Morphology of Melting Products of MgAl₂O₄ Obtained in a Thermal Plasma Environment

This work presents the morphology of the melt products of alumina-magnesia spinel (MgAl₂O₄), obtained in a thermal plasma environment. The energy of the thermal plasma was realized through an electric arc plasma torch with a power of 12 kW, where the plasma is considered an effective medium for heating and melting refractory materials. The initial materials for producing MgAl₂O₄ spinel were: pure magnesium oxide MgO and aluminum oxide Al₂O₃; natural materials: the source of Al₂O₃—boehmite from bauxite deposits, Northern Urals, and the source of MgO—magnesite from the Khalilov and Savinsky deposits. It was established that, regardless of the nature of the materials, the crystallized melt products have a bulk density of 3.84 g/cm³, and the weight loss varies from 2 to 6 wt %. The morphology of the obtained spinel is represented by well-defined crystals arranged over an area of ~1.75 μm², forming a textured surface with varying tilt angles. It is noteworthy that the morphology formation occurs in two interconnected stages: primary—surface crystallization of crystals with a diameter of 85 μm and a half-width into the matrix body h of 100 μm; secondary—localized crystallization of crystals with a diameter of 10 μm, randomly distributed throughout the matrix of the melt product. This is achieved through the development of convective flows from the surface into the melt droplet during intense heat exchange when the electric arc plasma torch is turned off.