Formation of carbon with a diamond-like lattice during the production of spinel MgAl2O4 by a combustion synthesis

Magnesium aluminate spinel (MAS) containing a carbon impurity was prepared by self-propagating high-temperature synthesis (SHS). Periclase MgO, alumina Al2O3, fuel Al powder, 2 wt% boron, and oxidizer Mg (NO3)2 & sdot;6H2O were used as starting reagents for MAS synthesis. The phase composition of original boron and synthesized products, the structure and surface morphology of the samples were investigated. EDS analysis and elemental mapping confirmed that the impurity detected as crystals formed during the synthesis was carbon. IR spectroscopy showed that the carbon detected in the synthesized product has a diamond-like lattice similar to that of detonation diamonds. The analysis of gases evolved during combustion was performed. A proton-boron reaction is shown to take place during fast self-propagating high-temperature synthesis of spinel. The probable mechanisms of carbon formation in the synthesis products are proposed using the experimental data.