International Journal of Applied Ceramic Technology最新文献

Reliable metallurgical bonding between Al₂O₃ ceramic and copper was achieved by vacuum brazing using Ag–23Cu–14.5In–3.3Ti (wt.%) alloy. The representative interfacial structure of the joint was Al₂O₃/Ti₃(Cu,Al)₃O + γ-TiO/Ag-based solid solution + (Cu,Ag)₇In₃ + Ag–Cu eutectic + Cu-based solid solution/copper. The interface microstructure evolved with process parameters, including the formation of γ-TiO and Ti₃(Cu,Al)₃O, as evidenced by microstructural analysis and etched surface morphology. The relationship between fracture path and shear strength was established by observing the fracture morphology and performing shear strength tests on joints with various process parameters, utilizing the degree of the Ag-based solid solution loss and the thickness of the reaction layer as evaluative factors. When brazed at 760 or 780°C for 20 min using a 100 µm brazing alloy foil, the brazed joints demonstrated a peak shear strength of 215 ± 25 MPa, and the fracture predominantly occurred in the Al₂O₃ matrix and Ti₃(Cu,Al)₃O layer.

Environmental barrier coatings (EBCs) are indispensable for the service of SiC-based turbine engines. The Si-bond coating is a critical layer that prevents oxidants from penetrating SiC substrates and determines the service lifetimes of EBCs. In this study, the oxidation behaviors and failure mechanisms of Si-based bond coatings were reviewed. The large growth rate and phase transformation of thermally grown oxides (TGOs, SiO₂) seriously deteriorate the service of Si-bond coatings. The low melting point of Si further limits its application in next-generation engines above 1 427°C. The results show that an isolated particle healing (IPH) treatment decreased the oxidation rate of the Si-bond coating by ∼24% at 1 300°C. Moreover, the Si–HfO₂ and Si-stabilizer (Si–Al₂O₃ or Si-mullite) composite/duplex bond coatings can eliminate SiO₂ phase transitions, thus improving the service lifetime. In addition, rare earth silicide (RESi), SiC and SiO₂–HfO₂ composite show potential for use in next-generation EBCs above 1 427°C. This review provides guidance for designing Si-based bond coatings with improved service lifetime.

Porous geopolymer composite (E51) reinforced by E51 epoxy resin was prepared by well-distributed dual-blending using red mud, metakaolin, and slag as raw materials. The effects of E51 content on microstructure, porosity, mechanical properties, and thermal insulation properties of the porous composites were investigated. The addition of E51 changed the setting time and viscosity of the slurry with high content of solid wastes (80%), which play an important role in the formation of pores during the direct foaming process. The addition of E51 had great influence on the porous properties of geopolymer composites, which in turn affected their compressive strength (0.19–1.44 MPa) and thermal conductivity (0.09–0.12 W/mK). The addition of E51 enabled the production of geopolymer composites in a rather large range of total porosity (67.3–81.1 vol%), with an optimal sample possessing a total porosity of up to 78.7 vol%, a thermal conductivity of 0.086 W/mK, and a compression strength of 0.47 MPa.

Zinc-doped indium oxide (IZO) thin films were deposited on silicon dioxide substrates by radio-frequency magnetron sputtering using an IZO ceramic target with In₂O₃/ZnO weight ratio of 9:1. The effects of power, pressure, and distance between target and substrate on microstructure and photoelectric properties of IZO films were investigated. The results show the performance of IZO films prepared under the conditions of power 80 W, air pressure .5 Pa, and target base distance 80 mm are the best, and the IZO films are amorphous with high transmittance (>86.0%), high mobility (>45.0 cm²/V s), and low resistivity (less than 2.0 × 10⁻⁴ Ω cm), which are the best photoelectric performance reported at present. This work provides a feasible research approach for preparing high-performance IZO thin films.

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.