Danilenko I. The physical action influences on phase transition and properties of the powders and consolidated systems on a base on zirconia

The thesis is devoted to the establishment of the regularities of phase transition at formation and consolidation doped zirconia nanoparticles under microwave (MW), pulse magnetic field (PMF), ultrasonic, high hydrostatic pressure and temperature conditions. The study was carried out using tetragonal zirconia nanopowders (ZrO2 - 3 mol% Y2O3) prepared by copre-cipitation method. It was established the microwave and pulse magnetic field influ-ence on zirconium hydroxide powders morphology by changing rates and mechanism of water molecules evaporation by micro-wave using and decreasing the surface OH-groups by using PMF action in comparison with conventional drying. It was al-low to established that zirconia particle size is depend from starting material structure and decrease the minimal particle size from 12,5 to 8 nm after heat treatment. The size effects at T-M phase transition in zirconia nanoparticles systems at high hydrostatic pressure conditions were discovered. It was established increasing thedegree of tetragonal to mono-clinic phase transition at tetragonal zirconia nanoparticles with increasing particle size from 8 to 21 nm. Was shown that T - M phase transition is the martensitic phase transition which oc-curred in shear stresses conditions. This transition depend on particle size, extend of tetragonal phase stability and external conditions (pressure and temperature). It was discovered that the using nonaglomerated nanopowders with sharp particle size distribution allow to decrease sintering temperature up to 150o and obtained the nanostructured ceram-ics with 100 - 200 nm grain size with lower phase degradation degree at hydrothermal conditions.