Hydroxyapatite-based ceramic materials prepared using solutions of different concentrations

Hydroxyapatite, Ca10(PO4)6(OH)2, powders with enhanced sinterability have been synthesized through precipitation from calcium nitrate and ammonium hydrogen phosphate solutions at pH 9, t= 60 deg C, and a Ca/P atomic ratio of 1.67, and their properties have been studied: phase composition, particle size distribution, loose density, and green density. The initial solution concentration is shown to influence the properties of the powders and the ceramics fabricated from them. Comparison of the particle size distributions in disaggregated powders and the grain size distributions in the ceramics indicates that the ceramics inherit the structure of the corresponding powders. Optimizing the synthesis conditions in order to enhance the sinterability of the powders, we obtained green compacts with the highest shrinkage rate in the range 850-950 deg C and shrinkage onset at 600 deg C, which is 100-150 deg C lower in comparison with powders synthesized in earlier studies from calcium nitrate and ammonium hydrogen phosphate.