Role of a silicate phase in the reduction of iron and chromium and their oxidation with carbide formation during the manufacture of carbon ferrochrome

Abstract

The reactions of reduction of chromium and iron from chromospinelide and the reactions of carbide formation from the reduced metals are separated in space in experiments performed on ore grains with an artificially applied silicate shell. It is found that the silicate layer that isolates spinelide fro direct contact with carbon takes part in the reactions of both reduction and carbide formation. Free carbon extracts oxygen anions from the layer at the contact surface with the formation of CO, and the forming anion vacancies transfer “excess” electrons to the iron and chromium cations in the spinelide lattice and reduce them. Free and carbide-fixed carbon extracts iron and chromium cations from the silicate layer, and carbides form on the surface. The cation vacancies and electron holes (high-charge cations) that form in the silicate phase under these conditions are involved in the oxidation of the metal reduced in spinelide and cause its dissolution in the silicate phase and the precipitation of lower carbides on the surface of the silicate phase. The structure that is characterized of carbon ferrochrome forms on the surface of the silicate phase. Carbide formation is slower than reduction because of higher energy consumed for the formation of high-charge cations and the transfer of cations from the spinelide volume to the outer surface of the silicate phase. In the absence of a silicate layer, a carbide shell blocks the contact of carbon with oxides, which leads to the stop of reduction and, then, carbide formation. In the presence of a silicate (slag) shell around a spinelide grain, the following two concentration galvanic cells operate in parallel: an oxygen (reduction) cell and a metal (oxidation) cell. The parallel operation of the two galvanic cells with a common electrolyte (silicate phase) results in a decrease in the electric potentials between spinelide inside the silicate phase and carbon and carbides on its surface, and each of the processes is significantly facilitated and accelerated. In other words, the production of carbon ferrochrome is accelerated.