Structural investigation of calcium borosilicate glasses with varying Si/Ca ratios by infrared and Raman spectroscopy

Abstract

Calcium borosilicate glasses with varying Si/Ca ratios (with constant Si/B value) have been successfully prepared using a normal melt-quench technique. Structural features were investigated through infrared (IR) spectroscopy, Raman spectroscopy and differential thermal analysis (DTA). The IR and Raman spectra showed a Si/Ca ratio-dependent structure of borosilicate, which can provide valuable information to predict the composition and structure relations in the glasses. Conversion of BO₃ to BO₄ units was driven mainly by the disproportionation reaction between BO₃ units and CaO when 0.5 ≤ Si/Ca ≤ 0.7. However, the BO₃ units captured the non-bridging oxygens of Q¹ units when 1.1 ≤ Si/Ca ≤ 1.3, resulting in the formation of more BO₄ and Si–O–Si bonds. Qⁿ (n = 0, 1, 2, 3, 4) notation was used to represent the SiO₄ tetrahedral units, where n is the number of bridging oxygen per SiO₄ unit. The intermediate phase was presented when 0.7 < Si/Ca < 1.1. Variations in density, glass transition temperature and thermal stability as functions of Si/Ca ratios correspond to the change in BO₄, BO₃ and SiO₄ structural units. The intermediate phase results in maximum density, minimum molar volumes and maximum T_g, which can be expected to be the optimum candidate for applications.