Tricalcium Silicate, 3CaO.SiO₂

The existence or otherwise of Tricalcium Silicate, 3CaO.SiO₂, has been in the past the subject of much discussion, earlier investigators being rather in favour of regarding it as a mixture or solid solution of the orthosilicate and calcium oxide. Recent work, however, seems to have established its claim to be regarded as a chemical individual.

Tricalcium silicate cannot be obtained by simple fusion of the constituents. Perhaps it is unstable at the melting-point, about 1700° C. It can, however, be prepared in the presence of small quantities of other oxides, for example, aluminium, boron, and chromium oxides, which probably act as a flux, allowing the reaction to take place at a lower temperature. It can also be prepared by heating the constituents for some time below the melting-point.

It is hydraulic and will hydrate and harden with water.