Calcium silicate

Calcium silicate can refer to several silicates of calcium including:

This article focuses on Ca₂SiO₄, also known as calcium orthosilicate, or by the shortened trade name Cal-Sil/Calsil. All calcium silicates are white free-flowing powders. Being strong, cheap and nontoxic, they are components of important structural materials.

Calcium silicates are produced by treating calcium oxide and silica in various ratios. Their formation is relevant to Portland cement.

Calcium silicate is a byproduct of the Pidgeon process, a major route to magnesium metal. The process converts a mixture of magnesium and calcium oxides as represented by the following simplified equation:

The calcium oxide combines with silicon as the oxygen scavenger, yielding the very stable calcium silicate and releasing volatile (at high temperatures) magnesium metal.

Via the carbonate–silicate cycle, carbonate rocks convert into silicate rocks by metamorphism and volcanism and silicate rocks convert to carbonates by weathering and sedimentation.

The production of sulfuric acid from anhydrous calcium sulfate produces calcium silicates. Upon being mixed with shale or marl, and roasted at 1400 °C, the sulfate liberates sulfur dioxide gas, a precursor to sulfuric acid. The resulting calcium silicate is used in cement clinker production.

As verified by X-ray crystallography, calcium silicate is a dense solid consisting of tetrahedral orthosilicate (SiO₄^4-) units linked to Ca²⁺ via Si-O-Ca bridges. There are two calcium sites. One is seven coordinate and the other is eight coordinate.