Analyze complex phases of slag–tundish plaster reactions by modified XRD ratio of slopes method for some kinetic considerations

Ratio of slopes method (RSM) is employed for quantitative analysis of complex phases formed in continuous casting as reaction products of tundish plaster (composed of high-MgO content) and alloy steel slag contained mainly oxides of SiO2, CaO, MgO, MnO and metallic Fe. XRD results indicated that at 1600 °C, Monticellite (CaMgSiO4), Merwinite (Ca3Mg(SiO4)2) and Tephroite (Mn2SiO4) were developed by reaction of slag with MgO grains of tundish plaster, with low melting points of, respectively, 1498, 1575 and 1345 °C. For quantitative XRD analysis, CaF2 was chosen as standard material and some modifications were used for overlapping of too many peaks and lack of materials of known purity. Results of analysis indicated the range of 41–53% MgO, 13–28% Monticellite, 7–33% Merwinite and 5–13% Tephroite in three different tundish plasters. It was found that the rate of dissolution of MgO because of reaction with slag increases as the original content in plaster is increased.The data of MgO content of the best tundish plaster before and after being used in industrial application is used for some kinetic considerations. The best kinetic equation was found to be:ln mM=−Ht2where m is the not dissolved amount of MgO from an original value of M after passage of time t and H is a constant of the specific system at the isothermal temperature of continuous casting.