A Raman Spectroscopic Study of the Structural Modifications Associated with the Addition of Calcium Oxide and Boron Oxide to Silica

Abstract

Raman spectroscopy as an instrumental technique for the determination of silicate structure is widely accepted. This method was utilized for analysis of structural modifications associated with the addition of network modifying species. Silicate melts are described by the extent of oxygen bridging. Therefore, understanding the effect different oxides have on modifying the silicate structure will provide valuable information regarding the removal of boron from silicon in slag refining processes. Samples in the range CaO/SiO₂ = 0.56 to 1.2 were evaluated with and without varying concentrations of B₂O₃. As expected, increasing the CaO content resulted in an increase in the Q ⁰ and Q ¹ species and a decrease in the Q ³ species indicating a depolymerization of the silicate network. The addition of B₂O₃ to the 36 wt pct CaO-64 wt pct SiO₂ system resulted in a decrease in ring-typed structures associated with the vibrational mode near 600 cm⁻¹, an increase in the Q ³ species and a decrease in the Q ² species. Adding B₂O₃ to the 54.5 wt pct CaO-45.5 wt pct SiO₂ system resulted in decrease in the Q ⁰ and Q ² species and an increase in the Q ³ species. Thus, both systems indicate the introduction of B₂O₃ to the more polymerized structural units in the silicate network. The increase in the peak near 630 cm⁻¹ signifies some formation of ring-type metaborate groups or ring-type danburite groups. A correlation between the experimentally determined Q ⁿ distribution and optical basicity is proposed. Viscosity and optical basicity are correlated for the CaO-SiO₂ system as well as viscosity and $Q_{\rm{exp}}^n$.