Self-Propagating High-Temperature Synthesis of MgAl2O4 Spinel

Abstract

Magnesium aluminate spinel, MgAl2O4, has been prepared by self-propagating high-temperature synthesis (SHS) in the MgO–Al2O3–Mg(NO3)2 ∙ 6H2O–Al–B system. The composition and structure of the synthesis product have been ascertained by X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Using time-resolved X-ray diffraction (TRXRD), we have studied the phase formation process during SHS and identified the key reaction paths. The addition of 2–4 wt % boron has been shown to result in the formation of a liquid phase during the combustion process owing to the formation of a low-melting-point boron oxide, favoring the growth of skeletal spinel crystals 1–10 μm in size. Our results demonstrate that the use of a mixture of aluminum and boron as combustible components of the starting mixture and heating at a rate above 100°C/min allow a material containing more than 95 wt % MgAl2O4 spinel to be obtained.