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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
in which the following abbreviations for calcium and aluminium oxides are defined as: ** C = CaO ** A = Al2O3
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
A phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions (pressure, temperature, volume, etc.) at which thermodynamically distinct phases (such as solid, liquid or gaseous ...
(formed at atmospheric pressure under an atmosphere of normal humidity) are:
* Tricalcium aluminate, 3CaO·Al2O3 (C3A)
* Dodecacalcium hepta-aluminate
Dodecacalcium hepta-aluminate (12CaO·7Al2O3, Ca12Al14O33 or ) is an inorganic solid that occurs rarely in nature as the mineral mayenite. It is an important phase in calcium aluminate cements and is an intermediate in the manufacture of Portland ...
, 12CaO·7Al2O3 (C12A7) (once known as mayenite)
* Monocalcium aluminate, CaO·Al2O3 (CA) (occurring in nature as krotite and dmitryivanovite - two polymorphs)
* Monocalcium dialuminate, CaO·2Al2O3 (CA2) (occurring in nature as grossite )
* Monocalcium hexa-aluminate, CaO·6Al2O3 (CA6) (occurring in nature as hibonite, a representative of magnetoplumbite group)
In addition, other phases include:
* Dicalcium aluminate, 2CaO·Al2O3 (C2A), which exists only at pressures above 2500 MPa. The crystal is orthorhombic
In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...
, 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.
* Pentacalcium trialuminate, 5CaO·3Al2O3 (C5A3), forms only under an anhydrous
A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...
and oxygen free atmosphere. The crystal is orthorhombic, with a density of 3067 kg·m−3. It reacts rapidly with water.
* Tetracalcium trialuminate, 4CaO·3Al2O3 (C4A3), is a metastable phase formed by dehydrating
In physiology, dehydration is a lack of total body water, with an accompanying disruption of Metabolism, metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental tempe ...
4CaO·3Al2O3·3H2O (C4A3H3).
See also
* Cement * Cement chemist notation (CCN)in which the following abbreviations for calcium and aluminium oxides are defined as: ** C = CaO ** A = Al2O3
References
{{DEFAULTSORT:Calcium Aluminates Aluminates Calcium compounds Cement Ceramic materials Refractory materials