Network structure of multi-component sodium borosilicate glasses by neutron diffraction

Neutron diffraction structure study has been performed on multi-component sodium borosilicate based waste glasses with the composition of (65 - x)SiO2 center dot xB(2)O(3) center dot 25Na(2)O center dot 5BaO center dot 5ZrO(2), x = 5-15 mol%. The maximum momentum transfer of the experimental structure factor was 30 angstrom(-1), which made available to determine the distribution function with high r-space resolution. Reverse Monte Carlo modelling was applied to calculate several partial atomic pair correlation functions, nearest neighbor distances and coordination numbers have been revealed, The characteristic features of Si-O and Si-Si distributions are similar for all glassy samples, suggesting that the Si-O network consisting of tetrahedral SiO4 units is highly stable even in the multi-component glasses. The B-O correlations proved to be fairly complex, two distinct first neighbor distances are present at 1.40 angstrom and 1.60 angstrom, the latter equals the Si-O distance. Coordination number distribution analyzes has revealed 3 and four-coordinated boron atoms. The O-O distribution suggests a network configuration consisting of boron rich and silicon rich regions. Our findings are consistent with a structure model where the boron rich network contains mostly trigonal BO3 units, and the silicon rich network is formed by a mixed continuous network of Si-[4]-O-Si-[4] with several different B-[4]-O-Si-[4] and B-[3]-O-Si-[4] linkages. (c) 2007 Elsevier B.V. All rights reserved.