A New Calcium Silicosulphate

Abstract

A COMPREHENSIVE investigation is in progress of high-temperature phase equilibria in the system CaO—SiO2—SO3 which is important in the chemistry of cements. A new compound has been located of molar composition at present best represented as (2CaO.SiO2)2.CaSO4. This compound has been prepared from calcium carbonate (99.9 per cent pure), crushed quartz (99.95 per cent pure) and AnalaR CaSO42H2O by ignition for 150 h at 1,150° C in platinum boats in a platinum-rhodium resistance furnace. For successful preparation the mixture has to be finely ground to pass a 300-mesh sieve in between periods of heating. The X-ray diffraction pattern of the new compound first became discernible after about 2 h of heating. On continued heating, the X-ray diffraction patterns of the reactants and of dicalcium silicate became progressively weaker until, after 150 h, they reached intensity-levels representative of trace quantities.