日本金属学会誌

J. Japan Inst. Metals, Vol. 63, No. 9 (1999),
pp. 1181-1190

Removal of Oxygen and Nitrogen from Iron and Cobaltby Hydrogen-Argon Plasma Arc Melting

Kouji Mimura, Koichi Saito and Minoru Isshiki

Institute for Advanced Materials Processing, Tohoku University, Sendai, 980-8577

Abstract:

Removal of oxygen and nitrogen of pure liquid iron and cobalt has been examined by Ar and (0.5% to20%)H2+Ar plasma arc melting under atmospheric pressure. While the removal rates of oxygen and nitrogen were very low when the plasma gas was noly Ar, they rose remarkable with addition of a small amount of hydrogen such as 0.5 to 1%H2 and increased with hydrogen content of the plasma gas. The oxygen and nitrogen concentrations finally decreased to the very low levels as follows; \underline{O}<2 and \underline{N}<1 mass ppm for iron and \underline{O}<5 and \underline{N}<1 mass ppm for cobalt. This excellent refining effect is supposed to be caused by activated hydrogen atoms dissociated in the high temperature plasma arc and to be expressed as the following reactions; \underline{O}+2H=H2O for deoxidation and \underline{N}+3H=NH3 for nitrogen removal.

The deoxidation of iron proceeded through two steps by the fast 1st step at the beginning of melting and, thereafter, the slow 2nd step. Both steps were of a first order rate low and the deoxidation rate of 1st step was found to increase in proportion to the about 1/2th power of the hydrogen content in the plasma generating gas. So, it is considered that, for the 1st step of deoxidation, the chemical reaction on the surface of the liquid iron is the rate determining step.


(Received February 26, 1999; In Final Form June 15, 1999)

Keywords:

iron, cobalt, deoxidation, nitrogen removal, decarburization, plasma arc melting, hydrogen plasma, purification


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