THERMODYNAMICS OF THE OXIDATION OF PHOSPHORUS, CARBON AND OTHER ELEMENTS IN MOLTEN IRON BATH DURING STEELMAKING

The sequence of oxidation of phosphorus, carbon and other elements in molten iron bath during steelmaking were analyzed thermodynamically by means of three methods of calculation, namely: (1) calculation of the dissociation pressure P_(o_2) of oxides; (2) calculation of the O] content in iron bath in equilibrium with the respective elements; and (3) calculation of the free energy change of the reaction of oxidation. All calculations were made with free use of activity data. The previous works of and for calculation of P_(o_2), and that of for calculation of O] content in iron bath in equilibrium with phosphorus and carbon were reviewed, and their impropriety and errors in calculation were discussed. It has been shown that: (1) Dephosphorization is a reaction occurring between boundary layers of liquid phases, and takes place only in the presence of a molten slag of proper composition; (2) By quick formation of a highly calcareous and ferruginous slag, it is possible in the Thomas blow, preferably at comparatively low temperatures, to eliminate phosphorus simultaneously with carbon; and (3) Increase in the partial pressure of CO would depress the oxidation of carbon and facilitate the preferential oxidation of phosphorus.