Thermodynamic Properties of Solid Solution between Di-Calcium Silicate and Tri-Calcium Phosphate at 1823 and 1873K

摘要

Since phosphorus is commonly considered as a harmful element in steel, it should be removed to meet the demand of high quality steel. In the dephosphorization process of steelmaking, CaO is usually used as a cheap and efficient dephosphorization agent. In order to proceed the dephosphorizationwell, extra CaO is added into slag, and the amount of slag containing solid CaO increases. Under this condition, the concept of multi-phase flux wasconsidered. According to the previous researches, di-calcium silicate and tri-calcium phosphate forms 2CaOSiO_2-3CaO-P_2O_5 solid solution over a wide composition range at the range of steelmaking temperature. In order to apply the multi-phase flux, it is necessary to clarify the thermodynamic properties of 2CaO-SiO_2-3CaO-P_2O_5 solid solution. In current research, activity of P_2O_5 in solid solution was measured by chemical equilibrium method. Molten iron and 2CaO-SiO_2-3CaO-P_2O_5 solid solution pellet was equilibrated in an MgO crucible at 1823 and 1873K. The oxygen partial pressure was controlled to be at 1823K and at 1873K. The sample was quenched by Ar flow and the content of phosphorus in Fe and the composition of solid solution was analyzed by chemical analysis. The activity of P_2O_5 relative to hypothetical pure liquid P_2O_5 was calculated. In the range of experimental composition of solid solution, the activity of P_2O_5 increased with the increase of 3CaO-P_2O_5 content in solid solution both at 1823 and 1873K and for a constant composition of solid solution the activity of P_2O_5 increased with the increase of the temperature.