Selective oxidation of elements in metal melt and their multireaction equilibria

Oxidation of elements in metal melt falls into two categories, as shown from the modified Ellingham‐Richardson diagram. For the first category, at which the Δ G–T lines of two reactions intersect, a concept of transition temperature has been introduced. With control of this transition temperature, blowing operation of the metal melt could be so conducted that a certain element is selectively oxidized while the other remains intact in the melt, so that separation of these elements could be accomplished. Practical application of this transition temperature is discussed with respect to Ni vs. S, Cr, V, Nb, Mn or P vs. C. For the second category with Δ G–T lines nearly parallel side by side, thermodynamic analysis has shown that selective oxidation of a certain element can also occur, but as oxidation continues, its free energy change becomes equal to that of another element, so that simultaneous oxidation of both elements takes place. This is followed by simultaneous oxidation of other elements, until the final equilibrium composition of the metal melt is attained. Examples of selective oxidation followed by simultaneous oxidation are set forth in respect to deoxidation of liquid iron with Al and Si, and the oxidizing blowing of Nb‐bearing hot metal. Computer calculation of the equilibrium composition of the melt with respect to the referred elements has been made. Lastly, the role in the oxidation played by Fe, the main ingredient of the melt, is briefly discussed.