Thermodynamic properties of the MgO-BO1.5, CaO-BO1.5, SiO2-BO1.5, MgO-BO,1.5-SiO2 and CaO-BO1.5-SiO2 slag systems at 1873 K

Abstract

Ferroboron alloys have been used in the production of various materials from conventional steels to metallic glasses. Recently, the demand for these alloys has been increasing. Commercial ferroboron processes strongly depend on the use of pure B2O3 or H3BO3 as starting materials in reduction processes. However, the use of pure B 203 instead of natural B minerals leads to the loss of B through evaporation and a decrease in process efficiency. In order to overcome this loss, this study evaluated raw materials other than pure B 203 from a thermodynamic point of view. Thermodynamic properties of the components in the binary MgO-BO1.5, CaO-BO 1.5, and Si02-BO1.5 systems, as well as in the ternary MgO-BO1.5-Si02 and CaO-BO1.5-Si0 2 systems, were investigated at 1 873 K by means of chemical equilibration, with Cu alloy as a reference melt. During experiments, considerable amounts of B and Si were dissolved in Cu. Prior to the analysis of the thermodynamic properties of the slags, such as activities and activity coefficients of BO1.5, those of the Cu-B and Cu-B-Si melts were clarified at 1 873 K. The investigated oxide melts were compared with each other for their possible use as raw materials in the production of ferroboron. Among the binary systems investigated, MgO-BO1.5 slags were found to be the most suitable candidates for the production of carbothermic ferroboron. Finally, it was found that in both ternary systems, the activities and activity coefficients of BO1.5 decrease significantly with the addition of SiO2. It was found that the effect of SiO2 in the MgO-BO1.5-SiO2 system was more pronounced than that in the CaO-BO1.5-SiO2 system. According to the results, the addition of SiO2 to binary slags is likely to cause a decrease in the smelting efficiency of ferroboron. © 2009 ISIJ.