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.