Effect of silane-coupling treatment on thermal decomposition of octacalcium phosphate

Octacalcium phosphate (OCP) has a unique layered structure. The layered structure is feasible for novel organic-inorganic hybrids. We treated OCP powder with a silane-coupling agent, vinyltrimethoxysilane (VS), and examined its thermal properties. The VS was not incorporated in the hydrated layer of OCP but reacted only with the surface. The non-treated OCP (Pure-OCP) and treated OCP (OCP-VS) showed the almost same dehydration behavior when they were examined by thermogravimetry and differential thermal analysis. However, the different behavior in 010 diffraction peaks was observed in X-ray diffraction patterns when they were heated at 150°C. The treatment with VS retarded the decomposition of the layered structure of OCP. Some of the VS molecules in OCP-VS might have undergone the condensation reaction among the silanol groups in VS. Due to this VS network on the surface of OCP, the framework of the layer of OCP becomes stable. When Pure-OCP and OCP-VS heated at 150°C were aged under ambient conditions for 1 week, rehydration occurred in both samples. The VS introduced on OCP may provide a novel organic modification of OCP.