Structural model for amorphous aluminosilicates

An analytical model is developed for the composition-dependent structure of the amorphous aluminosilicate materials (M2O)(x)(Al2O3)(y)(SiO2)(1-x-y) and (MO)(x)(Al2O3)(y)(SiO2)(1-x-y), where 0 & LE; x & LE; 1 and 0 & LE; y & LE; 1. The model is based on a simple set of reactions and contains a single adjustable parameter p (0 & LE; p & LE; 1). The latter is found from Al-27 solid-state nuclear magnetic resonance (NMR) experiments in the regime where R = x/y & GE; 1, aided by new experiments on the magnesium and zinc aluminosilicate systems. The parameter p decreases linearly as the cation field strength of M+ or M2+ increases, as per the observation previously made for the degree of aluminum avoidance [Lee et al., J. Phys. Chem. C 120, 737 (2016)]. The results indicate that as the cation field strength increases, there are less fourfold coordinated aluminum atoms to contribute toward the glass network, and Al-O-Al bonds become more prevalent in a progressive breakdown of Loewenstein's aluminum avoidance rule. The model gives a good account of the composition-dependent fraction of non-bridging oxygen (NBO) atoms for R & GE; 1, as assessed from the results obtained from solid-state NMR experiments. An extension of the model to (M2O3)x(Al2O3)(y)(SiO2)(1-x-y) glasses leads, however, to an excess of NBO atoms, the proportion of which can be reduced by invoking network-forming fivefold coordinated Al atoms and/or oxygen triclusters. The model provides a benchmark for predicting the structure-related properties of aluminosilicate materials and a starting point for predicting the evolution in the structure of these materials under the extreme conditions encountered in the Earth's interior or in processes such as sharp-contact loading.& nbsp;(c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).