Evolution Rates of SiO from CaO-SiO2-Al2O3 Slag Melted in a Graphite Crucible and Dissolution Rates of Carbon in Slag

This study was made on the evolution of SiO from CaO-SiO2-Al2O3 slag melted in a graphite crucible with or without carbon saturated iron. The dissolution of carbon in slag was also investigated.In the absence of metal, the mass loss measured by means of thermo-balance was due to the reaction, (SiO2)+C(s)=SiO(g)+CO(g). And then, in the presence of metal, the mass loss was due to both the reaction shown above and the transfer of silicon to metal, (SiO2)+2C=Si+2CO(g).The relation between the amount of SiO evolved and the reaction time was linear. The evolution rate of SiO was dependent on the viscosity of slag at the low concentrations of silica and on aSiO2 at the high concentrations, respectively. The apparent activation energies were varied from 298 to 543 kJ/mol corresponding to the slag compositions. The effect of stirring on the evolution rate of SiO was negligible at the small value of aSiO2, but it was significant at the large value of aSiO2.Under the above experimental conditions, SiO evolution was generally controlled by the breaking of Si-O bonds in slag, but, in the range of small aSiO2 value, the transport of silica also affected the rate.The dissolution of carbon in silicate slag proceeded slowly and its rate was varied from 2×10−5 to 5×10−5 mol·m−2·s−1 at 1873 K. It was supposed that silicate slag dissolved carbon as both CaC2 and SiC.