Effect of chlorine on the viscosities and structures of blast furnace slags

Abstract

The viscosity of CaO–SiO2–Al2O3–MgO–CaCl2 slags (C/S = 1.12) were investigated to elucidate the effects of chlorine ranging from 0.02 to 0.53 mass% on the blast furnace slags at high temperatures. Moreover, the Raman spectra of the quenched slags and the X-ray diffraction patterns of the slags cooled in air after viscosity measurement were thoroughly analysed to interpret the transformation of the structures of the slags with increasing the content of chlorine. The viscosity was found to decrease slightly with the increase of chlorine at a given temperature higher than 1673 K, and the critical temperature (TCR) decreased from about 1660 to 1590 K simultaneously which was possibly deriving from the precipitation of Ca2Al2SiO7, Ca3Al2(SiO4)3–xCl4x and SiO2 in higher chlorine content. The degree of polymerisation for silicon–oxygen tetrahedra was found to decrease estimating from the decrease of the average amount of bridging oxygen calculated from the deconvolution results of the Raman spectra of the quenched slags, which provided the explanation for the decrease in viscosity. And that the apparent activation energy of the slags was commonly reduced by chlorine increasing demonstrated the decrease in the degree of polymerisation of molten slags simultaneously.