Study of the formation of the phase composition and structure of magnesium-aluminate spinel obtained by the SHS method

Abstract

Magnesium-aluminate spinel was obtained by self-propagating high-temperature synthesis. Magnesium and aluminum oxides were used as initial components, and aluminum (ASD-4) with additives of amorphous boron was used as fuel. The structure and phase composition of the initial substances and reaction products were studied by means of X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. The synthesis products are shown to contain MgAl2O4 as a main phase and a small amount of α-Al2O3 corundum as an impurity. Partial substitution of Mg2+ by Co2+ and of Al3+ by Cr3+ leads to a shift of X-ray diffraction peaks towards smaller angles, increasing a parameter of the crystal lattice of spinel a, which indicates the formation of solid substitutional solutions. The colour of spinels becomes bright-blue and pink, respectively. A small amount of boron used as energetic additive forms boron oxide, low-melting borates, and eutectics in the MgO-B2O3, CoO-B2O3, Al2O3-B2O3 systems during combustion, which leads to the appearance of a liquid phase and the formation of skeletal crystals with the size of 1÷10 μm during the high-speed SHS process.