Solid state synthesis and thermal stability of HAP and HAP – β-TCP composite ceramic powders

Abstract

Powders of pure β-tricalcium phosphate (β-TCP), hydroxyapatite (HAP) and a biphasic composite mixture of HAP+β-TCP were prepared by solid state reaction between two commercially available calcium-based precursors namely, tricalcium phosphate (TCP) and calcium hydroxide (Ca(OH)2). These reactants mixed in the molar ratios ranging from 3 : 0 to 3 : 4 (designated T0 to T4) in deionized water, milled and slip-cast into discs were heat treated in the temperature range of 600°C to 1250°C. The products formed were characterized by X-ray diffraction (XRD) and i.r. spectroscopic techniques for identification of phases formed and functional groups present in them. While tricalcium phosphate and calcium hydroxide taken in the molar ratio of 3 : 2 and 3 : 3 resulted in pure HAP when heat treated at 1000°C for 8 h, the 3 : 1 and 3 : 1.5 molar ratio compositions resulted in a biphasic mixture of HAP+β-TCP for similar heat treatments. Heat treatment of 3 : 4 molar ratio composition of tricalcium phosphate and calcium hydroxide at 1000°C yielded HAP with free CaO as the secondary phase. Products of heat treatment at higher temperatures (1150 and 1250°C) for even shorter duration (2 h) while not differing from the products obtained from T0 and T2 cases at 1000°C (pure β-TCP and pure HAP), change in the case of T1, T1.5, T3 and T4 to products with lesser percentages of HAP containing β-TCP (in the case of T1 and T1.5) or CaO (in the case of T3 and T4) as the secondary phase.