Thermodynamics of Phosphorus in the MnO-SiO_2-Fe_tO System

摘要

Phosphorus, one of typical impurities in steel, has been traditionally tried to be removed to the refining slag in the conventional steel making process. On the other hand, the inverse-utilization of impurities in steel was introduced recently to provide a resource circulating society. In these processes, phosphorus can be and must be restored in the steel during the deoxidation and solidification. The usage of elements with high deoxidizing and low dephosphorizing abilities such as manganese and silicon will be beneficial for obtaining such kind of steel. However, the thermodynamic behavior of phosphorus in such oxide fluxes has not been established. Therefore, the phosphate capacity as the phosphorus containing ability for the MnO-SiO_2-Fe_tO system, one of the typical slags for deoxidation, has been investigated by measuring the phosphorus partition between the slag and solid or molten iron. The phosphate capacities for the present system were determined to be from 8.5 X 10~(14) to 3.8 X 10~(18) at temperatures from 1673 to 1923K. The present system has shown a much smaller phosphate capacity by several orders of magnitude compared to the conventional CaO bearing systems and provides the estimation of a very low phosphorus distribution ratio between the slag and the steel. In addition, the heats of the phosphate formation reaction were derived from the temperature dependence of phosphate capacities.