Fused aluminum oxide abrasive grain containing reduced titanium oxide

Claim 1

A process for producing a fused abrasive grain which is bluish black in color and consists essentially of: (1) titanium oxide containing from about 0.42 to about 0.84% titanium, by weight of the abrasive grain, said titanium being present as a reduced titanium oxide having an average oxidation state lower than in Ti 2 O 3 ; (2) from about 0.05 to about 0.3% by weight carbon; (3) from about 0.02 to about 0.1% by weight Na 2 O; (4) from 0 to about 0.1% by weight total of calcium and silicon oxides; and (5) alumina; said abrasive having a gain on ignition in air before roasting at 1300° C, when of a size of about 147 microns and finer, of from about 0.4 to about 0.7% by weight; comprising the steps of: (a) charging to an electric furnace a mixture of: (i) from about 0.7 to about 1.7 parts by weight high purity TiO 2 ; (ii) from about 98.6 to about 99.3 parts by weight alumina containing Na 2 O as the only oxide impurity present in an amount in excess of 0.1% by weight; and (iii) carbon, in an amount of from 1 to 10 times the theoretical amount necessary, based on the amount of TiO 2 and Na 2 O added, to reduce the TiO 2 and Na 2 O according to the following formulas: (A) 2TiO.sub.2 + C = Ti.sub.2 O.sub.3 + CO, and (B) Na.sub.2 O + C = 2Na + CO and (b) subjecting the mixture of titania, alumina and carbon to the heat of an electric arc, said electric arc being a reducing arc passed from carbon electrodes to the mixture of titania, alumina and carbon, for a time sufficient to melt the mixture; (c) solidifying the melted mixture; (d) crushing the solidified mixture to obtain abrasive grain; and (e) roasting the abrasive grain by subjecting the crushed grain to an oxidizing atmosphere for from about 5 minutes to about 64 hours at a temperature of from about 1250° to about 1450° C.