International Journal of Applied Ceramic Technology最新文献

Porous B₄C ceramics with varying densities and porosities were synthesized by a rapid hot-press sintering method at different temperatures and pressures. Their sound absorption performance and mechanical properties were investigated, showing that the mechanical strength and sound absorption coefficient can be tuned simultaneously by controlling the sintering parameters. The sound absorption coefficient of porous B₄C ceramics was found to be closely dependent on porosity, density, pore size, airflow resistance, and thickness. Furthermore, the sound absorption coefficient of B₄C ceramics can be fine-tuned to a wider range of frequencies (500–6400 Hz) by combining them with aluminum foam and an air gap, which can result in an average absorption coefficient (AAC) of 0.49 and a maximum sound absorption coefficient of 0.997 within the frequency range of 500 to 6400 Hz, approaching 1. The porous B₄C ceramics also exhibit excellent compressive strength, reaching up to 745.30 MPa, the fracture toughness was 0.86 MPa m^1/2, and with the load increased, the failure displacement of the ceramic reached 0.28 mm. The stress transition from compressive stress to tensile stress in the lattice, and the crystal structure from crystalline to a disordered structure caused by the variation of the pressures at 1700°C.

High-entropy carbides (HECs) exhibit enhanced mechanical properties and high temperature oxidation resistance as compared to their binary counterparts. However, their application as catalytic materials was restricted due to a lack of high specific surface area with conventional synthesis methods such as solid-state sintering. In the present work, porous high-entropy carbide nanocomposites with varying elemental composition were synthesized through the precursor-derived ceramic route, and their electrocatalytic activity for the oxygen reduction reaction (ORR) was assessed. Thus, the compositionally complex nanocomposite was prepared from a preceramic precursor, which was, upon modification of a polysiloxane with Ta, V, W, Mo, and Nb-based organometallic precursors via pyrolysis in an inert atmosphere. The pyrolyzed ceramic was subsequently modified with Fe-based precursor, with varying quantities and heat-treated at 1300°C to obtain Fe-containing high-entropy carbide nanocomposites. X-ray diffraction and ADF-STEM imaging coupled with EDX confirmed the incorporation of Fe into the HEC lattice. The onset potential for the electrocatalytic ORR increased from 0.81 to 0.85 V upon incorporation of Fe into the high-entropy carbide nanocomposite. Furthermore, with the addition of electron-rich Fe in HEC nanocomposite, the reaction mechanism moved toward a four-electron path. This suggests the positive effects of incorporating Fe into HEC nanocomposites.

Aluminum oxide-based materials exhibit significant potential for application in the aerospace industry, advanced manufacturing technologies, the automotive industry, power engineering, and other fields. However, the inherent brittleness of aluminum oxide limits its broader application. Therefore, an ongoing search is underway for methods to produce corundum ceramics with high mechanical properties, including the use of Al₂O₃ nanopowders. This paper is the first to investigate the production of corundum ceramics using Al₂O₃ nanopowder obtained by electric explosion of wire. The effect of mechanical activation of the nanopowder on characteristics of the sintered samples is appreciated. It is found that pre-treatment of the nanopowder in a high-speed planetary ball mill within 2 min facilitates the compaction of sintered ceramics up to a density of 3.85 g/cm³, which is 96% of the theoretical density. The highest strength under radial compression of the ceramic samples is achieved with a crystallite size of about 46 nm. A general relationship between the strength and mechanical activation time is similar to the Hall–Petch relationship.

In this study, we investigate how geometric miniaturization affects the sintering densification behavior of alumina cylinders with various wall thicknesses (down to ∼500 µm in green body) fabricated via digital light processing (DLP). As the wall thickness decreased, the density of the sintered samples consistently declined. Microstructural characterization revealed the presence of a crack-rich surface skin that is ∼500 µm thick. As the wall thickness decreases, the skin's volume fraction rises, and its poor local densification increasingly dominates the part average, leading to an overall decrease in the density of the sintered samples. For the thinnest wall (500 µm) cylinder, macroscopic warping occurred during sintering. We suggest that warping further disrupts particle packing and induces through-thickness nonuniformity, further impairing densification in addition to the skin-fraction effect. These results highlight how geometric miniaturization may adversely influence the sintering behavior and final density of DLP-printed ceramics through distinct densification-limiting mechanisms.

The hardness of ceramic is frequently taken as the key performance index to evaluate its wear resistance. As demonstrated in the present study, the hardness should not be taken as a sole index if a phase transformation is involved during the wear process. Two tetragonal zirconia polycrystals (TZPs) with a 15% difference in their hardness are prepared. A ball-on-disk self-mated wear test is then conducted; their wear rates differ by an order of magnitude. Though the amount of monoclinic (m) phase in the worn disk is low, the m-phase content in the wear debris is high. The phase and microstructure analyses confirm the role of phase transformation on wear resistance. Though a greater extent of phase transformation is a guarantee to the resistance to crack propagation, a thicker transformation surface layer could produce a larger amount of wear debris through a fatigue wear process.

Ti-Si targets are used in cutting tool coatings and semiconductor gate dielectrics. This study investigated densification mechanisms, phase evolution, and reactive sintering kinetics of Ti-25at%Si targets fabricated by spark plasma sintering using blended Ti and TiSi₂ powders. Significant shrinkage was observed between 600°C and 900°C with minor solid-state reactions. At 1000°C, reactions intensified, promoting further densification. The creep model determines the stress exponent (n) and apparent activation energies, revealing the transition from a grain boundary diffusion-dominated densification mechanism under high effective stress (n = 1.5, activation energy 108 ± 4 kJ/mol) to a dislocation-climb-assisted densification mechanism under low effective stress (n = 3, activation energy 205 ± 14 kJ/mol). Transmission electron microscopy confirms dislocation climb, while grain boundary diffusion is supported by the formation of new phases (such as Ti₅Si₃) generated through diffusion reactions. The Johnson–Mehl–Avrami kinetic equation was used to fit the reactive sintering experimental data around 1000°C, yielding an Avrami exponent of 1.16 ± 0.15, indicating that the reaction proceeds via two-dimensional nucleation and growth. The activation energy for Ti₅Si₃ formation, calculated using the Arrhenius equation, is 60 ± 7 kJ/mol, which is lower than the 205 kJ/mol obtained from the direct reaction between Ti and Si.

Femtosecond laser ablation technology can overcome the challenges associated with fabricating complex components and the low machining accuracy inherent in traditional processing of silicon carbide ceramics, showcasing its broad application potential. In this work, the effects of pulse number and polarized light state on the ablation threshold and morphology of ablation pits were systematically investigated. The variation in the ablation threshold could be divided into three stages as the number of pulses increases. The efficiency of multiphoton ionization under linearly polarized light was higher than that under circularly polarized light, resulting in a lower ablation threshold. The surface morphology of ablation pits induced by linearly polarized light predominantly exhibited periodic streak structures and an ordered assembly of nanoparticles. The growth rate of the diameter was lower than that of the depth of the ablation pit, resulting in the formation of a conical structure. Due to Coulomb explosion and the cavitation backflow effect, the ejected silicon and carbon underwent oxidation reactions outside the ablation pit. This investigation provides both theoretical frameworks and practical guidelines for femtosecond laser micromachining of SiC ceramic components.

Hydroxyapatite (HAp) hollow microspheres are one of the most promising bio-ceramics because of their excellent biocompatibility, strong osteo-conductivity, and hollow structure. In this study, a simple method was proposed to fabricate HAp hollow microspheres by directly sintering the HAp/gelatin microspheres at high temperature. Scanning electron microscopy observations showed that HAp/gelatin microspheres had a dense structure, while HAp microspheres had a hollow structure. The sintering process not only caused the removal of gelatin, but also led to a structural transformation from dense HAp/gelatin microspheres to HAp hollow microspheres. The analyses of X-ray diffraction patterns and Fourier transform infrared spectroscopy spectra indicated that HAp hollow microspheres were composed of apatite phase. Shell thickness of HAp hollow microspheres was increased with increasing the HAp/gelatin weight ratio. In vitro biocompatibility evaluation indicated that HAp hollow microspheres supported adhesion and proliferation of osteoblast MC3T3-E1 cells, having potential as biocompatible cell carriers.

Rare-earth hafnates show promising potential use in the development of a new generation of thermal/environmental barrier coatings (T/EBCs) owing to their high melting point, phase stability, and compatibility with SiC-based composites. In the current work, microstructural evolution and corrosion behavior of Yb₄Hf₃O₁₂ ceramics exposed to wet-oxygen and ambient air atmospheres at 1400°C were systematically investigated. Results revealed that sintering in air led to pronounced grain growth and homogenization, followed by secondary recrystallization at extended durations. Under wet-oxygen conditions, the ceramics underwent two distinct stages: initial Hf⁴⁺ hydration and volatilization (0–20 h), and subsequent formation of Al₅Yb₃O₁₂ corrosion products due to reactions with Al(OH)₃ impurities (20–40 h). These processes induced fluctuations in grain size distribution, including growth, refinement, and re-coarsening, accompanied by microstructural densification and grain boundary corrosion. The findings highlight the pronounced role of water vapor and trace environmental impurities, demonstrating that alumina-based furnace environments can act as a variable influencing the structural integrity and apparent degradation behavior of Yb₄Hf₃O₁₂, thereby providing valuable guidance for mechanistic studies of high temperature corrosion in future experimental investigations.

During the high-temperature calcination process of lithium-ion battery cathode materials, saggars are highly susceptible to corrosion by the cathode material. This leads to the formation of lithium-containing expansive products, subsequently causing structural damage and performance degradation. To extend their service life, various strategies have been developed, including the introduction of advanced corrosion-resistant phases, optimization of manufacturing processes to enhance densification, and the design of novel structures to mitigate thermal stresses. Building upon this foundation, this paper systematically analyzes the failure mechanisms of saggars, particularly the synergistic effects of alkali corrosion and thermal cycling fatigue, while summarizing advances in methods for improving saggar performance. Finally, future development trends are projected to provide guidance for the design, preparation, and application of saggars for lithium battery cathode materials.