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

Abstract

In situ synthesis has been attempted in the present study to form hydroxyapatite [HAP, Ca₁₀(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 °C. The Ca/P precursors with molar ratios of 1.67 and 1.69 have yielded the formation of β-tricalcium phosphate [β-TCP, β-Ca₃(PO₄)₂] with a content of less than 5 wt% together with HAP and t-ZrO₂ at 900 °C. The Ca/P precursors with a molar ratio of 1.68 have yielded only HAP and t-ZrO₂ composite powders at 900 °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 °C and 1100 °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.