International Journal of Applied Ceramic Technology最新文献

Photocatalysis presents a promising solution for environmental remediation, though conventional photocatalysts remain constrained to the ultraviolet and partially visible regions of the solar spectrum. To address this limitation, we developed a NaYF₄:Yb,Er/BiOBr (N/B) composite photocatalyst, leveraging upconversion luminescence to convert near-infrared photons into visible light while utilizing BiOBr's narrow bandgap for enhanced visible-light absorption. The composite photocatalyst was fabricated via a two-step solvothermal approach and evaluated for the degradation of methyl orange (MO). Remarkably, the N/B-120°C sample demonstrated superior photocatalytic activity, achieving degradation rates 2.4- and 5.4-fold higher than those of pristine BiOBr and commercial TiO₂ (P25), respectively. This enhanced performance is attributed to synergistic effects including an increased specific surface area (23.96 m²/g for N/B-120°C vs. 16.28 m²/g for BiOBr), reduced charge transfer resistance (as evidenced by electrochemical impedance spectroscopy (EIS) Nyquist plots), elevated oxygen vacancy concentration (as verified by x-ray photoelectron spectroscopy [XPS]), and extended solar spectral utilization range (400–980 nm). This work presents a viable strategy to improve the efficiency of photocatalysis.

The deposition of a 2.0 µm SiO₂ film on the alumina surface in Kovar^TM/94% alumina joints enables the formation of a silicide reaction layer on the alumina during brazing with 97Ag2Zr1Cu. Additionally, the average and standard deviation of joint thickness decrease from 50 to 15 and 29 to 4 µm, respectively compared to joints without added SiO₂. Finally, the average failure stress of these braze joints was 45 MPa, while that of similar joints without added SiO₂ was 90 MPa. Sessile drop experiments of 98Ag2Zr on SiO₂ and 99.6% Al₂O₃ substrates show that the braze wets and spreads to 3x its original area on SiO₂ with a wetting angle near 0°, but remains the same area on 99.6% Al₂O₃ with a wetting angle of 106.6°. Focused-ion-beam scanning electron microscopy analysis of a cross-section of the 98Ag2Zr sessile drop on the SiO₂ substrate has shown that Zr reacts with SiO₂ to form Zr oxide and silicide layers. Scanning transmission electron microscopy diffraction and energy dispersive X-ray spectroscopy analysis indicate this silicide layer contains tetragonal Zr₅Si₄. Analysis shows the silicide layer enhances wetting and joint uniformity while unreacted SiO₂ embrittles the joint and degrades strength.

The ceramic tile industry is energy intensive, characterized by long firing times and high temperatures. Therefore, flash sintering (FS), which greatly conserves energy by completing sintering in a few seconds at low temperature, is of interest to this industry. In this study, FS was applied for the first time to ceramic wall tile bodies. The experiments were carried out at a furnace temperature of 900°C, under an applied field of 100 V/cm, and current densities of 50, 100, 150, and 200 mA/mm². The influence of process parameters on phase and microstructure development, and water absorption and hardness properties were investigated. These results are compared to the traditional industrial/conventional process (CP). It was observed that the reactions among the raw materials were completed in a few seconds during flash. The microstructure was similar to the CP specimens. Water absorption (9.55%–10.32%), porosity (19.06%–23.92%), and bulk density (1.94–2 g/cm³) values were also found to be comparable. The bulk density increased and porosity decreased with higher current density. Besides quartz and anorthite, gehlenite phase was also detected in FS samples, which was absent in CP specimens. The hardness of the FS samples was approximately 25% lower than CP samples.

Creep rates of polycrystalline yttrium–aluminum garnet (Y₃Al₅O₁₂, YAG) and lutetium–aluminum garnet (Lu₃Al₅O₁₂, LuAG) under 50 to 200 MPa compressive stress were measured at 1300°C in air and in steam. Measurements for 2% Er and 2% Yb doped YAG were also done at 1300°C, and for YAG at 1400°C. The effect of 0.3 to 8 µm grain size variation on creep rate was determined. Flow stress exponents for all materials were determined, and the creep rate activation energy for YAG was determined. Creep rates in steam were slightly faster than those in air. Er and Yb dopants in YAG had little discernible effect on creep rates. LuAG creep rates, adjusted for grain size, were consistently higher than those for YAG. The Nabarro–Herring mechanism best describes the creep of polycrystalline doped and undoped YAG in air and steam for all samples except those with a grain size less than 0.5 µm. The creep mechanism for polycrystalline LuAG was not determined and may be a complex combination of mechanisms. Creep mechanisms for polycrystalline garnets are compared and discussed.

One-step synthesis of high-entropy diboride (HEB) samples from oxide-based precursors is reported in this study. HEB samples (Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)B₂ are prepared from metal oxide starting powders using reactive spark plasma sintering (R-SPS) to conduct borocarbothermal reduction (BCTR) and sample densification in an individual high-temperature processing unit. Excess precursor C black is added to the HEB precursor powders to aid in reducing residual oxygen in the final samples. The effect of precursor C black concentration on the phase state and microstructure of HEB samples is characterized. This study demonstrates that the conversion from metal oxide powder to the HEB through BCTR depends on the precursor C black concentration, which influences the secondary phase formation and microstructural features. The results reveal that 3.9 wt.% C black provides the optimal balance of oxide-to-HEB conversion, a more homogeneous microstructure, and intermediate grain sizes than HEB samples with both lower and higher amounts of precursor C black (0, 1.8, and 7.5 wt.%). We demonstrate the production of HEB samples from inexpensive oxide-based precursor powders through BCTR and sample densification using an individual high-temperature processing unit via R-SPS.

Reactive direct current (DC) magnetron sputtering (rDCMS) and reactive high target utilization sputtering (rHiTUS) of compositionally complex TiZrHfVNbTa–N coatings were systematically investigated with varying nitrogen flow. The study combined experimental measurements of total and partial nitrogen pressures with simulations based on Berg's model. Both deposition systems exhibited hysteresis-free behavior, characterized by two distinct nitrogen consumption regimes: (1) a nearly linear increase up to a critical nitrogen flow (≈4 sccm in rDCMS and ≈6 sccm in rHiTUS), and (2) a saturation regime. Simulations reproduced these trends and confirmed that hysteresis suppression originates from high pumping speeds (pumping speed/volume ratio > > 4 s⁻¹). The applicability of Berg's model to rHiTUS was validated by the strong agreement between experiments and modeling, supporting the assumption that the fundamental processes of reactive sputtering—target sputtering, poisoning, and nitride formation—are identical in DCMS and HiTUS. The main technological benefit of operating in a hysteresis-free regime is that coating composition and properties can be controlled solely through nitrogen flow adjustment.

To address the extreme service performance demands of aerospace heat-resistant components, wear-resistant tools, and marine corrosion-resistant structures, metal matrix ceramics have emerged as a major international research focus due to their stable crystal structures, high hardness, exceptional corrosion, and heat resistance. This study systematically analyzes the correlation between preparation processes and the formation mechanisms of interfacial compounds, interatomic bonding mechanisms, and resultant mechanical properties in TiB₂-reinforced ultrahigh strength steel matrix composites. It further reveals the regulatory effects of atomic-scale interfacial dislocation evolution and elemental segregation on toughening mechanisms. By establishing a cross-scale evolution model of the cast-infiltrated interface phase composition, the phase evolution behavior during the liquid–solid phase transition in TiB₂/steel composites is elucidated. Surface modification and gradient structure design as effective interfacial bonding enhancement strategies are critically assessed. Based on this comprehensive analysis, the paper concludes with perspectives on future research directions for TiB₂-reinforced steel matrix composites.

The waste glass, Bayer red mud, and marble were utilized as sintering raw materials (85: 5: 10 wt%) to prepare fully solid waste-based foam glass-ceramics (FGC) with excellent comprehensive properties at a relatively low sintering temperature range of 750–875°C. The impacts of sintering temperature and soaking time on the phase composition, microstructure, and physical-mechanical attributes of FGC were examined, and the optimal sintering process for producing these materials was also explored. The results suggested that the optimum sintering process of FGC is 825°C for 60 min. The bulk density, porosity, specific strength, and room-temperature thermal conductivity of the FGC were 0.26 g/cm³, 89.9%, 9.2 MPa·cm³·g⁻¹, and 0.091 W/(m·K), respectively. The uniformly distributed pore structure, with an average pore size of 3.18 mm, combined with relatively thin and dense pore walls (ranging from 50 to 100 µm), not only ensures high porosity in the FGC but also provides excellent specific strength and low thermal conductivity at room temperature. Furthermore, this process allows for the efficient and valuable utilization of multiple types of industrial solid waste.

Porous fibrous mullite ceramics have the characteristics of high-temperature resistance, lightweight, and thermal insulation, and have been widely used as the high-temperature thermal insulation materials in various thermal protection systems. In order to further improve the rebound-resilience property, a porous nanofibrous mullite ceramic with a lamellar structure was successfully fabricated by stacking electrospun mullite fiber membranes layer-by-layer. Results indicate that the introduction of zirconia into mullite fibers was able to inhibit the rapid growth of mullite grains. The porous nanofibrous mullite ceramics exhibited a lamellar structure, in which a large amount of space existed between adjacent fiber membrane layers, which provided enough space for the deformation of the mullite fibers. Therefore, the samples exhibited excellent compression resilience properties. Results show that the sample sintered at 1400°C still exhibited a high porosity (95.6%), low thermal conductivity (0.0399 W·m⁻¹·K⁻¹) and high compression resilience ratio (96.4%). This work provides an effective strategy for the fabrication of thermally insulating elastic porous fibrous ceramics, which can be widely used in the thermal protection systems of various aircraft and the thermal insulation layers of diverse industrial furnaces.

The influence of different processing parameters on the structure and dielectric behavior of the bismuth sodium titanate (BNT) multilayered thin films was investigated. Six-layered BNT thin films with a thickness of ∼300 nm were prepared using sol–gel method and deposited by spin coating. The selection of solvent ratios (acetic acid-to-water) in precursor sol preparation had a strong influence on the physical quality of layers and on the formation of a pure perovskite BNT phase. In addition, the influence of thermal treatment of both individual layers and multilayers on the structure and dielectric properties was also studied.