Room-temperature synthesis of apatite-type lanthanum silicates by mechanically milling constituent oxides

Apatite-type lanthanum silicates have been successfully prepared at room temperature by dry milling hexagonal A−La2O3 and either amorphous or low cristobalite SiO2. Milling a stochiometric mixture of these chemicals in a planetary ball mill with a moderate rotating speed (350 rpm), allows preparing the target phase in only 6 h although longer milling times are needed to eliminate all SiO2 traces. The mechanically activated chemical reaction proceeds faster when using amorphous silica than low cristobalite as silicon source and pure phases are obtained after only 9 and 18 h respectively. As obtained powder phases are not amorphous and show an XRD pattern as well as IR and Raman bands characteristic of the lanthanum silicate.