International Journal of Applied Ceramic Technology最新文献

The aims of this study were to explore the nitriding mechanism of Ti-6Al-4 V alloy in Al₂O₃-based refractories. Al₂O₃-based composite refractories were fabricated using Ti-6Al-4 V and sintered alumina as main materials, followed by nitriding at different temperatures in a nitrogen atmosphere. Phase and microstructure evolution of the products was analyzed by X-ray diffraction and field-emission scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. The results reveal a multi-stage nitridation process of Ti-6Al-4 V at different temperatures. At 900°C, nitridation of the Ti-6Al-4 V surface results in the formation of a (Ti,V)N solid solution, while Al and V migrate inward, forming intermetallic compounds Ti₃Al and a-Ti (Ti_1-x-yV_xAl_y) with rich Al and V. At 1100°C, nitridation of Ti₃Al produces intermediate products like Ti₂AlN or Ti₃AlN, with continued inward migration of Al or V to form the intermetallic α₂ phase of (Ti_1-xV_x)_3yAl_y in the center of the alloy particles. At 1300°C, decomposition of Ti₂AlN or Ti₃AlN results in the outward migration of Al atoms and the presence of AlN on the outer layer of Ti-6Al-4 V particles, thus forming a hollow structure. Finally, at 1500°C, the (Ti,V)N solid solution grains grow as a result of further diffusion and dissolution of nitrogen.

In the present work, WB₂–SiC composite powders containing 20 vol.% of SiC were in situ synthesized by the boro/carbothermal reduction with WO₃, SiO₂, B₄C, and carbon black as raw materials at 1400°C, 1500°C, and 1600°C, respectively. The as-synthesized composite powders were then consolidated by spark plasma sintering (SPS) technique to obtain WB₂–SiC composite bulk samples. The experimental results showed that the relative density of the WB₂–SiC composite ceramic samples achieved in this study was higher than 97.5%. Also, electronic microscopy observations showed that SiO₂ had reacted completely during the preparation process, and the SiC grains were homogenously embedded among the WB₂ grains with the formation of a three-dimensional structure. The Vickers hardness and fracture toughness values of the composite ceramic fabricated by powder heat treated at 1400°C were 24.6 ± 0.7 GPa and 5.4 ± 0.7 MPa·m^1/2, respectively, which were the highest among three samples prepared in this study.

The improper disposal of industrial wastes will cause environmental pollution and economic losses due to the loss of active ingredients. Solid waste silica fume and pyrolusite powder were used to synthesize quartz ceramic proppant by pelleting and sintering to replace natural quartz sand for unconventional oil and gas exploitation. The effects of pyrolusite powder content and sintering temperature on the apparent density, breakage ratio, and acid solubility of the proppant were thoroughly studied. The phase composition and microstructure of the proppant were characterized by X-ray diffraction and scanning electron microscopy, respectively. The results revealed that the main crystal phase of the proppant prepared without pyrolusite was cristobalite, while that with pyrolusite was cristobalite and quartz, and the content of quartz phase increased gradually with increasing the pyrolusite content. The addition of pyrolusite remarkably increased the density and improved the performance of the proppant due to the resulting glass phase at high temperatures and the presence of andradite. As adding 20% pyrolusite, the apparent density of the proppant sintered at 900°C was 2.26 g/cm³, while the breakage ratio under 28 MPa closed pressure and acid solubility reached the minimum, 9.89% and 5.3%, respectively, meeting the industrial standard requirements.

The main objective of this investigation is the consolidation and flexural strength of alpha silicon carbide ceramics produced without additives by spark plasma sintering. Using the design of the experiment method, we optimized temperature and dwell to achieve fully dense silicon carbide bulks. The consolidation process of silicon carbide was analyzed similarly to the creep of bulk ceramics, and it was determined that the activation energy for the densification process was 596 ± 39 kJ/mol, while the stress exponent n was below 2. Bulk additive-free silicon carbide ceramics gradually increased flexural strength as the temperature rose to 2000°C. The flexural strength at 2000°C was influenced by the loading rate, and under 2.5 mm/min, it reached a maximum of 2.08 GPa. To explain this phenomenon, a deformation mechanisms map was created, indicating that diffusion creep is the most probable mechanism for the strain sensitivity of SiC at 2000°C. Transmission electron microscopy indicated a substantial rise in twin density within the α-SiC grains at 2000°C, indicating the activation of a previously unreported self-reinforcing mechanism.

A method of enhancing the mechanical properties of porous silicon nitride ceramics by involving texture structure through tape casting was explored. The influence of grain orientation was systematically studied by varying the sintering temperature, casting speed, and gap height. The results indicate that increasing the sintering temperature and casting speed can improve the degree of grain orientation. The mechanical properties of ceramics are significantly affected by the degree of grain orientation, the sample with the highest Lotgering factor demonstrated a flexural strength of 441 ± 12 MPa and a fracture toughness of 5.6 MPa·m^1/2 at a porosity of 39%. The relative permittivity of ceramics is predominantly governed by the porosity, with the grain orientation exerting a relatively minor effect.

This work aims to synthesize new foaming laterite geopolymer foam using laterite, sodium silicate solution, sand, and aluminium powder. The porosity rapidly increased with the addition of the foaming agent. The foam matrix had thermal conductivity values of 0.10 W/m K with 0.7% of Al powder and 0.64 W/m K with 0% of Al powder. For fire resistance, samples exposed to high temperatures (200°C and 500°C) showed increased flexural strength, linear shrinkage at 500°C, and a decrease at 900°C due to structural weakening under high thermal pressure and the appearance of new phases such as nepheline and akermanite in X-ray diffraction analysis. The results also showed that a 30% increase in fine aggregate content increased the strength of the foam matrix, with flexural strength ranging from 5 to 9.1 MPa after 28 days of ambient curing. These laterite geopolymer foams have shown promising thermal insulation and mechanical qualities that are appropriate for building applications.

Tricalcium silicate (C3S) is one of the main components of mineral trioxide aggregates, which is used in dental endodontic treatment. C3S provides workable viscosity itself and fast hydration when water is added, and it is known to be nontoxic, noncarcinogenic, nongenotoxic, biocompatible, and insoluble in tissue fluids. In this study, C3S is added to synthetic bone-graft materials from 30% to 60% to deliver viscosity to increase workability in the early stage of implant surgical procedure and to attain some degree of compressive strength after the hydration. Additionally, the porosity is not overly reduced to maintain the ability for bone regeneration. The porosity of the samples was confirmed to be 40%–50% with the formation of the C3S matrices. Simultaneously, the maximum compressive strength was ensured at 14.9 MPa within 24 h of curing time. The radiopacity required for post-procedural diagnosis was evaluated. The radiopacity of the samples with 50% and 60% C3S was 1.0 mm Al and 1.1 mm Al, respectively. When ZrO₂ was added, the radiopacity was enhanced to 1.6 mm Al. Overall, the experimental results showed that the bone-graft added C3S would be suitable for alveolar bone support and rigid matrix formation in implant surgery.

Aiming at the fuzzy diffusion characteristics of microcrack regions in Si₃N₄ ceramic bearing rolling elements, an adaptive region segmentation method is proposed to achieve precise extraction of microcrack features. The fuzzy diffusion effect of the microcrack region is analyzed, and a structural complexity matrix is defined to represent the degree of structural variation in the image. A threshold point is determined through histogram analysis, and the matrix dispersion rate is calculated using a box plot to update the correction factor, optimizing the overlap of noise in the microcrack image. The causes of distortion in the microcrack region are analyzed, and pixel points are assigned based on spatial metrics and LAB color features. The fuzzy boundaries and overlapping regions are segmented using the fuzzy C-means clustering algorithm. A grid search algorithm is embedded to quantitatively evaluate the optimal combination of hyperparameters, enabling comprehensive extraction of microcrack features in Si₃N₄ ceramic bearing rolling elements. The optimized image achieves an average peak signal-to-noise ratio of 39.3, an information fidelity criterion of 7.9328, and an average extraction accuracy of approximately 0.92, effectively overcoming the impact of the fuzzy diffusion effect on the accuracy of microcrack feature extraction in Si₃N₄ ceramic bearing rolling elements.

A tubular proton-conducting fuel cell, anode-supported, was fabricated using dip-coating and followed by the co-sintering of anode and electrolyte at 1500°C. The electrolyte and anode thicknesses are respectively 6 and 500 µm. The outer diameter of the tubular cell is 5.8 mm, featuring an anode porosity of 23%. Ammonia-fueled single cell with Ru-catalyzed internal cracking reactor is operated at various temperatures from 400°C to 600°C. Calculation results indicate that double-ring current collection is an efficient current-collecting mode. At 600°C, the device exhibited a high open-circuit voltage of 1.02 V and a peak power density of 216 mW cm⁻², with a total active area of 2.28 cm². Exhaust gas analysis reveals a 99.13% ammonia decomposition rate at 600°C.

The viability of synergistic preparing refractory material from ferronickel slag (FNS) and ferrochromium slag (FCS) has been confirmed based on the phase and microstructural transformation behavior of FNS and FCS during the sintering process in this research. The thermodynamic analysis results have shown that increasing magnesia additions at varying FCS/(FCS+FNS) ratios can result in the development of high-melting-point phases. The thermogravimetric-differential thermal analysis, thermal expansion tester, X-ray diffraction, and scanning electron microscope and energy-dispersive X-ray spectrometer analysis indicated that both the FCS/(FCS+FNS) ratio and magnesia addition have a significant impact on the transformation behavior of FNS and FCS during the sintering process. Specifically, as the FCS/(FCS+FNS) ratio increased, the temperature for generating the liquid phase decreased. By controlling the FCS/(FCS+FNS) ratio of 0.3 and magnesia addition of 30 wt.%, the expansion ratio of the FCS/(FCS+FNS) system during the sintering process was noticeably lower compared to that of the FCS and FNS demonstrating excellent densification.