Thermochemistry and structure of glasses along the join NaAlSi 3 O 8 -NaBSi 3 O 8

Details Thermochemistry and structure of glasses along the join NaAlSi 3 O 8 -NaBSi 3 O 8 Thermochemistry and structure of glasses along the join NaAlSi 3 O 8 -NaBSi 3 O 8

Oct 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988gecoa..52.2405g&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 52, Issue 10, pp.2405-2414

Computer Science

3

Scientific paper

Glasses along the join NaAlSi 3 O 8 -NaBSi 3 O 8 and the end-member crystalline phases albite and reedmergnerite were investigated using 11 B, 23 Na, 27 Al and 29 Si MAS NMR spectroscopy and oxide-melt solution calorimetry. The glasses have substantial positive enthalpies of mixing described by the equation , where X is the mole fraction Rd component. 11 B MAS NMR spectra show that boron occurs in both trigonal and tetrahedral coordination in the glasses, with the percentage of B in trigonal coordination decreasing from about 60% at Rd 20 Ab 80 to about 29% at Rd 100 . Thus, the glasses are structurally more complex than the end-member crystals which are tetrahedral framework minerals. The NMR data suggest that all or most of the Si, Al and tetrahedral B occur in Q 4 (framework) sites. They are also consistent with the ideas that most of the tetrahedral B does not extensively copolymerize with trigonal boron, that at least some of the non-bridging oxygens formed by the presence of trigonal boron are located on SiO 4 tetrahedra, and that Si and trigonal B do not occur as next-nearest neighbors. Both the NMR and the H mix results indicate the presence of clustering. Such clustering might involve separation into framework regions and regions dominated by trigonal boron and/or into B-rich and Al-rich framework regions.

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