Glass aluminium coordination

Solid-state Al NMR studies have been carried out of the aluminium coordination environments in TaAl tellurite glasses containing from 60 to 95 cation-% Xe02. These data show the presence of 4-, 5- and 6-coordinate aluminium in all glasses. ... 

In these glasses (Table 5.6) the coordination state of aluminium depends on its chemical environment and can only be entirely fourfold when the Ca/Al... 

Not much needs to be said on these glasses, except that one, G-235 (Table 5.8) has been subjected to solid state NMR (Ellison Warrens, 1987). It would appear that aluminium is mainly in tetrahedral coordination with some octahedral and pentahedral coordination and that the structural units are mainly Q (lAl) and Q (2A1). 

The latter interpretation of data is more in accord with the recent Al and Si NMR findings of Ellison Warrens (1987), who found that the structure of an appreciable fraction of the glass changed under acid attack with some loss of aluminium including all in fivefold coordination (see Section 5.9.2). Thus, acid attack was not entirely confined to the surface layer of a glass particle. If this is so then silicic acid as well as ions must migrate from the body of the particle and it is reasonable to suppose that silicic acid deposits as siliceous gel at the particle-matrix interface. 

Solid-state NMR spectroscopy was used for studying the formation of cubic mesoporous aluminophosphate thin films and powders. The analysis of the initial gel, the as-deposited materials and the thermally-treated materials elucidated the changes in the coordination of phosphorus and aluminium atoms and thus revealed how the framework formation and condensation proceeds. The consolidation process in thin films was different than the process in powders. Most probably this could be attributed to the effect of glass substrate. 

The coordination numbers of the aluminium and magnesium, and the distributions of atoms and bonding patterns within the glass, e.g. variation in the number of Si-O-Al linkages compared with those of Si-O-Si and A1 0 AI. 

A Al MAS NMR study of a series of lanthanum aluminium phosphate glasses has shown the presence of Al in 4-fold, 5-foId and 6-fold coordination. The average Al coordination number increases with increasing Al/La ratio and decreases with increasing 0/P ratio, as can be understood in terms of the tendency of the structure to avoid forming Al-O-Al bonds (Karabulut et al. 2001). 

Glass formation and local structure in the related system P-Se-Al has also been studied by P and Al NMR which indicates that the local environments of both the P and Al are dominated by the selenium (Hudalla et al. 1998). Although there is evidence of interaction between the Al and P (the formation of four-coordinated P is facilitated by the presence of Al), a more quantitative assessment by Alp P) spin echo double resonance indicates that direct Al-Se-P links occur with less than statistical probability. These results suggest a glass structure which is partially segregated into phosphorus selenide and aluminium selenide-rich regions (Hudalla et al. 1998). 

Samples of impactite glass, known as Libyan Desert Glass (LDG), were analyzed by NMR MAS in order to study the coordination of silicon and aluminium. ... 

J.E. Stebbins, S. Kroeker, S.K. Lee, T.J. Kiczenski, Quantification of five- and six-coordinated aluminium ions in aluminosilicate and fluoride-containing glasses by high-field, high-resolution Al-27 NMR, J. Non-Cryst. Solids 275 (2000) 1-6. 

---