The reduction of stable oxides in carbon arc furnaces

Stable oxides, such as those of chromium, vanadium and titanium cannot be reduced to the metal by carbon and the production of these metals, which have melting points above 2000 K, would lead to a refractory solid containing carbon. The co-reduction of the oxides with iron oxide leads to the formation of lower melting products, the ferro-alloys, and this process is successfully used in industrial production. Since these metals form such stable oxides and carbides, the process based on carbon reduction in a blast furnace would appear to be unsatisfactory, unless a product saturated with carbon is acceptable. This could not be decarburized by oxygen blowing without significant re-oxidation of the refractory metal. 

Since the ferro-alloys are liquid over a wide range of composition at 1900 K, the temperature of operation of these processes is no higher than that used in electric arc steel scrap-melting furnaces, for which the technology is well established up to 100 megawatt power input. 

By the correct choice of the metal oxide/carbon ratio in the ingoing burden for the furnace, the alloy which is produced can have a controlled content of carbon, which does not lead to the separation of solid carbides during the reduction reaction. The combination of the carbon electrode, the gaseous oxides and the foamed slag probably causes the formation of a plasma region between the electrode and the slag, and this is responsible for the reduction of electrical and audible noise which is found in this operation, in comparison with the arc melting of scrap iron which is extremely noisy, and which injects unwanted electrical noise into the local electrical distribution network. 

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