Mechanochemically induced formation of La2SiO5

Abstract

A mechanochemical technique was applied to prepare La₂SiO₅ under conditions where the conventional solid-state synthesis shows unsatisfactory results. The effects of the mechanochemical treatment of a mixture of lanthana and silica gel (in molar ratio La₂O₃/SiO₂ = 4:3 has been studied by X-ray diffractometry (XRD), infrared spectroscopy (IR) and using a scanning electron microscope (SEM). Differential thermal analysis (DTA) and thermogravimetry (TG) have been used to follow the thermal behaviour of initial and milled samples. It was found that the amorphous silicate precursor of La_4.67(SiO₄)₃O is formed as a result of a mechanochemical solid-state reaction. The crystallization of the latter silicate occurs at 880°C during the subsequent heat treatment of the milled samples. The formation of La₂SiO₅ without any XRD—detectable traces of La_4.67(SiO₄)₃O takes place after heating at 1100°C for 2 h. The rate of conversion increases with increasing the milling time, reaching 96% after mechanochemical treatment for 3 h and subsequent heating at 1100°C.