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Calcium aluminates are a range of materials [2] 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 (formed at atmospheric pressure under an atmosphere of normal humidity) are:
The main constituent, and also the most reactive phase, of calcium aluminate cements is the monocalcium aluminate (CaAl 2 O 4 = CaO · Al 2 O 3, also written as CA in the cement chemist notation). It usually contains other calcium aluminates as well as a number of less reactive phases deriving from impurities in the raw materials.
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Calcium aluminates can form complex salts in combination with different types of anions.Two series of calcium aluminates are known in cement chemistry: AFm and AFt phases, being respectively mono- or tri-substituted with a given divalent anion X (e.g. SO 2− 4, CO 2− 3, or hosting a divalent impurity such as SeO 2− 4 [3]...), or with two units of a monovalent anion, e.g. OH −, Cl − ...
AFm form inter alia when tricalcium aluminate 3CaO·Al 2 O 3, or C 3 A in CCN, reacts with dissolved calcium sulfate (CaSO 4), or calcium carbonate (CaCO 3). As the sulfate form is the dominant one in AFm phases in the hardened cement paste (HCP) in concrete, AFm is often simply referred to as Aluminate Ferrite monosulfate or calcium aluminate ...
Dodecacalcium hepta-aluminate (12CaO·7Al 2 O 3, Ca 12 Al 14 O 33 or C 12 A 7) 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 cement. Its composition and properties have been the subject of much debate ...
Calcium silicate hydrate: C-A-H: Phase more complex than C-S-H: Calcium aluminate hydrate C-A-S-H: This is even more complex than C-S-H and C-A-H: Calcium aluminate silicate hydrate AFt: C 6 A S 3 H 32, sometimes with substitution of Fe for Al, and/or CO 2− 3 for SO 2− 4: Calcium trisulfoaluminate hydrate, or ettringite: AFm
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 .