ISSN:
1432-2021
Keywords:
Key words Loewenstein’s rule
;
Al/Al avoidance
;
Al/Si ordering
;
Bragg-Williams
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Abstract The main driving force behind Al/Si ordering in tetrahedral framework aluminosilicates is nearest-neighbour Al/Al avoidance. Computer simulation is used to explore the direct consequences of such Al/Al avoidance. The main result is that the order-disorder transition temperature T c falls dramatically as the concentration x of Al in the structure is reduced, and if the only interactions are those associated with nearest-neighbour Al/Al avoidance, T c becomes zero for x less than some critical value x c , where x c =0.31 for the feldspar framework and x c =0.34 for cordierite. Also a large degree of short range order is found above T c . Both results differ radically from the standard Bragg-Williams model. Plots of entropy and enthalpy of ordering are given as functions of x and T, which may be used to interpret experimental data or for extrapolation into ranges of x and T inaccessible to experiment.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002690050136
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