The split network analysis for exploring composition–structure correlations in multi-component glasses: II. Multinuclear NMR studies of alumino-borosilicates and glass-wool fibers

The preceding part [M. Edén, J. Non.-Cryst. Solids, 357, (2011) 1595–1602] introduced the “split network” strategy for estimating the network polymerization degree ( r _A) and mean number of bridging oxygen (BO) atoms ( N ¯ BO A ) for a network former A, given that these parameters are known for all other network builders in the multi-component oxide glass. However, as the detailed ordering of BO and non-bridging oxygen (NBO) species is often difficult to assess experimentally, we summarize some “rules of thumb” for predicting the coordination number and tendency to accept NBO ions for Al ³⁺, B ³⁺, Si ⁴⁺ and P ⁵⁺ cations: they are helpful in scenarios devoid of experimental data. Using the parameters r and N ¯ BO , we present expressions for the BO/NBO distributions among tetrahedrally coordinated cations, as predicted from the binary and random models. Multinuclear ¹¹B, ²⁷Al and ²⁹Si solid-state NMR is exploited to derive the split network representations of a set of Na–Ca–(Al)–(B)–Si–O glasses. These results are subsequently used to gain structural insight into two commercial glass-wool fibers that constitute alumino-borosilicate networks modified by Na ⁺, K ⁺, Ca ²⁺ and Mg ²⁺ ions.