Structure of mineral glasses--II. The SiO 2 ---NaAlSiO 4 join

Details Structure of mineral glasses--II. The SiO 2 ---NaAlSiO 4 join Structure of mineral glasses--II. The SiO 2 ---NaAlSiO 4 join

Sep 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979gecoa..43.1467t&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 43, Issue 9, pp.1467-1473

Computer Science

17

Scientific paper

The distribution of short range interatomic distances in NaAlSi 2 O 6 and NaAlSiO 4 glass has been determined by X-ray radial distribution analysis. The resulting radial distribution functions (RDF's) are interpreted by comparison with RDF's calculated for the Jadeite (NaAlSi 2 O 6 ) and nepheline (NaAlSiO 4 ) crystal structures and with previously determined RDF's for SiO 2 and NaAlSi 3 O 8 glass. The RDF of NaAlSi 2 O 6 glass is considerably different from that calculated for the Jadeite structure and suggests that the NaAlSi 2 O 6 melt at one atmosphere pressure has a stuffed tridymite-like structure with Al in tetrahedral coordination rather than a pyroxene-like structure with Al in octahedral coordination. The RDF of NaAlSiO 4 glass is also consistent with a stuffed tridymite-like structure similar to that of crystalline nepheline. Replacement of SiO 2 by NaAlO 2 across the SiO 2 -NaAlSiO 4 join causes 1. (1) a progressive expansion of the stuffed tridymite structure, 2. (2) an increase in the first T-O distance due to substitution of Al for Si in the tetrahedral sites, 3. (3) a decrease in the inferred Si, Al---O---Si, Al angle and 4. (4) a loss of detail in the RDF suggesting a progressive loss of structural regularity. The stuffed tridymite model is consistent with the observed densities of glasses along the SiO 2 ---NaAlSiO 4 join and offers a molecular interpretation of the high viscosity of melts in the Na 2 O---Al 2 O 3 ---SiO 2 system at Na/Al ratios of 1.0.

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