Reducing Dephosphorization of SiMn Alloy by Molten CaO-CaF2 Flux and Thermodynamic Stability of Ca3P2 under Atmospheric Cooling Conditions

摘要

This study consists of experimental measurement of the phosphide capacity of the CaO-CaF2 flux in equilibrium with SiMn alloy at 1823 K, and includes the thermodynamic analysis of the stability of reducing refining slags under wet atmospheric cooling conditions. The phosphide capacity increased with increasing CaO concentration in the flux, followed by a constant value. The composition for the saturating capacity is in good accordance to the saturation content of CaO in the CaO-CaF2 flux at 1823 K. When the Vee ratio (=CaO/SiO2) of the reducing dephosphorization slag is greater than about 1.35, CaO (lime) and Ca2SiO4 (dicalcium silicate) phases appeared during cooling cycle based on the CaO-SiO2-CaF2 phase diagram, resulting in an increase of the evolution rate of PH3 gas due to an increase in the reaction area. However, when the Vee ratio of the slag is lower than about 1.35, CaF2, Ca4Si2F2O7 (cuspidine), and CaSiO3 (wollastonite) phases appeared from the phase diagram, resulting in negligible amount of PH3 evolution during cooling because the reaction between Ca3P2 and H2O was restricted to the surface of bulk slag.