Monocalcium aluminate

Monocalcium aluminate (CaAl₂O₄) is one of the series of calcium aluminates^[1]. It does not occur in nature, but is important in the composition of calcium aluminate cements.

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Properties

Monocalcium aluminate is formed when the appropriate proportions of calcium carbonate and aluminium oxide are heated together until the mixture melts. It melts incongruently at 1390°C. The crystal is monoclinic 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 typical composition^[2] 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

1. ^ H F W Taylor, Cement Chemistry, Academic Press, 1990, ISBN 0-12-683900-X, p 35
2. ^ P. C. Hewlett (Ed)Lea's Chemistry of Cement and Concrete: 4th Ed, Arnold, 1998, ISBN 0-340-56589-6, p715