Structural model for amorphous aluminosilicates

Abstract

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 ≤ x ≤ 1 and 0 ≤ y ≤ 1. The model is based on a simple set of reactions and contains a single adjustable parameter p (0 ≤ p ≤ 1). The latter is found from 27Al solid-state nuclear magnetic resonance (NMR) experiments in the regime where R = x/y ≥ 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 ≥ 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.

Mg and Al mixed effects on thermal properties in aluminosilicate glasses

“…In addition, many investigations have been reported on the local coordination environments of the Mg and Al atoms in aluminosilicate glasses and how it is impacted by composition and other processing conditions, both by experiments and atomistic simulations. 6,[8][9][10] The formation of the oxygen triclusters ( [3] O) in peraluminous glasses is generally accepted. Despite its great importance, the verification of [3] O clusters in aluminosilicate glasses has been limited spectroscopically.…”