Materials

Article

20 pages, 6382 KiB

Open AccessEditor’s ChoiceArticle

Accelerated Direct Carbonation of Steel Slag and Cement Kiln Dust: An Industrial Symbiosis Strategy Applied in the Bergamo–Brescia Area

by Giada Biava, Annalisa Zacco, Alessandra Zanoletti, Giampiero Pasquale Sorrentino, Claudia Capone, Antonio Princigallo, Laura Eleonora Depero and Elza Bontempi

Materials 2023, 16(11), 4055; https://doi.org/10.3390/ma16114055 - 29 May 2023

Cited by 13 | Viewed by 3331

Abstract

The carbonation of alkaline industrial wastes is a pressing issue that is aimed at reducing CO₂ emissions while promoting a circular economy. In this study, we explored the direct aqueous carbonation of steel slag and cement kiln dust in a newly developed [...] Read more.

The carbonation of alkaline industrial wastes is a pressing issue that is aimed at reducing CO₂ emissions while promoting a circular economy. In this study, we explored the direct aqueous carbonation of steel slag and cement kiln dust in a newly developed pressurized reactor that operated at 15 bar. The goal was to identify the optimal reaction conditions and the most promising by-products that can be reused in their carbonated form, particularly in the construction industry. We proposed a novel, synergistic strategy for managing industrial waste and reducing the use of virgin raw materials among industries located in Lombardy, Italy, specifically Bergamo–Brescia. Our initial findings are highly promising, with argon oxygen decarburization (AOD) slag and black slag (sample 3) producing the best results (70 g CO₂/kg slag and 76 g CO₂/kg slag, respectively) compared with the other samples. Cement kiln dust (CKD) yielded 48 g CO₂/kg CKD. We showed that the high concentration of CaO in the waste facilitated carbonation, while the presence of Fe compounds in large amounts caused the material to be less soluble in water, affecting the homogeneity of the slurry. Full article

(This article belongs to the Special Issue Sustainable Advanced Composite Materials for the Built Environment)

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14 pages, 5467 KiB

Open AccessEditor’s ChoiceArticle

Interfacial Modification and Bending Performance of 3D Orthogonal Woven Composites with Basalt Filament Yarns

by Lihua Lyu, Fangfang Wen, Tingting Lyu, Xinghai Zhou and Yuan Gao

Materials 2023, 16(11), 4015; https://doi.org/10.3390/ma16114015 - 27 May 2023

Cited by 2 | Viewed by 1436

Abstract

To improve their interfacial properties, 3D orthogonal woven fabrics with basalt filament yarns were modified with functionalized carboxylated carbon nanotubes (KH570-MWCNTs) and polydopamine (PDA). Fourier infrared spectroscopy (FT-IR) analysis and scanning electron microscopy (SEM) testing were used. It was demonstrated that both methods [...] Read more.

To improve their interfacial properties, 3D orthogonal woven fabrics with basalt filament yarns were modified with functionalized carboxylated carbon nanotubes (KH570-MWCNTs) and polydopamine (PDA). Fourier infrared spectroscopy (FT-IR) analysis and scanning electron microscopy (SEM) testing were used. It was demonstrated that both methods could successfully modify basalt fiber (BF) 3D woven fabrics. The 3D orthogonal woven composites (3DOWC) were produced with epoxy resin and 3D orthogonal woven fabrics as raw material by the VARTM molding process. The bending properties of the 3DOWC were tested and analyzed by experimental and finite element analysis methods. The results showed that the bending properties of the 3DOWC modified by KH570-MWCNTs and PDA were significantly improved, and the maximum bending loads were increased by 31.5% and 31.0%. The findings of the finite element simulation and the experiment results were in good agreement, and the simulation error value was 3.37%. The correctness of the finite element simulation results and the model’s validity further reveal the material’s damage situation and damage mechanism in the bending process. Full article

(This article belongs to the Special Issue Advances in the Textile for Fashion and Biomedical Industry)

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13 pages, 2510 KiB

Open AccessEditor’s ChoiceArticle

Properties of Accelerating Edge Dislocations in Arbitrary Slip Systems with Reflection Symmetry

by Daniel N. Blaschke, Khanh Dang, Saryu J. Fensin and Darby J. Luscher

Materials 2023, 16(11), 4019; https://doi.org/10.3390/ma16114019 - 27 May 2023

Viewed by 1602

Abstract

We discuss the theoretical solution to the differential equations governing accelerating edge dislocations in anisotropic crystals. This is an important prerequisite to understanding high-speed dislocation motion, including an open question about the existence of transonic dislocation speeds, and subsequently high-rate plastic deformation in [...] Read more.

We discuss the theoretical solution to the differential equations governing accelerating edge dislocations in anisotropic crystals. This is an important prerequisite to understanding high-speed dislocation motion, including an open question about the existence of transonic dislocation speeds, and subsequently high-rate plastic deformation in metals and other crystals. Full article

(This article belongs to the Section Mechanics of Materials)

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20 pages, 17038 KiB

Open AccessEditor’s ChoiceArticle

Microstructural Understanding of Flow Accelerated Corrosion of SA106B Carbon Steel in High-Temperature Water with Different Flow Velocities

by Ying Hu, Long Xin, Chang Hong, Yongming Han and Yonghao Lu

Materials 2023, 16(11), 3981; https://doi.org/10.3390/ma16113981 - 26 May 2023

Cited by 13 | Viewed by 2373

Abstract

All light or heavy water reactors fabricated with carbon steels suffer from flow-accelerated corrosion (FAC). The FAC degradation of SA106B with different flow velocities was investigated in terms of microstructure. As flow velocity increased, the major corrosion type changed from general corrosion to [...] Read more.

All light or heavy water reactors fabricated with carbon steels suffer from flow-accelerated corrosion (FAC). The FAC degradation of SA106B with different flow velocities was investigated in terms of microstructure. As flow velocity increased, the major corrosion type changed from general corrosion to localized corrosion. Severe localized corrosion occurred in the pearlite zone, which can be the prior location for generating pits. After normalizing, the improvement in microstructure homogeneity reduced the oxidation kinetics and lowered cracking sensitivity, causing a decrease in FAC rates of 33.28%, 22.47%, 22.15%, and 17.53% at flow velocity of 0 m/s, 1.63 m/s, 2.99 m/s, and 4.34 m/s, respectively. Additionally, localized corrosion tendency was decreased by reducing the micro-galvanic effect and tensile stresses in oxide film. The maximum localized corrosion rate decreased by 21.7%, 13.5%, 13.8%, and 25.4% at flow velocity of 0 m/s, 1.63 m/s, 2.99 m/s, and 4.34 m/s, respectively. Full article

(This article belongs to the Special Issue Corrosion Mechanism and Protection Technology of Metallic Materials)

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13 pages, 4713 KiB

Open AccessEditor’s ChoiceArticle

Alloy Disordering Effects on the Thermal Conductivity and Energy Gap Temperature Dependence of Cd_1−xZn_xSe Ternary Crystals Grown by the Bridgman Method

by Karol Strzałkowski, Ali Abouais, Amine Alaoui-Belghiti, Diksha Singh and Abdelowahed Hajjaji

Materials 2023, 16(11), 3945; https://doi.org/10.3390/ma16113945 - 25 May 2023

Cited by 5 | Viewed by 1568

Abstract

Investigated in this work, Cd_1−xZn_xSe-mixed ternary compounds were grown by the Bridgman method. Several compounds with zinc content varying in the range 0 < x < 1 were produced between two binary parents, CdSe and ZnSe crystals. Using the [...] Read more.

Investigated in this work, Cd_1−xZn_xSe-mixed ternary compounds were grown by the Bridgman method. Several compounds with zinc content varying in the range 0 < x < 1 were produced between two binary parents, CdSe and ZnSe crystals. Using the SEM/EDS technique, the accurate composition of formed crystals was determined along the growth axis. Thanks to that, the grown crystals’ axial and radial uniformity were determined. Characterization of the optical and thermal properties was undertaken. The energy gap was measured using photoluminescence spectroscopy for different compositions and temperatures. The bowing parameter describing the behavior of the fundamental gap with composition for this compound was found to be 0.416 ± 0.06. The thermal characteristics of grown Cd_1−xZn_xSe alloys were systematically studied. The thermal diffusivity and effusivity of the crystals under investigation were experimentally determined, allowing the calculation of the thermal conductivity. We applied the semi-empirical model that Sadao Adachi developed to analyze the results. Thanks to that, it was possible to estimate the contribution arising from chemical disorder to the crystal’s total resistivity. Full article

(This article belongs to the Special Issue Crystallographic Design of Material Thermal Properties)

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20 pages, 9327 KiB

Open AccessEditor’s ChoiceArticle

Numerical Study of Ti6Al4V Alloy Tube Heated by Super-Frequency Induction Heating

by Cheng Liu, Jingtao Han, Ruilong Lu, Jiawei Liu and Xiaoyan Ma

Materials 2023, 16(11), 3938; https://doi.org/10.3390/ma16113938 - 24 May 2023

Cited by 2 | Viewed by 1516

Abstract

Ti6Al4V alloys have a narrow processing window, which complicates temperature control, especially during large-scale production. Therefore, a numerical simulation and experimental study on the ultrasonic induction heating process of a Ti6Al4V titanium alloy tube were conducted to obtain stable heating. The electromagnetic and [...] Read more.

Ti6Al4V alloys have a narrow processing window, which complicates temperature control, especially during large-scale production. Therefore, a numerical simulation and experimental study on the ultrasonic induction heating process of a Ti6Al4V titanium alloy tube were conducted to obtain stable heating. The electromagnetic and thermal fields in the process of ultrasonic frequency induction heating were calculated. The effects of the current frequency and current value on the thermal and current fields were numerically analyzed. The increase in current frequency enhances the skin and edge effects, but heat permeability was achieved in the super audio frequency range, and the temperature difference between the interior and exterior of the tube was less than 1%. An increase in the applied current value and current frequency caused an increase in the tube’s temperature, but the influence of current was more prominent. Therefore, the influence of stepwise feeding, reciprocating motion, and stepwise feeding superimposed motion on the heating temperature field of the tube blank was evaluated. The coil reciprocating with the roll can maintain the temperature of the tube within the target temperature range during the deformation stage. The simulation results were validated experimentally, which demonstrated good agreement between the results. The numerical simulation method can be used to monitor the temperature distribution of Ti6Al4V alloy tubes during the super-frequency induction heating process. This is an economical and effective tool for predicting the induction heating process of Ti6Al4V alloy tubes. Moreover, online induction heating in the form of reciprocating motion is a feasible strategy for processing Ti6Al4V alloy tubes. Full article

(This article belongs to the Special Issue Analytical and Computational Methods in Material and Mechanical Engineering)

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18 pages, 5017 KiB

Open AccessEditor’s ChoiceArticle

Core–Shell Spheroid Structure TiO₂/CdS Composites with Enhanced Photocathodic Protection Performance

by Tingting Chen, Bo Li, Xiaolong Zhang, Xiang Ke and Rengui Xiao

Materials 2023, 16(11), 3927; https://doi.org/10.3390/ma16113927 - 24 May 2023

Cited by 5 | Viewed by 1666

Abstract

In order to improve the conversion and transmission efficiency of the photoelectron, core–shell spheroid structure titanium dioxide/cadmium sulfide (TiO₂/CdS) composites were synthesized as epoxy-based coating fillers using a simple hydrothermal method. The electrochemical performance of photocathodic protection for the epoxy-based composite [...] Read more.

In order to improve the conversion and transmission efficiency of the photoelectron, core–shell spheroid structure titanium dioxide/cadmium sulfide (TiO₂/CdS) composites were synthesized as epoxy-based coating fillers using a simple hydrothermal method. The electrochemical performance of photocathodic protection for the epoxy-based composite coating was analyzed by coating it on the Q235 carbon steel surface. The results show that the epoxy-based composite coating possesses a significant photoelectrochemical property with a photocurrent density of 0.0421 A/cm² and corrosion potential of −0.724 V. Importantly, the modified composite coating can extend absorption in the visible region and effectively separate photoelectron hole pairs to improve the photoelectrochemical performance synergistically, because CdS can be regarded as a sensitizer to be introduced into TiO₂ to form a heterojunction system. The mechanism of photocathodic protection is attributed to the potential energy difference between Fermi energy and excitation level, which leads to the system obtaining higher electric field strength at the heterostructure interface, thus driving electrons directly into the surface of Q235 carbon steel (Q235 CS). Moreover, the photocathodic protection mechanism of the epoxy-based composite coating for Q235 CS is investigated in this paper. Full article

(This article belongs to the Special Issue Functional Nanomaterials for a Better Life (Volume II))

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14 pages, 2420 KiB

Open AccessEditor’s ChoiceArticle

Construction of Bio-TiO₂/Algae Complex and Synergetic Mechanism of the Acceleration of Phenol Biodegradation

by Jinxin Guo, Xiaoman Guo, Haiyan Yang, Daohong Zhang and Xiaogeng Jiang

Materials 2023, 16(10), 3882; https://doi.org/10.3390/ma16103882 - 22 May 2023

Cited by 3 | Viewed by 1814

Abstract

Microalgae have been widely employed in water pollution treatment since they are eco-friendly and economical. However, the relatively slow treatment rate and low toxic tolerance have seriously limited their utilization in numerous conditions. In light of the problems above, a novel biosynthetic titanium [...] Read more.

Microalgae have been widely employed in water pollution treatment since they are eco-friendly and economical. However, the relatively slow treatment rate and low toxic tolerance have seriously limited their utilization in numerous conditions. In light of the problems above, a novel biosynthetic titanium dioxide (bio-TiO₂ NPs)—microalgae synergetic system (Bio-TiO₂/Algae complex) has been established and adopted for phenol degradation in the study. The great biocompatibility of bio-TiO₂ NPs ensured the collaboration with microalgae, improving the phenol degradation rate by 2.27 times compared to that with single microalgae. Remarkably, this system increased the toxicity tolerance of microalgae, represented as promoted extracellular polymeric substances EPS secretion (5.79 times than single algae), and significantly reduced the levels of malondialdehyde and superoxide dismutase. The boosted phenol biodegradation with Bio-TiO₂/Algae complex may be attributed to the synergetic interaction of bio-TiO₂ NPs and microalgae, which led to the decreased bandgap, suppressed recombination rate, and accelerated electron transfer (showed as low electron transfer resistance, larger capacitance, and higher exchange current density), resulting in increased light energy utilization rate and photocatalytic rate. The results of the work provide a new understanding of the low-carbon treatment of toxic organic wastewater and lay a foundation for further remediation application. Full article

(This article belongs to the Special Issue Heterogeneous Catalysts for Biomass Conversion and Environmental Remediation)

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12 pages, 5403 KiB

Open AccessEditor’s ChoiceArticle

Effects of Steel Slag Powder Content and Curing Condition on the Performance of Alkali-Activated Materials Based UHPC Matrix

by Kangyi Shi, Hongyang Deng, Jinxuan Hu, Junqi Zhou, Xinhua Cai and Zhiwei Liu

Materials 2023, 16(10), 3875; https://doi.org/10.3390/ma16103875 - 21 May 2023

Cited by 20 | Viewed by 2633

Abstract

The accumulation of steel slag and other industrial solid wastes has caused serious environmental pollution and resource waste, and the resource utilization of steel slag is imminent. In this paper, alkali-activated ultra-high-performance concrete (AAM-UHPC) was prepared by replacing ground granulated blast furnace slag [...] Read more.

The accumulation of steel slag and other industrial solid wastes has caused serious environmental pollution and resource waste, and the resource utilization of steel slag is imminent. In this paper, alkali-activated ultra-high-performance concrete (AAM-UHPC) was prepared by replacing ground granulated blast furnace slag (GGBFS) powder with different proportions of steel slag powder, and its workability, mechanical properties, curing condition, microstructure, and pore structure were investigated. The results illustrate that the incorporation of steel slag powder can significantly delay the setting time and improve the flowability of AAM-UHPC, making it possible for engineering applications. The mechanical properties of AAM-UHPC showed a tendency to increase and then decrease with the increase in steel slag dosing and reached their best performance at a 30% dosage of steel slag. The maximum compressive strength and flexural strength are 157.1 MPa and 16.32 Mpa, respectively. High-temperature steam or hot water curing at an early age was beneficial to the strength development of AAM-UHPC, but continuous high-temperature, hot, and humid curing would lead to strength inversion. When the dosage of steel slag is 30%, the average pore diameter of the matrix is only 8.43 nm, and the appropriate steel slag dosage can reduce the heat of hydration and refine the pore size distribution, making the matrix denser. Full article

(This article belongs to the Collection Alkali‐Activated Materials for Sustainable Construction)

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12 pages, 2849 KiB

Open AccessEditor’s ChoiceArticle

Validating the Use of Gaussian Process Regression for Adaptive Mapping of Residual Stress Fields

by Chris M. Fancher, Singanallur Venkatakrishnan, Thomas Feldhausen, Kyle Saleeby and Alex Plotkowski

Materials 2023, 16(10), 3854; https://doi.org/10.3390/ma16103854 - 20 May 2023

Viewed by 1628

Abstract

Probing the stress state using a high density of measurement points is time intensive and presents a limitation for what is experimentally feasible. Alternatively, individual strain fields used for determining stresses can be reconstructed from a subset of points using a Gaussian process [...] Read more.

Probing the stress state using a high density of measurement points is time intensive and presents a limitation for what is experimentally feasible. Alternatively, individual strain fields used for determining stresses can be reconstructed from a subset of points using a Gaussian process regression (GPR). Results presented in this paper evidence that determining stresses from reconstructed strain fields is a viable approach for reducing the number of measurements needed to fully sample a component’s stress state. The approach was demonstrated by reconstructing the stress fields in wire-arc additively manufactured walls fabricated using either a mild steel or low-temperature transition feedstock. Effects of errors in individual GP reconstructed strain maps and how these errors propagate to the final stress maps were assessed. Implications of the initial sampling approach and how localized strains affect convergence are explored to give guidance on how best to implement a dynamic sampling experiment. Full article

(This article belongs to the Special Issue Neutron Scattering Studies in Materials Science)

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17 pages, 20289 KiB

Open AccessEditor’s ChoiceArticle

WO₃ Thin-Film Optical Gas Sensors Based on Gasochromic Effect towards Low Hydrogen Concentrations

by Michał Mazur, Paulina Kapuścik, Wiktoria Weichbrodt, Jarosław Domaradzki, Piotr Mazur, Małgorzata Kot and Jan Ingo Flege

Materials 2023, 16(10), 3831; https://doi.org/10.3390/ma16103831 - 19 May 2023

Cited by 7 | Viewed by 3159

Abstract

Hydrogen gas sensors have recently attracted increased interest due to the explosive nature of H₂ and its strategic importance in the sustainable global energy system. In this paper, the tungsten oxide thin films deposited by innovative gas impulse magnetron sputtering have been [...] Read more.

Hydrogen gas sensors have recently attracted increased interest due to the explosive nature of H₂ and its strategic importance in the sustainable global energy system. In this paper, the tungsten oxide thin films deposited by innovative gas impulse magnetron sputtering have been investigated in terms of their response to H₂. It was found that the most favourable annealing temperature in terms of sensor response value, as well as response and recovery times, was achieved at 673 K. This annealing process caused a change in the WO₃ cross-section morphology from a featureless and homogenous form to a rather columnar one, but still maintaining the same surface homogeneity. In addition to that, the full-phase transition from an amorphous to nanocrystalline form occurred with a crystallite size of 23 nm. It was found that the sensor response to only 25 ppm of H₂ was equal to 6.3, which is one of the best results presented in the literature so far of WO₃ optical gas sensors based on a gasochromic effect. Moreover, the results of the gasochromic effect were correlated with the changes in the extinction coefficient and the concentration of the free charge carriers, which is also a novel approach to the understanding of the gasochromic phenomenon. Full article

(This article belongs to the Special Issue Application of Emerging Materials for Advanced Imaging and Sensing)

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15 pages, 5859 KiB

Open AccessEditor’s ChoiceArticle

Influence of Alumina Grade on Sintering Properties and Possible Application in Binder Jetting Additive Technology

by Maciej Kwiatkowski, Joanna Marczyk, Piotr Putyra, Michał Kwiatkowski, Szymon Przybyła and Marek Hebda

Materials 2023, 16(10), 3853; https://doi.org/10.3390/ma16103853 - 19 May 2023

Cited by 9 | Viewed by 2919

Abstract

Alumina is one of the most popular ceramic materials widely used in both tooling and construction applications due to its low production cost, and high properties. However, the final properties of the product depend not only on the purity of the powder, but [...] Read more.

Alumina is one of the most popular ceramic materials widely used in both tooling and construction applications due to its low production cost, and high properties. However, the final properties of the product depend not only on the purity of the powder, but also, e.g., on its particle size, specific surface area, and the production technology used. These parameters are particularly important in the case of choosing additive techniques for the production of details. Therefore, the article presents the results of comparing five grades of Al₂O₃ ceramic powder. Their specific surface area (via Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods), particle size distribution, and phase composition by X-ray diffraction (XRD) were determined. Moreover, the surface morphology was characterized by the scanning electron microscopy (SEM) technique. The discrepancy between generally available data and the results obtained from measurements has been indicated. Moreover, the method of spark plasma sintering (SPS), equipped with the registration system of the position of the pressing punch during the process, was used to determine the sinterability curves of each of the tested grades of Al₂O₃ powder. Based on the obtained results, a significant influence of the specific surface area, particle size, and the width of their distribution at the beginning of the Al₂O₃ powder sintering process was confirmed. Furthermore, the possibility of using the analyzed variants of powders for binder jetting technology was assessed. The dependence of the particle size of the powder used on the quality of the printed parts was demonstrated. The procedure presented in this paper, which involves analyzing the properties of alumina varieties, was used to optimize the Al₂O₃ powder material for binder jetting printing. The selection of the best powder in terms of technological properties and good sinterability makes it possible to reduce the number of 3D printing processes, which makes it more economical and less time-consuming. Full article

(This article belongs to the Special Issue Recent Application of Powder Metallurgy Materials)

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16 pages, 6986 KiB

Open AccessEditor’s ChoiceArticle

Polysiloxanes and Silanes with Various Functional Groups—New Compounds for Flax Fibers’ Modification

by Weronika Gieparda, Marcin Przybylak, Szymon Rojewski and Beata Doczekalska

Materials 2023, 16(10), 3839; https://doi.org/10.3390/ma16103839 - 19 May 2023

Cited by 4 | Viewed by 1988

Abstract

There is an increasing desire to use natural products that will be both effective and biodegradable. The aim of this work is to investigate the effect of modifying flax fibers with silicon compounds (silanes and polysiloxanes), as well as examining the effect of [...] Read more.

There is an increasing desire to use natural products that will be both effective and biodegradable. The aim of this work is to investigate the effect of modifying flax fibers with silicon compounds (silanes and polysiloxanes), as well as examining the effect of the mercerization process on their properties. Two types of polysiloxanes have been synthesized and confirmed by infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Scanning electron microscopy (SEM), FTIR, thermogravimetry analysis (TGA) and pyrolysis-combustion flow calorimetry (PCFC) tests of the fibers were performed. On the SEM pictures, flax fibers purified and covered with silanes were visible after treatment. FTIR analysis showed stable bonds between the fibers and the silicon compounds. Promising results of thermal stability were obtained. It was also found that modification had a positive effect on the flammability. The conducted research showed that the use of such modifications, in the context of using flax fibers for composites, can yield very good results. Full article

(This article belongs to the Section Biomaterials)

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25 pages, 8623 KiB

Open AccessEditor’s ChoiceArticle

Potential of Fe-Mn-Al-Ni Shape Memory Alloys for Internal Prestressing of Ultra-High Performance Concrete

by Maximilian Schleiting, Alexander Wetzel, André Bauer, Johanna-Maria Frenck, Thomas Niendorf and Bernhard Middendorf

Materials 2023, 16(10), 3816; https://doi.org/10.3390/ma16103816 - 18 May 2023

Cited by 8 | Viewed by 1924

Abstract

Prestressing of concrete is a commonly used technique in civil engineering to achieve long spans, reduced structural thicknesses, and resource savings. However, in terms of application, complex tensioning devices are necessary, and prestress losses due to shrinkage and creep of the concrete are [...] Read more.

Prestressing of concrete is a commonly used technique in civil engineering to achieve long spans, reduced structural thicknesses, and resource savings. However, in terms of application, complex tensioning devices are necessary, and prestress losses due to shrinkage and creep of the concrete are unfavourable in terms of sustainability. In this work, a prestressing method using novel Fe-Mn-Al-Ni shape memory alloy rebars as a tensioning system in UHPC is investigated. A generated stress of about 130 MPa was measured for the shape memory alloy rebars. For the application in UHPC, the rebars are prestrained prior to the manufacturing process of the concrete samples. After sufficient hardening of the concrete, the specimens are heated inside an oven to activate the shape memory effect and, thus, to introduce the prestress into the surrounding UHPC. It is clearly shown that an improvement in maximum flexural strength and rigidity is achieved due to the thermal activation of the shape memory alloy rebars compared to non-activated rebars. Future research will have to focus on the design of the shape memory alloy rebars in relation to construction applications and the investigation of the long-term performance of the prestressing system. Full article

(This article belongs to the Section Construction and Building Materials)

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17 pages, 20268 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Mechanically Strong Silica Aerogels with the Thermally Induced Phase Separation (TIPS) Method of Poly(methyl methacrylate)

by Hainan Ma, Baomin Wang, Jiarui Qi, Yiheng Pan and Chao Chen

Materials 2023, 16(10), 3778; https://doi.org/10.3390/ma16103778 - 17 May 2023

Cited by 3 | Viewed by 1809

Abstract

Constructing and maintaining a three-dimensional network structure with high porosity is critical to the preparation of silica aerogel materials because this structure provides excellent properties. However, due to the pearl-necklace-like structure and narrow interparticle necks, aerogels have poor mechanical strength and a brittle [...] Read more.

Constructing and maintaining a three-dimensional network structure with high porosity is critical to the preparation of silica aerogel materials because this structure provides excellent properties. However, due to the pearl-necklace-like structure and narrow interparticle necks, aerogels have poor mechanical strength and a brittle nature. Developing and designing lightweight silica aerogels with distinct mechanical properties is significant to extend their practical applications. In this work, thermally induced phase separation (TIPS) of poly(methyl methacrylate) (PMMA) from a mixture of ethanol and water was used to strengthen the skeletal network of aerogels. Strong and lightweight PMMA-modified silica aerogels were synthesized via the TIPS method and supercritically dried with carbon dioxide. The cloud point temperature of PMMA solutions, physical characteristics, morphological properties, microstructure, thermal conductivities, and mechanical properties were investigated. The resultant composited aerogels not only exhibit a homogenous mesoporous structure but also achieve a significant improvement in mechanical properties. The addition of PMMA increased the flexural strength and compressive strength by as much as 120% and 1400%, respectively, with the greatest amount of PMMA (M_w = 35,000 g/mole), while the density just increased by 28%. Overall, this research suggests that the TIPS method has great efficiency in reinforcing silica aerogels with less sacrifice of low density and large porosity. Full article

(This article belongs to the Section Porous Materials)

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16 pages, 3861 KiB

Open AccessEditor’s ChoiceArticle

Tungsten and Copper (II) Oxide Mixtures as Gasless Time Delay Compositions for Mining Detonators

by Marcin Gerlich, Marcin Hara and Waldemar A. Trzciński

Materials 2023, 16(10), 3797; https://doi.org/10.3390/ma16103797 - 17 May 2023

Cited by 4 | Viewed by 1874

Abstract

The widespread use of pyrotechnic compositions in time delay detonators is the reason for research aimed at expanding knowledge of the combustion properties of new pyrotechnic mixtures, whose components react with each other in the solid or liquid state. Such a method of [...] Read more.

The widespread use of pyrotechnic compositions in time delay detonators is the reason for research aimed at expanding knowledge of the combustion properties of new pyrotechnic mixtures, whose components react with each other in the solid or liquid state. Such a method of combustion would make the rate of combustion independent of the pressure inside the detonator. This paper presents the effect of the parameters of W/CuO mixtures on their properties of combustion. As this composition has not been the subject of previous research and is not described in the literature, the basic parameters, such as the burning rate and the heat of combustion, were determined. In order to determine the reaction mechanism, a thermal analysis was performed, and the combustion products were determined using the XRD technique. Depending on the quantitative composition and density of the mixture, the burning rates were between 4.1–6.0 mm/s and the heat of combustion in the range of 475–835 J/g was measured. The gas-free combustion mode of the chosen mixture was proved using DTA and XRD. Determination of the qualitative composition of the combustion products and the heat of combustion allowed estimation of the adiabatic combustion temperature. Full article

(This article belongs to the Special Issue Newer Paradigms in Advanced Materials Characterisation)

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14 pages, 491 KiB

Open AccessEditor’s ChoiceArticle

Anharmonicity of Plasmons in Metallic Nanostructures Useful for Metallization of Solar Cells

by Zofia Krzemińska and Witold A. Jacak

Materials 2023, 16(10), 3762; https://doi.org/10.3390/ma16103762 - 16 May 2023

Viewed by 1495

Abstract

Metallic nanoparticles are frequently applied to enhance the efficiency of photovoltaic cells via the plasmonic effect, and they play this role due to the unusual ability of plasmons to transmit energy. The absorption and emission of plasmons, dual in the sense of quantum [...] Read more.

Metallic nanoparticles are frequently applied to enhance the efficiency of photovoltaic cells via the plasmonic effect, and they play this role due to the unusual ability of plasmons to transmit energy. The absorption and emission of plasmons, dual in the sense of quantum transitions, in metallic nanoparticles are especially high at the nanoscale of metal confinement, so these particles are almost perfect transmitters of incident photon energy. We show that these unusual properties of plasmons at the nanoscale are linked to the extreme deviation of plasmon oscillations from the conventional harmonic oscillations. In particular, the large damping of plasmons does not terminate their oscillations, even if, for a harmonic oscillator, they result in an overdamped regime. Full article

(This article belongs to the Special Issue Design, Performance, and Application of Lithium-Ion Batteries)

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23 pages, 4718 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Usability of Sorbents in Restoring Enzymatic Activity in Soils Polluted with Petroleum-Derived Products

by Jadwiga Wyszkowska, Agata Borowik, Magdalena Zaborowska and Jan Kucharski

Materials 2023, 16(10), 3738; https://doi.org/10.3390/ma16103738 - 15 May 2023

Cited by 20 | Viewed by 2346

Abstract

Due to their ability to adsorb or absorb chemical pollutants, including organic compounds, sorbents are increasingly used in the reclamation of soils subjected to their pressure, which results from their high potential in eliminating xenobiotics. The precise optimization of the reclamation process is [...] Read more.

Due to their ability to adsorb or absorb chemical pollutants, including organic compounds, sorbents are increasingly used in the reclamation of soils subjected to their pressure, which results from their high potential in eliminating xenobiotics. The precise optimization of the reclamation process is required, focused primarily on restoring the condition of the soil. This research are essential for seeking materials sufficiently potent to accelerate the remediation process and for expanding knowledge related to biochemical transformations that lead to the neutralization of these pollutants. The goal of this study was to determine and compare the sensitivity of soil enzymes to petroleum-derived products in soil sown with Zea mays, remediated using four sorbents. The study was conducted in a pot experiment, with loamy sand (LS) and sandy loam (SL) polluted with VERVA diesel oil (DO) and VERVA 98 petrol (P). Soil samples were collected from arable lands, and the effects of the tested pollutants were compared with those used as control uncontaminated soil samples in terms of Zea mays biomass and the activity of seven enzymes in the soil. The following sorbents were applied to mitigate DO and P effects on the test plants and enzymatic activity: molecular sieve (M), expanded clay (E), sepiolite (S), and Ikasorb (I). Both DO and P exerted a toxic effect on Zea mays, with DO more strongly disturbing its growth and development and the activities of soil enzymes than P. In sandy clay (SL), P was found to be a significant inhibitor of dehydrogenases (Deh), catalase (Cat), urease (Ure), alkaline phosphatase (Pal), and arylsulfatase (Aryl) activities, while DO stimulated the activity of all enzymes in this soil. The study results suggest that the sorbents tested, mainlya molecular sieve, may be useful in remediating DO-polluted soils, especially when alleviating the effects of these pollutants in soils of lower agronomic value. Full article

(This article belongs to the Special Issue Advances in Eco-Friendly Adsorbent Materials for Removal of Inorganic and Organic Pollutants (Volume II))

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11 pages, 2642 KiB

Open AccessEditor’s ChoiceArticle

Transparent Conducting Amorphous IZO Thin Films: An Approach to Improve the Transparent Electrode Quality

by Akhmed K. Akhmedov, Aslan Kh. Abduev, Eldar K. Murliev, Victor V. Belyaev and Abil Sh. Asvarov

Materials 2023, 16(10), 3740; https://doi.org/10.3390/ma16103740 - 15 May 2023

Cited by 12 | Viewed by 2900

Abstract

It is common knowledge that using different oxygen contents in the working gas during sputtering deposition results in fabrication of indium zinc oxide (IZO) films with a wide range of optoelectronic properties. It is also important that high deposition temperature is not required [...] Read more.

It is common knowledge that using different oxygen contents in the working gas during sputtering deposition results in fabrication of indium zinc oxide (IZO) films with a wide range of optoelectronic properties. It is also important that high deposition temperature is not required to achieve excellent transparent electrode quality in the IZO films. Modulation of the oxygen content in the working gas during RF sputtering of IZO ceramic targets was used to deposit IZO-based multilayers in which the ultrathin IZO unit layers with high electron mobility (μ-IZO) alternate with ones characterized by high concentration of free electrons (n-IZO). As a result of optimizing the thicknesses of each type of unit layer, low-temperature 400 nm thick IZO multilayers with excellent transparent electrode quality, indicated by the low sheet resistance (R ≤ 8 Ω/sq.) with high transmittance in the visible range (

\bar{T}

> 83%) and a very flat multilayer surface, were obtained. Full article

(This article belongs to the Special Issue Sputter Deposition/Physical Vapor Deposition (PVD) Materials and Processes)

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14 pages, 5703 KiB

Open AccessEditor’s ChoiceArticle

Comparative Study of Iron-Tailings-Based Cementitious Mortars with Incorporated Graphite Ore and Graphite Tailings: Strength Properties and Microstructure

by Jiale Zhang, Qi Wei, Na Zhang, Shuai Zhang and Yihe Zhang

Materials 2023, 16(10), 3743; https://doi.org/10.3390/ma16103743 - 15 May 2023

Cited by 3 | Viewed by 1838

Abstract

Graphite ore and graphite tailings were blended into iron-tailings-based cementitious mortars, and their mechanical properties and microstructure were experimentally investigated. The flexural and compressive strengths of the resulting material were tested to compare the effects of graphite ore and graphite tailings as supplementary [...] Read more.

Graphite ore and graphite tailings were blended into iron-tailings-based cementitious mortars, and their mechanical properties and microstructure were experimentally investigated. The flexural and compressive strengths of the resulting material were tested to compare the effects of graphite ore and graphite tailings as supplementary cementitious materials and fine aggregates on the mechanical properties of iron-tailings-based cementitious mortars. Additionally, their microstructure and hydration products were mainly analyzed using scanning electronic microscope and X-ray powder diffraction techniques. The experimental results showed that the mechanical properties of the mortar material incorporating graphite ore were reduced due to the lubricating properties of graphite ore. As a result, the unhydrated particles and aggregates were not tightly bound to the gel phase, making the direct application of graphite ore in construction materials unfeasible. In the iron-tailings-based cementitious mortars prepared in this work, the optimal incorporation rate of graphite ore as a supplementary cementitious material was 4 wt%. The compressive strength of the optimal mortar test block after 28 days of hydration was 23.21 MPa, and the flexural strength was 7.76 MPa. The mechanical properties of the mortar block were found to be optimal with a graphite-tailings content of 40 wt% and an iron-tailings content of 10 wt%, resulting in a 28-day compressive strength of 48.8 MPa and a flexural strength of 11.7 MPa. By observing the microstructure and XRD pattern of the 28-day hydrated mortar block, it was determined that the hydration products of the mortar with graphite tailings as an aggregate included ettringite, Ca(OH)₂, and C-A-S-H gel. Full article

(This article belongs to the Special Issue Industrial Solid Wastes for Construction and Building Materials)

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20 pages, 12745 KiB

Open AccessEditor’s ChoiceArticle

Durability and Additional Properties of Anodized Aluminum-Based Coatings with Different Wettability under Natural Conditions

by Klaudia Olkowicz, Kamil Kowalczyk, Zofia Buczko, Joanna Czwartos and Barbara Nasiłowska

Materials 2023, 16(10), 3729; https://doi.org/10.3390/ma16103729 - 14 May 2023

Cited by 4 | Viewed by 2917

Abstract

The study aimed to test the durability of coatings under natural conditions. The present study focused on the changes in wettability and additional properties of the coatings under natural conditions. The specimens were subjected to outdoor exposure and additionally immersed in the pond. [...] Read more.

The study aimed to test the durability of coatings under natural conditions. The present study focused on the changes in wettability and additional properties of the coatings under natural conditions. The specimens were subjected to outdoor exposure and additionally immersed in the pond. Impregnating porous anodized aluminum is a popular production method for hydrophobic and superhydrophobic surfaces. However, prolonged exposure of such coatings to natural conditions causes leaching of the impregnate and, thus, the loss of hydrophobic properties. After the loss of hydrophobic properties, all kinds of impurities and fouling adhere better to the porous structure. Additionally, deterioration of anti-icing and anti-corrosion properties was observed. Finally, the self-cleaning, anti-fouling, anti-icing and anti-corrosion properties were comparable or even worse to those of the hydrophilic coating. In the case of superhydrophobic specimens, during outdoor exposure there was no loss of superhydrophobicity, self-cleaning and anti-corrosion properties. Still, despite this, the icing delay time dropped. During outdoor exposure, the structure, which initially had anti-icing properties, may degrade. Nevertheless, the hierarchical structure responsible for the superhydrophobic effect can still be preserved. The superhydrophobic coating initially had the best anti-fouling properties. However, the coating was also gradually losing its superhydrophobic properties during water immersion. Full article

(This article belongs to the Special Issue New Insights in Wettability and Surface Repellency of Advanced Materials)

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15 pages, 4711 KiB

Open AccessEditor’s ChoiceArticle

In Situ Reactive Formation of Mixed Oxides in Additively Manufactured Cobalt Alloy

by Jack Lopez, Rok Cerne, David Ho, Devin Madigan, Qing Shen, Bo Yang, Joseph Corpus, William Jarosinski, Haiyan Wang and Xinghang Zhang

Materials 2023, 16(10), 3707; https://doi.org/10.3390/ma16103707 - 13 May 2023

Cited by 4 | Viewed by 2342

Abstract

Oxide-dispersion-strengthened (ODS) alloys have long been considered for high temperature turbine, spacecraft, and nuclear reactor components due to their high temperature strength and radiation resistance. Conventional synthesis approaches of ODS alloys involve ball milling of powders and consolidation. In this work, a process-synergistic [...] Read more.

Oxide-dispersion-strengthened (ODS) alloys have long been considered for high temperature turbine, spacecraft, and nuclear reactor components due to their high temperature strength and radiation resistance. Conventional synthesis approaches of ODS alloys involve ball milling of powders and consolidation. In this work, a process-synergistic approach is used to introduce oxide particles during laser powder bed fusion (LPBF). Chromium (III) oxide (Cr₂O₃) powders are blended with a cobalt-based alloy, Mar-M 509, and exposed to laser irradiation, resulting in reduction–oxidation reactions involving metal (Ta, Ti, Zr) ions from the metal matrix to form mixed oxides of increased thermodynamic stability. A microstructure analysis indicates the formation of nanoscale spherical mixed oxide particles as well as large agglomerates with internal cracks. Chemical analyses confirm the presence of Ta, Ti, and Zr in agglomerated oxides, but primarily Zr in the nanoscale oxides. Mechanical testing reveals that agglomerate particle cracking is detrimental to tensile ductility compared to the base alloy, suggesting the need for improved processing methods to break up oxide particle clusters and promote their uniform dispersion during laser exposure. Full article

(This article belongs to the Special Issue Advances in Materials Processing Engineering)

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19 pages, 2602 KiB

Open AccessEditor’s ChoiceArticle

Plasmonic Nanodomains Decorated on Two-Dimensional Oxide Semiconductors for Photonic-Assisted CO₂ Conversion

by Mohammad Karbalaei Akbari, Nasrin Siraj Lopa, Jihae Park and Serge Zhuiykov

Materials 2023, 16(10), 3675; https://doi.org/10.3390/ma16103675 - 11 May 2023

Cited by 2 | Viewed by 2172

Abstract

Plasmonic nanostructures ensure the reception and harvesting of visible lights for novel photonic applications. In this area, plasmonic crystalline nanodomains decorated on the surface of two-dimensional (2D) semiconductor materials represent a new class of hybrid nanostructures. These plasmonic nanodomains activate supplementary mechanisms at [...] Read more.

Plasmonic nanostructures ensure the reception and harvesting of visible lights for novel photonic applications. In this area, plasmonic crystalline nanodomains decorated on the surface of two-dimensional (2D) semiconductor materials represent a new class of hybrid nanostructures. These plasmonic nanodomains activate supplementary mechanisms at material heterointerfaces, enabling the transfer of photogenerated charge carriers from plasmonic antennae into adjacent 2D semiconductors and therefore activate a wide range of visible-light assisted applications. Here, the controlled growth of crystalline plasmonic nanodomains on 2D Ga₂O₃ nanosheets was achieved by sonochemical-assisted synthesis. In this technique, Ag and Se nanodomains grew on 2D surface oxide films of gallium-based alloy. The multiple contribution of plasmonic nanodomains enabled the visible-light-assisted hot-electron generation at 2D plasmonic hybrid interfaces, and therefore considerably altered the photonic properties of the 2D Ga₂O₃ nanosheets. Specifically, the multiple contribution of semiconductor–plasmonic hybrid 2D heterointerfaces enabled efficient CO₂ conversion through combined photocatalysis and triboelectric-activated catalysis. The solar-powered acoustic-activated conversion approach of the present study enabled us to achieve the CO₂ conversion efficiency of more than 94% in the reaction chambers containing 2D Ga₂O₃-Ag nanosheets. Full article

(This article belongs to the Special Issue Novel Nanostructured Materials for Optoelectronic Applications)

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15 pages, 4464 KiB

Open AccessEditor’s ChoiceArticle

Thermal Programming of Commercially Available Orthodontic NiTi Archwires

by Andrea Wichelhaus, Amelie Mehnert, Thomas Stocker, Uwe Baumert, Matthias Mertmann, Hisham Sabbagh and Corinna L. Seidel

Materials 2023, 16(10), 3683; https://doi.org/10.3390/ma16103683 - 11 May 2023

Cited by 3 | Viewed by 2257

Abstract

The shape of superelastic Nickel-Titanium (NiTi) archwires can be adjusted with thermal treatments using devices such as the Memory-Maker^TM (Forestadent), which potentially affects their mechanical properties. The effect of such treatments on these mechanical properties was simulated by means of a laboratory [...] Read more.

The shape of superelastic Nickel-Titanium (NiTi) archwires can be adjusted with thermal treatments using devices such as the Memory-Maker^TM (Forestadent), which potentially affects their mechanical properties. The effect of such treatments on these mechanical properties was simulated by means of a laboratory furnace. Fourteen commercially available NiTi wires (0.018″ × 0.025″) were selected from the manufacturers American Orthodontics, Dentaurum, Forestadent, GAC, Ormco, Rocky Mountain Orthodontics and 3M Unitek. Specimens were heat treated using different combinations of annealing duration (1/5/10 min) and annealing temperature (250–800 °C) and investigated using angle measurements and three-point bending tests. Complete shape adaptation was found at distinct annealing durations/temperatures for each wire ranging between ~650–750 °C (1 min), ~550–700 °C (5 min) and ~450–650 °C (10 min), followed by a loss of superelastic properties shortly afterwards at ~750 °C (1 min), ~600–650 °C (5 min) and ~550–600 °C (10 min). Wire-specific working ranges (complete shaping without loss of superelasticity) were defined and a numerical score (e.g., stable forces) was developed for the three-point bending test. Overall, the wires Titanol Superelastic (Forestadent), Tensic (Dentaurum), FLI CuNiTi²⁷ (Rocky Mountain Orthodontics) and Nitinol Classic (3M Unitek) proved to be the most user-friendly. Thermal shape adjustment requires wire-specific working ranges to allow complete shape acceptance and high scores in bending test performance to ensure permanence of the superelastic behaviour. Full article

(This article belongs to the Special Issue Characterization of Shape Memory Alloy Materials)

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19 pages, 4852 KiB

Open AccessEditor’s ChoiceArticle

Combined DFT-D3 Computational and Experimental Studies on g-C₃N₄: New Insight into Structure, Optical, and Vibrational Properties

by Paolo Negro, Federico Cesano, Silvia Casassa and Domenica Scarano

Materials 2023, 16(10), 3644; https://doi.org/10.3390/ma16103644 - 10 May 2023

Cited by 22 | Viewed by 4325

Abstract

Graphitic carbon nitride (g-C₃N₄) has emerged as one of the most promising solar-light-activated polymeric metal-free semiconductor photocatalysts due to its thermal physicochemical stability but also its characteristics of environmentally friendly and sustainable material. Despite the challenging properties of g-C [...] Read more.

Graphitic carbon nitride (g-C₃N₄) has emerged as one of the most promising solar-light-activated polymeric metal-free semiconductor photocatalysts due to its thermal physicochemical stability but also its characteristics of environmentally friendly and sustainable material. Despite the challenging properties of g-C₃N₄, its photocatalytic performance is still limited by the low surface area, together with the fast charge recombination phenomena. Hence, many efforts have been focused on overcoming these drawbacks by controlling and improving the synthesis methods. With regard to this, many structures including strands of linearly condensed melamine monomers, which are interconnected by hydrogen bonds, or highly condensed systems, have been proposed. Nevertheless, complete and consistent knowledge of the pristine material has not yet been achieved. Thus, to shed light on the nature of polymerised carbon nitride structures, which are obtained from the well-known direct heating of melamine under mild conditions, we combined the results obtained from XRD analysis, SEM and AFM microscopies, and UV-visible and FTIR spectroscopies with the data from the Density Functional Theory method (DFT). An indirect band gap and the vibrational peaks have been calculated without uncertainty, thus highlighting a mixture of highly condensed g-C₃N₄ domains embedded in a less condensed “melon-like” framework. Full article

(This article belongs to the Special Issue Graphene and Other 2D Layered Nanomaterials and Hybrid Structures: Synthesis, Properties and Applications (Volume II))

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16 pages, 12362 KiB

Open AccessEditor’s ChoiceArticle

Full-Scale Fatigue Test and Finite Element Analysis on External Inclined Strut Welded Joints of a Wide-Flanged Composite Box Girder Bridge

by Bin Wang, Laijun Liu, Yuqing Liu, Xudong Jia, Xiaoqing Xu, Kaixiang Miao and Jiandong Ji

Materials 2023, 16(10), 3637; https://doi.org/10.3390/ma16103637 - 10 May 2023

Cited by 2 | Viewed by 2439

Abstract

For a wide-flanged composite box girder bridge, the risk of fatigue cracking in the external inclined strut welded joint under the fatigue vehicle load is a problem. The main purposes of this research are to verify the safety of the main bridge of [...] Read more.

For a wide-flanged composite box girder bridge, the risk of fatigue cracking in the external inclined strut welded joint under the fatigue vehicle load is a problem. The main purposes of this research are to verify the safety of the main bridge of the Linyi Yellow River Bridge, a continuous composite box girder bridge, and to propose suggestions for optimization. In this research, a finite element model of one segment of the bridge was established to investigate the influence surface of the external inclined strut, and, using the nominal stress method, it was confirmed that the fatigue cracking of the welded details of the external inclined strut was risky. Subsequently, a full-scale fatigue test of the external inclined strut welded joint was carried out, and the crack propagation law and S-N curve of the welded details were obtained. Finally, a parametric analysis was conducted with the three-dimensional refined finite element models. The results showed that the welded joint in the real bridge has a fatigue life larger than that of the design life, and methods such as increasing the flange thickness of the external inclined strut and the diameter of the welding hole are beneficial to improve its fatigue performance. Full article

(This article belongs to the Special Issue Experimental Study, Numerical Simulation & Structural Applications of Construction Materials)

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15 pages, 9508 KiB

Open AccessEditor’s ChoiceArticle

Evolution of Toughening Mechanisms in PH13-8Mo Stainless Steel during Aging Treatment

by Honglin Zhang, Peng Mi, Luhan Hao, Haichong Zhou, Wei Yan, Kuan Zhao, Bin Xu and Mingyue Sun

Materials 2023, 16(10), 3630; https://doi.org/10.3390/ma16103630 - 10 May 2023

Cited by 3 | Viewed by 2478

Abstract

PH13-8Mo stainless steel has been widely used in aerospace, petroleum and marine construction, obtaining continuous investigation attention in recent years. Based on the response of a hierarchical martensite matrix and possible reversed austenite, a systematic investigation of the evolution of the toughening mechanisms [...] Read more.

PH13-8Mo stainless steel has been widely used in aerospace, petroleum and marine construction, obtaining continuous investigation attention in recent years. Based on the response of a hierarchical martensite matrix and possible reversed austenite, a systematic investigation of the evolution of the toughening mechanisms in PH13-8Mo stainless steel as a function of aging temperature was carried out. It showed there was a desirable combination of high yield strength (~1.3 GPa) and V-notched impact toughness (~220 J) after aging between 540 and 550 °C. With the increase of aging temperature, the martensite matrix was recovered in terms of the refined sub-grains and higher ratio of high-angle grain boundaries (HAGBs). It should be noted there was a reversion of martensite to form austenite films subjected to aging above 540 °C; meanwhile, the NiAl precipitates maintained a well-coherent orientation with the matrix. Based on the post mortem analysis, there were three stages of the changing main toughening mechanisms: Stage I: low-temperature aging at around 510 °C, where the HAGBs contributed to the toughness by retarding the advance of cracks; Stage II: intermediate-temperature aging at around 540 °C, where the recovered laths embedded by soft austenite facilitated the improvement of toughness by synergistically increasing the advance path and blunting the crack tips; and Stage III: without the coarsening of NiAl precipitates around 560 °C, more inter-lath reversed austenite led to the optimum toughness, relying on “soft barrier” and transformation-induced plasticity (TRIP) effects. Full article

(This article belongs to the Special Issue Advanced Special and High-Strength Steels)

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22 pages, 13507 KiB

Open AccessEditor’s ChoiceArticle

Signal-Decay Based Approach for Visualization of Buried Defects in 3-D Printed Ceramic Components Imaged with Help of Optical Coherence Tomography

by Malgorzata Kopycinska-Müller, Luise Schreiber, Eric Schwarzer-Fischer, Anne Günther, Conner Phillips, Tassilo Moritz, Jörg Opitz, Yeong-Jin Choi and Hui-suk Yun

Materials 2023, 16(10), 3607; https://doi.org/10.3390/ma16103607 - 9 May 2023

Cited by 2 | Viewed by 2252

Abstract

We propose the use of Optical Coherence Tomography (OCT) as a tool for the quality control of 3-D-printed ceramics. Test samples with premeditated defects, namely single- and two-component samples of zirconia, titania, and titanium suboxides, were printed by stereolithography-based DLP (Digital Light Processing) [...] Read more.

We propose the use of Optical Coherence Tomography (OCT) as a tool for the quality control of 3-D-printed ceramics. Test samples with premeditated defects, namely single- and two-component samples of zirconia, titania, and titanium suboxides, were printed by stereolithography-based DLP (Digital Light Processing) processes. The OCT tomograms obtained on the green samples showed the capability of the method to visualize variations in the layered structure of the samples as well as the presence of cracks and inclusions at depths up to 130 µm, as validated by SEM images. The structural information was visible in cross-sectional images as well as in plan-view images. The optical signal measured from the printed zirconia oxide and titanium oxide samples showed strong attenuation with depth and could be fit with an exponential decay curve. The variations of the decay parameter correlated very well with the presence of defects and material variation. When used as an imaging quantity, the decay parameter projects the position of the defects into 2-D (X,Y) coordinates. This procedure can be used in real time, it reduces the data volume up to 1000 times, and allows for faster subsequent data analysis and transfer. Tomograms were also obtained on sintered samples. The results showed that the method can detect changes in the optical properties of the green ceramics caused by sintering. Specifically, the zirconium oxide samples became more transparent to the light used, whereas the titanium suboxide samples became entirely opaque. In addition, the optical response of the sintered zirconium oxide showed variations within the imaged volume, indicating material density variations. The results presented in this study show that OCT provides sufficient structural information on 3-D-printed ceramics and can be used as an in-line tool for quality control. Full article

(This article belongs to the Special Issue Recent Advances in Ceramic Manufacturing)

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12 pages, 7301 KiB

Open AccessEditor’s ChoiceArticle

Structure and Wear Performance of a Titanium Alloy by Using Low-Temperature Plasma Oxy-Nitriding

by Haidong Li, Haifeng Wang, Shijie Wang, Yange Yang, Yunsong Niu, Shenglong Zhu and Fuhui Wang

Materials 2023, 16(10), 3609; https://doi.org/10.3390/ma16103609 - 9 May 2023

Cited by 3 | Viewed by 2015

Abstract

To solve the problems of high nitriding temperature and long nitriding time with conventional plasma nitriding technologies, a kind of low-temperature plasma oxy-nitriding technology containing two-stage processes with different ratios of N to O was developed on a TC4 alloy in this paper. [...] Read more.

To solve the problems of high nitriding temperature and long nitriding time with conventional plasma nitriding technologies, a kind of low-temperature plasma oxy-nitriding technology containing two-stage processes with different ratios of N to O was developed on a TC4 alloy in this paper. A thicker permeation coating can be obtained with this new technology compared to conventional plasma nitriding technology. The reason for this is that the oxygen introduction in the first two-hour oxy-nitriding step can break the continuous TiN layer, which facilitates the quick and deep diffusion of the solution-strengthening elements of O and N into the titanium alloy. Moreover, an inter-connected porous structure was formed under a compact compound layer, which acts as a buffer layer to absorb the external wear force. Therefore, the resultant coating showed the lowest COF values during the initial wear state, and almost no debris and cracks were detected after the wear test. For the treated samples with low hardness and no porous structure, fatigue cracks can easily form on the surface, and bulk peeling-offcan occur during the wear course. Full article

(This article belongs to the Special Issue Advances in Coating Materials Research: From Preparation to Application)

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15 pages, 2304 KiB

Open AccessEditor’s ChoiceArticle

Fabrication and Arc Erosion Behavior of Ag-SnO₂-ZnO Electrical Contact Materials

by Danny Guzmán, Felipe González, Diego Muranda, Claudio Aguilar, Alexis Guzmán, Álvaro Soliz, Lorena Lozada, Iñigo Iturriza and Felipe Castro

Materials 2023, 16(10), 3618; https://doi.org/10.3390/ma16103618 - 9 May 2023

Cited by 16 | Viewed by 2859

Abstract

This study investigated the synthesis of Ag-SnO₂-ZnO by powder metallurgy methods and their subsequent electrical contact behavior. The pieces of Ag-SnO₂-ZnO were prepared by ball milling and hot pressing. The arc erosion behavior of the material was evaluated using [...] Read more.

This study investigated the synthesis of Ag-SnO₂-ZnO by powder metallurgy methods and their subsequent electrical contact behavior. The pieces of Ag-SnO₂-ZnO were prepared by ball milling and hot pressing. The arc erosion behavior of the material was evaluated using homemade equipment. The microstructure and phase evolution of the materials were investigated through X-ray diffraction, energy-dispersive spectroscopy and scanning electron microscopy. The results showed that, although the mass loss of the Ag-SnO₂-ZnO composite (9.08 mg) during the electrical contact test was higher than that of the commercial Ag-CdO (1.42 mg), its electrical conductivity remained constant (26.9 ± 1.5% IACS). This fact would be related to the reaction of Zn₂SnO₄’s formation on the material’s surface via electric arc. This reaction would play an important role in controlling the surface segregation and subsequent loss of electrical conductivity of this type of composite, thus enabling the development of a new electrical contact material to replace the non-environmentally friendly Ag-CdO composite. Full article

(This article belongs to the Special Issue Powder Metallurgy: Materials and Processing)

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18 pages, 4636 KiB

Open AccessEditor’s ChoiceArticle

Experimental and Numerical Investigation into the Effect of Water Uptake on the Capacitance of an Organic Coating

by Steven A. Policastro, Rachel M. Anderson, Carlos M. Hangarter, Attilio Arcari and Erick B. Iezzi

Materials 2023, 16(10), 3623; https://doi.org/10.3390/ma16103623 - 9 May 2023

Cited by 10 | Viewed by 1961

Abstract

Water uptake by organic coating systems used for corrosion prevention on airframes is one of the principal contributors to the loss of barrier properties of the coating. We used equivalent circuit analyses of electrochemical impedance spectroscopy (EIS) data to track changes in coating [...] Read more.

Water uptake by organic coating systems used for corrosion prevention on airframes is one of the principal contributors to the loss of barrier properties of the coating. We used equivalent circuit analyses of electrochemical impedance spectroscopy (EIS) data to track changes in coating layer capacitance for a two-layer coating system consisting of an epoxy primer and polyurethane topcoat immersed in NaCl solutions with different concentrations and temperatures. The capacitance curve exhibited two different response regions, consistent with the “two-stage kinetics” mechanisms for water uptake by the polymers. We tested several numerical diffusion models of water sorption and found the most successful to be one that varied the diffusion coefficient as a function of polymer type and immersion time and accounted for physical aging processes in the polymer. We employed the Brasher mixing law along with the water sorption model to estimate the coating capacitance as a function of water uptake. The predicted capacitance of the coating was found to be consistent with the capacitance obtained from the EIS data, which is consistent with theories that water uptake occurs via initial rapid transport followed by a much slower aging process. Thus, both these water uptake processes need to be considered when making EIS measurements to assess the state of a coating system. Full article

(This article belongs to the Special Issue Advanced Polymer-Coated Materials: Fabrication, Characterization and Applications)

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15 pages, 5624 KiB

Open AccessEditor’s ChoiceArticle

The Application of Additive Composites Technologies for Clamping and Manipulation Devices in the Production Process

by Richard Joch, Michal Šajgalík, Mário Drbúl, Jozef Holubják, Andrej Czán, Vladimír Bechný and Miroslav Matúš

Materials 2023, 16(10), 3624; https://doi.org/10.3390/ma16103624 - 9 May 2023

Cited by 7 | Viewed by 2056

Abstract

Additive technologies have been widely adopted in various industries. The choice of additive technology and material directly affects the functionality of the manufactured components. The development of materials with better mechanical properties has led to a growing interest in replacing traditional metal components [...] Read more.

Additive technologies have been widely adopted in various industries. The choice of additive technology and material directly affects the functionality of the manufactured components. The development of materials with better mechanical properties has led to a growing interest in replacing traditional metal components with those manufactured using additive technologies. The application of Onyx as a material comes into consideration, which contains short carbon fibers to increase the mechanical properties. This study aims to experimentally verify the viability of substituting metal gripping elements with nylon and composite materials. The design of the jaws was customized to meet the requirements of a three-jaw chuck of a CNC machining center. The evaluation process involved monitoring the functionality and deformation effects on the clamped PTFE polymer material. When the metal jaws were applied, significant deformation of the clamped material occurred, which varied with the clamping pressure. This deformation was evidenced by the formation of spreading cracks on the clamped material and permanent shape changes in the tested material. Conversely, nylon and composite jaws manufactured using additive technology demonstrated functionality across all tested clamping pressures, without causing permanent deformation of the clamped material, unlike the traditional metal jaws. The results of this study confirm the applicability of the Onyx material and provide practical evidence of the potential for reducing deformation caused by clamping mechanisms. Full article

(This article belongs to the Special Issue 3D & 4D Printing in Engineering Applications)

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16 pages, 9623 KiB

Open AccessEditor’s ChoiceArticle

Synergistic Effects of 2-Butyne-1,4-Diol and Chloride Ions on the Microstructure and Residual Stress of Electrodeposited Nickel

by Ming Sun, Chao Zhang, Ruhan Ya, Hongyu He, Zhipeng Li and Wenhuai Tian

Materials 2023, 16(9), 3598; https://doi.org/10.3390/ma16093598 - 8 May 2023

Cited by 1 | Viewed by 1977

Abstract

To assess the individual and synergistic effects of 2-butyne-1,4-diol (BD) and chloride ions on the microstructure and residual stress of electrodeposited nickel, various nickel layers were prepared from sulfamate baths comprising varying concentrations of BD and chloride ions by applying direct-current electrodeposition. And [...] Read more.

To assess the individual and synergistic effects of 2-butyne-1,4-diol (BD) and chloride ions on the microstructure and residual stress of electrodeposited nickel, various nickel layers were prepared from sulfamate baths comprising varying concentrations of BD and chloride ions by applying direct-current electrodeposition. And their surface morphologies, microstructure, and residual stress were tested using SEM, XRD, EBSD, TEM, and AFM. While the nickel layers composed of pyramid morphology were prepared from additive-free baths, the surface flattened gradually as the BD concentration of the baths was increased, and the acicular grains in the deposits were replaced with <100> oriented columnar grains or <111> oriented nanograins; additionally, the residual tensile stress of the deposits increased. The addition of chloride ions to the baths containing BD significantly increased the residual stress in the nickel layers, although it only slightly promoted surface flattening and columnar grain coarsening. The effects of BD and chloride ions on the growth mode and residual stress of nickel deposits were explained via analysis of surface morphologies and microstructure. And the results indicate that the reduction of chloride ion concentration is a feasible way to reduce the residual stress of the nickel deposits when BD is included in the baths. Full article

(This article belongs to the Special Issue Advances in Coatings Prepared by Deposition: Microstructure, Properties and Applications)

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18 pages, 6570 KiB

Open AccessEditor’s ChoiceArticle

Fracture Response of X80 Pipe Girth Welds under Combined Internal Pressure and Bending Moment

by Li Zhu, Naixian Li, Bin Jia and Yu Zhang

Materials 2023, 16(9), 3588; https://doi.org/10.3390/ma16093588 - 7 May 2023

Cited by 2 | Viewed by 2219

Abstract

In order to determine the effect of defect size on the pipeline fracture performance of girth welds in oil and gas pipelines, ABAQUS was used to simulate the fracture responses of X80 pipelines with girth weld defects under internal pressure and bending moment [...] Read more.

In order to determine the effect of defect size on the pipeline fracture performance of girth welds in oil and gas pipelines, ABAQUS was used to simulate the fracture responses of X80 pipelines with girth weld defects under internal pressure and bending moment conditions based on damage mechanics. In particular, the length and depth of defects were parametrically studied; the defect depth range was 20–80% of the wall thickness, and the circumferential length range of the defects was 5–20% of the pipeline circumference. The results show that, under the combined action of internal pressure and bending moment, the defect depth was more associated with adverse effects than the circumferential length of the defect. The failure load did not linearly decrease as the size of the defect increased, but when the depth of the defect reached a certain value, the failure load suddenly decreased. Full article

(This article belongs to the Special Issue Mechanics Behavior, Fatigue Damage, and Microstructure Evolution of Metallic Material)

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14 pages, 22598 KiB

Open AccessEditor’s ChoiceArticle

Microstructure Evolution and Mechanical Response of a Direct Quenched and Partitioned Steel at Different Finishing Rolling Temperatures

by Yajun Liu, Xiaolong Gan, Wen Liang, Guang Xu, Jianghua Qi and Man Liu

Materials 2023, 16(9), 3575; https://doi.org/10.3390/ma16093575 - 6 May 2023

Cited by 6 | Viewed by 1947

Abstract

The effects of finishing rolling temperature on the microstructure and mechanical properties of a direct quenched and partitioned (DQ&P) steel were investigated by a thermal simulation machine, a field emission scanning electron microscope (FE-SEM), electron backscattering diffraction (EBSD), and a transmission electron microscope [...] Read more.

The effects of finishing rolling temperature on the microstructure and mechanical properties of a direct quenched and partitioned (DQ&P) steel were investigated by a thermal simulation machine, a field emission scanning electron microscope (FE-SEM), electron backscattering diffraction (EBSD), and a transmission electron microscope (TEM). The results show that the original austenite grain size was refined by 31% as the finishing rolling temperature decreased from 920 °C to 840 °C, leading to the formation of the finest martensite lath at 840 °C. At the same time, the lower finishing rolling temperature resulted in a higher dislocation density, and consequently improved the stability of the retained austenite. Moreover, compared to the conventional Q&P process, the comprehensive mechanical properties of a steel with similar chemical composition can be enhanced by DQ&P processing. With the decrease of finishing rolling temperature from 920 °C to 840 °C, the strength and total elongation increases. The yield strength, tensile strength, and total elongation reach the maximum values of 1121 MPa, 1134 MPa, and 11.7%, respectively, at 840 °C. Full article

(This article belongs to the Special Issue Microstructure, Mechanical Properties and Wear Performance of High-Strength Steels)

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18 pages, 2294 KiB

Open AccessEditor’s ChoiceArticle

Mechanistic Study of Fast Performance Decay of PtCu Alloy-based Catalyst Layers for Polymer Electrolyte Fuel Cells through Electrochemical Impedance Spectroscopy

by Maximilian Grandi, Matija Gatalo, Ana Rebeka Kamšek, Gregor Kapun, Kurt Mayer, Francisco Ruiz-Zepeda, Martin Šala, Bernhard Marius, Marjan Bele, Nejc Hodnik, Merit Bodner, Miran Gaberšček and Viktor Hacker

Materials 2023, 16(9), 3544; https://doi.org/10.3390/ma16093544 - 5 May 2023

Cited by 2 | Viewed by 2339

Abstract

In the past, platinum–copper catalysts have proven to be highly active for the oxygen reduction reaction (ORR), but transferring the high activities measured in thin-film rotating disk electrodes (TF-RDEs) to high-performing membrane electrode assemblies (MEAs) has proven difficult due to stability issues during [...] Read more.

In the past, platinum–copper catalysts have proven to be highly active for the oxygen reduction reaction (ORR), but transferring the high activities measured in thin-film rotating disk electrodes (TF-RDEs) to high-performing membrane electrode assemblies (MEAs) has proven difficult due to stability issues during operation. High initial performance can be achieved. However, fast performance decay on a timescale of 24 h is induced by repeated voltage load steps with H₂/air supplied. This performance decay is accelerated if high relative humidity (>60% RH) is set for a prolonged time and low voltages are applied during polarization. The reasons and possible solutions for this issue have been investigated by means of electrochemical impedance spectroscopy and distribution of relaxation time analysis (EIS–DRT). The affected electrochemical sub-processes have been identified by comparing the PtCu electrocatalyst with commercial Pt/C benchmark materials in homemade catalyst-coated membranes (CCMs). The proton transport resistance (R_pt) increased by a factor of ~2 compared to the benchmark materials. These results provide important insight into the challenges encountered with the de-alloyed PtCu/KB electrocatalyst during cell break-in and operation. This provides a basis for improvements in the catalysts’ design and break-in procedures for the highly attractive PtCu/KB catalyst system. Full article

(This article belongs to the Special Issue Novel Materials for Green Hydrogen Production, Energy Conversion, and Fuel Cell Applications)

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17 pages, 4713 KiB

Open AccessEditor’s ChoiceArticle

Novel Graphene-Based Materials as a Tool for Improving Long-Term Storage of Cultural Heritage

by George Gorgolis, Steffen Ziemann, Maria Kotsidi, George Paterakis, Nikos Koutroumanis, Christos Tsakonas, Manfred Anders and Costas Galiotis

Materials 2023, 16(9), 3528; https://doi.org/10.3390/ma16093528 - 4 May 2023

Cited by 7 | Viewed by 2350

Abstract

The very serious problem of temperature and humidity regulation, especially for small and medium-sized museums, galleries, and private collections, can be mitigated by the introduction of novel materials that are easily applicable and of low cost. Within this study, archive boxes with innovative [...] Read more.

The very serious problem of temperature and humidity regulation, especially for small and medium-sized museums, galleries, and private collections, can be mitigated by the introduction of novel materials that are easily applicable and of low cost. Within this study, archive boxes with innovative technology are proposed as “smart” boxes that can be used for storage and transportation, in combination with a nanocomposite material consisting of polyvinyl alcohol (PVA) and graphene oxide (GO). The synthesis and characterization of the PVA/GO structure with SEM, Raman, AFM, XRD, Optical Microscopy, and profilometry are fully discussed. It is shown that the composite material can be integrated into the archive box either as a stand-alone film or attached onto fitting carriers, for example, those made of corrugated board. By applying the PVA/GO membrane this way, even with strong daily temperature fluctuations of ΔT = ±24.1 °C, strong external humidity fluctuations can be reduced by −87% inside the box. Furthermore, these humidity regulators were examined as Volatile Organic Compounds (VOCs) adsorbers since gas pollutants like formic acid, formaldehyde, acetic acid, and acetaldehyde are known to exist in museums and induce damages in the displayed or stored items. High rates of VOC adsorption have been measured, with the highest ones corresponding to formic acid (521% weight increase) and formaldehyde (223% weight increase). Full article

(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)

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16 pages, 3316 KiB

Open AccessEditor’s ChoiceArticle

Insights into the Contribution of Oxidation-Reduction Pretreatment for Mn_0.2Zr_0.8O_2−δ Catalyst of CO Oxidation Reaction

by Denis D. Mishchenko, Zakhar S. Vinokurov, Tatyana N. Afonasenko, Andrey A. Saraev, Mikhail N. Simonov, Evgeny Yu. Gerasimov and Olga A. Bulavchenko

Materials 2023, 16(9), 3508; https://doi.org/10.3390/ma16093508 - 2 May 2023

Cited by 1 | Viewed by 2077

Abstract

A Mn_0.2Zr_0.8O_2−δ mixed oxide catalyst was synthesized via the co-precipitation method and studied in a CO oxidation reaction after different redox pretreatments. The surface and structural properties of the catalyst were studied before and after the pretreatment using [...] Read more.

A Mn_0.2Zr_0.8O_2−δ mixed oxide catalyst was synthesized via the co-precipitation method and studied in a CO oxidation reaction after different redox pretreatments. The surface and structural properties of the catalyst were studied before and after the pretreatment using XRD, XANES, XPS, and TEM techniques. Operando XRD was used to monitor the changes in the crystal structure under pretreatment and reaction conditions. The catalytic properties were found to depend on the activation procedure: reducing the CO atmosphere at 400–600 °C and the reaction mixture (O₂ excess) or oxidative O₂ atmosphere at 250–400 °C. A maximum catalytic effect characterized by decreasing T₅₀ from 193 to 171 °C was observed after a reduction at 400 °C and further oxidation in the CO/O₂ reaction mixture was observed at 250 °C. Operando XRD showed a reversible reduction-oxidation of Mn cations in the volume of Mn_0.2Zr_0.8O_2−δ solid solution. XPS and TEM detected the segregation of manganese cations on the surface of the mixed oxide. TEM showed that Mn-rich regions have a structure of MnO₂. The pretreatment caused the partial decomposition of the Mn_0.2Zr_0.8O_2−δ solid solution and the formation of surface Mn-rich areas that are active in catalytic CO oxidation. In this work it was shown that the introduction of oxidation-reduction pretreatment cycles leads to an increase in catalytic activity due to changes in the origin of active states. Full article

(This article belongs to the Section Catalytic Materials)

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17 pages, 5358 KiB

Open AccessEditor’s ChoiceArticle

Production of AC from Bamboo, Orange, and Paulownia Waste—Influence of Activation Gas and Biomass Maturation

by Carlos Grima-Olmedo, Laura M. Valle-Falcones, Dulce Gómez-Limón Galindo and Ramón Rodríguez-Pons Esparver

Materials 2023, 16(9), 3498; https://doi.org/10.3390/ma16093498 - 1 May 2023

Cited by 10 | Viewed by 2531

Abstract

The production of agricultural waste is associated with environmental problems and risks to public health. The general interest demands, as an ecological alternative, the proper management of waste generated by industrial activity through its transformation into value-added products. Carbonization/activation (2 h/2 h) at [...] Read more.

The production of agricultural waste is associated with environmental problems and risks to public health. The general interest demands, as an ecological alternative, the proper management of waste generated by industrial activity through its transformation into value-added products. Carbonization/activation (2 h/2 h) at 700 °C in a vertical furnace (20 K/min), to produce biochar and activated carbon (AC) from bamboo, orange, and paulownia residue, was carried out in a laboratory facility with physical activation by CO₂ and steam. The characterization of the carbonaceous material obtained was based on the determination of the N₂ adsorption–desorption isotherms at 77 K, the specific surface area with the BET procedure, and its internal structure by means of SEM images. The BET surface area values obtained as a function of the CO₂/steam agent used were 911/1182 m²/g, 248/388 m²/g, and 800/1166 m²/g for bamboo, orange, and paulownia, respectively. The range of variation of porosity in paulownia residue generated after steam activation was 485–1166 m²/g, varying depending on the degree of maturity of the biomass used. Research has shown that both the type of activation agent used to produce AC and the degree of plant maturation of the precursor residue affect the quality and characteristics of the final product. Full article

(This article belongs to the Section Carbon Materials)

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26 pages, 7496 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of Early Concrete Damage Caused by Chloride-Induced Steel Corrosion Using a Deep Learning Approach Based on RNN for Ultrasonic Pulse Waves

by Julfikhsan Ahmad Mukhti, Kevin Paolo V. Robles, Keon-Ho Lee and Seong-Hoon Kee

Materials 2023, 16(9), 3502; https://doi.org/10.3390/ma16093502 - 1 May 2023

Cited by 15 | Viewed by 3100

Abstract

The objective of this study is to explore the feasibility of using ultrasonic pulse wave measurements as an early detection method for corrosion-induced concrete damages. A series of experiments are conducted using concrete cube specimens, at a size of 200 mm, with a [...] Read more.

The objective of this study is to explore the feasibility of using ultrasonic pulse wave measurements as an early detection method for corrosion-induced concrete damages. A series of experiments are conducted using concrete cube specimens, at a size of 200 mm, with a reinforcing steel bar (rebar) embedded in the center. The main variables include the water-to-cement ratio of the concrete (0.4, 0.5, and 0.6), the diameter of the rebar (10 mm, 13 mm, 19 mm, and 22 mm), and the corrosion level (ranging from 0% to 20% depending on rebar diameter). The impressed current technique is used to accelerate corrosion of rebars in concrete immersed in a 3% NaCl solution. Ultrasonic pulse waves are collected from the concrete specimens using a pair of 50 kHz P-wave transducers in the through-transmission configuration before and after the accelerated corrosion test. Deep learning techniques, specifically three recurrent neural network (RNN) models (long short-term memory, gated recurrent unit, and bidirectional long short-term memory), are utilized to develop a classification model for early detection of concrete damage due to rebar corrosion. The performance of the RNN models is compared to conventional ultrasonic testing parameters, namely ultrasonic pulse velocity and signal consistency. The results demonstrate that the RNN method outperforms the other two methods. Among the RNN methods, the bidirectional long short-term memory RNN model had the best performance, achieving an accuracy of 74% and a Cohen’s kappa coefficient of 0.48. This study establishes the potentiality of utilizing deep learning of ultrasonic pulse waves with RNN models for early detection of concrete damage associated with steel corrosion. Full article

(This article belongs to the Section Construction and Building Materials)

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25 pages, 4714 KiB

Open AccessEditor’s ChoiceArticle

Vibration Analysis of a Unimorph Nanobeam with a Dielectric Layer of Both Flexoelectricity and Piezoelectricity

by Ali Naderi, Tran Quoc-Thai, Xiaoying Zhuang and Xiaoning Jiang

Materials 2023, 16(9), 3485; https://doi.org/10.3390/ma16093485 - 30 Apr 2023

Cited by 4 | Viewed by 2109

Abstract

In this study, for the first time, free and forced vibrational responses of a unimorph nanobeam consisting of a functionally graded base, along with a dielectric layer of both piezoelectricity and flexoelectricity, is investigated based on paradox-free local/nonlocal elasticity. The formulation and boundary [...] Read more.

In this study, for the first time, free and forced vibrational responses of a unimorph nanobeam consisting of a functionally graded base, along with a dielectric layer of both piezoelectricity and flexoelectricity, is investigated based on paradox-free local/nonlocal elasticity. The formulation and boundary conditions are attained by utilizing the energy method Hamilton’s principle. In order to set a comparison, the formulation of a model in the framework of differential nonlocal is first presented. An effective implementation of the generalized differential quadrature method (GDQM) is then utilized to solve higher-order partial differential equations. This method can be utilized to solve the complex equations whose analytic results are quite difficult to obtain. Lastly, the impact of various parameters is studied to characterize the vibrational behavior of the system. Additionally, the major impact of flexoelectricity compared to piezoelectricity on a small scale is exhibited. The results show that small-scale flexoelectricity, rather than piezoelectricity, is dominant in electromechanical coupling. One of the results that can be mentioned is that the beams with higher nonlocality have the higher voltage and displacement under the same excitation amplitude. The findings can be helpful for further theoretical as well as experimental studies in which dielectric material is used in smart structures. Full article

(This article belongs to the Special Issue Piezoelectric Energy Harvesting and Sensing Technology: Materials, Mechanisms, and Applications)

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13 pages, 1258 KiB

Open AccessEditor’s ChoiceArticle

Understanding Chloride Diffusion Coefficient in Cementitious Materials

by Zhiyuan Xu and Guang Ye

Materials 2023, 16(9), 3464; https://doi.org/10.3390/ma16093464 - 29 Apr 2023

Cited by 5 | Viewed by 3115

Abstract

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination [...] Read more.

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination of the chloride diffusion coefficient will help to predict the chloride profile inside the cementitious materials and estimate the service life with regard to chloride-induced corrosion. However, this paper shows that the chloride diffusion coefficient in the literature is sometimes misunderstood. Such a misunderstanding results in the overestimation of the chloride resistance of cementitious materials. To clarify the chloride diffusion coefficient, this paper first presents the steady- and non-steady-state diffusion equations in cementitious materials. The factors that influence the diffusive flux are identified. The effective and apparent diffusion coefficients are then clearly explained and properly defined. We also point out the obscure definitions of the effective diffusion coefficient in the literature. The varied definitions of the effective diffusion coefficient are the result of the consideration of different factors affecting the diffusion process. Subsequently, this paper discusses two natural diffusion test methods that are frequently employed in cementitious materials to measure the chloride diffusion coefficient. The influencing factors considered by the measured diffusion coefficients are analyzed in detail. Then, the diffusion coefficients determined in some of the studies are reviewed. It is shown that three typical errors could occur when numerically determining the diffusion coefficients. Full article

(This article belongs to the Collection Concrete and Building Materials)

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15 pages, 5346 KiB

Open AccessEditor’s ChoiceArticle

GAM: General Auxetic Metamaterial with Tunable 3D Auxetic Behavior Using the Same Unit Cell Boundary Connectivity

by Ismael Ben-Yelun, Guillermo Gómez-Carano, Francisco J. San Millán, Miguel Ángel Sanz, Francisco Javier Montáns and Luis Saucedo-Mora

Materials 2023, 16(9), 3473; https://doi.org/10.3390/ma16093473 - 29 Apr 2023

Cited by 10 | Viewed by 2219

Abstract

Research on auxetic metamaterials is important due to their high performance against impact loadings and their usefulness in actuators, among other applications. These metamaterials offer a negative Poisson’s ratio at the macro level. However, usual auxetic metamaterials face challenges in (1) grading the [...] Read more.

Research on auxetic metamaterials is important due to their high performance against impact loadings and their usefulness in actuators, among other applications. These metamaterials offer a negative Poisson’s ratio at the macro level. However, usual auxetic metamaterials face challenges in (1) grading the effect, (2) coupling and combining auxetic metamaterials with non-auxetic materials due to boundary compatibility, (3) obtaining the same auxetic behavior in all directions in the transverse plane, and (4) adapting the regular geometry to the component design boundary and shape. The goal of this paper is to present a novel, recently patented tunable 3D metamaterial created to reproduce a wide spectrum of 3D auxetic and non-auxetic Poisson’s ratios and Young’s moduli. This wide range is obtained using the same basic unit cell geometry and boundary connections with neighboring cells, facilitating designs using functionally graded metamaterials as only the connectivity and position of the cell’s internal nodes are modified. Based on simple spatial triangularization, the metamaterial is easily scalable and better accommodates spatial curvatures or boundaries by changing the locations of nodes and lengths of bars. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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17 pages, 5116 KiB

Open AccessEditor’s ChoiceArticle

Numerical Simulations of the Low-Velocity Impact Response of Semicylindrical Woven Composite Shells

by Luis M. Ferreira, Carlos A. C. P. Coelho and Paulo N. B. Reis

Materials 2023, 16(9), 3442; https://doi.org/10.3390/ma16093442 - 28 Apr 2023

Cited by 17 | Viewed by 3401

Abstract

This paper presents an efficient and reliable approach to study the low-velocity impact response of woven composite shells using 3D finite element models that account for the physical intralaminar and interlaminar progressive damage. The authors’ previous work on the experimental assessment of the [...] Read more.

This paper presents an efficient and reliable approach to study the low-velocity impact response of woven composite shells using 3D finite element models that account for the physical intralaminar and interlaminar progressive damage. The authors’ previous work on the experimental assessment of the effect of thickness on the impact response of semicylindrical composite laminated shells served as the basis for this paper. Therefore, the finite element models were put to the test in comparison to the experimental findings. A good agreement was obtained between the numerical predictions and experimental data for the load and energy histories as well as for the maximum impact load, maximum displacement, and contact time. The use of the mass-scaling technique was successfully implemented, reducing considerably the computing cost of the solutions. The maximum load, maximum displacement, and contact time are negligibly affected by the choice of finite element mesh discretization. However, it has an impact on the initiation and progression of interlaminar damage. Therefore, to accurately compute delamination, its correct definition is of upmost importance. The validation of these finite element models opens the possibility for further numerical studies on of woven composite shells and enables shortening the time and expenses associated with the experimental testing. Full article

(This article belongs to the Special Issue Experimental Testing, Manufacturing and Numerical Modelling of Composite and Sandwich Structures)

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11 pages, 4118 KiB

Open AccessEditor’s ChoiceArticle

Charge Transport Enhancement in BiVO₄ Photoanode for Efficient Solar Water Oxidation

by Zhidong Li, Zhibin Xie, Weibang Li, Hafiz Sartaj Aziz, Muhammad Abbas, Zhuanghao Zheng, Zhenghua Su, Ping Fan, Shuo Chen and Guangxing Liang

Materials 2023, 16(9), 3414; https://doi.org/10.3390/ma16093414 - 27 Apr 2023

Cited by 6 | Viewed by 2343

Abstract

Photoelectrochemical (PEC) water splitting in a pH-neutral electrolyte has attracted more and more attention in the field of sustainable energy. Bismuth vanadate (BiVO₄) is a highly promising photoanode material for PEC water splitting. Additionally, cobaltous phosphate (CoPi) is a material that [...] Read more.

Photoelectrochemical (PEC) water splitting in a pH-neutral electrolyte has attracted more and more attention in the field of sustainable energy. Bismuth vanadate (BiVO₄) is a highly promising photoanode material for PEC water splitting. Additionally, cobaltous phosphate (CoPi) is a material that can be synthesized from Earth’s rich materials and operates stably in pH-neutral conditions. Herein, we propose a strategy to enhance the charge transport ability and improve PEC performance by electrodepositing the in situ synthesis of a CoPi layer on the BiVO₄. With the CoPi co-catalyst, the water oxidation reaction can be accelerated and charge recombination centers are effectively passivated on BiVO₄. The BiVO₄/CoPi photoanode shows a significantly enhanced photocurrent density (J_ph) and applied bias photon-to-current efficiency (ABPE), which are 1.8 and 3.2 times higher than those of a single BiVO₄ layer, respectively. Finally, the FTO/BiVO₄/CoPi photoanode displays a photocurrent density of 1.39 mA cm⁻² at 1.23 V_RHE, an onset potential (V_on) of 0.30 V_RHE, and an ABPE of 0.45%, paving a potential path for future hydrogen evolution by solar-driven water splitting. Full article

(This article belongs to the Special Issue Novel Nanostructured Materials for Optoelectronic Applications)

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17 pages, 6118 KiB

Open AccessEditor’s ChoiceArticle

CFD–PBM Simulation for Continuous Hydrothermal Flow Synthesis of Zirconia Nanoparticles in a Confined Impinging Jet Reactor

by Qingyun Li, Zihua Wang and Xuezhong Wang

Materials 2023, 16(9), 3421; https://doi.org/10.3390/ma16093421 - 27 Apr 2023

Cited by 3 | Viewed by 2340

Abstract

Computational fluid dynamics (CFD) and population balance models (PBM) were coupled together for the first time to simulate the synthesis of zirconia nanoparticles in a continuous hydrothermal flow synthesis (CHFS) system with a self-designed confined impinging jet mixing (CJM) reactor. The hydrodynamic and [...] Read more.

Computational fluid dynamics (CFD) and population balance models (PBM) were coupled together for the first time to simulate the synthesis of zirconia nanoparticles in a continuous hydrothermal flow synthesis (CHFS) system with a self-designed confined impinging jet mixing (CJM) reactor. The hydrodynamic and thermodynamic behaviors within the CJM reactor strongly influenced the formation of the ZrO₂ nanoparticles. Crucial parameters, such as velocities, temperatures, mixing conditions, and reaction rates, were analyzed under various supercritical conditions. Temperature and velocity measurements as functions of distance were also investigated. Normal particle size distribution (PSD) patterns were observed in all cases. The mean particle sizes in this study were calculated and compared using PBM aggregation analysis. Full article

(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)

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8 pages, 2210 KiB

Open AccessEditor’s ChoiceCommunication

Boron-Related Defects in N-Type 4H-SiC Schottky Barrier Diodes

by Tihomir Knezevic, Eva Jelavić, Yuichi Yamazaki, Takeshi Ohshima, Takahiro Makino and Ivana Capan

Materials 2023, 16(9), 3347; https://doi.org/10.3390/ma16093347 - 25 Apr 2023

Cited by 4 | Viewed by 2129

Abstract

We report on boron-related defects in the low-doped n-type (nitrogen-doped) 4H-SiC semitransparent Schottky barrier diodes (SBDs) studied by minority carrier transient spectroscopy (MCTS). An unknown concentration of boron was introduced during chemical vapor deposition (CVD) crystal growth. Boron incorporation was found to lead [...] Read more.

We report on boron-related defects in the low-doped n-type (nitrogen-doped) 4H-SiC semitransparent Schottky barrier diodes (SBDs) studied by minority carrier transient spectroscopy (MCTS). An unknown concentration of boron was introduced during chemical vapor deposition (CVD) crystal growth. Boron incorporation was found to lead to the appearance of at least two boron-related deep-level defects, namely, shallow (B) and deep boron (D-center), with concentrations as high as 1 × 10¹⁵ cm⁻³. Even though the boron concentration exceeded the nitrogen doping concentration by almost an order of magnitude, the steady-state electrical characteristics of the n-type 4H-SiC SBDs did not deteriorate. Full article

(This article belongs to the Section Electronic Materials)

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12 pages, 2948 KiB

Open AccessEditor’s ChoiceArticle

Evolution of the Growth Mode and Its Consequences during Bulk Crystallization of GaN

by Tomasz Sochacki, Robert Kucharski, Karolina Grabianska, Jan L. Weyher, Magdalena A. Zajac, Malgorzata Iwinska, Lutz Kirste and Michal Bockowski

Materials 2023, 16(9), 3360; https://doi.org/10.3390/ma16093360 - 25 Apr 2023

Cited by 4 | Viewed by 1730

Abstract

A detailed analysis of morphology of gallium nitride crystal growth obtained by ammonothermal and halide vapor phase epitaxy methods was carried out. The work was conducted to determine the source of triangular planar defects visible in X-ray topography as areas with locally different [...] Read more.

A detailed analysis of morphology of gallium nitride crystal growth obtained by ammonothermal and halide vapor phase epitaxy methods was carried out. The work was conducted to determine the source of triangular planar defects visible in X-ray topography as areas with locally different lattice parameters. It is shown that the occurrence of these defects is related to growth hillocks. Particular attention was paid to analyzing the manner and consequences of merging hillocks. In the course of the study, the nature of the mentioned defects and the cause of their formation were determined. It was established that the appearance of the defects depends on the angle formed between the steps located on the sides of two adjacent hillocks. A universal growth model is presented to explain the cause of heterogeneity during the merging of growth hillocks. Full article

(This article belongs to the Section Electronic Materials)

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10 pages, 3360 KiB

Open AccessEditor’s ChoiceArticle

Ferroelectricity and Oxide Reliability of Stacked Hafnium–Zirconium Oxide Devices

by Ruo-Yin Liao, Hsuan-Han Chen, Ping-Yu Lin, Ting-An Liang, Kuan-Hung Su, I-Cheng Lin, Chen-Hao Wen, Wu-Ching Chou, Hsiao-Hsuan Hsu and Chun-Hu Cheng

Materials 2023, 16(9), 3306; https://doi.org/10.3390/ma16093306 - 23 Apr 2023

Viewed by 2793

Abstract

In this work, we investigate the ferroelectricity of stacked zirconium oxide and hafnium oxide (stacked HfZrO) with different thickness ratios under metal gate stress and simultaneously evaluate the electrical reliability of stacked ferroelectric films. Based on experimental results, we find that the stacked [...] Read more.

In this work, we investigate the ferroelectricity of stacked zirconium oxide and hafnium oxide (stacked HfZrO) with different thickness ratios under metal gate stress and simultaneously evaluate the electrical reliability of stacked ferroelectric films. Based on experimental results, we find that the stacked HfZrO films not only exhibited excellent ferroelectricity but also demonstrated a high performance on reliability. The optimized condition of the 45% Zr proportion exhibited a robust ferroelectric polarization value of 32.57 μC/cm², and a polarization current with a peak value of 159.98 μA. Besides this, the ferroelectric stacked HfZrO also demonstrated good reliability with a ten-year lifetime under >−2 V constant voltage stress. Therefore, the appropriate modulation of zirconium proportion in stacked HfZrO showed great promise for integrating in high-performance ferroelectric memory. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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11 pages, 1439 KiB

Open AccessEditor’s ChoiceArticle

Dentinal Tubule Penetrability and Bond Strength of Two Novel Calcium Silicate-Based Root Canal Sealers

by Karissa Shieh, Jack Yang, Elsa Heng Zhu, Ove Andreas Peters and Sepanta Hosseinpour

Materials 2023, 16(9), 3309; https://doi.org/10.3390/ma16093309 - 23 Apr 2023

Cited by 9 | Viewed by 2385

Abstract

Background: Once the chemo-mechanical preparation of root canals is finished, achieving a complete seal of the root canal system becomes crucial in determining the long-term success of endodontic treatment. The important goals of root canal obturation are to minimize leakage and achieve an [...] Read more.

Background: Once the chemo-mechanical preparation of root canals is finished, achieving a complete seal of the root canal system becomes crucial in determining the long-term success of endodontic treatment. The important goals of root canal obturation are to minimize leakage and achieve an adequate seal. Thus, a material that possesses satisfactory mechanical characteristics, is biocompatible, and has the ability to penetrate the dentine tubules adequately is needed. Aim: This study aimed to compare the penetrability and bond strength between two calcium silicate-based sealers and an epoxy resin-based sealer, as well as examine the relationship between penetrability and bond strength for the different sealers. Method and materials: Thirty-nine recently extracted single-rooted human premolar teeth were instrumented and divided evenly into three groups (n = 13), according to the sealer used for obturation: AH Plus Jet, EndoSequence, and AH Plus Bioceramic Sealer. Three teeth (30 slices) were randomly selected out of each for analysis using confocal laser scanning microscopy to assess penetrability. The remaining ten teeth (90 slices) in each group were subject to push-out tests using a universal testing machine. All teeth were sectioned into nine transverse slices of 0.9 mm thickness for their respective tests (apical, middle, coronal). Results: AH Plus Jet exhibited significantly lower penetrability and significantly higher bond strength compared to EndoSequence BC sealer (p = 0.002) and AH Plus Bioceramic Sealer (p = 0.006). There was no significant difference between EndoSequence BC sealer and AH Plus Bioceramic Sealer in terms of either penetrability or bond strength. No correlation was found between penetrability and bond strength. Conclusions: Within the limitation of this study and regardless of the location in the canal, the bioceramic based root canal sealers appeared to perform better than the epoxy resin-based sealer in terms of dentinal penetration rate. Further studies are required to compare other biomechanical properties of bioceramic sealers including setting characteristics and bacterial leakage. Full article

(This article belongs to the Special Issue Novel Dental Materials: Recent Developments, Advances, and Applications)

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