Effect of Heat Treatment on the Structure and Phase Composition of the Nanosized Powder Based on a ZrO(2)Solid Solution

摘要

The nanosized 90 mol.% ZrO2-2 mol.% Y2O3-8 mol.% CeO(2)powder was produced by hydrothermal synthesis in an alkaline environment and heat-treated in the range 400-1300 degrees C. The powder properties were examined by X-ray diffraction (XRD), SEM and TEM, petrography, and BET. According to the XRD data, a low-temperature metastable cubic ZrO2(F-ZrO2) solid solution formed after hydrothermal synthesis. According to the petrography and electron microscopy data, TZrO(2)began to form already in the hydrothermal synthesis process. The F-ZrO2 -> T-ZrO(2)phase transformation was completed in the range 700-850 degrees C. Some T-ZrO(2)particles were characterized by a twin substructure. The T-ZrO(2)unit cell volume monotonically increased from 133.58 center dot 10(-3)nm(3)to 137.09 center dot 10(-3)nm(3)and the degree of tetragonality from 1.0033 to 1.0140. No M-ZrO(2)was found to form. The powder specific surface area decreased from 94 to 2 m(2)/g in the heat treatment process. The sizes of primary powder particles (5-10 nm) remained almost unchanged in heat treatment up to 1150 degrees C. The Vickers hardness of the ceramics produced from the powder treated at 850 degrees C was 3.1 GPa and critical fracture toughness factor K(Ic)was 8.4 MPa center dot m(1/2). The preservation of the tetragonal structure (T-ZrO2), which is capable of the martensitic T-ZrO2 -> M-ZrO(2)transformation, and the strength characteristics determined open ways for microstructural design of smart materials, including shape memory ones, in the ZrO2-Y2O3-CeO(2)system.