The influence of water on the structure of hydrous sodium tetrasilicate glasses

Abstract

The structure of sodium tetrasilicate (Na 2 Si 4 O 9 ) glasses containing 0 to 10 wt% water was investigated by a combination of Raman, IR, and NMR methods. Both the 29 Si magic angle spinning NMR data and Raman spectra in the Si-O stretching region clearly show that water depolymerizes the silicate network of the glasses. Q-species distributions calculated from Raman spectra, assuming equal scattering cross sections of all bands in the Si-O stretching region, closely agree with results obtained from NMR data. At low total water contents, the silicate network is depolymerized mainly by breaking of Q 4 -Q 4 bonds, whereas breaking of Q 3 -Q 3 bonds dominates at high water contents. Near IR spectra show the presence of both OH groups and molecular H 2 O in the glasses. The number of nonbridging O atoms per silicon atom, calculated from the near IR data, closely agrees with the results obtained from Raman and NMR, and confirms the assignment of the 4500 cm Ϫ1 band in the near IR to a combination mode of Si-OH groups. Moreover, the intensity of the fundamental Si-OH stretching band at 910 cm Ϫ1 in the Raman spectra varies proportionally to the intensity of the 4500 cm Ϫ1 near IR band. Both IR and Raman spectra show three main bands in the OH-stretching region, centered at 3580, 3000, and 2350 cm Ϫ1 , due to hydrous species with different hydrogen bond strengths. The relative intensities of these three bands are insensitive to total water content and OH/H 2 O ratio, suggesting that both OH and H 2 O contribute to each of these bands. This is consistent with the fine structure of the H 2 O bending vibration in the IR spectra around 1640 cm Ϫ1 and with the polarization dependence of the OH-stretching bands in the Raman spectra. Near IR spectra of hydrous sodium tetrasilicate glasses and hydrous aluminosilicate glasses are very similar and show a similar dependence of band intensity on total water content, suggesting that there is no fundamental difference in the dissolution mechanism of water in these systems.

Quantification of water content and speciation in natural silicic glasses (phonolite, dacite, rhyolite) by confocal microRaman spectrometry

“…This band is present in both infrared (e.g., Stolper, 1982) and Raman spectra (e.g., Mysen et al, 1997) and results from the overlap of the O-H stretching vibrations from hydroxyl groups (OH) and water molecules (H 2 O m ). Further low-intensity bands at 910 cm −1 (possibly due to stretching of (Si,Al)-OH) and 1620-1630 cm −1 (bending of molecular H 2 O m ) occur in the low-frequency region of spectra (Zotov and Keppler, 1998) (Fig. 2 and Fig.…”

“…Its area or height are not correlated with total dissolved water. Irrespective of the detailed interpretation of all spectral component of the TOT1 band, a general agreement exists on the correlation of the intensity of TOT1 high-frequency side with the degree of depolymerization of the glass network (see Mysen, 1988 andKeppler, 1998 for detailed discussion). More specifically, the 580 cm −1 band can be attributed to a mixed stretch-bend vibration in Si 2 O 5 2− structural units (Furukawa et al, 1981).…”

“…Laser Raman spectroscopy has been extensively used for structural studies of hydrous natural and synthetic silicate glasses (e.g., Mysen et al, 1980, McMillan and Remmele, 1986, Mysen and Virgo, 1986b, Mysen, 1990, Zotov and Keppler, 1998and Zotov, 2003 and for chemical and physical characterization of fluid inclusions (e.g., Dubessy et al, 1989, Chou et al, 1990, Wopenka et al, 1990, Pasteris et al, 1996and Chen et al, 2004. Recently, new Raman analytical routines have been proposed for the quantitative analysis of total water content (H 2 O T ) and speciation (H 2 O m molecular/hydroxyl OH) in natural and synthetic aluminosilicate glasses (Thomas, 2000, Thomas, 2002, Chabiron et al, 2004and Arias et al, 2006.…”

Melting phase relations in the systems Mg2SiO4–H2O and MgSiO3–H2O and the formation of hydrous melts in the upper mantle

“…Silver and Stolper 1985;Medard and Grove, 2008;Hirschmann et al, 2009;Myhill et al, 2016 (Burnham 1975(Burnham , 1979(Burnham , 1994Stolper, 1982;Silver and Stolper, 1989;Zotov and Keppler, 1998), i.e.…”

“…Stolper, 1982, Dixon andStolper, 1995), and their properties are temperature-dependent (Nowak and Behrens, 1995;Zotov and Keppler, 1998 …”