Thermal transformations of composites based on hydroxyapatite and zirconia

Abstract

We have examined the effect of synthesis and heat-treatment conditions on the phase composition of composites based on hydroxyapatite and zirconia. The zirconia present in the composite based on a mechanical powder mixture crystallizes predominantly in tetragonal symmetry at heat-treatment temperatures in the range 400–600°C and in monoclinic symmetry at 800°C. The zirconia present in the composites prepared via the mixing of hydroxyapatite gel with hydrated zirconia sol or coprecipitation crystallizes only in monoclinic symmetry. Annealing at 1300°C leads to the formation of a solid solution with the composition Ca_0.15Zr_0.85O_1.85 in all of the composites as a consequence of complete or partial hydroxyapatite decomposition and the thermal diffusion of Ca²⁺ ions into the ZrO₂ lattice. In the composites prepared by liquid-phase processes, heat treatment in the range 800–1300°C produces the smallest changes in the hydroxyapatite structure, which ensures high biological activity of the material.