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Author Mortlock, R. F. ♦ Bell, A. T. ♦ Radke, C. J.
Sponsorship USDOE
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword CHEMISTRY ♦ GALLIUM COMPOUNDS ♦ NUCLEAR MAGNETIC RESONANCE ♦ SILICATES ♦ QUATERNARY COMPOUNDS ♦ EQUILIBRIUM
Abstract {sup 29}Si and {sup 71}Ga NMR spectroscopies are used to characterize the distribution of species present in highly alkaline solutions of alkylammonium gallosilicate. The solution compositions ranged from 0.1 to 2 mol % SiO{sub 2}, silicate ratios (R=[SiO{sub 2}]/M{sub 2}O); M{sup +}=TPA{sup +} or TMA{sup +} from 0.05 to 2, and Si/Ga molar ratios from 2 to {infinity}. Based on similiar studies of alkylammonium aluminosilicate solutions, tetraprpoylammonium (TPA) gallosilicate solutions being displayed {sup 29}Si NMR peaks assigned to Si atoms in cyclic trimer (S3R), branched cyclic trimer (b-S3R), and double three membered ring (D3R) anions with one incorporated Ga atom. Due to the larger size of GaO{sub 4}{sup 5-} tetrahedra compared to SiO{sub 4}{sup 4-} tetrahedra, gallosilicate anions with rather acute (<90{degrees}) SiO-Ga-OSi bond angles are especially stable. For example, S3R(1Ga) anions are the dominant species in TPA gallosilicate solutions at elevated temperatures. DMSO/water mixtures were used to promote the formation of ring silicate and gallosilicate. In TPA gallosilicate solutions with 50 vol % DMSO, {sup 29}Si NMR resonances are observed only for Si atoms in monomeric, S3R, S3R(1Ga), D3R, D3R(1Ga), and D4R anions. {sup 29}Si NMR studies of the tramethylammonium (TMA) gallosilicate solutions provide evidence for large concentrations of D4R anions but no evidence for any Si-O-Ga bonds. On the other, {sup 71}Ga NMR experiments do provide evidence for gallosiloxane bonds in both TMA and TPA gallosilicate solutions. Trends in the distribution of solution species with SiO{sub 2}, Ga, and base concentration changes are explained with a simple set equilibria between soluble silicate, gallate, and gallosilicate anions. 57 refs., 14 figs.
ISSN 00223654
Educational Use Research
Learning Resource Type Article
Publisher Date 1992-04-02
Publisher Place United States
Journal Journal of Physical Chemistry
Volume Number 96
Issue Number 7


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