Mineralizing Magnesium Aluminate Spinel Formation With B ₂ O ₃

Abstract

B 2 O 3 mineralizes spinel formation from stoichiometric (1:1 mole ratio) calcined magnesia and alumina. After 3 h at 1100°C, X‐ray diffraction (XRD) shows the mineralization effect of B 2 O 3 is limited to 1.5 wt% additions with higher B 2 O 3 contents leading to Mg 3 B 2 O 6 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.