International Journal of Applied Ceramic Technology最新文献

Porous Si₃N₄ ceramics were prepared using the low-toxicity monomer HEMA (2-hydroxyethyl methacrylate) via a modified gel casting method. The rheological properties of Si₃N₄ slurries were investigated. Triethanolamine with high activity was used as a catalyst and modifier for gelation reactions, effectively improving the curing rate and suppressing the inherent surface oxygen inhibition in such process systems. With an increase in solid loading of the slurry, the drying shrinkage (12.3% to 5.4%) significantly decreased, while the green body density (44.0%–49.0%) and flexural strength (9.65–16.46 MPa) increased, demonstrating an excellent mechanical strength. After sintering at 1700°C, the porous Si₃N₄ ceramics prepared with 24–36 vol% solid loading slurry exhibited a flexural strength of 144.39–193.66 MPa and a porosity of 55.8% to 49.0%. The dielectric constant and loss tangent at 30 GHz ranged from 2.88 to 3.38 and 1.17–1.56 × 10⁻³, respectively. These ceramics show promising potential applications in high-performance structural ceramics and high-temperature wave-transparent materials.

Magnesium potassium phosphate hexahydrate (MgKPO₄·6H₂O) was used as solidification matrix to immobilize some radioactive element and some heavy metal ions, the stability of MgKPO₄·6H₂O under different conditions had become the focus. This work gives new insights on the stability of synthesized MgKPO₄·6H₂O in the different temperatures and pH values solutions. The solid phase transformed from synthesized MgKPO₄·6H₂O was characterized by X-ray diffractometer (XRD), thermal gravity analysis (TG/DSC), Fourier-transform infrared spectrum (FTIR) and scanning electron microscope (SEM) at different temperature and pH values solution. Results indicated MgKPO₄·6H₂O had almost no phase transition at the temperature of 50°C and 60°C. Mg₃(PO₄)₂·22H₂O appears with the increase of solution temperature. The main phase is MgKPO₄·6H₂O at the pH of 9 and 12, minor MgHPO₄·3H₂O formed at the pH of 6, next Mg₃(PO₄)₂·22H₂O formed at the pH of 3 and 6. High pH value environment is beneficial for the maintenance of MgKPO₄·6H₂O. This study is an important guidance for the application of MgKPO₄·6H₂O crystal.

Laminated ceramics containing layers of pottery materials with high and low Young's moduli were developed to mimic the nacre structure of abalone shells with high resistances against dynamic fractures. The layers with the low Young's modulus moderated crack deflection and impact, thereby exhibiting a high fracture resistance. The ceramic pores were formed by the CO₂ gas generated through the oxidation of SiC during firing. The dynamic fracture resistance was enhanced by elastic wave scattering owing to the difference between the Young's moduli of the dense and porous layers. The effect of lamination on the dynamic fracture resistance was observed because the elastic waves were scattered owing to the difference in the elastic modulus between the porous and dense layers, and their propagation to the back sample surface was suppressed. The fracture energy of the 5-layer laminate was determined to be about four times larger than that of the dense monolayer, which indicates that the introduction of intentional defects is effective in improving the dynamic fracture resistance of the pottery ceramics.

The energy consumption of MOS (metal oxide semiconductor) sensors has always been a challenge in improving their performance. In this study, bougainvillea-like Au/ZnO nanostructures were successfully synthesized using the hydrothermal method and the sol fixation technique. The composition, crystallinity, crystal structure, and morphology of the materials were characterized using X-ray diffraction, energy-dispersive spectroscopy, and field emission scanning electron microscopy. The experimental results confirm the successful synthesis of a substantial quantity of bougainvillea-like Au/ZnO nanostructures through nanoparticle self-assembly. The sensitive performance of the bougainvillea-like Au/ZnO sensor was evaluated using a CGS-8 intelligent gas-sensitive analysis system. Results demonstrate that modification of ZnO with Au in a bougainvillea-like nanostructure significantly enhances sensitivity to ethanol vapor compared to those of unmodified material sensors. Specifically, the optimal work temperature was greatly reduced by 64%, whereas the sensitivity increased approximately 12 times and the response time decreased nearly 5 times. The significantly enhanced ethanol sensitivity can be attributed to the precious metal modification and unique three-dimensional morphology. It provides the necessary experimental exploration for reducing energy consumption and improving the performance of MOS gas sensors.

The methane steam reforming (MSR) reaction is a significant process for hydrogen production, and developing catalysts with high activity and stability is crucial. In this work, the supported perovskite catalysts of Ni/LaBO₃ and Ru-Ni/LaBO₃ (B = Al, Fe) were prepared by the sol–gel method using citric acid as a gelling agent for MSR to hydrogen production. The phase composition, pore structure, and surface morphology of the prepared catalysts were characterized by X-ray diffractometer, Brunauer–Emett–Teller, scanning electron microscopy and energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. The reaction activity and stability of the prepared catalysts were tested in the fixed-bed reactor with the temperature range of 500–800°C. The effect of Ru addition on the structure of perovskite and catalytic performance of MSR is explored. The results showed that 1wt%Ru–15wt%Ni/LaAlO₃ catalyst exhibited the most excellent activity and stability during the reaction compared with the other three catalysts. The CH₄ conversion, H₂ selectivity, and H₂ yield of the 1wt%Ru–15wt%Ni/LaAlO₃ catalyst could reach 94.68%, 79.78%, and 48.65%, respectively, under the reaction temperature of 800°C and gas hourly space velocity of 36 000 mL/(gh), which were higher than those of a commercial catalyst. It was because that the relatively large surface area of perovskite support provides more active site and the addition of Ru enable Ni to have a smaller size and more dispersion. This study could provide a reference of perovskite catalysts for hydrogen production by MSR.

Effect of heat-treatment (900°C∼1600°C) on the microstructure and mechanical properties of alumina–silica fiber was well investigated. The results indicated that the recommended temperature threshold for the use of the alumina–silica fiber was not more than 1100°C to maintain its mechanical integrity. Above this temperature, the elastic modulus of the fibers increased, and the tensile strength significantly decreased, mainly because of the transformation of the structure from γ-Al₂O₃ and amorphous SiO₂ to mullite. The tensile strength of the fiber was 0.87 GPa at 1200°C. Compared to the as-received fibers, the strength retention was only 63.50%. Moreover, as revealed by Weibull statistical analysis, the formation of more defects due to mullite phase transformation resulted in higher dispersion of the fiber tensile strength. However, at this temperature, the Young's modulus of the fiber increased from the initial value 146.24 ± 5.19 GPa to 183.06 ± 5.83 GPa. Finally, the rate of mullite reaction was seen to be strongly temperature dependent. The higher the heat-treated temperature, the shorter the time required for γ-Al₂O₃ and amorphous SiO₂ to completely transform into mullite grains.

A phosphate glass-ceramic wasteform incorporating cerium monazite was synthesized through a two-step solid phase sintering methodology, aimed at immobilizing waste salts derived from the pyrochemical reprocessing of spent nuclear fuel. The initial phase involved the synthesis of cerium monazite powder, employing a stoichiometric mixture of CeF₃ and NH₄H₂PO₄ in a molar ratio of mol(Ce:PO₄) = 1:1.4, which was subjected to a thermal treatment at 900°C. Subsequently, the glass-ceramic matrix was fabricated by sintering a composite mixture of the synthesized cerium monazite and iron phosphate glass (IPG) powder at a temperature of 1000°C for a duration of 2 h, resulting in a cerium incorporation exceeding 36.5 wt%. Microstructural analysis and structural characterization of the glass-ceramic sample elucidated the presence of monazite crystallites (CePO₄) with dimensions ranging from .2 to 5.5 µm. The chemical durability of the wasteform was assessed through modified ASTM C1308 tests conducted in deionized water over a period of 28 days, revealing a total elemental leaching rate of 2.58 × 10⁻⁷ g m⁻² min⁻¹.

The development of dense alumina ceramics through additive manufacturing necessitates the careful analysis of various parameters. The extrusion pressure during printing is a crucial but often overlooked factor in the literature. This study investigates the impact of extrusion pressure on the densification and mechanical properties of alumina ceramics. The primary objective is to analyze extrusion pressure to achieve superior physical and mechanical characteristics while maintaining minimal shrinkage. All other printing parameters were kept constant, and the extrusion pressure was varied from 1 to 2.85 bar during the extrusion-based additive manufacturing of alumina green bodies. The printed and sintered samples were analyzed for linear shrinkage, density, compressive strength, and microhardness. The results indicate that an extrusion pressure in the 2.2–2.5 bar range leads to alumina ceramics with the best combination of densification and other mechanical properties. Additionally, the interparticle bonding mechanisms contributing to the improved properties of the alumina ceramics were examined. This study provides valuable insights into the role of extrusion pressure in the additive manufacturing process, underscoring its significance in achieving high-quality alumina ceramics.

Mullite–cordierite saggar materials commonly used in the industry are easily corroded by LiNi_xCo_yMn_1−x–yO₂ (LNCM) materials during the synthesis of Li-ion batteries. To extend their service life, the influence of varying the proportion of calcium hexaluminate (CA₆) ranging from 0 to 12 wt% on the sintering behavior of the mullite–cordierite system was investigated. These samples were then tested to evaluate their physical characteristics, resistance to corrosion by LNCM materials, and thermal shock stability. The experimental results show that the open-pore structure formed by the interstacking grains of CA₆ effectively impedes further penetration of the corrosion phase. Moreover, the addition of CA₆ resulted in the in situ formation of anorthite within the material, enhancing its sintering and bonding properties and significantly improving the material's corrosion resistance. Consequently, incorporating CA₆ effectively enhances the saggar's thermal shock stability and corrosion resistance.

Dense C_f/(ZrHfNbTaCr)B₂–SiC (CBS-Co) composite is successfully prepared at a low temperature of 1500°C by adding 5 vol.% Co. Liquid Co accelerates the particle rearrangement and significantly enhances the relative density of CBS-Co (95.2%). In situ formed Co₂B phase by diffusion reaction bonds tightly with high entropy diboride (HEB) and SiC grains in CBS-Co. Due to the promotion of relative density and interfacial bonding strength, CBS-Co exhibits a high flexural strength (283 ± 23 MPa). Structural damages of carbon fibers are effectively prevented by compact fiber coating. The well-preserved fibers play dominant roles to increase the fracture toughness of CBS-Co (4.77 ± .5 MPa·m^1/2). Moreover, SiO₂-rich oxide layer can effectively heal flaws and inhibit oxygen diffusion, achieving relatively high flexural strength after oxidation at 1300°C of CBS-Co composite. This work provides a stepping stone for developing high-performance carbon fiber toughened HEB composites based on low temperature liquid-phase sintering technology.