Studies on the system sodium oxide‐calcium oxide‐silica‐water

In hydrothermal reactions of lime and quartz with water or aqueous NaOH at 150 °C or 180 °C and Ca: Si = 0.83, the rate of reaction of the quartz increases with NaOH concentration. At 180 °C and Ca: Si = 0.83, the conversion into tobermorite of the semi‐crystalline calcium hydrosilicate initially formed occurs more slowly at NaOH concentrations of 0.15–2.00 M (NaOH: SiO2 = 0.05 to 0.63) than in water or 5 M‐NaOH. With long reaction times at 180 °C and Ca: Si = 0.83, increasing NaOH concentration causes pectolite to replace xonotlite as the main product. At very low water contents, NaCaHSiO4 is formed; this compound is conveniently made by grinding together solid NaOH, Ca(OH)2 and quartz in normally humid air and heating the mixture in a closed vessel at 180 °C.