Kinetics and mechanism of formation of forsterite (Mg 2 SiO 4 ) by solid state reaction of MgO and SiO 2

The development of forsterite, Mg2SiO4, by solid state reaction in mixed powders of MgO and SiO2 in various mole ratios at temperatures 1100–1400°c and for times up to 144 hrs is followed by quantitative x-ray diffraction measurements. Powders are used consisting of coarse (15 μ) particles of one component in a fine-grained matrix of the other component. The results are consistent with a diffusion-controlled mechanism and up to about 60–70% reaction to agree with the Ginstling-Brounshtein equation. Reaction constants are evaluated and activation energies in the range 70–80 kcal/mole are obtained. Studies, using platinum markers, indicate that Mg is the main diffusing species. A cathode-luminescent image shows a thin product layer of enstatite between the principal product (forsterite) and the SiO2 phase, which is confirmed by electron microprobe measurements. It is considered that a thin zone of enstatite moves ahead of the main product forsterite as the reaction progresses into the silica component.