Nucleation of hydroxyapatite on silica-gel:: Experiments and thermodynamic explanation

Silica-gels prepared from ethanol, TEOS and water, using a hydrochloric acid as catalyst, were slowly dried and heated in air up to 900 degrees C. Plate-like pieces of heat treated silica-gel were used for hydroxyapatite nucleation experiments in a simulated body fluid (SBF) medium since sol-gel processing gives the silica an active surface. The SBF was changed every 3 days. After 9 days in the SBF, hydroxyapatite was observed by SEM on the surface of the silica-gel samples. The presence of hydroxyapatite was confirmed by FTIR. Subsequent growth of hydroxyapatite was evaluated after 12 and 21 days total soaking time in SBF. A thermodynamic analysis was made in order to explain the nucleation and growth of the hydroxyapatite on the silica-gel.