APATITE CRYSTALLIZATION FROM METASTABLE CALCIUM-PHOSPHATE SOLUTION ONSOL GEL-PREPARED SILICA

Rehydration of silica gels sintered at 900-1100-degrees-C can stimulat e apatite crystallization from a metastable calcium phosphate solution on their surfaces. This precipitation reaction is related to the ther mal history of the silica. Increasing sintering temperature can retard apatite formation on the silica gel. Sintering at 1200-degrees-C can make the silica gel insoluble and thereby unable to induce apatite cry stallization. It is believed that apatite crystallization on the silic a can be modulated by the rate of hydrolysis on its surface. Certain c overage of silanol group is required to trigger heterogeneous nucleati on of apatite from the metastable calcium phosphate solution.