Precise measurement of the activity/composition relations of H2O-N2 and H2O-CO2 fluids at 500°C, 500 bars

Lawrence M. Anovitz; James G. Blencoe; David B. Joyce; Juske Horita

doi:10.1016/S0016-7037(98)00027-1

Precise measurement of the activity/composition relations of H₂O-N₂ and H₂O-CO₂ fluids at 500°C, 500 bars

Lawrence M. Anovitz, James G. Blencoe, David B. Joyce, Juske Horita

Geochemistry & Interfacial Science

Research output: Contribution to journal › Article › peer-review

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Abstract

The activity/composition relations of H₂O-N₂ and H₂O-CO₂ fluids have been measured at 500°C, 500 bars. The results are more accurate, and much more precise, than any currently available, especially for H₂O-poor compositions. Samples were reacted at fixed water activities (0.062 ≤ a_H2o ≤ 0.777), using Cu₃N as the source of N₂, and Ag-oxalate as the source of CO₂. After each experiment the masses of water and gas in the samples were analyzed manometrically. Results depend on the value used for the hydrogen fugacity for pure H₂O in equilibrium with the oxide buffer, but using a newly measured value for Ni-NiO and fitting the data to a two-parameter Margules equation yields: for H₂O-N₂ fluids: W_G,H2o = 3455.0 J/mol, W_G,H2o = 3455.0 J/mol, W_G,N2 = 1990.l J/mol; and for H₂O-CO₂ fluids: W_G,H2o = 3882.5 J/mol, W_G,co2 = 4902.6 J/mol. As uncertainties are not orthogonal, standard errors cannot be given. The data suggest that H₂O-CO₂ fluids exhibit large positive deviations from ideality at 500°C, 500 bars, in marked contrast to values predicted by available equations of state. These results indicate that more accurate models for both H₂O-N₂ and H₂O-CO₂ fluids are needed.

Original language	English
Pages (from-to)	815-829
Number of pages	15
Journal	Geochimica et Cosmochimica Acta
Volume	62
Issue number	5
DOIs	https://doi.org/10.1016/S0016-7037(98)00027-1
State	Published - Mar 1998

Funding

This research was sponsored by the Division of Engineering and Geosciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-96OR22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corporation, and by National Science Foundation Grant number NSF EAR 9590695. Leon Maya and Carlos Bamberger provided valuable advice concerning the use of nitrides as sources of nitrogen in hydrothermal experiments. The alundum and steel mesh used in our Shaw membranes were supplied free-of-charge by Saint-Gobian/Norton Industrial Ceramics Corp. (Norton Materials) and Buckbee-Mears Corp., respectively. Reviews by I-Ming Chou, Dave Wesolowski, and an anonymous reviewer were helpful and greatly appreciated.

Funders	Funder number
Division of Engineering and Geosciences
Lockheed Martin Energy Research Corporation
National Science Foundation	EAR 9590695
U.S. Department of Energy	DE-AC05-96OR22464
Basic Energy Sciences
Oak Ridge National Laboratory

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10.1016/S0016-7037(98)00027-1

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@article{822edb1ffffe4ece9bfe4adde216479b,

title = "Precise measurement of the activity/composition relations of H2O-N2 and H2O-CO2 fluids at 500°C, 500 bars",

abstract = "The activity/composition relations of H2O-N2 and H2O-CO2 fluids have been measured at 500°C, 500 bars. The results are more accurate, and much more precise, than any currently available, especially for H2O-poor compositions. Samples were reacted at fixed water activities (0.062 ≤ aH2o ≤ 0.777), using Cu3N as the source of N2, and Ag-oxalate as the source of CO2. After each experiment the masses of water and gas in the samples were analyzed manometrically. Results depend on the value used for the hydrogen fugacity for pure H2O in equilibrium with the oxide buffer, but using a newly measured value for Ni-NiO and fitting the data to a two-parameter Margules equation yields: for H2O-N2 fluids: WG,H2o = 3455.0 J/mol, WG,H2o = 3455.0 J/mol, WG,N2 = 1990.l J/mol; and for H2O-CO2 fluids: WG,H2o = 3882.5 J/mol, WG,co2 = 4902.6 J/mol. As uncertainties are not orthogonal, standard errors cannot be given. The data suggest that H2O-CO2 fluids exhibit large positive deviations from ideality at 500°C, 500 bars, in marked contrast to values predicted by available equations of state. These results indicate that more accurate models for both H2O-N2 and H2O-CO2 fluids are needed.",

author = "Anovitz, {Lawrence M.} and Blencoe, {James G.} and Joyce, {David B.} and Juske Horita",

year = "1998",

month = mar,

doi = "10.1016/S0016-7037(98)00027-1",

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T1 - Precise measurement of the activity/composition relations of H2O-N2 and H2O-CO2 fluids at 500°C, 500 bars

AU - Anovitz, Lawrence M.

AU - Blencoe, James G.

AU - Joyce, David B.

AU - Horita, Juske

PY - 1998/3

Y1 - 1998/3

N2 - The activity/composition relations of H2O-N2 and H2O-CO2 fluids have been measured at 500°C, 500 bars. The results are more accurate, and much more precise, than any currently available, especially for H2O-poor compositions. Samples were reacted at fixed water activities (0.062 ≤ aH2o ≤ 0.777), using Cu3N as the source of N2, and Ag-oxalate as the source of CO2. After each experiment the masses of water and gas in the samples were analyzed manometrically. Results depend on the value used for the hydrogen fugacity for pure H2O in equilibrium with the oxide buffer, but using a newly measured value for Ni-NiO and fitting the data to a two-parameter Margules equation yields: for H2O-N2 fluids: WG,H2o = 3455.0 J/mol, WG,H2o = 3455.0 J/mol, WG,N2 = 1990.l J/mol; and for H2O-CO2 fluids: WG,H2o = 3882.5 J/mol, WG,co2 = 4902.6 J/mol. As uncertainties are not orthogonal, standard errors cannot be given. The data suggest that H2O-CO2 fluids exhibit large positive deviations from ideality at 500°C, 500 bars, in marked contrast to values predicted by available equations of state. These results indicate that more accurate models for both H2O-N2 and H2O-CO2 fluids are needed.

AB - The activity/composition relations of H2O-N2 and H2O-CO2 fluids have been measured at 500°C, 500 bars. The results are more accurate, and much more precise, than any currently available, especially for H2O-poor compositions. Samples were reacted at fixed water activities (0.062 ≤ aH2o ≤ 0.777), using Cu3N as the source of N2, and Ag-oxalate as the source of CO2. After each experiment the masses of water and gas in the samples were analyzed manometrically. Results depend on the value used for the hydrogen fugacity for pure H2O in equilibrium with the oxide buffer, but using a newly measured value for Ni-NiO and fitting the data to a two-parameter Margules equation yields: for H2O-N2 fluids: WG,H2o = 3455.0 J/mol, WG,H2o = 3455.0 J/mol, WG,N2 = 1990.l J/mol; and for H2O-CO2 fluids: WG,H2o = 3882.5 J/mol, WG,co2 = 4902.6 J/mol. As uncertainties are not orthogonal, standard errors cannot be given. The data suggest that H2O-CO2 fluids exhibit large positive deviations from ideality at 500°C, 500 bars, in marked contrast to values predicted by available equations of state. These results indicate that more accurate models for both H2O-N2 and H2O-CO2 fluids are needed.

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Precise measurement of the activity/composition relations of H₂O-N₂ and H₂O-CO₂ fluids at 500°C, 500 bars

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