The Effect of Small Additions of Alumina on the Reactions in the Mixture 6SiO₂.Na₂CO₃.CaCO₃

_{JSGT 1937 V21 T299-T309}

_{The addition to 1 g charges of a mixture of molecular composition Na2CO3.CaCO3.6SiO2 of progressive· amounts of calcined alumina up to approximately 5% has no measurable effect on the rate of decomposition at 700° or upon the amount of reacted silica formed. Some of the alumina, however, is rendered soluble in acid, due to reaction with sodium carbonate. Alumina does not react with calcium carbonate or with silica to any appreciable extent, even at 800°. The addition of alumina increases the rate of decomposition of a mixture of sodium and calcium carbonates, owing to reaction with the former. In the complex mixture, however, where silica is also present, the reaction between alumina and sodium carbonate is relatively too small to affect appreciably the rate of decomposition. The addition of up to 5% alumina decreases the melting rate, but the effect is less marked as the melting temperature is raised from 1100° to 1400°, and at the last-mentioned value it is slight. The presence of fine seed, however, is a feature of the melts at 1100–1400° containing alumina.}

J. E. Stanworth & W. E. S. Turner