Corundum



Chemical formula: Al2O3
Modifications: Alpha-Al2O3, beta-Al2O3, gamma-Al2O3
Melting point: 2050oC
Density: 3.96 g/cm3
Microhardnes: 3000-4500 kp/mm2
Hardness (Moh's): 9
Luminescence: Corundum often shows a red fluorescence in the EPMA.
Colour in air, bright field reflection: Grey
Colour, polarized reflection: No data
Shape: Rosste-shaped, not deformable
Crystal system: Trigonal
Cell dimensions: a=5.028 A, b=5.208 A, c=13.73 A
PDF number: 00-001-1296
ICSD number: 031545
Note: Only alpha-Al2O3 was observed in steel inclusions. Corundum is a comon phase which may arise from both steelmaking additions and contamination of the liquid steel by refractory particles. A common source of indogenous corundum inclusions is aluminium used for deoxidation. Many ceramic materials, such as chamotte firebricks, contain a large amount of Al2O3 and are possible sources of exogenous inclusions.



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