Nano-scale synthesis of the complex silicate minerals forsterite and enstatite

Abstract

Olivine is a relatively common family of silicate minerals in many terrestrial and extraterrestrial environments, and is also useful as a refractory ceramic. A capability to synthesize fine particles of olivine will enable additional studies on surface reactivity under geologically relevant conditions. This paper presents a method for the synthesis of nanocrystalline samples of the magnesium end-member, forsterite (Mg₂SiO₄) in relatively large batches (15-20g) using a sol-gel/surfactant approach. Magnesium methoxide and tetraethylorthosilicate (TEOS) are refluxed in a toluene/methanol mixture using dodecylamine as a surfactant and tert-butyl amine and water as hydrolysis agents. This material is then cleaned and dried, and fired at 800°C. Post-firing reaction in hydrogen peroxide was used to remove residual organic surfactant. X-ray diffraction showed that a pure material resulted, with a BET surface area of up to 76.6m²/g. The results of a preliminary attempt to use this approach to synthesize nano-scale orthopyroxene (MgSiO₃) are also reported.

Keywords: Clinopyroxene; Enstatite; Forsterite; Nanosynthesis; Olivine; Orthopyroxene; Pyroxene.