Studying Phase Formation Processes in the CaO–Al2O3–SiO2 System Subjected to Plasma-Assisted Melting

The kinetics of plasma synthesis of anorthite from a multicomponent charge based on limestone, boehmite, and quartz sand has been studied. Phase transformations in a partially melted sample have been studied by X-ray diffraction (XRD) and thermal analysis. Three structural zones have been identified: a solidified melt, a transition layer of the sintered charge, and the unreacted charge. It has been found that plasma-assisted melting provides high-temperature conditions (>1500°C) required for synthesizing anorthite (CaAl2Si2O8). The solidified melt is mostly amorphous; however, it undergoes crystallization to form anorthite after heat treatment at 950°C. Anorthite and quartz (SiO2) phases have been identified in the transition layer; this finding suggests that reactions occurring during plasma treatment are gradient in nature. The results have shown that the use of plasma technologies is promising for synthesizing high-purity aluminosilicate materials.