Search Results (1,108)

Partial oxidation of methane (POM) is a thermodynamically favorable process for hydrogen and syngas production. Cerium oxide (CeO₂) was investigated as a textural promoter for nickel (Ni)-based catalysts in POM. In this study, CeO₂ was incorporated into Ni/Al₂O₃ catalysts with varying cerium loadings (1–3 wt.%) to examine its role as a structural and functional promoter. Comprehensive physicochemical characterization using BET, XRD, H₂-TPR, and TEM analyses indicated that incorporation of ceria influenced the textural and structural properties, leading to reduced Ni crystallite size from 10 nm to 2.9–3.3 nm, and modified metal-support interactions. The 2 wt.% CeO₂-modified Ni/Al₂O₃ (Ni/2Ce-Al) catalyst demonstrated superior catalytic performance, achieving 70% methane (CH₄) conversion and 64% hydrogen (H₂) yield at 650 °C with stable performance over 275 min time-on-stream with minimal deactivation. Temperature-programmed reduction studies revealed a non-monotonic trend in reduction behavior with an optimal 2 wt.% cerium loading exhibiting the lowest reduction temperature (865 °C). The H₂/CO ratio of 2.92 indicates favorable syngas composition under the conditions studied. Raman spectroscopy showed a decrease in the D/G intensity ratio from 1.55 to 1.33 with increasing cerium loading, indicating enhanced structural ordering and improved coke resistance. The improved catalytic performance may be associated with redox properties of ceria (Ce³⁺/Ce⁴⁺ cycling), its enhanced oxygen storage capacity, and modified Ni-support interactions which can contribute to improved resistance to carbon deposition and Ni sintering. Response surface methodology (RSM) was also successfully used to model the interaction of temperature, space velocity and feed ratio and to confirm the significant positive effect of temperature on conversion. The long-term performance of the optimized catalyst, over a 20 h period, demonstrated the excellent durability of the catalyst, resulting in a stable H₂ yield of ca. 87% and CH₄ conversion of ca. 90%. This work demonstrates that optimized cerium promotion on alumina-supported Ni catalysts can improve catalytic activity and stability, providing a potentially cost-effective, thermally stable catalyst system for industrial hydrogen and syngas production from (CH₄). Full article

The effect of drying, thermal decomposition, and sintering conditions during the sol–gel synthesis of BaTi₅O₁₁ nanocrystals was investigated to optimize levofloxacin (LEV) photodegradation. Sintering emerges as the dominant factor, and BaTi₅O₁₁ nanocrystals synthesized at 700 °C for 120 min exhibit the smallest grain size, highest specific surface area and abundant active sites, achieving 93.2% LEV degradation within 30 min under UV irradiation. In contrast, excessive sintering temperatures or time induce grain coarsening and size homogenization, which reduce surface area and active sites, thereby impairing photocatalytic performance. The optimized nanocrystals also efficiently degrade other antibiotic pollutants, including ciprofloxacin, norfloxacin, and tetracycline. Radical trapping experiments confirm that •OH is the primary reactive species. Photoluminescence and photoelectrochemical analyses reveal a competition between grain size variation and charge carrier dynamics; however, photocatalytic degradation underscores the dominant role of surface-active sites and specific surface area. Kelvin probe force microscopy (KPFM) further corroborates efficient charge separation, showing a cross-line contact potential difference (ΔV_CPD) of approximately 90 mV, indicative of facile hole migration to the crystal surface. Collectively, these findings elucidate the processing–microstructure–property relationships in BaTi₅O₁₁ nanocrystals and provide a robust basis for the rational design of high-performance photocatalytic systems for antibiotic pollutant remediation. Full article

This study evaluates the rapid tooling feasibility and structural significance of utilizing digital light processing (DLP)-printed alumina as a near-net-shape ceramic mold-insert preform route for replication of curved polymer optics. While conventional production tooling for precision optics demands immediate optical-grade tolerances, the fundamental mechanisms governing polymer replication close to additively manufactured ceramic interfaces remain insufficiently understood. To isolate these multi-factor processing signatures, alumina specimens incorporating concave and convex parabolic surfaces were synthesized via lithography-based ceramic manufacturing. Our design acts as a geometric control lens, ensuring that thermal shrinkage trends, slicing kinematics, and interfacial replication behaviors are clearly exposed and quantified under uniform boundary conditions. Following debinding and sintering, exploratory hot-pressing cycles were executed to evaluate gross profile transfer and surface inheritance on poly(methyl methacrylate) (PMMA) replicas. Quantitative laser scanning confocal microscopy confirmed successful gross curvature generation and revealed geometry-dependent post-sintering shrinkage trends. The convex inserts exhibited an average peak-to-valley (PV) error of 123.48 ± 3.30 µm and an RMS error of 29.76 ± 1.23 µm, whereas the concave alumina inserts showed an average PV error of 137.98 ± 5.80 µm and an RMS error of 34.68 ± 1.20 µm. The PMMA replicas also showed substantial form deviation, with an average PV error of 163.72 ± 15.64 µm and RMS error of 27.37 ± 2.03 µm. Our work presents a route for producing near-net-shape ceramic mold-insert preforms that transforms complex processing variations into a predictable, mathematically addressable roadmap. A geometry-specific CAD pre-compensation can then be performed while the remaining precision gap can be selectively closed via targeted post-polishing depending on the desired optical application tier. Full article

Geoelectric field observations play a vital role in geophysical exploration, geological disaster early warning, and underground resource detection. Traditional contact non-polarisable electrodes, which require burial and electrolyte coupling, are hindered by several issues, such as limited adaptability to challenging terrain, significant electrode potential drift, and high susceptibility to environmental interference. Existing non-contact electric field sensors often exhibit insufficient coupling capacitance, poor impedance matching for ultra-weak high-impedance signals, and inadequate low-frequency noise suppression, rendering them unsuitable for the precise acquisition of natural microvolt-level geoelectric field signals. To address these challenges, this study introduces an innovative non-contact geoelectric field sensor with a three-layer composite structure. The sensor operates based on the principle of a parallel-plate capacitor, with a conductive silver paste layer at the top acting as the signal acquisition electrode plate, which forms an equivalent parallel-plate capacitance model with the ground to achieve non-contact capacitive coupling for geoelectric field detection. The intermediate layer uses lead zirconate titanate (PZT) piezoelectric ceramics as a support medium with a high dielectric constant. At the bottom is a silicon-based, flexible, sensitive ground-contacting layer with high elasticity, which allows it to adapt to micro-level surface irregularities, eliminating air gaps between the electrode plate and the ground, increasing plate-to-ground coupling capacitance, and ensuring the stability of the capacitance. The three-layer structure was created using a dry-press sintering integration approach, which eliminates interlayer bonding materials while ensuring consistent dielectric performance and efficient charge transfer. Additionally, a specialised signal-conditioning circuit was designed to match the ultra-high-impedance sensitive unit, utilising the ADA4528-2 ultra-low-noise precision operational amplifier, which achieved low-loss conversion and strong noise suppression for ultra-weak high-impedance charge signals. The circuit simulation results demonstrate that the designed circuit achieves an input impedance of no less than 10 TΩ, an effective operating bandwidth from 0.02 Hz to 20 kHz, and a voltage noise density lower than 1.5 μV/√Hz at 10 Hz, fully covering the ultra-low-frequency effective band of natural geoelectric fields. Field experiments comparing artificial and natural field signals revealed that the proposed sensor could be quickly deployed by simply attaching it to the ground without burial. Its time-domain waveform consistency and frequency-domain component matching were nearly identical to those of commercial standard solid non-polarisable electrodes, with a cross-correlation coefficient greater than 0.98, indicating no significant potential drift or power-frequency interference. By structurally eliminating the inherent electrode potential difference, the sensor offers advantages such as ease of deployment, strong environmental adaptability, high precision for weak signal acquisition, and excellent engineering substitutability. It is well suited for long-term geoelectric field observations in complex field scenarios, including deserts, Gobi areas, and frozen soil regions, and provides a high-performance, novel sensing solution for geoelectric field detection in extreme environments. Full article

Large-scale high-value utilization of industrial solid waste is urgently required worldwide. Porous ceramics prepared from single-type solid waste face great limitations in balancing mechanical properties and thermal insulation performance. In this work, various types of industrial solid wastes—red mud, waste electric porcelain, and coal gangue—were fully adopted as primary raw materials, while SiC was employed as a foaming agent to prepare porous ceramics. Results show that at 3% SiC addition and 1140 °C sintering temperature, the apparent porosity of the ceramics reaches to 21.8%, with thermal conductivity of 0.08 W/(m·K). Moreover, favorable pore-size distribution and desirable crystalline phases (Mg–Fe–Al spinel and sodium calcium feldspar) are obtained under this optimal condition, accompanied by a favorable compressive strength of 2.91 MPa, making it a promising low-cost, high-performance high-temperature insulation material. Full article

Self-lubricating iron-based composites produced by powder metallurgy are promising materials for reducing friction and improving component durability under dry-sliding conditions. In this study, three composites reinforced with graphite and/or graphene oxide (Fe10%Gr, Fe10%GO, and Fe5%Gr5%GO) were fabricated to evaluate the influence of solid lubricants on densification, hardness, and tribological behavior. Powders were uniaxially compacted at 500 MPa and low-temperature-sintered at 880 °C under an argon atmosphere. The tribological performance was assessed by pin-on-disk tests against an AISI 52100 steel ball. Pure Fe exhibited the highest hardness (approximately 97 HV) and a final porosity of 17.5%, whereas the lubricant-containing composites showed porosities ranging from 17.3% to 22.8% and lower hardness values of 45–60 HV. Despite the reduction in hardness, all lubricant-containing compositions decreased the coefficient of friction relative to pure Fe (~0.33). Fe10%Gr and Fe5%Gr5%GO exhibited the lowest friction coefficients, reaching ~0.08 and ~0.05, respectively, while Fe10%GO showed the highest wear rate (~1.1 × 10⁻² mm³/Nm). Among the compositions studied, Fe5%Gr5%GO showed the best friction–wear balance among the self-lubricating formulations, combining low friction and moderate wear due to a surface synergy where graphite promotes continuous low-shear lubrication while GO promotes the formation of a more compact and resilient protective tribolayer. Full article

This study investigates the synthesis of La_0.6Ca_0.4FeO₃ (LCF) perovskite via a ball milling method for application in reverse water–gas shift chemical looping (RWGS-CL) for CO₂-to-CO conversion. Unlike conventional wet-chemical routes such as the Pechini method, the ball milling approach offers a solvent-free, scalable synthesis using low-cost metal oxide precursors (e.g., La₂O₃, CaO, Fe₂O₃). Structural analysis by XRD confirmed the successful formation of single-phase cubic perovskite, with no secondary phases when using oxide precursors. Crystallite size increased with calcination temperature, from 118.9 Å (no calcination) to 404.3 Å (1050 °C). BET analysis revealed a decrease in surface area from 2.5 m²/g (no calcination) to 0.51 m²/g (1050 °C), consistent with sintering at higher temperatures. TPR-H₂ and TPO-CO₂ studies revealed that non-calcined LCF possesses slightly enhanced redox properties, with oxygen vacancy formation and CO₂ reoxidation activity both at 500 °C. RWGS-CL experiments demonstrate that all LCF samples exhibit stable CO production (910–970 µmol/g_LCF) over multiple cycles at 500 °C, with comparable performance across calcination conditions. A cost and sensitivity analysis reveals that the ball milling method had lower synthesis costs by approximately 92% at the laboratory-scale and 88% at the industrial-scale compared to the Pechini method, highlighting its strong potential for large-scale perovskite production. Full article

The growing demand for sustainable and environmentally friendly materials has accelerated interest in the valorization of industrial wastes within the framework of the circular economy. In this study, porous wollastonite-based ceramics were successfully fabricated using cement kiln bypass dust (CKD) and waste glass cullet as low-cost and sustainable secondary raw materials. The proposed approach aims to mitigate environmental pollution, reduce landfill disposal, conserve natural resources, and promote the recycling of industrial by-products into value-added ceramic products. Different batch compositions containing varying proportions of CKD and glass cullet were prepared, compacted, and subsequently sintered under controlled conditions to induce crystallization. The crystallization behavior and phase development were characterized by X-ray diffraction (XRD), while the microstructural features were examined using scanning electron microscopy (SEM). Physical and dielectric properties, including bulk density, open porosity, dielectric constant (ε′), dielectric loss (ε″), and electrical conductivity (σ), were also evaluated. The results confirmed the successful formation of parawollastonite as the predominant crystalline phase, accompanied by a relatively homogeneous porous microstructure. The prepared ceramics exhibited high open porosity values ranging from 52.55 to 63.63% and low bulk densities between 1.050 and 1.318 g cm⁻³, making them suitable for lightweight construction and insulation applications. Dielectric measurements performed over the frequency range of 50 Hz–8 MHz revealed that both dielectric constant (ε′) and dielectric loss (ε″) decreased with increasing frequency. At 50 Hz, ε′ and ε″ ranged from 8.44–9.39 and 0.709–0.733, respectively. The electrical conductivity values (~10⁻² μS cm⁻¹) at low frequencies indicated insulating behavior, whereas poor-to-fair semiconducting characteristics were observed at higher frequencies. The incorporation of large amounts of recycled CKD and waste glass significantly reduced dependence on virgin raw materials while providing a sustainable route for waste utilization. Consequently, this work demonstrated an environmentally responsible and economically viable strategy for producing porous wollastonite-based ceramics with potential applications in both the construction and electrical sectors, thereby contributing to resource efficiency, waste valorization, carbon-emission reduction, and sustainable industrial development. Full article

The oxygen blast furnace (OBF) represents a key pathway toward deep decarbonization in ironmaking. The main difference between it and the traditional blast furnace is that the atmosphere in the furnace has high reduction potential and little nitrogen content. However, the burden metallurgical performance under CO-H₂-rich, N₂-lean atmospheres remains unclear. This study investigated the isothermal and non-isothermal reduction and softening–melting behavior of sinter and pellets. As CO increased from 59.2 to 79.2 vol%, the reduction degree rose from ~27% to ~90% within 180 min, with a rate index of 0.72–0.75%·min⁻¹. The apparent activation energies of sinter and pellets were 113.0 kJ·mol⁻¹ and 57.9 kJ·mol⁻¹, respectively, indicating that the gas–solid interfacial chemical reaction is the rate-controlling step. Under non-isothermal conditions, the reduction start temperatures of both sinter and pellets decreased, and complete reduction was achieved at 1200 °C. Microstructural analysis revealed a four-stage structural evolution pathway. The softening–melting behavior indicated that oxygen-enriched conditions decrease the softening start temperature, whereas the melting start temperature increases due to the thickening of the metallic iron shell. The maximum pressure difference of the cohesive zone was reduced by 32.9%, and the air permeability was significantly improved. This study reveals the mechanism of charge reaction and structure evolution under OBF conditions and provides a theoretical basis for charge optimization and OBF operation control. Full article

This article is devoted to the development of a combined sulfation method (CSM) for processing low-grade copper-sulfide concentrates with a copper grade of 0.34–3.5%. The relevance of the study is driven by the depletion of Kazakhstan’s high-grade copper deposits and the need to incorporate off-balance sulfide raw materials into processing. CSM is based on the spatial separation of two thermally coupled zones in the filter bed of a shaft furnace: a zone of endothermic sulfation of sulfide minerals with ammonium hydrosulfate at 360–650 °C and a zone of exothermic oxidative roasting of residual sulfur at 640–660 °C. Excess oxidation heat compensates for the thermal losses of sulfation, ensuring an autogenous process without sintering of the charge. Flotation enrichment of off-balance ore from the Annenskoye deposit yielded a concentrate with a Cu grade of 7.59% and a copper recovery of 89.13–92.13%. Thermodynamic modeling was used to validate the temperature conditions for sulfation of individual minerals, and analytical relationships were developed for calculating reagent consumption and sulfur distribution. Laboratory tests confirmed the adequacy of the calculation model; the discrepancy between calculated and experimental data did not exceed 1.5%. The feasibility of regenerating ammonium hydrosulfate and extracting copper from the processed products was demonstrated. A basic flow chart for waste-free processing of low-grade copper-sulfide raw materials was proposed. Full article

The reliable joining of graphite and Cu holds significant promise for applications in electronic heat dissipation and sliding electrical contacts. However, the substantial differences in their physicochemical properties, poor wettability, and mismatch in coefficients of thermal expansion often result in low joint strength. In this study, a two-step joining strategy combines surface modification with low-temperature sintering, and this is proposed for fabrication of Cu/graphite joints. First, the graphite surface is modified using an AgCuTi active filler alloy under vacuum conditions. Ti preferentially segregates at and reacts with the graphite interface, leading to the formation of an Ag-Cu eutectic modified layer on the graphite surface. Subsequently, low-temperature joining of the modified graphite to a Cu substrate is achieved via a hot-pressing sintering process using a Ag paste. In the sintered joint, the Ag sintered layer forms sound metallurgical bonds with both the Cu substrate and the graphite-modified layer. When the sintering temperature is 250 °C, the joint exhibits a shear strength of 30 MPa, which is significantly higher than that of a directly brazed joint. This strategy effectively reduces thermal residual stress in the joint during cooling and shifts the failure location from the brittle graphite substrate to the ductile Ag sintered layer, thereby substantially enhancing the mechanical performance. Full article

Iron-based Fischer–Tropsch synthesis (Fe-FTS) catalysts are central to coal-to-liquid (CTL) processes but suffer from rapid and complex deactivation under industrial conditions. This review critically examines the key deactivation mechanisms, including carbon/wax deposition, hydrothermal sintering, chemical poisoning (S, Cl, As), and mechanical attrition, and evaluates modern regeneration strategies. These strategies include supercritical fluid extraction for wax removal, controlled oxidative decoking, reductive reconstruction of active iron carbides (χ-Fe₅C₂), chemical de-poisoning, and structural upcycling. We also discuss emerging techniques such as non-thermal plasma and supercritical fluid-assisted reactivation. Finally, we highlight challenges in irreversible phase transformation, in -situ regeneration engineering, and economic feasibility, and outline future directions toward regeneration-friendly catalyst design and advanced syngas purification for a circular CTL economy. Full article

Ultra-high-temperature materials (UHMs) are indispensable for extreme thermal environments (e.g., temperatures exceeding 2000 °C); however, their practical implementation remains severely constrained by demanding processing conditions, including extreme sintering temperatures, prolonged cycles, densification barriers and high equipment cost. In order to meet the low-cost and ablation-resistant requirements of aircraft nose cones, a facile organic–inorganic hybrid strategy is proposed to fabricate ZrB₂–HfC–SiC composites using a high-char-yield 1,2-dicyanobenzene (DCB) binder, enabling low-temperature moulding at merely 250 °C (2 h; 20 MPa). Upon high-temperature oxidative exposure, the DCB matrix undergoes in situ pyrolysis and synergistic co-sintering with the ceramic powders, producing a multi-layered, self-protective structural architecture. A comprehensive structure–temperature map correlating temperature-dependent phase evolution with flexural strength and thermal conductivity is established, thereby elucidating the underlying self-healing and ablation-resistance mechanisms. The hybrid material in this work exhibits excellent flexural strength, ablation resistance and thermal stability. This study successfully reconciles the long-standing contradiction between low-temperature processability and ultra-high-temperature (2600 °C) service durability, offering a scalable route for next-generation thermal protection systems. Full article

Tritium breeding blanket is a key component of future fusion power plants, and its performance depends on the selection, fabrication, and qualification of lithium-based ceramic material. Among the proposed lithium ceramics materials, the main candidates for ceramic breeders are lithium orthosilicate (Li₄SiO₄) and lithium metatitanate (Li₂TiO₃). These advanced ceramics and their biphasic composites are the leading candidates due to their high lithium density, favorable tritium breeding ratio (TBR ≈ 1.15–1.25 with Be₁₂Ti multiplier and 90% ⁶Li enrichment), and robust thermo-mechanical behavior within the 200–900 °C operational window of helium-cooled pebble bed (HCPB) blankets. This review provides an engineering-oriented assessment covering fabrication routes (solid-state, hydrothermal, melt-based, drip casting, powder injection molding, microwave sintering, and digital light processing additive manufacturing); microstructure–property relationships and performance under neutron irradiation; and tritium generation, retention, and release as functions of chemical composition, defect structure, and operating temperature. Induced radioactivity of Li-based ceramics and key impurity elements is quantified using activation formalisms applied to WWR-K reactor conditions, providing guidance for raw-material selection and waste-management assessment. Authors’ original contributions include (i) an empirical model of pebble crush load vs. biphasic composition (R² > 0.99); (ii) two universal semi-empirical kinetic models (exponential growth and non-linear strength degradation, R² = 0.97–0.99) for nine structural and mechanical parameters of Li₂TiO₃ under He²⁺ and H⁺ irradiation; (iii) a consolidated table of Arrhenius tritium diffusion parameters from reactor experiments and DFT; and (iv) an induced radioactivity calculation for the biphasic system with two-exponential post-irradiation decay analysis. The review identifies biphasic Li₄SiO₄–Li₂TiO₃ composites with ~30 ± 5 mol.% Li₂TiO₃ as particularly promising and formulates specific data gaps and modeling needs for the reliable deployment of ceramic breeder pebbles in helium-cooled fusion blanket systems. It should be specifically noted that Li₄SiO₄ pebbles fabricated via the melt method, as an example, typically exhibit exceptionally high densities, generally exceeding 90% of the theoretical density (TD). Building on the calculation of induced radioactivity, it is crucial to consider the microstructural distribution of highly radioactive nuclides (e.g., Co, Mn) within the ceramic matrix. If these impurities segregate at grain boundaries rather than being homogeneously distributed, there is a potential pathway to develop targeted wet-chemical methods, such as selective acid leaching, to remove these impurities post-irradiation, thereby lowering the waste disposal classification. Full article

Silicon nitride ceramics exhibit excellent structural strength and electromagnetic wave transmission performance, yet demonstrate significant thermal shock instability under extreme conditions. Boron nitride (BN), on the other hand, possesses outstanding thermal shock resistance and electromagnetic wave transmission properties but exhibits relatively lower structural strength. Compositing these two materials holds promise for developing an integrated material that combines high-temperature load-bearing capacity with wave transmission capability. This study employed spark plasma sintering (SPS) technology to systematically investigate how varying BN content affects the sintering densification process and microstructural evolution of Si₃N₄/BN composite ceramics. Furthermore, we elucidated the mechanisms by which material composition and processing parameters influence key mechanical properties, dielectric characteristics, and other multifunctional attributes of the composites, providing a theoretical foundation for synergistic optimization design. The results indicate that BN incorporation suppresses both the phase transition from α-Si₃N₄ to β-Si₃N₄ during sintering and the growth of elongated β-Si₃N₄ crystals: the former hinders densification while the latter promotes it, resulting in a dual competitive mechanism that initially increases followed by decreases in sintered density. The effects of BN content on elastic modulus and fracture toughness align with trends in sintering density, whereas hardness, flexural strength, dielectric constant, and dielectric loss all show a monotonically decreasing trend with increasing BN content. Full article