Calcium aluminates
[Image:CaAluminatesPhaseDiagram.JPG|thumb|400px|Calcium aluminates phase diagram]
Calcium aluminates are a range of materials obtained by heating calcium oxide and aluminium oxide together at high temperatures. They are encountered in the manufacture of refractories and cements.
The stable phases shown in the phase diagram are:
- Tricalcium aluminate, 3CaO·Al2O3
- Dodecacalcium hepta-aluminate, 12CaO·7Al2O3
- Monocalcium aluminate, CaO·Al2O3
- , CaO·2Al2O3
- Monocalcium hexa-aluminate, CaO·6Al2O3
- Dicalcium aluminate, 2CaO·Al2O3, which exists only at pressures above 2500 MPa. The crystal is orthorhombic, with density 3480 kg·m−3. The natural dicalcium aluminate, brownmillerite, may form at normal pressure but elevated temperature in pyrometamorphic zones, e.g., in burning coal-mining heaps.
- , 5CaO·3Al2O3, forms only under an anhydrous and oxygen free atmosphere. The crystal is orthorhombic, with a density of 3067 kg·m−3. It reacts rapidly with water.
- , 4CaO·3Al2O3, is a metastable phase formed by dehydrating 4CaO·3Al2O3·3H2O.