Nanocrystalline powders of the ZrO₂—Y₂O₃—CeO₂ system for bioinert coatings

Abstract

An effective approach to surface modification of medical metal implants is the deposition of bioinert composite layers in the ZrO₂—Y₂O₃—CeO₂ system on their surface. The co-stabilization of ZrO₂ with ceria and yttria allows one to increase both the strength characteristics of the bioinert material and the resistance to low-temperature degradation (aging) in a humid environment. The low-temperature phase stability of the ZrO₂—Y₂O₃—CeO₂ system composites was studied depending on the temperature (700 and 850 °С) during heat treatment of the initial powders. The composition of the initial nanocrystalline powders is (% (mol.)) : 95ZrO₂—3Y₂O₃—2CeO₂ and 90ZrO₂—2Y₂O₃—8CeO₂. Powders were produced by hydrothermal synthesis in an alkaline medium. Sintering of composites from the initial powders thermally treated at 700 °С was accompanied by the phase transformation F-ZrO₂ → T-ZrO₂. This transformation was absent during the sintering of composites from the initial powders thermally treated at 850 °C. It was found that the low-temperature phase stability of the investigated composites in the ZrO₂—Y₂O₃—CeO₂ system depends on the composition of the ZrO₂-based solid solution and the porosity of the ceramic after sintering. It was found that in order to increase the aging resistance of ceramics, it is necessary to increase the amount of CeO₂ in the ZrO₂-based solid solution, reduce the porosity of the ceramic, and prevent the phase transformation of the low-temperature cubic ZrO₂-based solid solution into tetragonal ZrO₂-based solid solution during sintering. The investigations performed are necessary for the microstructural design of bioinert coatings based on ZrO₂ that are resistant to the lowtemperature degradation of properties in a humid environment.