Search Results (705)

Recently, the kinetic improvement of the nitrogenation reaction of lithium hydride (LiH) to form lithium imide (Li₂NH) by adding a scaffold was reported. The scaffold prevents agglomeration of Li₂NH and maintains the activity of LiH, achieving a reduction in reaction temperature and an increase in reaction rate. In this work, a Li–Si alloy, Li₂₂Si₅, was used as a starting material to form nano-sized LiH dispersed in a Li alloy matrix. Lithium nitride (Li₃N) is generated by the reaction between Li₂₂Si₅ and N₂ to form Li₇Si₃, and then Li₃N is converted to LiH with ammonia (NH₃) generation during heat treatment under H₂ flow conditions. Since Li₃N is formed at the nano-scale on the surface of alloy particles, LiH generated from the above nano-Li₃N is also nano-scale. The differential scanning calorimetry results indicate that direct nitrogenation of LiH in the alloy matrix occurred from around 280 °C, which is much lower than that of the LiH powder itself. Such a highly active state might be achieved due to the nano-crystalline LiH confined by the Li alloy as a self-transformed scaffold. From the above experimental results, the nano-confined LiH in the alloy matrix was recognized as a potential NH₃ synthesis technique based on the LiH-Li₂NH type chemical looping process. Full article

High-performance SiC_p/Al composites were fabricated via a vacuum hot-pressing powder metallurgy process. The effects of SiC particle size on the composite microstructures and their thermal and mechanical properties were systematically investigated. The vacuum hot-pressed SiC_p/Al composites exhibited a well-bonded interface between the SiC particles and Al matrix, while not exhibiting any Al₄C₃ brittle phase. Particle gradation effectively enhanced the densification of SiC_p/Al composites, resulting in dense bulks with a relative density of 99.7%. When the SiC particle size increased from 5 to 50 μm, the fracture morphologies gradually transitioned from intergranular to transgranular, while the relative density, bending strength, and thermal conductivity increased. Overall, SiC_p/Al composites with excellent thermal conductivity (201.42 W/(m·K)) and bending strength (523 ± 29.45 MPa) were obtained. To address the scarcity of research on SiC_p/Al composites’ thermal properties, this study establishes SiC size/gradation–property relationships, innovatively filling the gap in thermal performance regulation. Full article

B₄C-HfB₂-SiC (BCHS) ceramic composites were fabricated by in situ reaction with B₄C and HfSi₂ mixed powders through spark plasma sintering in this work. Effects of sintering temperature and sintering additive (HfSi₂) content on the density, microstructure, and mechanical properties of the BCHS specimens were studied. The BCHS composite containing 15–30 vol.% HfSi₂ reached over 98% theoretical density in the temperature range of 1600–1750 °C under the pressure of 50 MPa. The Vickers hardness, fracture toughness, and room temperature flexural strength of BCHS sintered at 1650 °C with 25 vol.% HfSi₂ reached a maximum value of 31.3 GPa, 5.6 MPa·m^1/2, and 573.9 MPa, respectively. The flexural strength was not decreased at elevated temperatures, and the flexural strength at temperatures of 400 °C, 600 °C, and 800 °C was evaluated to be 540.7 MPa, 518.8 MPa, and 586.9 MPa, respectively. Dense B₄C-HfB₂-SiC composites were fabricated by the spark plasma sintering process. The introduction of HfSi₂ can significantly enhance the density and mechanical properties of B₄C ceramic. Full article

Utilizing abundant volcanic rock resources as supplementary cementitious materials is a critical pathway for regional low-carbon construction. However, the high crystallinity of natural volcanic rocks limits their reactivity. This study systematically investigates the regulation mechanisms of Triethanolamine (TEA) and Triisopropanolamine (TIPA) on the hydration kinetics and microstructure of a cement system containing Volcanic Rock Powder (VRP) thermally treated at 700 °C. Dissolution kinetics reveal that both TEA and TIPA inhibit Si release but exhibit distinct structural selectivity in promoting metal ion dissolution: TEA demonstrates superior efficiency in promoting the release of Al and Ca ions due to lower steric hindrance, whereas TIPA exhibits a stronger specific activation capacity for insoluble Fe, which is likely attributed to the electron-donating inductive effect. Macroscopic tests show that TEA at 0.05% dosage significantly improved the 28-day compressive strength by 20.4%, attributed to the synergistic effect of efficient chemical activation and pore structure refinement. In contrast, the stronger surface activity of TIPA introduced substantial detrimental macropores; this deterioration in physical structure severely offset its chemical contributions, leading to slow late-age strength development. The study highlights the critical trade-off between chemical activation and microstructural evolution, confirming that TEA is a more suitable activator than TIPA for the Al/Fe-rich thermally treated VRP. Full article

This study explores the feasibility of constructing a microwave kiln for artisanal ceramics using accessible materials and homemade susceptors. Two modified microwave ovens (18 L and 50 L) were equipped with insulation and susceptors to achieve temperatures up to 1280 °C. Susceptors were fabricated from silicon carbide (SiC) and magnetite (Fe₃O₄) powders via microwave-assisted reactive sintering. Magnetite-poor susceptors (SiC/Fe₃O₄ > 2 by weight) demonstrated excellent durability, maintaining stable thermal performance over multiple cycles. In contrast, magnetite-rich susceptors (SiC/Fe₃O₄ ∼ 1) exhibited high initial efficiency and the ability to control redox conditions but degraded significantly after 10–15 cycles due to partial melting. The microwave kiln achieved significant time savings, completing the ramp-up of the firing cycles in 1 h, compared to 8–10 h in conventional kilns. Energy consumption per litre was comparable to large electric kilns but significantly lower than small ones. The fired ceramics, including porcelain and earthenware, showed excellent mechanical and aesthetic qualities, with glazes performing well even at lower temperatures than recommended. The study highlights the advantages of microwave heating, such as faster processing, energy efficiency, and the ability to control redox conditions, which mimic traditional gas-fired kilns. The developed susceptors are cost-effective and easy to manufacture, making this approach accessible to craftspeople and amateurs. While magnetite-rich susceptors enable redox control, their limited lifespan requires further optimisation. This work demonstrates the potential of microwave kilns for artisanal ceramics, offering flexibility, efficiency, and quality comparable to traditional methods, with promising applications for unique or small-scale production. Future research should focus on refining susceptors durability and validating redox control effects on ceramic glazes. Full article

The conventional production of electronic-grade, high-purity, spherical silicon dioxide (SiO₂) faces challenges of high raw material costs and poor control over particle morphology. This study presents an alternative route using low-cost, powdered quartz as a starting material. The quartz was first purified by flotation to remove any associated minerals, such as talc. Subsequently, deep purification was achieved through a hydrothermal alkaline process, which leveraged the distinct leaching kinetics of SiO₂ and impurity ions (Al³⁺, Ca²⁺, Fe³⁺) under precisely controlled hydrothermal conditions (10 mL/g liquid-to-solid ratio, 3 mol/L NaOH, 200 °C, 8 h). This step yielded a sodium silicate solution with a purity of 99.999%. Spherical SiO₂ particles were then synthesized from solutions of varying moduli via chemical precipitation. The condensation kinetics of silicate anionic species (Qn) during acidification were investigated, revealing how the Qn distribution governs the final particle size and morphology. The optimal product exhibited excellent characteristics: a sphericity ≥ 0.98, a median particle size (D₅₀) of 400–500 nm, and a narrow particle size distribution (polydispersity index, PDI of 0.178–0.192). These properties surpass the requirements for the QYG-H Type 002 grade specified in the Chinese National Standard GB/T 32661-2016 (“Spherical Silica Powder”) and meet the standard for electronic-grade spherical SiO₂. This work provides a fundamental insight into morphology control and a feasible technical pathway for the value-added utilization of powdered quartz and the production of electronic-grade spherical SiO₂ with a narrow particle size distribution. Full article

This study systematically investigates the catalytic degradation performance and reaction mechanism of Fe₈₀P₁₃C₇ Metal Glass (MG) in a Fenton-like system for the removal of Methylene Blue (MB). Kinetic experiments on degradation reveal that under acidic conditions (pH = 3), Fe₈₀P₁₃C₇ MG exhibits exceptional catalytic activity, achieving complete degradation of a 50 mg/L MB solution within 12 min. Its degradation rate significantly surpasses that of Fe₇₈Si₉B₁₃ MG and commercially available ZVI powder. Key parameters such as catalyst dosage, H₂O₂ concentration, solution pH, and initial dye concentration were systematically examined to determine the optimal reaction conditions. The characterization results indicate that Fe₈₀P₁₃C₇ MG maintains high activity even after multiple cycles of use, attributed to surface selective corrosion and crack formation during the reaction process. This “self-renewal” mechanism continuously exposes fresh active sites. Mechanistic studies confirm that the degradation process is driven by an efficient redox cycle between Fe²⁺/Fe³⁺ within the material, ensuring sustained and stable generation of •OH, which ultimately leads to the complete mineralization of MB molecules. This research provides solid experimental and theoretical foundations for the application of Fe₈₀P₁₃C₇ MG in dye wastewater treatment. Full article

Waste stone powder is a major solid waste byproduct of stone operations. This study developed a novel “alkali activation-calcination” process that efficiently converts waste stone powder into high-value-added silicon-based materials (SSM). This study elucidated the morphological evolution of silicon during the conversion process and revealed the formation mechanism of active silicon. Through further integration of batch adsorption experiments and multi-technique characterization analysis, the immobilization efficacy of this material for heavy metals cadmium/lead was elucidated, revealing both direct and indirect interfacial reaction mechanisms. The results demonstrate that in-creasing the calcination temperature, alkali activator concentration, and calcination duration enhances the reactive silica content in SSM. NaOH as activator, the calcination process significantly reduces both the thermal decomposition temperature of raw materials and the initial temperature required for silicon conversion. Under optimized conditions (WG:MD:activator = 1:0.8:0.32, temperature = 800 °C, time = 1 h), the reactive silica content reached 24.30%. The generation rate of reactive silica is governed by the combined effects of interfacial chemical reactions and solid-phase product layer diffusion. Under idealized laboratory conditions, the maximum adsorption capacities (Qm) of SSM were determined to be 57.40 mg/g for cadmium and 496 mg/g for lead, which are significantly higher than those of many other adsorbents. Continuous desorption experiments and characterization analyses confirm that Cd and Pb adsorption by SSM is primarily driven by electro-static interactions, complexation, precipitation, and coordination, while ion ex-change plays a secondary role. Highly reactive silica facilitates interactions between Cd/Pb and oxygen-containing functional groups (e.g., -OH, ≡Si-OH, Si-O-Si), promoting precipitate formation for effective heavy metal removal. This work offers theoretical guidance for valorizing silica-rich waste rock powder. It is important to note, however, that while the adsorption capacity of SSM is encouraging, its practical implementation requires resolving key issues identified during the lab-to-application transition. Full article

This research constitutes a novel experimental approach to valorizing an industrial by-product: the ‘brick’. Studies put emphasis on the importance of detailed structural characterization of brickminerals and their chemical evolution upon heating, contributing rationally to the design and development of new glass–ceramic forms that would be suitable for efficiently encapsulating radio-nuclides. The brick used is a complex material composed of metakaolinite, illite, sand and impurities such as rutile and iron oxides/hydroxides. Raw brick was first activated with a range of sodium hydroxide concentrations, and, second, cured at different temperatures from 90 °C to 1200 °C. Alkali-brick frameworks gradually decomposed during the firing, and turned into crystalline ceramic phases (analcime and leucite) embedded inside an amorphous silica-rich phase. After each heating stage, the cured-brick sample was exhaustively characterized by using a variety of advanced analytical techniques, including powder X-ray diffraction, ESEM/EDS microscopy and ²⁹Si-²⁷Al-MAS-NMR spectroscopy. Ultra-high magnetic field NMR (28.2 T) was used to distinguish and quantify Al(IV), Al(V) and Al(VI) configurations, and to better follow distinctive changes in ²⁷Al environments of brickminerals under thermal effects. Glass-ceramized brick exhibited high specific density (~2.6 g·cm⁻³), high compactness and good corrosion resistance under static, mild and aggressive conditions, attesting to its high solidification and chemical durability. Full article

In this study, TiB₂/AlSi10Mg, 2 wt.% SiC + TiB₂/AlSi10Mg, and 5 wt.% SiC + TiB₂/AlSi10Mg composite powders were prepared via high-energy ball milling. For the first time, TiB₂ and SiC hybrid particle-reinforced aluminum matrix composites (AMCs) were fabricated using the Laser-Directed Energy Deposition (LDED) technique. The effects of processing parameters on the microstructure evolution and mechanical properties were systematically investigated. Using areal energy density as the main variable, the experiments combined microstructural characterization and mechanical testing to elucidate the underlying strengthening and failure mechanisms. The results indicate that both 2 wt.% and 5 wt.% SiC + TiB₂/AlSi10Mg composites exhibit excellent formability, achieving a relative density of 98.9%. However, the addition of 5 wt.% SiC leads to the formation of brittle Al₄C₃ and TiC phases within the matrix. Compared with the LDED-fabricated AlSi10Mg alloy, the tensile strength of the TiB₂/AlSi10Mg composite increased by 21.4%. In contrast, the tensile strengths of the 2 wt.% and 5 wt.% SiC + TiB₂/AlSi10Mg composites decreased by 3.7% and 2.6%, respectively, mainly due to SiC particle agglomeration and the consumption of TiB₂ particles caused by TiC formation. Nevertheless, their elastic moduli were enhanced by 9% and 16.3%, respectively. Fracture analysis revealed that the composites predominantly exhibited ductile fracture characteristics. However, pores larger than 10 μm and SiC/TiB₂ clusters acted as crack initiation sites, inducing stress concentration and promoting the propagation of secondary cracks. Full article

Utilizing waste red-clay brick powder (WRCBP) as a precursor for manufacturing geopolymers is increasingly popular due to its environmental and economic benefits. However, the geopolymerization of this waste remains insufficiently explored. This study evaluates the differences in physical–mechanical properties and microstructural evolution of WRCBP- and fly ash (FA)-based geopolymers to determine the reactivity of WRCBP. Mineral admixtures, including granulated blast furnace slag (GF) and metakaolin (MT), were incorporated with WRCBP to fabricate geopolymer pastes, while FA was used in parallel for comparison. The effects of activator modulus (1.2 and 1.4 for Na₂SiO₃) and curing conditions (65 °C and 90 °C) on the mechanical and microstructural performance of the prepared pastes were investigated through water demand analysis, compressive strength testing, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). The results indicate that WRCBP-based pastes achieved a comparable compressive strength (39.8 MPa) under appropriate alkali-activated and curing conditions relative to FA-based pastes (42.5 MPa). The modulus of the alkaline activator exerted a greater influence on strength development than the raw material composition. For both WRCBP- and FA-based pastes, 65 °C was identified as a more suitable curing temperature. Moreover, compared with FA-based pastes, pastes produced using WRCBP provide enhanced social and economic benefits. Overall, this study confirms that high-performance binders can be engineered by incorporating WRCBP, thereby supporting the development of sustainable low-carbon construction materials. Full article

This work presents a comparative study of TiSiC and TiSiCN composite coatings deposited on stainless steel by reactive plasma spraying using mechanically activated powders. Microstructure, phase composition, and hardness were assessed by SEM/EDS, XRD, and Vickers indentation, while corrosion, erosion, and high-temperature tribological behavior were systematically evaluated. The TiCN + SiC + Si system forms a stable TiC_xN_1−x solid solution with amorphous Si₃N₄ grain-boundary phases, leading to densification and enhanced chemical stability. Compared with TiSiC, TiSiCN coatings exhibit higher hardness (2599 N/mm², ≈324 HV), lower erosion loss (<1 mg), and stable friction coefficients (0.45–0.50 at 600 °C) due to protective oxide/nitride tribofilms. Electrochemical tests in 3.5 wt.% NaCl show a >6-fold reduction in corrosion rate (from 0.0506 to 0.008 mm·year⁻¹) relative to bare steel. Overall, TiSiCN coatings deposited at 500–600 A provide an optimal balance of hardness, wear, and corrosion resistance, indicating strong potential for gas-turbine and power-generation components operating in aggressive environments. Full article

In recent years, porous carbon-based materials have demonstrated their potential as electrode materials, particularly as supercapacitors for energy storage. The specific capacitance of a carbon-based material is strongly influenced by its porosity. Herein, activated biochar (BCA) from millet was prepared using ZnCl₂ as an activator at temperatures of 400, 700, and 900 °C. Activation was achieved through wet and dry impregnation of millet bran powder particles. The porosity of BCAs was assessed by determining the iodine and methylene blue numbers (N_I and N_MB, respectively), which provide information on microporosity and mesoporosity, respectively. Characterization of the BCAs was carried out using Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and cyclic voltammetry. The data show that the BCA prepared at 700 °C following dry impregnation, P700(p), has the highest N_I and the highest geometric mean value ($ñ=\sqrt{N_I\times N_{MB}}$), a descriptor we introduce to characterize the overall porosity of the biochars. P700(p) biochar exhibited remarkable electrochemical properties and a maximum specific capacitance of 440 F g⁻¹ at a current density of 0.5 A g⁻¹, in the three-electrode configuration. This value drops to 110 F g⁻¹, in the two-electrode configuration. The high specific capacitance is not due to ZnO, but essentially to the textural properties of the biochar (represented by ñ descriptor), and possibly but to a lesser extent to small amounts of Zn₂SiO₄ left over in the biochar. Moreover, the capacitance retention increases with cycling, up to 130%, thus suggesting electrochemical activation of the biochar during the galvanostatic charge-discharge process. To sum up, the combination of pyrolysis temperature and the method of impregnation permitted to obtaining of a porous biochar with excellent electrochemical properties, meeting the requirements of supercapacitors and batteries. Full article

Against the backdrop of China’s Western Development Strategy, numerous infrastructure projects are being constructed in desert regions. Utilizing local aeolian sand (AS) as a raw material for concrete production offers significant cost-saving potential but is hindered by challenges such as limited applicability and inadequate mechanical strength of the resulting concrete. To address these limitations, aeolian sand was ground into aeolian sand powder (ASP) and subjected to treatment with single alkali activators (NaOH, Na₂SiO₃) and a composite alkali activator (NaOH + Na₂SiO₃). The treated and untreated ASP was then used to replace 50% of cement by mass for the preparation of aeolian sand powder–aeolian sand concrete (ASPC). Mechanical performance tests and advanced characterization techniques (SEM, TG-DSC, XRD, FTIR, nanoindentation, and NMR) were employed to investigate the effects of different activators on the mechanical properties of ASPC and elucidate the underlying enhancement mechanisms. The results demonstrated that the composite activator outperformed its single-activator counterparts: ASPC-4-6 (incorporating 4% NaOH and 6% Na₂SiO₃) exhibited 16.3–23.1% higher compressive strength and 12.1–17.6% higher splitting tensile strength across all curing ages compared to plain ASPC. Under the influence of OH⁻ from the composite activator, ASP showed more pronounced reductions in potassium feldspar, montmorillonite, and SiO₂ content, accompanied by the formation of C-S-H gel—replacing the amorphous, water-absorbent N-A-S-H generated by single activators. The presence of highly polymerized hydration products and more stable potassium A-type zeolites in ASPC-4-6 led to a reduction in macropore volume, optimization of pore structure, and refinement of the aggregate–mortar inter-facial transition zone. These micro-structural improvements collectively contributed to the significant enhancement of mechanical properties. This study provides novel insights into the large-scale and multi-dimensional utilization of aeolian sand in concrete. Full article

The present study investigated the microstructure, processability, and mechanical strength of an AlSi9Mg-20vol.%SiC composite to assess its processing and mechanical performance during the laser powder bed fusion process. A simple laser surface remelting approach was adopted to simulate laser-based rapid solidification. The results revealed that this composite generally exhibited good laser processability, and the samples with the highest laser energy density and lowest scan speed possessed the best processability owing to the elimination of microcracks and pores. After laser processing, all the samples displayed a fine Al-Si cellular structure accompanied by in-situ formed fine needle-shaped Al₄SiC₄ particles. Increasing laser energy density considerably increased the area fraction of the Al₄SiC₄. The T5 aging treatment preserved the fine cellular structure and promoted the precipitation of a large number of Si nanoparticles and MgSi precipitates. During T6 solid solution treatment, the Si networks were broken down into coarse Si particles, disintegrating the cellular structure and reducing the strength. The T5 treatment was identified as the most suitable post-heat treatment for enhancing the microhardness and strength of the composite. Compared to conventionally laser-processed AlSi10Mg alloys, the AlSi9Mg-20vol.%SiC composite exhibited a significant increase in microhardness and yield strength. Full article