Mineralizing magnesium aluminate spinel formation with B2O3

B2O3 mineralizes spinel formation from stoichiometric (1:1 mole ratio) calcined magnesia and alumina. After 3 h at 1100 degrees C, X-ray diffraction (XRD) shows the mineralization effect of B2O3 is limited to 1.5 wt% additions with higher B2O3 contents leading to Mg3B2O6 formation and reduced spinel content. Boron nuclear magnetic resonance, electron probe microanalysis (EPMA), scanning electron microscopy, transmission electron microscopy (TEM) and XRD reveal formation of a boron-containing liquid. Energy dispersive spectroscopy in the TEM and EPMA of the glassy phases formed from solidification of the liquid reveal that initially it is Mg borate, later becoming a magnesia-modified boroaluminate, composition suggesting dissolution-precipitation as opposed to templated growth as the mechanism of this liquid phase mediated mineralization.