The sol-gel process in the 5Ca glycolate-3H 3PO 4 system

Abstract

When Ca glycolate is mixed with H 3PO 4 in a Ca/P ratio of 1.67 containing acetic acid contents in a range of HOAC/Ca ratios from zero to six, the as-prepared mixtures have fine particles. The as-prepared mixtures are transformed to precipitates or solution depending on the HOAC contents and the amount of stirring. If the as-prepared mixtures are further stirred for 8 h, precipitation occurs for all mixtures with various 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 for one day, and the solution is transformed to a transparent gel after keeping for 20 h. The transparent gel is transformed to a poorly developed hydroxyapatite phase after drying at 150 °C for 24 h and to a pure and well-developed hydroxyapatite phase after calcining at above 750 °C for 1 h. HOAC in the mixtures is suggested to play a role in retarding the reactions between Ca glycolates and H 3PO 4, and the critical role of stirring in forming a transparent gel is proposed as the occurrence of a heterogeneous reaction process in the system.