TY - JOUR

T1 - Different water solubility mechanisms in hydrous glasses along the Qz-Ab join

T2 - Evidence from NMR spectroscopy

AU - Schmidt, B. C.

AU - Riemer, T.

AU - Kohn, S. C.

AU - Behrens, H.

AU - Dupree, R.

N1 - Funding Information: BCS and TR were supported by a European Community TMR network grant (FMRX-CT96-0064). This research was completed during the stay of BCS as a visiting fellow in the Departments of Earth Sciences at the Universities of Bristol and Cambridge while funded by the TMR network. BCS would like to thank Dr. Ian Farnan for technical support and discussions. Andreas Becker, Frank Schulze and Max Wilke are thanked for their assistance for sample hydrations. SCK thanks NERC for provision of an advanced research fellowship. HB would like to thank DFG for financial support. EPSRC is thanked for supporting NMR work at Warwick University.

PY - 2000/2

Y1 - 2000/2

N2 - The compositional dependence of water incorporation mechanisms in melts and glasses belonging to the quartz (Qz)-albite (Ab) join was studied with nuclear magnetic resonance (NMR) spectroscopy. Dry and hydrous glasses (containing 3.8 ± 0.1 wt% water) ranging in composition from Qz90Ab10 to Qz28Ab72 (in wt%) were synthesised and studied with 1H, 23Na, 27Al and 29Si magic angle spinning (MAS) NMR and 1H-29Si cross polarisation (CP) MAS NMR at magnetic fields of 8.45 and 14.1 T. The results show that both molecular H2O and OH groups are present in the hydrous glasses, represented by a broad and a narrow component in the static 1H NMR spectra. The changes in the 23Na MAS NMR spectra of the hydrated glasses indicate that sodium associates with water in all compositions studied. In contrast to the Ab-rich glasses, the 29Si MAS spectra of Qz-rich glasses (Qz73Ab27-Qz90Ab10) change upon water incorporation, indicating the presence of Si-OH groups at least in the Qz-richest sample. The 27Al MAS data demonstrate that Al is only present in tetrahedral coordination for all glasses studied and that unless δ(iso) for Al Q4(4Si) and Al Q3(3Si)-OH are identical, Al-OH groups cannot be present in significant concentrations. Thus, in hydrous Ab-rich glasses there is probably no significant depolymerisation as suggested by Kohn et al. (1989a). However, more 27Al data for appropriate model compounds or reliable calculations of 27Al shifts and quadrupolar coupling constants are required before this conclusion can be considered to be definitive. For Qz-rich glass compositions a second solubility mechanism involving the formation of Si-OH and depolymerisation of the silicate network is inferred. The data suggest that only in Qz-rich glasses do both mechanisms coexist. Copyright (C) 2000 Elsevier Science Ltd.

AB - The compositional dependence of water incorporation mechanisms in melts and glasses belonging to the quartz (Qz)-albite (Ab) join was studied with nuclear magnetic resonance (NMR) spectroscopy. Dry and hydrous glasses (containing 3.8 ± 0.1 wt% water) ranging in composition from Qz90Ab10 to Qz28Ab72 (in wt%) were synthesised and studied with 1H, 23Na, 27Al and 29Si magic angle spinning (MAS) NMR and 1H-29Si cross polarisation (CP) MAS NMR at magnetic fields of 8.45 and 14.1 T. The results show that both molecular H2O and OH groups are present in the hydrous glasses, represented by a broad and a narrow component in the static 1H NMR spectra. The changes in the 23Na MAS NMR spectra of the hydrated glasses indicate that sodium associates with water in all compositions studied. In contrast to the Ab-rich glasses, the 29Si MAS spectra of Qz-rich glasses (Qz73Ab27-Qz90Ab10) change upon water incorporation, indicating the presence of Si-OH groups at least in the Qz-richest sample. The 27Al MAS data demonstrate that Al is only present in tetrahedral coordination for all glasses studied and that unless δ(iso) for Al Q4(4Si) and Al Q3(3Si)-OH are identical, Al-OH groups cannot be present in significant concentrations. Thus, in hydrous Ab-rich glasses there is probably no significant depolymerisation as suggested by Kohn et al. (1989a). However, more 27Al data for appropriate model compounds or reliable calculations of 27Al shifts and quadrupolar coupling constants are required before this conclusion can be considered to be definitive. For Qz-rich glass compositions a second solubility mechanism involving the formation of Si-OH and depolymerisation of the silicate network is inferred. The data suggest that only in Qz-rich glasses do both mechanisms coexist. Copyright (C) 2000 Elsevier Science Ltd.

UR - http://www.scopus.com/inward/record.url?scp=0034113687&partnerID=8YFLogxK

U2 - 10.1016/S0016-7037(99)00331-2

DO - 10.1016/S0016-7037(99)00331-2

M3 - Article

AN - SCOPUS:0034113687

VL - 64

SP - 513

EP - 526

JO - Geochimica et cosmochimica acta

JF - Geochimica et cosmochimica acta

SN - 0016-7037

IS - 3

ER -