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The influence of H2O and SiO2 on the structure of silicoborate glasses

2019; Elsevier BV; Volume: 519; Linguagem: Inglês

10.1016/j.jnoncrysol.2019.05.030

1873-4812

Robert Balzer, Harald Behrens, Stephan Schuth, Tina Waurischk, Stefan Reinsch, Ralf Müller, Michael Fechtelkord, Joachim Deubener,

Luminescence Properties of Advanced Materials

To understand the impact of dissolved water on structure and properties, four boron-rich glasses of molar compositions 15-x Na2O x CaO 15 SiO2 70 B2O3 (with x = 0, 7.5, 10) and 10 Na2O 15 SiO2 75 B2O3 were prepared and subsequently hydrated (up to 8 wt% H2O). Density measurements show a non-linear trend upon hydration implying large structural changes in particular at water contents 2 wt%. 11B MAS NMR spectra show that the abundance of BO4 species is mainly controlled by ratio of (Na2O + CaO)/B2O3 while incorporation of water plays a minor role. Compared to borate glasses, the efficiency of formation of BO4 tetrahedra is favored by crosslinking of the network by SiO4-units. The glass transition temperatures, determined by differential thermal analysis, decreases continuously with water content due to breakage of B-O-B bonds by hydrolysis. However, compared to silicates and aluminosilicates, the effect of dissolved water is less pronounced which can be explained by weaker B-O-B bonds in comparison to Si-O-Si bonds.