conductivity with BaTiO3 content can reduce the maximum local electric field by up to 6.7% and 13.7% for the two kinds of typical structure of triple points, respectively. Thus, nano-BaTiO3 effectively tailors dielectric response and charge transport but introduces interfacial complexity that degrades breakdown and mechanical performance. However, a trade-off between intrinsic insulation, tensile strength, and field grading capability can be obtained. This work offers experimental insights for designing epoxy-based encapsulation materials with tunable electrical properties for flexible DC systems.

Materials doi: 10.3390/ma19101974

Authors: Chuheng Zhong Wenhao Deng Jinzhi Zhou

This study tested the mechanical properties of sugarcane bagasse fiber-reinforced recycled aggregate concrete (SFRAC) with sugarcane bagasse fiber (SF) volume fractions of 0.5%, 1.5%, and 3%, and recycled coarse aggregate (RCA) replacement rates of 20%, 40%, and 60% by the mass of coarse aggregate. Evaluated parameters included compressive strength and flexural strength. Based on the mechanical performance test results, seven specimens with superior performance were selected for further flexural fatigue testing. This identified the optimal SF and RCA replacement ratios that balance mechanical performance, fatigue resistance, and economic/environmental considerations. The study concluded that sugarcane bagasse fiber significantly enhances the mechanical properties of recycled aggregate concrete (RAC). At a fiber volume concentration of 1.5%, compressive strength increased by up to 15.1%, while flexural strength improved by up to 24.6%. Regarding fatigue performance, the flexural fatigue life of SFRAC increased synchronously with rising SF content, with test results highly consistent with the three-parameter Weibull distribution. Based on this, the P-lgS-lgN equation and the S-λf-N equation incorporating failure probability and fiber parameters were derived. A fatigue strain-based damage evolution model was established to predict damage levels and remaining life of SFRAC. SEM experiments confirmed SF’s reinforcing effect on SFRAC at the microstructural level. These studies demonstrate that SFRAC with a 1.5% SF content and 40% RCA substitution offers optimal performance and environmental sustainability.

Materials doi: 10.3390/ma19101972

Authors: Mohammed Amine Benziada Antonio Javier Sanchez-Herencia Isamil Daoud Hossein Besharatloo Begoña Ferrari Djamel Miroud Ana Ferrandez-Montero

Additive manufacturing (AM) techniques are becoming key factors for repairing and replacing damaged bone. These techniques enable the customization of implants, which can be tailored to the specific area to be treated or healed. Additionally, the combination of absorbable and osteoconductive biomaterials with 3D printing could eliminate second surgeries to remove implants, which is particularly relevant in pediatric and geriatric patients. The capabilities of AM in this context affect not only the external shape but also the internal microarchitecture, where the arrangement of struts to develop complex infills enhances relevant properties such as specific strength, degradation rate, and vascularization. In this study, auxetic scaffold structures made of both polylactic acid (PLA) and a PLA-hydroxyapatite (PLA-HA) composite with 40 wt% of hydroxyapatite (HA) are designed and produced using Fused Filament Fabrication (FFF). Samples of PLA and PLA-HA were 3D printed in dense samples and with auxetic infills. In dense samples, the characterization is performed by X-ray diffraction (XRD), Raman spectroscopy, wettability tests, nanoindentation, and tribological assessments. Two auxetic cellular models have been tested after degradation in PBS media, and their microstructural, structural, and mechanical properties are analyzed. Results show that the addition of hydroxyapatite (HA) significantly improves the hydrophilicity of the PLA matrix, as evidenced by a decrease in water contact angle from 73.4 ± 4.4° to 52.6 ± 2.8° (≈28% reduction), while also enhancing its mechanical and tribological properties, with hardness increasing from 207 ± 30 MPa to 241 ± 28 MPa (≈15%) and Young’s modulus from 4.08 ± 0.55 GPa to 6.24 ± 0.61 GPa (≈53%). Additionally, biodegradation of PLA-HA composites reveals a significant reduction in mechanical properties after 15 days, while the auxetic re-entrant structures mostly retain their shape during compression testing.

Materials doi: 10.3390/ma19101973

Authors: Agata Kołkowska Wojciech Lisieński Łukasz Gardas Weizhi Shang Aleksander Gąsior Artur Maciej Marta Wala-Kapica Wojciech Simka

The growing demand for sustainable energy technologies has intensified interest in direct urea fuel cells as an environmentally friendly energy conversion system. In this work, a ternary NiCuZn electrocatalyst is synthesized via a single-step electrodeposition process, offering a rapid and scalable alternative to commonly used hydrothermal or multistep fabrication routes. Structural and compositional analyses (SEM, EDX) confirm the formation of coral-shaped particles of NiCuZn powders. Electrochemical evaluation in alkaline media demonstrates that powders of both tested variants exhibit clear anodic activity, with peak potentials in the range of 0.4–0.6 Vvs Ag|AgCl (sat. KCl). Zinc presence was confirmed also after the process. Upon urea addition, a pronounced enhancement in anodic current density is observed. Notably, variant NiCuZn powder, which was produced using higher current density during electrodeposition, shows superior catalytic activity from approximately 0.4 Vvs Ag|AgCl (sat. KCl), reaching a maximum of 10 mA/cm2 near 0.75 Vvs Ag|AgCl (sat. KCl), and stability, which are attributed to its highly homogeneous microstructure and dynamic surface activation mechanism uniquely by partial zinc leaching during operation. These findings demonstrate that electrodeposited NiCuZn systems can deliver competitive performance despite their structural simplicity, highlighting their potential as cost-effective and scalable anode materials for direct urea fuel cell applications. We address a critical bottleneck in fuel cell manufacturing by replacing time-intensive hydrothermal syntheses with a rapid, highly scalable electrodeposition method. Furthermore, the identification of zinc-leaching mechanisms provides crucial new insights into dynamic catalyst activation, moving beyond traditional, static anode designs.

Materials doi: 10.3390/ma19101971

Authors: Afef Tarhouni Marcelo Augusto Malagutti Tanguy Bernard Narges Ataollahi Eleonora Isotta Andrea Chiappini Hassen Dahman Lassaad El Mir Paolo Scardi

The need for sustainable and cost-effective thermoelectric materials has brought attention to earth-abundant and mineral compounds, like Cu2ZnSnS4 (CZTS). In this work, CZTS nanoparticles (NPs) were synthesized via the sol–gel method using environmentally friendly solvents based on water and ethanol mixtures. The resulting CZTS NPs were then processed into inks through ball milling to produce a thin-film thermoelectric generator (TEG). Structural and microstructural properties were investigated via X-ray diffraction and Raman spectroscopy, confirming the kesterite CZTS phase upon sintering. The chalcogenide exhibited p-type semiconductor behaviour, with a Seebeck coefficient reaching ~69 µV/K at 385 K. Van-der-Pauw measurements of conductivity confirmed a non-degenerate semiconducting behaviour, achieving ~1.77 S/cm at 323 K. A two-leg CZTS thin-film TEG reaching a maximum power output of 32(3) nW at a ΔT ~160 K was used, measured with a home-made setup. The volume-specific power of the generator reached 4×10−4 μW cm−3 K−2. These results point to an effective use of sol–gel-based techniques to produce a functional thermoelectric generator, providing a costless and environmentally friendly approach to CZTS NPs.

Materials doi: 10.3390/ma19101970

Authors: Qingdong Tao Tianhong Xia Desheng Yang Hao Xiang Ruizhe Si

To evaluate the susceptibility of styrene–butadiene–styrene (SBS)-modified asphalt to modifier segregation during high-temperature storage, this study examined its segregation behavior and microstructural evolution under storage conditions ranging from 70 to 163 °C over durations of 48–144 h, with varying warm-mix agent dosages (0%, 3%, 4%, and 5%). The investigation was conducted using softening point measurements, dynamic shear rheometry, infrared spectroscopy, and optical microscopy. The results indicated that the incorporation of the warm-mix agent significantly reduced the difference in softening point, diminished the discrepancies in complex modulus and phase angle between the upper and lower layers, and inhibited SBS aggregation and phase separation. When the warm-mix agent content reached 5%, the softening point difference in the modified asphalt at 163 °C and 48 h decreased from 14.4 °C to 1.6 °C, essentially eliminating segregation. Infrared spectroscopy confirmed that the warm-mix agent did not induce chemical bond changes but improved the compatibility between the SBS modifier and the base asphalt. Microscopic observation further verified that the warm-mix agent facilitated a uniform dispersion of SBS modifier particles, forming a stable microphase structure. The research findings provide valuable insights for improving the storage stability and engineering performance of SBS-modified asphalt.

Materials doi: 10.3390/ma19101965

Authors: Ekaterina N. Muratova Igor A. Vrublevsky Vyacheslav A. Moshnikov Dmitry A. Kozodaev Alena Yu. Gagarina Stepan E. Parfenovich Danila A. Kavalenka

The paper presents the results of a study on the structure and electrical properties of graphite-like amorphous carbon films deposited by electron-beam evaporation with vacuum heat treatment. The current–voltage characteristics of the films were analyzed in weak and strong electric fields in the temperature range from 25 to 155 °C. For the contact of carbon films with nickel, the Schottky barrier height was calculated based on the obtained current–voltage characteristics. It was found that in the temperature range of 25–45 °C, the mechanism of direct tunneling of charge carriers through the narrow Schottky barrier dominates (φb = 0.055 eV). In the range of 55–75 °C, a transition to the thermally assisted tunneling mechanism is observed (φb = 0.076 eV). At temperatures above 85 °C, charge carrier transport through the Schottky barrier occurs via thermionic emission (φb = 0.3 eV). The analysis of the current–voltage characteristics of graphite-like carbon films allowed us to establish the main mechanisms of hopping conductivity via localized states. It is shown that in the temperature range of 298–348 K, conductivity is determined by states near the Fermi level. The temperature interval of 348–428 K corresponds to conductivity through the band tail of localized states near the conduction band. It is shown that the increase in conductivity in strong electric fields is due to the Poole–Frenkel effect.

Materials doi: 10.3390/ma19101968

Authors: Chunyan Wang Yafan Yang Fangyuan Gong Xuejiao Cheng Bohan Ma

The rapid development of tropical island tourism has put forward a higher demand for asphalt pavement construction on the island. However, the asphalt pavement engineering in the offshore area is generally faced with high material transportation costs. Additionally, challenges such as high-temperature climate and heavy-load traffic may lead to permanent pavement deformation. As a typical marine solid waste, shells have high calcium carbonate content and porous structures, which have the potential advantage of modified asphalt. In this study, mixed shell powder was used as a modified material, and 70 # base asphalt and SBS-modified asphalt were mixed, respectively. The effect of asphalt modification was analyzed by basic performance tests and high-temperature rheological tests. An asphalt mixture was prepared by replacing limestone powder with mixed shell powder in equal volume, and its road performance was systematically tested. The modification mechanism was revealed by means of a microscopic test. The results show that the recommended content of mixed shell powder in SBS-modified asphalt is 9%, and 50–100% mixed shell powder can be used to replace mineral filler in base asphalt and single SBS modified asphalt mixture. This study provides effective technical support for the utilization of shell solid waste in offshore areas and the optimization of asphalt pavement performance.

Materials doi: 10.3390/ma19101969

Authors: Kai Zhang Wei Li Shaoping Wang Conglin Wang Xiaojun Huang Min Zhu Zhixin Wang Min Deng

Iron ore mining requires the surrounding rock to be excavated, and the beneficiation process generates tailings. When used as construction aggregates, these materials can cause concrete to crack due to the presence of pyrite. Currently, there are no established technical methods to prevent damage caused by pyrite, which limits the resource recovery of such solid waste. In this study, we selected the surrounding rock and tailings to serve as coarse or fine aggregates for C50 concrete based on standard engineering mix proportions. We found that surface-exposed pyrite on aggregates oxidizes first to form ettringite, triggering expansion, with the expansion rate positively correlated with the surface-exposed pyrite content. The deformation process was quantitatively characterized using the Arrhenius equation and by analyzing the acceleration effect of temperature on expansion, yielding an apparent activation energy of 8.28–9.47 kJ/mol. Using a 0.04% expansion value as the failure criterion, the results indicate that at an annual average temperature of 20 °C, C50 concrete with surface-exposed pyrite introduced by concrete aggregates exceeding 20 kg/m3 will fail within its service life.

Materials doi: 10.3390/ma19101967

Authors: Md Jonaet Ansari Elias J. G. Arcondoulis Anthony Roccisano Christiane Schulz Thomas Schläfer Colin Hall

This study evaluates the feasibility of airborne acoustic source localisation (ASL) for in situ crack localisation in industrial laser-based directed energy deposition (DED-LB/M) fabricated structures. A four-microphone array combined with a Generalised Cross-Correlation with Phase Transform (GCC-PHAT) algorithm was used to estimate crack positions from time differences of arrival (TDOAs) extracted from raw acoustic emissions during multi-layer single-track fabrication. Prior to experimentation, the microphone array geometry was numerically optimised under industrial placement constraints by introducing controlled TDOA perturbations and minimising three-dimensional localisation uncertainty using alpha-shape volume analysis. Experimental validation was performed on six-layer single-track structures, with estimated crack positions compared against post-process microscopic measurements. Localisation errors ranged from 12 to 68 mm in the X-direction, 0.7–32 mm in the Y-direction, and 5–100 mm in the Z-direction. While horizontal localisation demonstrated centimetre-scale accuracy for most cracks, depth estimation exhibited greater variability. The results confirm that airborne ASL can provide meaningful spatial information regarding crack formation during DED-LB/M. However, localisation performance remains sensitive to TDOA estimation accuracy, microphone array constraints, and the complex acoustic environment inherent to the process. This work demonstrates the industrial feasibility of ASL for in situ crack investigation while highlighting the need for further advancements in array design and signal processing to achieve robust three-dimensional defect localisation in additive manufacturing systems.

Materials doi: 10.3390/ma19101966

Authors: Qinghui Zhang Shuchen Wang Yiming Ma Xuehua Li Zhijun Li Xianzhe Shi

Magnesium alloys that are low density and have a high specific strength are widely utilized as lightweight structural materials. Due to their hexagonal close-packed crystal structure, plastic deformation in magnesium alloys is strongly limited in dislocation slip and mainly accommodated by deformation twinning, which results in distinct mechanical anisotropy and tension–compression asymmetry. This paper, centered on mechanism competition and microstructure regulation, systematically reviews the recent progress in the compressive mechanical responses of magnesium alloys. Key results reveal the cooperative and competitive mechanisms between slip and twinning, the significant controlling effects of temperature and strain rate on deformation behavior, and the effective design strategies of gradient and heterogeneous structures that achieve superior strength–ductility synergy. This review provides essential theoretical support for the development and performance optimization of high-performance magnesium alloys.

Materials doi: 10.3390/ma19101964

Authors: Yuqing Yang Yisong Lei Xinxi Li Wenzeng Bing Hongbo Li Yongjun Xiang Shuming Peng

In energy conversion semiconductor devices, radiation damage is directly related to the long-term stability of β-voltaic batteries. In this study, single-crystalline silicon P+NN+ devices and P+-silicon materials with SiO2 surface passivation were irradiated using a ~70 keV accelerator electron beam in a nitrogen atmosphere for 2 min, 10 min, 1 h, 6 h, and 12 h. The tritium-voltaic output decreased rapidly within the first 2 min of electron beam irradiation and then decayed slowly. After 1 h of irradiation, both the output short-circuit current (Isc) and open-circuit voltage (Voc) remained stable. The effects of the damage were analyzed using typical samples irradiated for 1 h. Neutron reflectometry (NR) was employed as the primary characterization method, while X-ray photoelectron spectroscopy (XPS)—combined with Ar+ etching—and secondary ion mass spectrometry (SIMS) were used to verify radiation-induced structural changes at the SiO2 surface and SiO2/Si interface. It was found that nitrogen atoms from the atmosphere penetrated the SiO2 layer to a depth of approximately 5–10 nm, forming a non-stoichiometric SiON structure, without further diffusion into deeper layers. Irradiation significantly increased the thickness of the SiO2/Si interface transition layer to about 14–18.5 nm, and the SiO2 structure within this layer became relatively loose. It can be inferred that tritium-voltaic batteries using SiO2-surface-passivated single-crystalline silicon P+NN+ devices as energy-conversion units and packaged in a nitrogen atmosphere can stably provide power for 10 years, with an Isc reduction of no more than 12% and a Voc reduction of no more than 6%, excluding the spontaneous decay of tritium.

Materials doi: 10.3390/ma19101963

Authors: Yaping He Zihui Sun Changhu Zhang Limei Song Quan Han

Three types of graphene–single crystal titanium dioxide composite (GR–TiO2SCs) were prepared using the hydrothermal method, employing TiF4 and graphite as raw materials with hydrofluoric acid serving as the morphology-directing agent. The phase composition and morphological features of the resultant composites were systematically characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction. These complementary characterization results clearly demonstrate that graphene and TiO2 single crystals have been successfully hybridized to form a well-defined heterostructure, rather than a simple physical mixture. Photocatalytic performances were evaluated by monitoring the photodegradation behaviors of methylene blue, rhodamine B, and methyl orange solutions under simulated light irradiation, with real-time concentration variations recorded by UV–visible absorption spectroscopy. The composite sample in which TiO2SCs were in situ grown and uniformly anchored onto graphene oxide substrates effectively suppressed the self-stacking and agglomeration of individual crystallites, thus delivering the best photocatalytic response. Increased exposure of the active catalytic interfaces of TiO2SCs was found to play a key role in elevating the overall photocatalytic activity. The hierarchical assembly protocol developed in this work provides a feasible pathway for the rational design of functional composites with controllable microstructures and tailored properties, which can be further extended to the development of advanced sensing materials.

Materials doi: 10.3390/ma19101962

Authors: Józef Iwaszko Krzysztof Kudła Małgorzata Lubas

The main aim of the work was to analyse the microstructure and selected properties of a metal-matrix surface composite reinforced with a product of vitrification of asbestos-cement waste (ACW) and glass cullet from cathode-ray tubes (CRTs). The composite matrix was an AA7075 (Al-5.5Zn-2.4Mg-1.6Cu-0.2Cr) aluminium alloy. The FSP (friction stir processing) method was used to produce the composite. The composites were tested in the context of the possibility of using vitrified material as a substitute for other reinforcing materials. As a result of treatment, a composite surface layer was obtained, characterised by uniform distribution of the reinforcing phase with a good bond with the matrix. This process was accompanied by strong grain refinement in the stirring zone and partial dissolution of intermetallic phases. These microstructural changes, combined with the introduction of hard particles into the metal-matrix, resulted in a significant increase in the composite’s hardness and wear resistance. As a result of the conducted research, it was found that using the product of vitrification of ACW and CRT cullet in the composites manufacturing process is beneficial, as it is not only a competitive solution to other reinforcing phases, but also an effective way to manage waste hazardous to the environment and humans, thus adding new functionalities to products processed in this way.

Materials doi: 10.3390/ma19101960

Authors: Zarina Aringozhina Bauyrzhan Rakhadilov Arnur Askhatov Meruyert Adilkanova Nurtoleu Magazov

This study investigates the influence of preliminary severe plastic deformation on the efficiency of ion-plasma nitriding (IPN) and the formation of a nitrided layer in 12Kh18N10T austenitic stainless steel. Two types of surface mechanical treatment were compared: vibro-impact ball mechanical treatment (VIMT) and ultrasonic nanocrystalline surface modification (UNSM). After the preliminary treatments, the samples were subjected to ion-plasma nitriding at 500 °C for 10 h using ammonia (NH3) as the working gas. The phase composition, microstructure, elemental distribution, surface roughness, microhardness, and scratch resistance were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) analysis, profilometry, instrumented indentation, and progressive scratch testing. The results show that both types of preliminary treatment promote the formation of a nitrogen-enriched diffusion layer. The UNSM-treated samples exhibited more pronounced peak broadening and shifting in XRD patterns, indicating a higher level of lattice distortion and nitrogen supersaturation. The maximum nitrogen concentration in the near-surface region reached 15.56 wt.%. Microhardness increased significantly after nitriding for both treatments. Under the selected processing conditions, the UNSM + IPN samples demonstrated a thicker diffusion layer, lower surface roughness, and higher critical loads in scratch testing, indicating improved resistance to surface damage compared with VIMT + IPN samples. The obtained results highlight the important role of the defect structure formed during preliminary treatment in controlling nitrogen diffusion and the resulting mechanical and tribological properties of ion-plasma nitrided austenitic stainless steel.

Materials doi: 10.3390/ma19101961

Authors: Xing Li Hao Qiu Erkai He

With the rapid pace of industrialization and urbanization, environmental pollution has emerged as a critical global challenge that severely threatens ecological health [...]

Materials doi: 10.3390/ma19101959

Authors: William A. González Susanna Nilsson Diego Fuentes-Cano Alicia Ronda Alberto Gómez-Barea

The calcination kinetics of limestone and dolomite under conditions relevant to sorption-enhanced gasification (SEG) were investigated: mild temperature (775–850 °C), low CO2 partial pressure (0.05–0.10 bar), and a steam-rich (H2O balance) atmosphere. Experiments with two Ca-based sorbents (limestone and dolomite) were conducted in a fluidized bed reactor to assess both initial calcination kinetics and multicycle deactivation during 10 cycles under SEG carbonation conditions at 650 °C. Dolomite exhibited markedly higher calcination rates than limestone, which is consistent with the structural modifications induced by MgCO3 decomposition and the presence of MgO, resulting in a slightly lower apparent activation energy (115.96 kJ mol−1 for dolomite compared to 120.27 kJ mol−1 for limestone). Both sorbents showed a strong sensitivity to the deviation from the equilibrium CO2 partial pressure, with reaction orders near 2. The presence of steam was confirmed to have a significant catalytic effect, accelerating the first-cycle calcination rate compared to dry N2 conditions. Sorbent deactivation caused by sintering was more pronounced at higher temperatures and CO2 pressures. Dolomite showed significantly less deactivation, compared to limestone, which can be attributed to the increase in structural stability due to the presence of MgO. The kinetics obtained in this work contribute to the design of stable SEG based on dual fluidized bed reactors, particularly to assist in the selection of calcination operating conditions to minimize sorbent deactivation and in the development of stable CO2-sorbents.

Materials doi: 10.3390/ma19101958

Authors: Bianca Costa Rodrigues Renata Jesuina Takahashi Vera Lúcia Othéro de Brito Danieli Aparecida Pereira Reis

This study investigates how processing parameters and powder characteristics influence the mechanical performance of thermal barrier coatings (TBCs) applied to a Ti-6Al-4V alloy. Two TBCs were deposited by Atmospheric Plasma Spray (APS) using different processing conditions, feedstock characteristics, and coating thicknesses (thin and thick configurations). TBC characterization included powder size analysis, scanning electron microscopy (SEM), surface roughness, X-ray diffraction, instrumented indentation, and scratch testing. Mechanical behavior was assessed using creep testing at 125 MPa and 500 °C for coated and uncoated samples. Fracture surfaces of crept samples were analyzed by SEM and stereomicroscopy. Thicker TBC exhibited higher elastic modulus but contained microcracks and higher porosity, resulting in a higher steady-state creep rate (0.0006 h−1, approximately 167% above the uncoated substrate) and reduced rupture time. Conversely, thinner TBC remained initially crack-free, promoting stress redistribution and leading to a lower creep rate (0.0002 h−1, about 67% below the substrate) and delayed failure. Fractographic analysis revealed ductile fracture of Ti-6Al-4V in all conditions, indicating that coatings influenced damage accumulation rather than fracture mode. These findings underscore the combined effect of processing parameters and coating architecture on TBC performance for aerospace applications.

Materials doi: 10.3390/ma19101955

Authors: Yuxi Zheng Xiaofei Guan

Liquid gallium (Ga) provides a dynamic reaction interface covered by a self-limiting native oxide layer, yet the reaction behavior of liquid Ga with different inorganic nitrogen sources and the surface-layer evolution remains insufficiently clarified. Herein, we have comparatively investigated interfacial reactions of pure liquid gallium (Ga) with N2, NH3, and NH4Cl under controlled thermal treatments (400, 450, or 500 °C for a 6 h duration), and further examined the reaction with NH4Cl in non-contact versus direct-contact configurations. The resulting surface films were analyzed using a combination of multiple characterization tools after removing residual liquid Ga underneath. Under N2 at 400–500 °C, the surface products obtained were dominated by oxygen-containing gallium species and no distinguishable nitride phase was detected, indicating sluggish kinetics of nitridation in this temperature range. In comparison, NH3 promoted nitrogen incorporation more effectively. Nitrogen-related signals were also detected in the surface products of the NH4Cl experiments in non-contact and direct-contact modes, whereas direct contact resulted in significantly stronger interfacial restructuring and characteristic morphologies, such as spheres and hollow-shell structures. Overall, the extent of nitrogen incorporation and the morphology evolution are jointly governed by nitrogen-source reactivity, temperature, and local contact conditions, with the native oxide layer mediating the competing oxidation and nitridation processes.

Materials doi: 10.3390/ma19101957

Authors: Mohammad Reza Saeb

The term “sustainable material” has become widely used in materials science, yet its conceptual foundation remains inconsistently interpreted. Despite major progress in sustainability assessment, circularity metrics, life cycle analysis, and policy-oriented frameworks, sustainability is still commonly treated as an intrinsic material property instead of a multidimensional and context-dependent outcome. This perspective addresses this unresolved conceptual gap by critically distinguishing widely used but often interchangeably applied terms such as bio-based, recyclable, biodegradable, circular, green, renewable, and sustainable materials. It is argued that none of these descriptors alone can define sustainable materials, since each captures a specific or only a limited aspect of material behavior while overlooking interacting factors, including processing conditions, infrastructure, embodied impacts, end-of-life management, and application-dependent constraints. Accordingly, the present work challenges binary classification of materials as “sustainable” or “non-sustainable” and proposes a shift toward a more integrated and context- dependent interpretation of sustainable materials. By clarifying the boundaries and limitations of existing terminology, this perspective aims to strengthen scientific communication, improve sustainability-oriented materials selection, and motivate the development of more structured multidimensional frameworks for future “sustainable material” classification.

Materials doi: 10.3390/ma19101951

Authors: Li Jin Siqi Jia Ze Zhang Zicong An Zhenkun Lu

Solid rocket propellants based on hydroxyl-terminated polybutadiene (HTPB), in which HTPB acts as the polymeric binder and fuel matrix, are widely used in aerospace propulsion. During storage, transport, and service, these composite energetic materials are exposed to sustained mechanical loads as well as environmental variations, which may induce time-dependent inelastic deformation. Such creep deformation can alter the grain geometry, affect combustion stability, and reduce the structural reliability of rocket motors. In this work, room-temperature tensile creep tests were conducted on an HTPB-based solid propellant under different stress levels. Several viscoelastic and power-law constitutive models were compared, and a composite time-hardening creep model was established to describe the experimental strain–time response. The model was further implemented in Abaqus through a Fortran user subroutine for finite element simulation. The results provide a useful basis for creep deformation assessment, formulation optimization, and structural reliability analysis of HTPB-based propellants.

Materials doi: 10.3390/ma19101952

Authors: Yamei Zang Yulin Zhan Dongchen Guo Shixin Liang Qi Zhao Qinghua Tao Hongfa Yu

To investigate the bond performance between reinforcement and tunnel lining concrete under freeze–thaw cycles in plateau regions, pull-out tests were conducted on secondary-lining-reinforced concrete specimens subjected to different numbers of freeze–thaw cycles. The variations in the fundamental properties of the lining concrete, as well as the bond stress and maximum slip between the reinforcement and the concrete, were examined. The results indicate that, with an increasing number of freeze–thaw cycles, the mass of the lining concrete first increases and then decreases, while the compressive strength and splitting strength gradually decrease. The bond stress between the reinforcement and concrete shows a decreasing trend, whereas the maximum slip exhibits an increasing trend. Furthermore, a finite element model of the reinforced concrete pull-out specimen was established using ABAQUS software to simulate the bond performance under different freeze–thaw cycles. The comparison between experimental and simulated results validates the rationality of the finite element model. This study provides a reference for understanding the bond–slip behavior of tunnel lining reinforced concrete subjected to freeze–thaw environments in cold plateau regions.

Materials doi: 10.3390/ma19101956

Authors: Zhongyuan Li Hongda Yang Minhu Xu Xiaohua Tian

The severe performance degradation of lithium-ion batteries at low temperatures limits their applications in extreme environments. Herein, we report the development of a low-temperature-capable 2.5 Ah 18650 cylindrical battery employing a LiNi0.8Co0.15Al0.05O2 cathode with optimized conductive additive formulations. The ternary conductive architecture is rationally designed based on dimensional complementarity: a zero-dimensional Super P (SP) nanoparticle ensures percolation through point-to-point contacts, a one-dimensional multi-walled carbon nanotube (MWCNT) establishes long-range electron highways via line-to-point bridging, and a two-dimensional graphene nanoplatelet (GNP) provides face-to-point encapsulation of active particles, mechanically buffering volume expansion and suppressing interfacial degradation. This hierarchical point–line–plane network generates redundant electron transport pathways while steric hindrance effects mitigate aggregation of each component. Through systematic comparative investigation of GNP/MWCNT/SP ternary and MWCNT/SP binary conductive systems, we elucidate the distinct roles of low-dimensional nanocarbons in electrochemical performance enhancement. Film resistivity measurements reveal that the ternary system achieves a 67% reduction in cathode resistivity (to 9.1 Ω·cm at 20 °C) compared to conventional SP (27.5 Ω·cm), outperforming previously reported binary nanocarbon systems for high-nickel cathodes (typically 40–55% reduction at comparable loadings). This enhancement is achieved at a constant total conductive additive loading of 2.5 wt%, demonstrating that dimensional optimization rather than quantity increase governs electrical transport properties. Electrochemical evaluations demonstrate that the fabricated 18650 cells deliver exceptional rate capability (10C continuous and 20C pulse discharge) and remarkable low-temperature performance (76.8% capacity retention at −40 °C under 1C). Notably, while both conductive formulations exhibit comparable rate performan ce and temperature adaptability, the ternary GNP/MWCNT/SP system demonstrates significant superiority in cycling stability, achieving 94.9% capacity retention after 1000 cycles at ambient temperature versus inferior retention for the binary counterpart. Electrochemical impedance spectroscopy analyses indicate reduced polarization and enhanced lithium-ion diffusion kinetics in the ternary system. This study establishes a high-performance low-temperature 18650 battery chemistry and provides quantitative mechanistic insights into how dimensional synergy in conductive additive design governs the rate capability, thermal behavior, and cycling stability of nickel-rich cathodes operating under extreme conditions.

Materials doi: 10.3390/ma19101954

Authors: Jialeen Sairike Kamale Tuokedaerhan Serikbek Sailanbek Zhengang Cai Haotian Yang

With the continuous advancement of display technology and advanced integrated circuits, oxide thin-film transistors (TFTs) have become core devices due to their high mobility, low leakage current and excellent large-area uniformity. To achieve low power consumption, high performance and high reliability, the introduction of high-k gate insulating layers is crucial. Among the numerous high-k materials, hafnium oxide (HfO2) has attracted significant attention due to its excellent dielectric properties and good compatibility with CMOS processes. In this paper, uniform and dense HfO2 films were successfully fabricated using the sol–gel method to serve as insulating layers for TFT devices. Through experimental analysis, 400 °C was determined to be the optimal annealing temperature. At this temperature, the effects of replacing SiO2 with HfO2 as the insulating layer, as well as the impact of reducing film thickness, on TFT devices were investigated. Ultimately, at an annealing temperature of 400 °C, an 85 nm-thick HfO2 film achieved the highest on/off current ratio (Ion/off = 1.11 × 106), the lowest subthreshold swing (SS = 0.53 V/dec), the lowest threshold voltage (Vth = −1.1 V) and the lowest off-current ratio (Ioff = 2.5 × 10−12 A). It was confirmed that replacing SiO2 with HfO2 as the insulating layer is a viable approach for reducing the volume of TFT devices.

Materials doi: 10.3390/ma19101953

Authors: Yingfei Liu Yuxuan Wang Xiyuan Sun Chong Peng Zhe Pang Dafu Zhao Kefeiyang Hu Jiaqian Que Xingbo Huang Yong Liu

The electrochemical nitrate reduction reaction (NO3RR) represents a promising strategy for wastewater remediation and sustainable ammonia (NH3) production. However, its practical application is hindered by low selectivity and competition from the hydrogen evolution reaction (HER). Herein, a series of PtBi-CoX (X = 4.9, 5.3, and 6.1) ternary alloy nanoplates was synthesized via a one-pot method with tunable Co content. Structural characterization indicates that Co incorporation does not significantly alter the hexagonal crystal structure of the PtBi phase. Electrochemical measurements reveal that the NO3RR performance varies with PtBi-CoX (X = 4.9, 5.3, 6.1), with PtBi-Co5.3 exhibiting the optimal balance of activity and selectivity among the studied samples. At −0.5 V vs. RHE, it achieves a Faradaic efficiency (FE) of 97.75 ± 0.75% and an NH3 yield rate of 9.33 ± 0.50 mg h−1 mgcat−1 under the tested conditions. In addition, the catalyst exhibits relatively suppressed HER activity compared to samples with higher Co content, along with good stability. These findings provide useful insights into the design of PtBi-based ternary alloy catalysts for efficient nitrate reduction.

Materials doi: 10.3390/ma19101947

Authors: Zhilong Zhao Xiang An Fan Feng Jiaxing Luo Zijian Lin Chuke Zhao Ran Ang

The inherent coupling of electrical and thermal transport parameters poses a significant challenge for enhancing the thermoelectric figure of merit (zT) in PbTe-based materials. Herein, we report a synergistic co-doping strategy employing Mn and Sn in p-type PbTe to simultaneously optimize the band structure and suppress lattice thermal conductivity. Sn incorporation not only induces additional Pb vacancies, thereby increasing hole carrier concentration, but also facilitates the enhanced solubility of Na dopants within the matrix, as confirmed by microscopic and compositional analyses. More importantly, the cooperative effect of Mn and Sn substantially enhances convergence between the L and Σ valence bands, leading to an increased density-of-states effective mass and a pronounced enhancement of the Seebeck coefficient. Meanwhile, multiscale lattice defects introduced by co-doping effectively scatter phonons over a broad frequency spectrum, reducing the lattice thermal conductivity to near the theoretical minimum (~0.5 W m−1 K−1). As a result, the Pb0.91−xNa0.04Mn0.04SnxTe system achieves an exceptional peak zT of ~2.2 at 823 K, a high room-temperature zT of ~0.4, and a favorable average zT of ~1.3 over the temperature range of 303–823 K. Notably, the room-temperature zT of ~0.4 represents the highest value reported to date for p-type PbTe in the room-temperature region. This work demonstrates that Mn and Sn co-doping provides a compelling pathway for realizing both high peak and average thermoelectric performance, advancing PbTe-based materials toward practical waste-heat recovery applications.

Materials doi: 10.3390/ma19101945

Authors: Tenglong Xie Chao Ding Peng Wang Minghao Huang Shenghang Xu Zhen Wang Huiping Tang

Additively manufactured lightweight lattice structures typically consist of thin walls with thicknesses ranging from hundreds of micrometers to millimeters. Within this range, such thin walls exhibit a pronounced size effect. Despite extensive research on the topic, a clear mapping between key influencing factors and mechanical properties remains lacking. This gap makes it challenging to accurately predict mechanical performance across different wall thicknesses, especially for those below 500 μm. In this work, Ti-6Al-4V thin-walled tensile specimens with thicknesses ranging from 0.2 mm to 1.0 mm were fabricated via laser powder bed fusion (LPBF). The variations in mechanical properties, microstructure, surface defects, and internal defects were investigated. The results indicate that yield strength (YS) and ultimate tensile strength (UTS) decreased significantly as thickness decreased, dropping from 794.1 MPa to 471.7 MPa and from 910.7 MPa to 485.2 MPa, respectively. Printing defects were identified as the dominant factors governing the size effect: strength was jointly affected by surface and internal defects, whereas failure mode and ductility were primarily governed by internal defects. By introducing an effective thickness ratio parameter, a semi-empirical predictive model was developed to characterize the strength-thickness relationship and to quantify the individual contributions of surface defects and other coupled interior factors. Subsequently, ultra-thin specimens were subjected to surface grinding and polishing to alleviate surface defects, leading to improvements in YS and UTS of approximately 27–39% and 22–45%, respectively. The model-predicted strengths of the surface-treated specimens were in good agreement with the measured values, further validating the effectiveness of the proposed model.

Materials doi: 10.3390/ma19101950

Authors: Kaiyu Zhang Wanliang Zhang Chengshuang Zhou Lin Zhang

Local chemical heterogeneity is a typical feature of selective laser melted (SLM) austenitic stainless steel and is closely related to its hydrogen-assisted deformation behavior. In this work, molecular dynamics simulations are performed to investigate the effects of local segregation on stacking fault energy, hydrogen diffusion, and dislocation motion in austenitic stainless steel. Three representative alloy compositions, Fe71Cr17Ni12, Fe71Cr23Ni6, and Fe71Cr11Ni18, are used to describe local composition variation associated with segregation in SLM-relevant austenitic stainless steel. The results show that Ni-rich regions exhibit relatively higher stacking fault energy and faster hydrogen diffusion, whereas Cr-rich regions show lower stacking fault energy and reduced hydrogen mobility. Hydrogen further decreases the stacking fault energy in all three alloy models and exerts a stronger influence on local defect energetics than composition variation alone. Shear simulations indicate that elemental segregation itself has only a limited direct effect on dislocation motion, whereas its interaction with hydrogen leads to a more evident retardation of partial dislocation propagation within the segregation region. These findings highlight the coupled roles of local composition variation and hydrogen in governing defect evolution and local deformation behavior in segregation-containing regions.

Materials doi: 10.3390/ma19101949

Authors: Wei Chen Yang Bai Rong Jin Fei Chi Xinsheng Yang

In practical applications, high-temperature superconducting (HTS) cables or magnets may carry AC with DC bias, such as in superferric magnets, which can increase the AC loss of the cables or magnets. When the DC bias current is high, the resulting high loss can lead to a significant temperature rise in the cable or magnet and may even cause quench. Furthermore, different waveforms of the alternating current also result in different losses and temperature rises. Therefore, it is essential to investigate the AC loss of the cable under different current waveforms and DC bias levels using an electromagnetic–thermal coupling method. In this paper, an electromagnetic–thermal coupling model is used to investigate the AC loss and temperature rise characteristics of four stacked REBCO tapes under four typical current waveforms and various DC bias levels. The actual multilayer structure of REBCO tapes is considered in the numerical simulation, which facilitates the analysis of current distribution among different layers and its contribution to the total loss of the stacked cable. The results show that under zero DC bias or a small DC bias (0.1Idc), the square-wave current yields the largest AC loss, while the triangular-wave current results in the smallest AC loss. The losses generated by the sawtooth and sinusoidal currents are comparable and intermediate between those of the two aforementioned waveforms. When the DC bias current is moderate (0.5Idc) and the amplitude of the alternating current is greater than 0.5Icable, the loss of the cable increases rapidly. The loss generated by the square-wave current is the largest, followed by the sinusoidal current, while the sawtooth and triangular currents produce the smallest losses. When the DC bias current is high (0.9Idc), even a small amplitude alternating current results in high AC loss in the cable.

Materials doi: 10.3390/ma19101948

Authors: Rongrong Feng Xiaoxiao Wang Feiquan Guo Xiangdong Meng Yuefei Lyu Jie Liu

Conventional cement production relies heavily on the consumption of natural resources, posing significant challenges to sustainable development. Incorporating activated coal gangue (CG) into cementitious materials not only reduces cement usage but also promotes the resource utilization of solid waste. In this study, the compressive strength (CS) and microstructural evolution of CG-based composite cementitious materials were systematically investigated under activated CG replacement levels of 0–50% and water-to-binder ratios (w/b) of 0.40–0.50. The results showed that the optimal performance was achieved at a CG replacement level of 30% and a w/b of 0.40, where the 28-day CS reached 59.1 MPa, representing an 18.9% improvement compared with the control group. The pozzolanic reaction of CG reduced the Ca(OH)2 (CH)content within the cementitious matrix and promoted the formation of ettringite (AFt) and C-(A)-S-H, thereby enhancing matrix compactness. These findings provide theoretical support for the application of CG in sustainable cementitious materials.

Materials doi: 10.3390/ma19101946

Authors: Zehua Chen Longfei Mei Dali Zhang Jiajun Ji Xiaoyi Ban Zengping Zhang

To optimize the dry mixing preparation process for permeable asphalt mixtures and elucidate the microscopic mechanism of high-viscosity modifiers, this study employed Response Surface Methodology (RSM). Independent variables, including mixing temperature, dry mixing time, and wet mixing time, were selected, with Marshall stability, −10 °C splitting tensile strength, and residual stability as response indicators. The significance and fitting accuracy of the model were evaluated through Analysis of Variance and residual diagnosis. Additionally, the morphological evolution, spatial distribution, and chemical interactions of the modifier were characterized using scanning electron microscopy (SEM), fluorescence microscopy (FM), and Fourier Transform Infrared Spectroscopy (FTIR). The results revealed distinct differences in factor effects: mixing temperature most strongly influenced high-temperature performance, while wet-mixing time primarily governed low-temperature performance and water stability. Furthermore, significant interactions were observed among the variables. Multi-objective optimization determined the optimal process parameters to be a mixing temperature of 182 °C, dry mixing time of 180 s, and wet mixing time of 102 s. Experimental validation confirmed that the relative error between predicted and actual values was within 5%. Microscopic characterization revealed that under the dry mixing process, the modifier undergoes four stages: rapid melting, viscous flow, permeation diffusion, and swelling development. An appropriate mixing temperature combined with sufficient dry and wet mixing times promotes the formation of a uniform, dense spatial network structure of the modifier within the asphalt. This study validated the reliability of RSM in process optimization, providing theoretical foundations and key technical parameters for the green and efficient production of high-performance permeable asphalt mixtures.