International Journal of Applied Ceramic Technology最新文献

Johnson's approximation is implemented in a finite element code to simulate the electric field dependence of a core–shell microstructure material. We show how the microstructure, based here on a 50:50 volume fraction, influences the measured effective permittivity as a function of applied voltage. Using a Johnson's parameter of β = 1.0 × 10¹⁰ Vm⁵/C³, verified from commercial BaTiO₃-based multilayer ceramic capacitors (MLCC), we show how the microstructure and the difference in core and shell conductivities alter the local fields generated and how this influences the voltage dependence of the effective permittivity. Systems that comprise a conductive core-like material surrounded by a resistive shell experience little or modest voltage dependence due to the shell material providing shielding to large electric fields within the cores. Conversely, if the core material is more resistive than the shell material, substantial voltage dependence occurs with simulations showing over a 50% decrease in the effective permittivity. These simulations give improved understanding of voltage dependence and provide a method to help guide the design of future materials for MLCCs with improved performance.

In this study, the dense and fine-grained zirconia toughened alumina (ZTA) composite ceramics were efficiently prepared by 3D gel printing technology. Zirconia powder, zirconium oxychloride, and zirconium sol were introduced into boehmite gel as zirconium sources, and their effects on rheological properties, drying characteristics, microstructure, and mechanical properties of ceramics were discussed. The results showed that all gels exhibit reversible shear thinning properties. The gel with zirconia powder has a relaxation phenomenon; zirconium sol forms another gel network in the boehmite gel network, and two linear viscoelastic regions are observed. The gel with zirconia powder has the highest solid loading, small drying shrinkage, and fewer drying defects. The grain growth of ZTA ceramics with zirconium sol was inhibited, and the zirconia grains were evenly distributed, with the highest bending strength of 518 ± 103 MPa. The new gel preparation method and gel drying process offer great possibilities for manufacturing optical glasses and functional ceramics with high-performance geometric structures, which cannot be achieved by traditional manufacturing methods.

Porous mullite ceramics have good properties for high-temperature applications, but porosity gives place to ceramics with low mechanical strength, which restricts the service life in their potential applications. Therefore, performing modifications at the microscale to increase the mechanical strength has become a current challenge to expand its application fields. This work describes the properties of a porous mullite–zirconia composite produced by ceramic processing, using industrial kaolin and stabilized zirconia as raw materials. The growth of mullite needle-like grains to reinforce the ceramic was promoted by the addition of a molybdenum oxide precursor. The effect of zirconia on the composite was analyzed through an experimental multi-technique approach and considering a pure mullite sample, identically processed, as a reference. The novel composite has a porosity of about 50%, and presents a homogeneous microstructure, with interlocked mullite needle-like grains and dispersed rounded zirconia grains. This morphology restricts the mullite tendency to shrink during sintering, giving the material a higher stiffness. In particular, the presence of zirconia in the composite improves both the flexural strength and the apparent Young modulus of the material (about 20% and up to 600%, respectively). These results encourage further investigations to establish this composite for different technological applications.

In this work, the corrosion behavior of rare-earth Lu₄Hf₃O₁₂ ceramic when exposed to a CaO-FeO_1.5-AlO_1.5-SiO₂ (CFAS) environment at a temperature of 1400°C was investigated, with a focus on exploring the associated phase transformation, microstructure evolution, and corrosion reaction mechanism. Results reveal that during the corrosion process, the CFAS melt infiltrates Lu₄Hf₃O₁₂ particles through cracks, resulting in the formation of a continuous reaction layer. This reaction leads to the generation of several high-melting-point garnets, including HfO₂, Lu₃Al₅O₁₂, Ca₃Fe₂(SiO₄)₃ (Ca-Fe garnet), and Ca₃Al₂Si₃O₁₂ (Grossular). These garnets effectively fill the voids within the Lu₄Hf₃O₁₂ ceramics, preventing further infiltration of the CFAS melts. As time progresses, the rate of the reaction gradually increases, while the rate of infiltration consistently decreases. Consequently, a relatively stable corrosion layer is achieved, effectively impeding further corrosion.

This study evaluates Algerian kaolin (Djebel Debbagh (DD1) and Tamazart (KT2)) as potential substitutes for commercial kaolin (Lab) in the production of mullite-based ceramics. Three compositions were prepared by incorporating the appropriate percentage of alumina to each calcined kaolin to achieve stoichiometric mullite precursors. The phase evolution of individual kaolin powders, as well as their mixtures with alumina, depends strongly on the calcination temperature and kaolin impurities. The differential scanning calorimetry combined with thermogravimetric analysis (TGA) showed lower secondary mullite formation temperature for the KT2-based mixture. However, X-ray diffraction revealed a complete mullitization in DD1 mixture. The K₂O hindered cristobalite formation and reduced secondary mullite formation rate. Microstructure analysis showed lath-shaped primary mullite and equi-axed secondary mullite particles. After sintering at 1600°C, The KT2-based sample (M3) exhibited higher density (3.013 g/cm³) and hardness (9.9 GPa), whereas the DD2-based sample (M2) showed moderate densification (2.91 g/cm³) and higher flexural strength (159.42 MPa). Impurities (mainly Fe₂O₃, and K₂O) promoted liquid phase sintering, resulting in greater densification in M3, whereas M2 showed more homogeneous microstructure, refined grains, and lower glassy phase content, contributing to enhanced strength.

This paper brings out an innovation in fabricating porous magnesia-stabilized zirconia components by infiltrating free-flowing suspension into polyurethane foam. The process enables the production of samples with different levels of porosity and pore structure by easily controlling the amount of slurry infiltrated into the foam. The process uses Isobam, a nontoxic binder, which makes the fabrication simple and environment-friendly. Samples with five different levels of total porosity ranging from 41.7% to 62.4% were fabricated. Microstructural studies revealed multimodal pore structure comprising both open and closed porosities. Measurements on thermal properties and compressive strength of the samples showed that the sample with the lowest porosity exhibited a thermal conductivity of 0.495 W/mK and a compressive strength of 45.7 MPa. The measured values of thermal conductivity of the samples with different porosity levels could be described by modified effective medium theory. Present work opens up enormous possibilities for economical industrial production of porous magnesia-stabilized zirconia components for biomedical and thermal insulation applications.

To confer light-blocking properties upon the Al2O3 encapsulation material, this study employed a one-step method using α-Al2O3 as the main raw material to synthesize CaCu3Ti4O12(CCTO)–MnO2–Co2O3 series black Al2O3 ceramics. The research investigated their coloring effect, sintering behavior, dielectric, and mechanical properties. The results indicate that the CCTO–MnO2–Co2O3 series colorants successfully dyed the Al2O3 ceramics black, while their introduction resulted in the formation of various spinel-type compounds and facilitated the sintering of Al2O3 ceramics. The sintering mechanism and performance effects of black Al2O3 ceramics were thoroughly investigated, revealing that with an increase in the colorant content, all properties of the samples improved. When the colorant content reached 15.0 wt.%, the coloring effect reached its optimum, with a relative density of 96.7%, a dielectric constant of 12.5, a dielectric loss of .0081, a flexural strength of 314.4 MPa, and a Vickers hardness of 1254.5 Hv.

Corrosion behavior of (Cr_2/3Ti_1/3)₃AlC₂ and Ti₃AlC₂ in static oxygen-saturated liquid lead–bismuth eutectic (LBE) at 550°C and (Cr_2/3Ti_1/3)₃AlC₂ in static oxygen-depleted LBE at 500°C were investigated. In oxygen-saturated corrosion, the loose and porous corrosion layer consisting of (PbTiO₃ + TiO₂) was generated on the surface of Ti₃AlC₂. In contrast, (Cr_2/3Ti_1/3)₃AlC₂ formed the protective Cr₂O₃ layer with better corrosion resistance. Moreover, dissolution corrosion of (Cr_2/3Ti_1/3)₃AlC₂ in oxygen-depleted corrosion was intensified without a protective oxide film. And impurity phase TiC on the surface also caused the decomposition of matrix, thus impairing corrosion resistance.

The reliable jointing of SiC_f/SiC is considered to be a key factor limiting the application in the field of nuclear cladding. In this work, a jointing layer with interconnected SiC nanowires (SiCNWs) toughening network is prepared by a typical two-step routine. The high-viscosity slurry containing the precursor is pyrolyzed to form a porous SiC-based jointing layer, which is then densified by chemical vapor infiltration. Besides, SiC powders are introduced into the slurry to further increase the density of the jointing layer. The homogeneous SiC jointing material enables the strength and effectively avoids the mismatch between the thermal expansion coefficient of the jointing layer and SiC_f/SiC composites, and the apparent shear strength of the jointing specimen reaches 7.211 MPa. It is found that the joint with SiCNWs shows better shear strength than the joint without SiCNWs, and the improved mechanical properties could be attributed to the pull-out and bridging of SiCNWs.

Al₂O₃-based composite seal with 10 wt% Al powder addition (A10) possesses excellent plastic and mechanical performance under wide temperature range of solid oxide fuel cell. The thickening phenomenon of A10 seal between 250°C–400°C and 600°C–750°C is caused by the thermal expansion of organic additives and the volume expansion when solid–liquid Al react with oxygen to form Al₂O₃. The thickness change rate reaches the maximum which is about 5% at 300°C and is about 4.46% at 650°C. The Gibbs free energy for reaction between Al and Al₂O₃ in the temperature range of 523–1 023 K is all less than 0, which is proved by the fact that A10 exhibits excellent self-expansion and thermodynamic properties in the solid oxide fuel cell operating temperature.