Properties of zirconium ceramics and film stabilized by yttrium

Full text: Unstable zirconium dioxide phase transformation can be eliminated by stabilization of the cubic phase with an addition of a selected alkaline earth or rare-earth oxide. Stabilized ZrO2 has been widely utilized in various high-temperature refractory applications. These stabilized ZrO2-base solid solutions also possess rather unique electrical properties, and as a result have considerable potential as solid electrolytes in galvanic and fuel cells and, possibly, as heating elements in high-temperature furnaces. The complex study of synthesis processes, structure and properties of metal alkoxide organic sols have been developed. These have allowed to create main principles of their formation and to show the practical realization of obtained theoretical and experimental results. The correlation between hydrolysis conditions of (Zr+Y) metal alkoxide sols and synthesis of stable colloid multi-component systems has been established. Systematic research of zirconium and yttrium bi-alkoxide electrophoretic deposition was conducted for the first time. The formation mechanism of electrophoretic deposits has been offered and general scientific principles of the electrophoretic process have been formulated. The model of gel deposits structure was proposed. It has enabled to analyze the main (for example, cluster) effects, which have been exhibited in technological procedure for thin film preparation. The structure investigation of stabilized zirconium dioxide thin films and ceramics has been studied. The researches were based on the comparative analysis of the initial gel microstructure and dried gel by the various drying methods. The new approach for drying of gel electrophoretic deposits was formulated theoretically and experimentally has been proved. The modeling of the aggregate kinetics as a type of 'cluster-cluster' has been proposed like a qualitative description of the process. The data of fractal dimensions of aggregates which have been formed at the various technological regimes and conditions were determined. The model of the heat treatment process for ceramics and thin oxid films has been offered. Qualitative description of the experimental results for the sol-gel transition of thin oxide film has been found. It was known that a pyrochlore phase, Y2Zr2O7, may exist in the Y2O3-ZrO2 system. However, since Y3+ and Zr4+ have similar scattering factors, the detection of the pyrochlore phase by X-ray techniques would be most difficult. In the present paper, no pyrochlore lines were detected for any of the specimens. The alkoxide-based sol-gel process is one of the most promising methods for synthesizing Y2O3-ZrO2 ceramic powders and, especially, films at relatively low-temperatures. Sol-gel process has many advantages, such as easy composition control and fabrication of large area thin films, film homogeneity, low cost, and a simple fabrication cycle. Therefore, it could be practical to make use of sol-gel technique to prepare thin films of desired properties. The choice of precursors can affect the chemical-reaction kinetics, microstructures and properties of the product, so in this report author compared the crystallization behavior of oxide functional films derived from the same precursors, stressing the influence of experiment conditions and where it was possible to obtain the uniform films