Silicon Incorporation in Hydroxylapatite Obtained by Controlled Crystallization

Silicon-containing hydroxylapatites have been prepared by an aqueous precipitation method, partially substituting phosphate with silicate groups. The as-prepared products contain two phases: an amorphous phase and an apatite phase. At this first stage, the phosphate deficiency is not primarily compensated by silicate incorporation, but by carbonates contained in the aqueous media. The silicon plays a very important role at the microstructural level, taking part in increasing the amount of the amorphous phase, as well as leading to smaller crystallite size. After removing the carbonates by treating the samples at 900 °C, the Si seems to get into the apatite structure. This incorporation also leads to structural changes and higher tetrahedral distortion compared to that of pure hydroxylapatite, which can explain the higher reactivity of these compounds previously reported by other authors.