CORUNDUM
Corundum is a natural oxide of alumina having a formula A12O3

In hardness it is next only to diamond and is valued mostly for its abrasive property. It is also refractory, the malting point being 2010o C and hence it is used in a sintered form in the manufacture of special refectory crucibles, rods other materials. Ruby and Sapphire are the gem varieties of corundum. These are used as pilot supports in delicate scientific instrument and as jewel bearings in watches.

There is no BIS specification for corundum to be used in any industry.

The user industries prescribe the specification as under: -

Abrasives:

For abrasive purposes, the corundum should have a bright and glassy lusture; the broken grains should be angular and sharp and should have no cleavage or parting planes. Corundum of fine and flour grades is used as loose grains for polishing metals, rooks and gems and for grinding and beveling glass. For lens grinding and polishing corundum grains of rigid size and quality are required. Corundum grains are used in the manufacture of grinding wheels, corundum cloth and paper.

Spark Plugs:

Small quantities are used for this purpose, finely ground corundum passing through 200 mash having alumina content not below 90% is used.

Cement Tiles:

Low-grade corundum is used for making ceramic tiles and concrete slabs. Corundum used for this purpose should pass through 120 mesh with Fe content preferably below 2% while presence of feldspar is not objectionable. For cement tiles, a coarse grade of corundum between 20 40 mesh is used.

Foundry:

For this industry alumina is limited to 70%. Future trends these days artificially prepared abrasive like fused alumina (synthetic corundum) and these products are sold under the trade names as abundum, aloxite, borolum, lionite and oxaluma.

The reserves have been classified in to semi-precious industries and abrasive grades as the basis of identification made and reported by the exploration and exploitation agencies, in the inventories as on 01.01.1980 and as on 01.01.1985, where no information is available about the grade, the same is classified under "Unclassified category".

The following grades for classification of reserves of corundum are recommended.

Reserves:

1.

Industrial

Al2O3               -           70% min.

Physical bright, glassy, lustre & devoid of cleavage and inclusions.

2.

Semi-precious

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