PREPARATION OF HYDROXYAPATITE POROUS BODY AND TUBULAR PARTICLES FROM GYPSUM

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The conversion of hardened gypsum (G_2H) into hydroxyapatite (HAp) was investigated as an effective materials recycling of waste G_2H. Calcium-deficient HAp hardened porous bodies were obtained by soaking a porous hardened G_2H in 1.0 mol dm^-3 (NH₄)₂HPO₄ solution at 45°C over 6 days. Nearly stoichiometric HAp hardened bodies were obtained at 100-140°C by using a dense hardened G_2H. HAp hardened bodies were composed of aggregates of fine crystals, and contained partly tubular HAp aggregates. Tubular HAp aggregates formed advantageously from comparatively porous hardened G_2H. Sintered porous ceramics consisting of tubular HAp and tubular β-Ca₃(PO₄)₂ were obtained by heating hardened calcium-deficient tubular HAp at 600°C and 800°C, respectively.