:Calcium aluminates

{{Short description|Chemical compound}}

Image:CaAluminatesPhaseDiagram.JPG

File:Calcium heptaaluminate str.png, 12CaO·7Al₂O₃ ({{chem2|C12A7}}).{{Cite journal | doi = 10.1088/1468-6996/16/3/033503| pmid = 27877784| title = Exploration of new superconductors and functional materials, and fabrication of superconducting tapes and wires of iron pnictides| journal = Science and Technology of Advanced Materials| volume = 16| issue = 3| pages = 033503| year = 2015| last1 = Hosono | first1 = H. | last2 = Tanabe | first2 = K. | last3 = Takayama-Muromachi | first3 = E. | last4 = Kageyama | first4 = H. | last5 = Yamanaka | first5 = S. | last6 = Kumakura | first6 = H. | last7 = Nohara | first7 = M. | last8 = Hiramatsu | first8 = H. | last9 = Fujitsu | first9 = S. |pmc=5099821|bibcode = 2015STAdM..16c3503H |arxiv = 1505.02240}}]]

Calcium aluminates are a range of materialsTaylor H.F.W (1990) Cement Chemistry, Academic Press, {{ISBN|0-12-683900-X}}, pp. 34–38. 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:

• Tricalcium aluminate, 3CaO·Al₂O₃ ({{chem2|C3A}})
• Dodecacalcium hepta-aluminate, 12CaO·7Al₂O₃ ({{chem2|C12A7}}) (once known as mayenite{{Cite web|url=https://www.mindat.org/min-43612.html|title = Mayenite Supergroup}})
• Monocalcium aluminate, CaO·Al₂O₃ (CA) (occurring in nature as krotite and dmitryivanovite – two polymorphs{{Cite web|url=https://www.mindat.org/min-40468.html|title = Krotite}})
• Monocalcium dialuminate, CaO·2Al₂O₃ ({{chem2|CA2}}) (occurring in nature as grossite {{Cite web|url=https://www.mindat.org/min-1754.html|title=Grossite}})
• Monocalcium hexa-aluminate, CaO·6Al₂O₃ ({{chem2|CA6}}) (occurring in nature as hibonite, a representative of magnetoplumbite group{{Cite web|url=https://www.mindat.org/min-1897.html|title=Hibonite}})

In addition, other phases include:

• Dicalcium aluminate, 2CaO·Al₂O₃ ({{chem2|C2A}}), which exists only at pressures above 2500 MPa.Taylor H.F.W (1990) Cement Chemistry, Academic Press, {{ISBN|0-12-683900-X}}, pp. 28, 29. 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.{{Cite web|url=https://www.mindat.org/min-790.html|title = Brownmillerite}}
• Pentacalcium trialuminate, 5CaO·3Al₂O₃ ({{chem2|C5A3}}), 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.
• Tetracalcium trialuminate, 4CaO·3Al₂O₃ ({{chem2|C4A3}}), is a metastable phase formed by dehydrating 4CaO·3Al₂O₃·3H₂O ({{chem2|C4A3H3}}).