Physics
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997gecoa..61.3089z&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 61, Issue 15, pp.3089-3100
Physics
17
Scientific paper
This paper presents a new calibration for infrared analyses of dissolved water and its species concentrations in rhyolitic glasses. The new calibration combines infrared/manometry measurements and infrared study of hydrous rhyolitic glasses heated at different temperatures. The heating experiments show that the ratio of the molar absorptivity of the 5230 cm -1 band to that of the 4520 cm -1 band varies with water concentration. Therefore, earlier calibrations assuming constant molar absorptivities are not accurate. Using our new calibration, total water concentration, and species concentrations can be calculated as follows: , where C 1 , C 2 , and C are the mass fractions of molecular H 2 O, H 2 O present as OH, and total H 2 O, / 0 is the ratio of the density of the hydrous glass to that of the anhydrous glass and is approximately and are the absorbances (peak heights) of the 5230 cm -1 and 4520 cm -1 bands per mm sample thickness and relative to a baseline that was fit by a flexicurve, a 0 = 0.04217 mm, b 0 = 0.04024 mm, b 1 = -0.02011 mm 2 , and b 2 = 0.0522 mm 2 . The new calibration has a high internal reproducibility in calculating H 2 O total , six times better than the calibration of Newman et al. (1986). We expect the new calibration to be accurate in retrieving H 2 O total for H 2 O total 5.5 wt% and in retrieving molecular H 2 O and OH concentrations for H 2 O total 2.7 wt%. Using the new calibration, the equilibrium coefficient K for the reaction H 2 O + O = 2OH is independent of H 2 O total (for H 2 O total 2.4 wt%) at a given temperature and can be expressed as ln K = 1.876 - 3110/ T , where T is in K. The bulk water diffusivity reported before is not affected by the new calibration, but the molecular H 2 O diffusivity will be roughly 4-30% greater.
Belcher R.
Ihinger P. D.
Newman Sally
Wang Liping
Xu Zhengjiu
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