HR: 0830h
AN: V41C-0310    [PDF]
TI: Cl-35 and F-19 MAS NMR Studies on Silicate and Aluminosilicate Glasses Containing Multiple Volatile Species.
AU: * Sandland, T O
EM: sandland@pangea.stanford.edu
AF: Stanford University, GES Department Building 320, Stanford, CA 94305-2115 United States
AU: Kiczenski, T J
EM: tj@pangea.stanford.edu
AF: Stanford University, GES Department Building 320, Stanford, CA 94305-2115 United States
AU: Du, L
EM: lsdu@pangea.stanford.edu
AF: Stanford University, GES Department Building 320, Stanford, CA 94305-2115 United States
AU: Stebbins, J F
EM: stebbins@pangea.stanford.edu
AF: Stanford University, GES Department Building 320, Stanford, CA 94305-2115 United States
AB: Cl-35 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra have been collected at 14.1 and 18.8 T fields to determine the atomic scale structural environments of Cl in Ca- and Na-silicate and aluminosilicate glasses. Data, in addition to that previously presented, suggest that in mixed modifier (Ca-Na) silicate glasses, a large portion of Cl is in a mixed coordination environment (coordinated by both Ca and Na). Relative peak positions, however, suggest a slight preference for Cl to coordinate Na over Ca. Calculated quadrupolar coupling constants (C$_{Q}$) increase as Ca/(Ca+Na) increases, indicating that the Cl site is on average more asymmetric at higher Ca/(Ca+Na) ratios. In a series of sodium aluminosilicate glasses containing both water and Cl, data previously presented show a shift to higher frequency NMR signal with increasing water content while C$_{Q}$ remains constant. This change in observed frequency suggests Cl is not directly associated with H$_{2}$O in the samples and rather that the shift reflects a slight change in the average Cl coordination environment. Current work on a similar series of calcium aluminosilicate glasses promises to further elucidate the interaction of Cl and water in these glasses. While the addition of water has a significant effect on the environment of Cl in the glasses studied, the effect of F on the coordination environment of Cl in these glasses is much less pronounced. Previous work on F-containing mixed modifier silicate glasses has shown that F demonstrates a preference to coordinate higher field strength modifier cations. Preliminary $^{35}$Cl MAS NMR data suggest that the addition of F appears to slightly order the Cl environment, as evidenced by a slight narrowing of the peak. Conversely, in $^{19}$F data collected at 9.4 T, there is little to no noticeable effect on the environment of F with the addition of Cl in the compositions studied. The current $^{19}$F data do show a larger preference for Ca over Na coordination than previously reported.
DE: 1099 General or miscellaneous
DE: 3699 General or miscellaneous
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
DE: 8439 Physics and chemistry of magma bodies
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting