Structural Roles of Boron and Silicon in the CaO-SiO₂-B₂O₃ Glasses Using FTIR, Raman, and NMR Spectroscopy

The present paper provided not only a deep insight of network structures of borosilicate glasses but also a basic linkage between the network structures and the viscous flow behaviors of many borosilicate melts. The structures of a ternary system of CaO-SiO₂-B₂O₃ were characterized using Fourier transformation infrared (FTIR), Raman, and magic angular spinning nuclear magnetic resonance spectroscopy. The results of FTIR and Raman spectra complementally verified that the main Si-related units were SiO₄ tetrahedral with zero, one, two, and three bridging oxygens [Q⁰(Si), Q¹(Si), Q²(Si), and Q³(Si)]; the added B₂O₃ leaded to an increase of Q³(Si) at the cost of Q⁰(Si) and Q²(Si), and therefore an increasing degree of polymerization (DOP) was induced. Additionally, the ¹¹B NMR spectra demonstrated that the dominant B-related groups were BO₃ trigonal and BO₄ tetrahedral, while an increasing B₂O₃ content facilitated the existence of BO₄ tetrahedral. Moreover, there was a competitive effect between the enhanced DOP and the presence of BO₃ trigonal and BO₄ tetrahedral in the networks, which therefore resulted in a decreasing viscosity of borosilicate melts in numerous studies.