Brychevskyi M. Structure formation, mechanical behavior and oxygen-ionic conductivity of zirconia based ceramics

The thesis is concerned the structure - properties relationships and finding of principles of the influence of porosity, the size of the effective structural components and the state of their boundary on mechanical behavior and oxygen-conductivity of zirconium ceramic electrolytes in the example of 1Ce10ScSZ. The influence of sintering temperature on the features of structure formation, mechanical behavior and conductivity of ceramics made of 1Ce10ScSZ zirconia powders of three types, which differ by morphology and composition and distribution of stabilizers and impurities along virgin particles and their agglomerates, was studied. On the example of solid electrolytes 1Ce10ScSZ the analytical dependence of the fracture strength on structural parameters (porosity, grain and subgarin sizes, state of boundaries) resulting from the joint action of powder types and sintering temperatures was established for different fracture micromechanisms. The imaginary activation energies of structure alterations and processes responsible for strengthening or softening of 1Ce10ScSZ ceramics were determined. The activation energies have the inflection points in vicinity of 1400-1450 °C sintering temperature. In chemically pure ceramics 1Ce10ScSZ was obtained boundary complexes transformation with increasing temperature of sintering, which leads to a jump-like drop in strength and electrical resistance. In technically pure ceramic 1Ce10ScSZ was found that the influence of porosity and sizes of structural components on the total electrical conductivity take plase only in low-temperature interval, which is explained by the availability of significant influence of the boundary state between the effective structure components. In the high-temperature interval, the dependence of the total electrical conductivity of the porosity and size of the constituent structure was not detected.