Calcium aluminate

Chemical formula: 3CaO x Al2O3 (C3A), 12CaO x 7Al2O3 (C12A7), 5CaO x 3Al2O3 (C5A3), CaO x Al2O3 (CA), CaO x 2Al2O3 (CA2), CaO x 6Al2O3 (CA6)
Modifications: Six intermediate phases have been reported to exist in the binary system CaO-Al2O3.
Melting point: C3A: 1535, C12A7: 1455, CA: 1605, CA2: 1750, CA6: 1850oC
Density: C3A: 3.04, C12A7: 2.83, CA: 2.98, CA2: 2.91, CA6: 3.38 g/cm3
Microhardnes: CA: 930, CA2: 1100, CA6: 2200 kp/mm2
Hardness (Moh's): No data
Crystal system: C3A: cubic, C12A7: cubic, CA: unknown, CA2: monoclinic, CA6: hexagonal
Cell dimensions: No data
PDF number: Different
ICSD number: Defferent
Note: Oxide inclusions with calcium aluminates in steel ingots usually have a spherical shape. The inclusions have been spherical droplets in the steel bath, which then soldidify. If they are free of MgO and contain small amounts of MnO and SiOe it is probable that orginate from the deoxidation process However, when MgO can be detected in an inclusion, this indicates that it has originated from other ssources. Deoxidation alloys are generally free of magnesium, whereas many refractories have a high MgO content, and several furnace and ladle slag also contain magnesia. Calcium aluminate inclusions, which are free of SiO2 are comparatively hard. They often keep their spherical shape even after a deformation of the steel matrix. If the steel is more heavily deformed especially at higher temperatures, they split into strings od aluminates and other non-silica phases present , e.g. spinels. These strings are orientated in the deformation directions. The calcium aluminates do not crystallize readily under the condition found in steel practice and therefore CaO and Al2O3 in inclusions are often found as components of the glassy inclusion matrix. The most common calcium aluminate in steel inclusions seems to be phase CaO x 2Al2O3 (Kiessling and Lange, 1964).

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