Phase purity of sol-gel-derived hydroxyapatite ceramic

Calcium oxide was reported in the sol-gel-derived hydroxyapatite (HA) as an unavoidable major impurity. In this study phase purity of HA synthesized b y sol-gel route was explored using precursors of calcium nitrate tetrahydra te and triethyl phosphate. Two different drying methods, the fast drying of as-prepared precursors and the slow drying of aged precursors were adopted as major processing variables. The dried gels were subsequently calcined u p to 600 degreesC. In the calcined powder from fast-dried gel, X-ray diffra ction (XRD) patterns revealed an intense CaO peak. For the slow-dried gel, thermogravimetric analysis revealed a 2-step weight-loss behavior during he ating. XRD analysis of the calcined powder, corresponding to the second wei ght-loss step, showed major peaks of hydroxyapatite and a very weak CaO pea k. P-31 NMR analysis indicated formation of calcium phosphate complex durin g aging. Complete incorporation of Ca(NO3)(2) into the complex due to prope r aging therefore diminishes CaO formation. It was also found that the mino r CaO derived in the slow drying method can be easily and completely washed out just by distilled water. (C) 2001 Elsevier Science Ltd. All rights res erved.