Quantitative analysis of the structural stability and degradation ability of hydroxyapatite and zirconia composites synthesized in situ

In situ synthesis has been attempted in the present study to form hydroxyapatite [HAP, Ca-10(PO4)(6)(OH)(2)] and zirconia [ZrO2] composite powders. The synthesis has been attempted using an aqueous precipitation technique in which alterations have been made to the starting Ca/P molar ratio of calcium phosphate suspensions together with five different concentrations of ZrO2 precursors. An additive in the form of yttria to stabilize tetragonal ZrO2 (t-ZrO2) has not been used in the present investigation. The precipitated powders resulting were heat treated at different temperatures before determination of the phase stability and degradation ability of the HAP-ZrO2 composites. The powders were characterized by X-ray diffraction, Raman spectroscopy and quantitative analysis by Rietveld refinement. The results from the investigation confirmed the formation of HAP-ZrO2 composites at 900 degrees C. The Ca/P precursors with molar ratios of 1.67 and 1.69 have yielded the formation of beta-tricalcium phosphate [beta-TCP, beta-Ca-3(PO4)(2)] with a content of less than 5 wt% together with HAP and t-ZrO2 at 900 degrees C. The Ca/P precursors with a molar ratio of 1.68 have yielded only HAP and t-ZrO2 composite powders at 900 degrees C. The increased addition of ZrO2 precursors had resulted in the enhanced formation of t-ZrO2 with a simultaneous reduction in the amount of the HAP phase formed. However, heat treatment at 1000 degrees C and 1100 degrees C has initiated the degradation of HAP and t-ZrO2 composite powders resulting in the formation of monoclinic ZrO2 (m-ZrO2). It is surmised from the present results that there is active involvement of the ZrO2 content in the degradation behaviour of the HAP-ZrO2 composite powders.