Alite

Alite is an impure form of tricalcium silicate, Ca3SiO5, sometimes formulated as 3CaO·SiO2 (C3S in cement chemist notation, CCN) with typically 3-4% of substituent oxides. It is the major, and characteristic, mineral phase in Portland cement. The name was given by Törneborn in 1897 to a crystal identified in microscopic investigation of Portland cement. Alite is a name in common use in the cement industry, but it is very rare in nature (known as hatrurite). Alite is an impure form of tricalcium silicate, Ca3SiO5, sometimes formulated as 3CaO·SiO2 (C3S in cement chemist notation, CCN) with typically 3-4% of substituent oxides. It is the major, and characteristic, mineral phase in Portland cement. The name was given by Törneborn in 1897 to a crystal identified in microscopic investigation of Portland cement. Alite is a name in common use in the cement industry, but it is very rare in nature (known as hatrurite). The alite found in Portland cement differs in composition from simple tricalcium silicate. It is a solid solution and contains minor amounts of other oxides besides CaO and SiO2. A typical composition is: Based on this, the formula can be expressed as Ca2.90Mg0.06Na0.01Fe0.03Al0.04Si0.95P0.01O5. In practice, the composition varies with the bulk composition of the clinker, subject to certain limits. Substitution of calcium ions or orthosilicate ions requires that electric charges be kept in balance. For instance, a limited number of orthosilicate (SiO44−) ions can be replaced with sulfate (SO42−) ions, provided that for each sulfate ion, two aluminate (AlO45−) ions are also substituted. Tricalcium silicate is thermodynamically unstable below 1250 °C, but can be preserved in a metastable state at room temperature by fast cooling: on slow cooling it tends to revert to belite (Ca2SiO4) and CaO.