Thermal transformations in ultrafine plasmochemical zirconium dioxide powders
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The methods of thermal analysis and X-ray diffraction are used to investigate polymorphic transformations taking place under heating and cooling in nonstabilized ultrafine ZrO2 powders (ZrO2 UFP) synthesized in a plasmochemical process. It is found out that ZrO2 UFP is characterized by an increased content (up to 55 mass%) of tetragonal-phase particles, which is associated with the size effect of its stabilization. Heating of UFP within T = (25–700) °C, which is followed by the release of H2O, CH2O, and CO2, does not result in a change in its structural-phase state, while annealing within the temperature interval T = (700–1,000) °C gives rise to an increased growth of the size of t-ZrO2 crystallites and results in an elevated tetragonality of the crystal lattice (c/a). A complete t-ZrO2 → m-ZrO2 transition occurs as a result of heating the powder up to T = 1,300 °C. The effect of the dimensional factor on temperature characteristics of polymorphic m ↔ t transitions and the value of their temperature hysteresis is established. It is shown that the powder particle size exerts the most pronounced influence on the temperature-dependent position of the point of martensitic transformation M s. As this influence is increased, M s is shifted toward the region of higher temperatures. This is followed by a decreased temperature hysteresis of the m ↔ t martensitic transformations.
KeywordsUltrafine powders Zirconium dioxide Methods of thermal analysis Size factor Polymorphic transformations Temperature hysteresis
This research is supported by The Ministry of Education and Science of the Russian Federation in part of the “Science” program.
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