Influence of MgO precursors on mechanically activated forsterite synthesis

Brucite-fumed silica and hydromagnesite-fumed silica mixtures were used to investigate the influence of MgO precursors on mechanically activated forsterite synthesis. The changes in morphology, chemical bond and phase composition of the ground and calcined mixtures were examined with scanning electron microscopy (SEM), Si 2p X-ray photoelectron spectroscopy (XPS) and 29Si magic angle spinning nuclear magnetic resonance (MAS-NMR), and X-ray diffraction (XRD), respectively. The XPS and MAS-NMR analyses show that high-energy milling generates more Mg–O–Si chemical bonds in the brucite-fumed silica mixture than in the hydromagnesite-fumed silica sample. This is because brucite has a higher concentration of Mg–OH bonds than hydromagnesite. However, single-phase forsterite forms at a higher temperature of 1000 °C in the milled brucite-fumed silica mixture than that of 800 °C in the ground hydromagnesite-fumed silica sample after the same grinding. The different forsterite completion temperature is probably due to the longer Mg2+ and Si4+ diffusion distance of over 500 nm in the former milled mixture than that of less than 300 nm in the latter ground sample.