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Non-stoichiometric hydroxyapatite was prepared by the hydrolysis of a-tricalcium phosphate. The apatite was obtained as a powder and hardened with and without stirring during the hydrolysis. The apatite had a general formula, characteristic dehydration and pyrolysis behaviour similar to that of precipitated non-stoichiometric hydroxyapatite. In addition, it exhibited some new phenomena (i.e. thermal reaction between lattice HzO and Po43-above 473 K, formation of ESR centres above 473 K and disappearance at 873-973 K, and a slight weight loss at 873-973 K). Apatite particles were composed of aggregates of cylindrical rods or thin blades grown along the c-axis or (100) faces of apatite structure. Hardened apatite materials with various porosities above 5 5 % and bulk densities below 1.4 g c w 3 were obtained by using different water-soluble additives. The strength of the hardened materials was 20-500 kg cm-2 in compression and 10-1 20 kg cm-2 in bending. The strengths were improved at least two to three times by impregnating the hardened materials with methyl methacrylate polymer.

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