Monocalcium aluminate (CaAl₂O₄) is one of the series of calcium aluminates. It does occur in nature, although only very rarely, as two polymorphs known as

krotite Krotite is a natural mineral composed of calcium, aluminium and oxygen, with the molecular formula CaAl2O4. It is the low-pressure dimorph of CaAl2O4, of which the high-pressure dimorph is named dmitryivanovite. Krotite was reported in 2011 in a ...

and dmitryivanovite, both from meteorites. It is important in the composition of

calcium aluminate cements Calcium aluminate cements are cements consisting predominantly of hydraulic calcium aluminates. Alternative names are "aluminous cement", "high-alumina cement", and "Ciment fondu" in French. They are used in a number of small-scale, specialized ...

Properties

Monocalcium aluminate is formed when the appropriate proportions of

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

and

aluminium oxide Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several Aluminium oxide (compounds), aluminium oxides, and specifically identified as alum ...

are heated together until the mixture melts. It melts incongruently at 1390 °C. The crystal is

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

and pseudohexagonal, and has density 2945 kg·m⁻³. In calcium aluminate cements, it exists as a solid solution in which the amount of minor elements depends upon the bulk composition of the

cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...

. A typical compositionP. C. Hewlett (Ed)''Lea's Chemistry of Cement and Concrete: 4th Ed'', Arnold, 1998, , p715 is Ca_0.93Al_1.94Fe_0.11Si_0.02O₄. It reacts rapidly with water, forming the metastable hydrate CaO·Al₂O₃·10H₂O, or a mixture of 2CaO·Al₂O₃·8H₂O, 3CaO·Al₂O₃·6H₂O and Al(OH)₃ gel. These reactions form the first stage of strength development in calcium aluminate cements.

References

{{Calcium compounds Cement Calcium compounds Aluminates