THE SOL-GEL PROCESS IN THE 5CA GLYCOLATE 3H(3)PO(4) SYSTEM

When Ca glycolate is mixed with H3PO4 in a Ca/P ratio of 1.67 containi ng acetic acid contents in a range of HOAC/Ca ratios from zero to six, the as-prepared mixtures have fine particles. The as-prepared mixture s are transformed to precipitates or solution depending on the HOAC co ntents and the amount of stirring. If the as-prepared mixtures are fur ther stirred for 8 h, precipitation occurs for all mixtures with vario us HOAC contents. If an as-prepared mixture has a HOAC/Ca ratio of six , without further stirring it can become a solution after being kept f or one day, and the solution is transformed to a transparent gel after keeping for 20 h. The transparent gel is transformed to a poorly deve loped hydroxyapatite phase after drying at 150 degrees C for 24 h and to a pure and well-developed hydroxyapatite phase after calcining at a bove 750 degrees C for 1 h. HOAC in the mixtures is suggested to play a role in retarding the reactions between Ca glycolates and H3PO4, and the critical role of stirring in forming a transparent gel is propose d as the occurrence of a heterogeneous reaction process in the system. (C) 1998 Elsevier Science S.A. All rights reserved.