Search Results (719)

Dry reforming of methane and ethanol is a promising catalytic process for the conversion of carbon dioxide and hydrocarbon feedstocks into synthesis gas (H₂/CO), which serves as a key platform for the production of fuels and chemicals. Over the past decade, substantial progress has been achieved in the design of catalysts with enhanced activity and stability under the demanding conditions of these strongly endothermic reactions. This review summarizes the latest developments in catalyst systems for DRM and EDR, including Ni-based catalysts, perovskite-type oxides, MOF-derived materials, and high-entropy alloys. Particular attention is given to strategies for suppressing carbon deposition and preventing metal sintering, such as oxygen vacancy engineering in oxide supports, rare earth and transition metal doping, strong metal–support interactions, and morphological control via core–shell and mesoporous architectures. These approaches have been shown to improve coke resistance, maintain metal dispersion, and extend catalyst lifetimes. The review also highlights emerging concepts such as multifunctional hybrid systems and innovative synthesis methods. By consolidating recent findings, this work provides a comprehensive overview of current progress and future perspectives in catalyst development for DRM and EDR, offering valuable guidelines for the rational design of advanced catalytic materials. Full article

NASICON-type Li_1+XFe_XTi_2-X(PO₄)₃ (x = 0.1, 0.3, 0.4) solid electrolytes for all-solid-state Li-ion batteries were synthesized using a sol–gel method. This study investigated the impact of substituting Fe³⁺ (0.645 Å), a trivalent cation, for Ti⁴⁺ (0.605 Å) on ionic conductivity. Li_1+XFe_XTi_2-X(PO₄)₃ samples, subjected to various sintering temperatures, were characterized using TG-DTA, XRD with Rietveld refinement, XPS, FE-SEM, and AC impedance to evaluate composition, crystal structure, fracture-surface morphology, densification, and ionic conductivity. XRD analysis confirmed the formation of single-crystalline NASICON-type Li_1+XFe_XTi_2-X(PO₄)₃ at all sintering temperatures. However, impurities in the secondary phase emerged owing to the high sintering temperature above 1000 °C and increased Fe content. Sintered density increased with the densification of Li_1+XFe_XTi_2-X(PO₄)₃, as evidenced by FE-SEM observations of sharper edges of larger quasi-cubic grains at elevated sintering temperatures. At 1000 °C, with Fe content exceeding 0.4, grain coarsening resulted in additional grain boundaries and internal cracks, thereby reducing the sintered density. Li_1.3Fe_0.3Ti_1.7(PO₄)₃ sintered at 900 °C exhibited the highest density among the other conditions and achieved the maximum total ionic conductivity of 1.51 × 10⁻⁴ S/cm at room temperature, with the lowest activation energy for Li-ion transport at 0.37 eV. In contrast, Li_1.4Fe_0.4Ti_1.6(PO₄)₃ sintered at 1000 °C demonstrated reduced ionic conductivity owing to increased complex impedance associated with secondary phases and grain crack formation. Full article

Background: To overcome the esthetic limitations of dental monolithic zirconia restorations, multichromatic systems were developed to combine improved structural integrity with a natural shade gradient that mimics the optical properties of natural teeth. In response to the clinical demand for time-efficient, i.e., chairside fabrication of zirconia restorations, rapid sintering protocols have become necessary to adjust clinical efficiency along with material performance. This study addresses the challenges of a rapid sintering protocol related to optical performance and phase transformation of the final restoration and the zirconia–cell interaction. Methods: The influence of a rapid sintering protocol on the color stability of the final dental restoration was evaluated by the CIE L*a*b* color space. Phase transformation was assessed through X-ray diffraction analysis. Cellular behavior was evaluated by measuring wettability, the material’s surface energy, and a cell mitochondrial activity assay on human gingival fibroblasts. Results: Optical measurements demonstrated that the total color change in all layers after rapid sintering was above the perceptibility threshold (ΔE* > 1.2), while only the polished enamel layer (ΔE* = 3.01) exceeded the acceptability threshold (ΔE* > 2.7), resulting in a clinically perceptible mismatch. Results of X-ray diffraction analysis, performed for fixed occupancy at Z_0.935Y_0.065O_0.984, revealed that rapid sintering caused a decrease in the cubic (C-) phase and an increase in the total amount of tetragonal (T-) phases. Conventionally sintered zirconia consists of 54% tetragonal (T-) and 46% cubic (C-) phase, whereas in the speed-sintered specimens, an additional T1 phase was detected (T = 49%; T1 = 27%), along with a reduced cubic fraction (C = 24%). Additionally, a small amount of the monoclinic (M) phase is noticed. Although glazing as a surface finishing procedure resulted in increased hydrophilicity, both polished and glazed surface-treated specimens showed statistically comparable cell adhesion and proliferation (p > 0.05). Conclusions: Rapid sintering induced perceptible color changes only in the enamel layer of multichromatic zirconia, suggesting that even layer-specific alterations may have an impact on the overall esthetic outcome of the final prosthetic restoration. Five times higher heating and cooling rates caused difficulty in reaching equilibrium, leading to changes in lattice parameters and the formation of the metastable T1 phase. Full article

Ceramic membrane technology plays an important role in water and wastewater treatment. Strategic sourcing of various natural mineral resources has contributed to developing low-cost ceramic membranes. The combination with calcination of inorganic and organic wastes from domestic and agricultural activities results in fully sustainable ceramic membrane materials. In this work, ceramic membranes were developed using 96% clay, 2% almond shells and 2% lime. Sintering at 900, 950, and 1000 °C enabled the production of membranes (MK-900, MK-950, and MK-1000) in a clean, simple, and cost-effective manner. The average pore diameter and porosity decreased slightly from 44 to 42 nm and from about 30% to 26% with increasing sintering temperature, while the flexural strength increased from 25 to 40 MPa. The pure water permeability was 68 and 59 L·m⁻²·h⁻¹·bar⁻¹ for MK-900 and MK-950, respectively. Effective color (as Indigo blue) removal of 78% and 92% was observed for MK-900 and MK-950, respectively. More than 90% of the initial permeability was recovered after three cycles of dye filtration using water backwashing at each stage, indicating good fouling resistance of the prepared membranes. Full article

To solve the problem of purifying concentrates of rutile and zircon, a new method of electric separation after thermal activation roasting at 800 °C was proposed to strengthen the separation of Ti/Zr-bearing minerals. The results showed that the grade of TiO₂ in the conductor increased by 2.55~6.45% and the content of ZrO₂ decreased by 0.83~2.60% after thermal activation roasting and electronic separation, in contrast with electronic separation without roasting. To further explore the mechanism of activation roasting, the electrical conductivity, the phase evolution, and the microstructure of the gravity separation concentrate (GSC), pure rutile and pure zircon before and after roasting were investigated. The results of conductivity testing showed that the roasting pretreatment significantly improved the conductive difference between rutile and zircon, thus strengthening their separation performance. The XRD results revealed that the thermal activation roasting made the anatase in the GSC transform into rutile, thus enhancing the conductivity. Meanwhile, the crystallinity of both of the pure minerals was improved. The SEM results showed that the GSC particles formed loose and porous sinters, suggesting the reconstruction of the unstable anatase into rutile. Small amounts of cracks and protrusions occurred on the surface of both pure minerals, ascribed to the dehydration and deoxygenation at a high temperature. Full article

This study investigates the use of preliminary thermochemical activation in a NaHCO₃ solution under elevated pressure and temperature to modify the chemically stable and hard-to-process phase composition of various mineral raw materials and improve the recovery of valuable components. The method was tested on various types of mineral raw materials, including slag from the reductive smelting of red mud from alumina production prior to acid leaching, ash before chemical beneficiation, gibbsite–kaolinite bauxite prior to gravity separation, and nephelines, for which the sintering process was replaced with chemical beneficiation. The slag from the reductive smelting of red mud was also tested before acid leaching. The activation of slag enhanced tricalcium silicate formation lead to leaching recoveries of ~96% for rare earth elements, ~92% for TiO₂, ~98% for CaO and Al₂O₃, and 50% for Fe₂O₃, compared to much lower values without activation. With ash, activation eliminated the sillimanite and hedenbergite phases, increased mullite and free silica, and formed calcite, resulting in a 15–20% higher silica recovery. With gibbsite–kaolinite bauxite, activation altered kaolinite, siderite, quartz, and hematite contents; eliminated calcium silicate; and improved the silicon modulus of the sand fraction by 35.9% during gravity beneficiation. For nepheline ore, activation promoted the formation of albite and hydrosodalite, eliminated corundum and andradite, and increased silica recovery from 33.58% to 59.6%. These results demonstrate that thermochemical activation effectively transforms mineral structures and significantly improves the efficiency of subsequent beneficiation processes. Full article

Dry reforming of methane (DRM) is an effective strategy to simultaneously convert CH₄ and CO₂ into valuable syngas. However, the widely employed Ni-based catalysts often suffer from rapid deactivation due to metal sintering and deposited carbon under harsh conditions. Herein, Ni/Ce_0.2Zr_0.8O₂ catalysts were synthesized using the evaporation-induced self-assembly (EISA) method with the addition of the triblock copolymer surfactant P123. The addition of an appropriate amount of P123 improved the Ni dispersion; reduced Ni particle size; and enhanced the activation efficiency of both CH₄ and CO₂, thus increasing the reaction rate. In addition, the addition of P123 also enhanced the surface basicity and increased the concentration of oxygen vacancies of the catalyst, which enhanced its carbon removal capability and reduced deposited carbon. The catalyst with 0.2% P123 maintained excellent catalytic activity and stability for 300 min at 700 °C, with CH₄ and CO₂ conversion of 75% and 78%, respectively. These findings provide valuable guidance for the rational design of efficient and stable Ni-based catalysts for DRM. Full article

Chemical looping combustion (CLC) provides an inherently cost-effective method for carbon capture by employing a solid oxygen carrier (OC) to transfer lattice oxygen from air to fuel. The search for low-cost, high-performance natural OCs is crucial for the large-scale deployment of this technology. A natural iron ore containing 41.34% Fe₂O₃ was systematically evaluated as OC for the CLC of CO. Its redox performance was quantified in a fixed-bed reactor between 750 °C and 900 °C with CO concentrations of 10–20%. Multi-cycle tests were conducted to assess stability. Kinetic analysis of the initial cycles was performed using an integral model fitting method. Multi-cycle tests revealed that the fresh ore achieved peak conversions of 48.9% at 750 °C and 77.2% at 900 °C. However, severe sintering occurred beyond 850 °C after the first cycle, causing approximately a 50% drop in OC conversion. Interestingly, once sintered, a self-activation phenomenon was observed during subsequent cycles; the OC conversion slowly recovered from 32% to 37% from the second to the fifteenth cycle under the aggressive conditions (900 °C, 20% CO). Kinetic analysis of the initial cycles (before sintering) revealed low apparent activation energies, ranging from 15.93 to 19.13 kJ mol⁻¹, which are significantly lower than the typical literature values for iron-based ores. This work underscores the potential of natural iron ores as economical and sustainable OCs for CO-rich fuels. The observed self-activation ability of the sintered OC is a promising finding for long-term operation. The results also highlight the critical importance of operating conditions to avoid deep reduction and sintering, necessitating a high solids inventory and a moderate oxygen-to-fuel ratio in practical CLC systems. Full article

This study investigated the potential use of fluorine-containing semiconductor industrial sludge as a mineralizer in Portland cement clinker production. Raw mixes were prepared by partially replacing raw materials with 6%, 9%, and 12% sludge and sintered between 1300 and 1500 °C. The clinker burnability, phase composition, and chemical integrity were evaluated through FreeCaO measurements, X-ray diffraction (XRD) with Rietveld refinement, and X-ray fluorescence (XRF) analyses. The results showed that sludge addition reduced the sintering temperature by up to 150 °C, enabling near-complete clinker formation at 1300 °C for blends containing 9% and 12% sludge (FreeCaO ≤ 0.6 wt.% compared to 62 wt.% in the reference sample). Fluorine incorporation stabilized the re-active β–C₂S polymorph and shifted the alite (C₃S) phase distribution from stable M1 to metastable M3 and T3 phases. Additionally, the C₃A phase content decreased, and a unique fluorine-containing phase, Al₇Ca₆O₁₆F, formed, promoting clinker formation. Lowering the sintering temperature led to energy savings of 15–22.5% and reduced CO₂ emissions by 0.10–0.20 tons per ton of clinker, positively impacting the environment. This study demonstrates that recycling industrial sludge can enhance cement production efficiency and support environmental sustainability. Full article

Ti–Al alloys have widespread applications as targets in hard coatings by PVD (Physical Vapor Deposition). While the importance of target density is recognized, the densification mechanisms of Ti-67 at% Al targets, particularly during spark plasma sintering (SPS), remain poorly understood, hindering process optimization. This study aims to clarify these mechanisms by fabricating Ti-67 at% Al targets via SPS and examining their densification behavior through a detailed analysis of the creep model based on the stress exponent (n) and apparent activation energy (Q_d). The target’s relative density gradually increased in the temperature range of 370–530 °C, whereas the grain size remained relatively constant, indicating that the densification process dominated during this period. The results reveal that densification is primarily controlled by intergranular diffusion (n ≈ 2, Q_d = 97.29 kJ/mol) and dislocation climbing (n ≈ 3, Q_d = 158.74 kJ/mol). The target’s relative density reached 98.25% at 530 °C, with a corresponding grain size of 10.86 ± 1.08 μm. Additionally, as the temperature increased, the Vickers hardness of the target increased from 61.56 HV to 129.66 HV, and the electrical conductivity rose from 0.23 S/cm to 0.86 S/cm. This work provides a fundamental understanding of the densification kinetics in Ti-67 at% Al alloys during SPS, establishing a crucial guideline for fabricating high-performance PVD targets. Full article

Coal gangue, a primary solid waste by-product of coal mining and processing, constitutes approximately 10–15% of total coal output. Its accumulation poses substantial environmental challenges, including land occupation, spontaneous combustion, acid mine drainage, and heavy metal leaching. Despite its high silica and alumina content (typically exceeding 70% combined), the highly stable and crystalline structure of raw coal gangue limits its pozzolanic activity and adsorption efficiency. To address this limitation, this review emphasizes recent advances in activation strategies such as thermal (500–900 °C), mechanical (dry/wet grinding to less than 200 µm), chemical (acid/alkali treatments), microwave, and hybrid methods. The activated coal gangue resulted in an enhanced surface area (up to 55 m²/g), amorphization of kaolinite to metakaolinite, and the generation of mesoporosity under optimal conditions. This review critically examined the geotechnical applications, such as soil stabilization and mine backfill, highlighting the replacement of 50–75% of cementitious binder in backfilling and meeting the subgrade/base material strength criteria (UCS > 2 MPa). In geoenvironmental applications (adsorption of phosphate, dyes, heavy metals, and CO₂ mineralization), more than 90% of pollutant removal is attained. In construction applications, supplementary cementitious materials and sintered bricks are examined. Several critical knowledge gaps, including limited understanding of long-term durability, inconsistent activation optimization across different coal gangue sources, and insufficient assessment of environmental impacts during large-scale implementation, are clearly addressed. This review provides a roadmap for advancing sustainable coal gangue utilization and highlights emerging opportunities for cost-effective applications in the mining and construction sectors. Full article

Oxygen transport membranes (OTMs) have gained a lot of attention for their application in different innovative fields, but the development of new materials able to combine high oxygen permeability and good chemical stability is crucial to boost the exploitation of such membrane-based technologies. Perovskite oxides are widely studied as mixed ionic-electronic conductors for the realization of OTMs. In this article, we focus on _Sr1-xCa_xTi_0.8Fe_0.2O_3-ẟ (SCTF) perovskites and investigate the effect of Ca content on the A-site of the permeation properties, both in single-phase SCTF membranes and in dual-phase membranes obtained by combining SCTF and the ionic conductor Ce_0.8Gd_0.2O₂ (CGO). In single-phase samples, we observed that the substitution of 40% Ca preserves the permeation performances of the non-substituted SrTi_0.8Fe_0.2O_3−ẟ membrane while allowing for a substantial decrease in the sintering temperature, thus facilitating membrane manufacturing. In dual-phase membranes, the increase in the Ca content in the perovskite causes an increase in grain size. The permeation is, at least partially, controlled by the kinetics of the surface exchange reactions. This limitation can be overcome by the addition of an activation layer; however, the permeance of activated CGO-SCTF membranes still remains lower compared to the single-phase parent perovskitic membranes. Full article

An activation reaction sintering process was utilized to produce Cr-Cu-Mo-Ni porous alloys. Subsequently, weight loss measurements and electrochemical methods were applied to investigate the effect of Cr content ranging from 10wt% to 30wt% on the corrosive properties of Cr-Cu-Mo-Ni alloys in a 0.5 mol/L HF solution. Scanning electron microscopy (SEM) and X-ray diffraction analyses (XRD) were performed to assess the structural morphology and phase composition. As the results illustrated, Cr-Cu-Mo-Ni porous alloys possess good corrosion resistance, which is significantly higher than that of dense Ni and Cu alloys. The anti-corrosion performance of porous alloys is not proportional to the Cr content when the Cr concentration is gradually increased. When the chromium content is 20%, it exhibits the best corrosion resistance. Electrochemical measurements yielded similar results to weight loss measurements. With an increasing Cr content, double capacitive loops in electrochemical impedance spectroscopy (EIS) tests for Cr-Cu-Mo-Ni porous alloys first increased and then decreased, indicating that the corrosion process can be regulated by an electrochemical reaction. Meanwhile, after analysis, the results show that the corrosion products on the material surface adhere to the inner surface of the pores, thus improving the corrosion resistance. Full article

Dry reforming of methane (DRM) into synthesis gas (CO + H₂) is one of the most important chemical reactions for industrial hydrogen production. It also enables the synthesis of hydrocarbons (liquid fuels) and other valuable products, providing an effective route for utilizing greenhouse gases. However, a major challenge limiting the implementation and scale-up of DRM is the high cost of stable and active noble metal-based catalysts, or the rapid deactivation of nickel- and cobalt-based catalysts due to coking and sintering of the active metal particles. In this context, the present work demonstrates that combining a highly active and inexpensive component (Ni) with tungsten carbide produces a composite material exhibiting high catalytic activity and resistance to oxidation and coking during DRM. Tungsten carbide was synthesized using a vacuum-free electric arc method, and nickel was subsequently deposited in varying amounts (1–25 wt.%) using the deposition–precipitation method with NaOH (DP). The resulting catalysts were characterized by X-ray diffraction, temperature-programmed reduction and Raman spectroscopy. Their performance was evaluated under DRM conditions, at atmospheric pressure and 800 °C, using different CH₄:CO₂ ratios. The most effective oxidation/(re)carbonization cycle, ensuring catalyst stability during DRM by balancing the rates of carbon formation and removal from the catalyst surface, was achieved with a nickel content of 20 wt.% and a CH₄ to CO₂ ratio of 0.67 in the feed gas mixture. Full article

This study employed the solid-state method to prepare perovskite-type high-entropy oxide materials La(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃ and La(Co_0.2Cr_0.2Ni_0.2Ga_0.2Ge_0.2)O₃ with equimolar ratios at the B-site and explored the effects of sintering temperature on the phase structure and electrochemical properties of high-entropy oxide ceramics. The results show that after sintering at 1300$°\mathrm{C}$, both samples exhibit orthorhombic perovskite structures. Both have a relative density of >97%, while La(Co_0.2Cr_0.2Ni_0.2Ga_0.2Ge_0.2)O₃ has a significantly larger grain size. Using these materials as electrodes, the cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) results indicate that the working electrode made of La(Co_0.2Cr_0.2Ni_0.2Ga_0.2Ge_0.2)O₃ shows higher oxidation reaction activity in CV measurements and achieved a specific capacitance of 74.3 F/g at a current density of 1 A/g in GCD measurements, which still maintained 73% of its initial specific capacitance (54.3 F/g) when the current density was increased to 10 A/g. Its capacitance retention rate is 10 percentage points higher than that of La(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃ at high current densities, demonstrating superior rate performance. Full article