Nucleation and crystal growth mechanism of apatite formation on porous silica gel derived by a sol-gel procedure was investigated by the use of several simulated body fluids (SBF's) that had different concentrations of Ca(II), P(V), and OH- but had the same degree of supersaturation for hydroxyapatite. Induction time of apatite crystallization in SBF's was evaluated by thin film X-ray diffractometry. The effect of each ion on the induction time increased in the order: Ca(II)-rich SBF < P(V)-rich SBF ≪ OH--rich SBF, while that for the rate of initial crystal growth of apatite increased in the order: P(V)-rich SBF < Ca(II)-rich SBF < OH--rich SBF. It suggested that amorphous calcium phosphate (ACP) deposited as the precursor of apatite and ACP transformed into apatite nuclei by the incorporation of OH-. Moreover, the transformation was accelerated by large amount of ACP and was assisted by the rearrangement of silicate units in the gel surface. Ca(II) was richer in ACP deposited in Ca(II)-rich SBF and OH--rich SBF than that deposited in P(V)-rich SBF. Ca(II)-rich ACP was favorable for crystal growth.
All Science Journal Classification (ASJC) codes
- Ceramics and Composites
- Condensed Matter Physics
- Materials Chemistry