EFFECT OF ZrO₂-BASED SOLID SOLUTION ON LOW-TEMPERATURE PHASE STABILITY

Abstract

The low-temperature phase stability of 97 mol.% ZrO₂–3 mol.% Y₂O₃, 95 mol.% ZrO₂–3 mol.% Y₂O₃–2 mol.% CeO₂, 92.5 mol.% ZrO₂–2.5 mol.% Y₂O₃–5 mol.% CeO₂, 90 mol.% ZrO₂–2 mol.% Y₂O₃–8 mol.% CeO₂, and 88 mol.% ZrO₂–12 mol.% CeO₂ materials in the ZrO₂−Y₂O₃−CeO₂ system was studied. To determine the phase stability, the method of accelerated aging in hydrothermal conditions for 7 h and 14 h was used. The evaluation criterion was the amount of the M-ZrO₂ phase that formed in the samples when aged in hydrothermal conditions. The properties of the materials were analyzed by X-ray diffraction and electron microscopy. The T-ZrO₂ ® M-ZrO₂ phase transformation occurred to varying degrees in all samples except for the 88 mol.% ZrO₂–12 mol.% CeO₂ sample after the first and second aging cycles. The smallest amount of M-ZrO₂ formed in the 90 mol.% ZrO₂–2 mol.% Y₂O₃–8 mol.% CeO₂ sample. After both aging cycles, the fracture patterns of the 90 mol.% ZrO₂–2 mol.% Y₂O₃–8 mol.% CeO₂ and 88 mol.% ZrO₂–12 mol.% CeO₂ samples did not change significantly. With the complex stabilization of zirconia by yttria and ceria, the T-ZrO₂ ® M-ZrO₂ phase transformation was controlled in the aging process by the number of oxygen vacancies resulting from the presence of yttria and by stresses induced by the presence of ceria in the solid solutions. The number of oxygen vacancies decreased as ceria content in the ZrO₂-based solid solutions increased, slowing down the rate of water diffusion and increasing the low-temperature phase stability in the ZrO₂–Y₂O₃–CeO₂ materials. The effectiveness of using the 90 mol.% ZrO₂–2 mol.% Y₂O₃–8 mol.% CeO₂ and 88 mol.% ZrO₂–12 mol.% CeO₂ composites for the microstructural design of medical materials with increased resistance to low-temperature degradation in a humid environment was shown.