A Study of the Fundamental Reactions in the Formation of Soda–Lime–Silica Glasses

JSGT 1934 V18 T290-T306

 Mixtures of fine grained quartz, calcite and sodium carbonate in the molecular proportions Na₂CO₃+CaCO₃+SiO₂, Na₂CO₃+CaCO₃+4SiO₂, Na₂CO₃+CaCO₃+6SiO₂, Na₂CO₃+CaCO₃+8SiO₂ were heated at thirteen temperatures from 600° to 1400°, the rate of reaction being ascertained at intervals in the range from 600° to 900°. The rate of reaction increases rapidly with the temperature. In the case of the Na₂CO₃+CaCO₃+6SiO₂ mixture in 100 minutes there was 9·5% decomposition at 600° and 95% at 800°, whilst practically complete decomposition was obtained at 900° in 10 minutes. The rate of reaction also increased with the proportion of silica present. Up to 750° or 775°, the main reaction appeared to be due to calcite decomposition, the reaction Na₂CO₃– SiO₂ then becoming prominent. Evidence from microscopic examination of the products was in harmony with this view. Moreover, sintering took place slowly below 750° but much more rapidly at 775°. The 4SiO₂ mixture more rapidly melted down to give a clear glass than did the 6SiO₂mixture. A mixture Na₂CO₃+CaCO₃+6SiO₂,  made up with Fontainebleau sand, commercial calcium carbonate (30–80 IMM mesh) and soda ash, showed a rate of reaction not differing greatly at 600° from that of the mixture with standard fine grained materials, but being increasingly slower relative to the fine, pure materials as the temperature was raised in stages to 800°.

J. T. Howarth, R. F. R. Syres & W. E. S. Turner