Effect of B2O3 on Structure of Glassy F-Free CaO-SiO2-B2O3 Systems by 29Si MAS NMR and Raman Spectroscopy

Abstract

Raman and 29Si magic-angle spinning nuclear magnetic resonance spectroscopy have been employed to analyze the structure of CaO-SiO2-B2O3-based F-free glassy mold fluxes. B3+ was in the form of [BO3] and [BO4]. The content of both [BO3] and [BO4] increased with increasing concentration of B2O3. The [BO4] tetrahedral structural unit could connect with the [SiO4] tetrahedral to enhance the complexity of the silicate network. The degree of polymerization increased with increasing B2O3 content. When CaF2 was replaced by the same concentration of B2O3, the main structural units of both systems were Q1 and Q2, while the percentage of Q3 in B2O3-containing glass was much higher than that in CaF2-containing glass. The structural network of the B2O3-containing system was more complex than that of the CaF2-containing mold flux. This may be one of the most important factors leading to the difference in physicochemical properties between B2O3- and CaF2-containing slags.