Phase equilibria in the H2O-CO2 system between 250-330 K and 0-1.7 GPa: Stability of the CO2 hydrates and H2O-ice VI at CO2 saturation

Research areas:
Year:
2013
Authors:
Journal:
GEOCHIMICA ET COSMOCHIMICA ACTA
Volume:
119
Pages:
322-339
Month:
OCT 15
ISSN:
0016-7037
Abstract:
Although carbon dioxide is of interest in planetary science, few studies
have been devoted so far to the H2O-CO2 system at pressures and
temperatures relevant to planetary interiors, especially of the icy
moons of the giant planets. In this study, new sapphire and diamond
anvil cell experiments were conducted in this binary system to constrain
the stability of the CO2 hydrates and H2O-ice VI at CO2 saturation in
the 250-330 K and 0-1.7 GPa temperature and pressure ranges. Phases and
equilibria were characterized by in situ Raman spectroscopy and optical
monitoring. The equilibrium between the CO2 sI clathrate hydrate and the
H2O-rich liquid phase was constrained over the entire pressure range of
stability of the hydrate, up to 0.7-0.8 GPa, with results in agreement
with previous studies at lower pressures. Above this pressure and below
1 GPa, our experiments confirmed the existence of the new CO2
high-pressure hydrate reported recently. Finally, the melting curve of
the H2O-ice VI at CO2 saturation in the absence of CO2 hydrates was
determined between 0.8 and 1.7 GPa. Using an available chemical
potential model for H2O, a first assessment of the solubility of CO2
along the H2O-ice VI melting curve is given. Consistent with these new
results and previous studies of the H2O-CO2 system, a P-T-X description
of the binary system is proposed. The evolution with pressure of the
Raman signatures of the two CO2 hydrates is detailed, and their
stability is discussed in light of other clathrate hydrate-forming
systems. (C) 2013 Elsevier Ltd. All rights reserved.