X-ray powder diffraction study of the stability of clathrate hydrates in the presence of salts with relevance to the Martian cryosphere

Safi, Emmal; Thompson, Stephen P.; Evans, Aneurin; Day, Sarah J.; Murray, Claire A.; Baker, Annabelle R.; Oliveira, Joana M.; Van Loon, Jacco Th.

Abstract

Water on the present day Martian surface is thought to exist in two thermally distinct sub-surface reservoirs: as ice in the cryosphere and as groundwater located deeper in the crust. These sub-surface environments are thought to contain saline, rather than pure, water and laboratory studies on whether or not clathrate hydrates can form in such environments are lacking. We fill this gap by performing synchrotron radiation X-ray powder diffraction to investigate the formation and evolution of clathrate hydrates in weak chloride solutions at CO2 pressures, and over temperature ranges, that are similar to those found in the Martian regolith. We have found that clathrate hydrates can form under conditions relevant to the Martian cryosphere, despite the presence of chloride salts. We find that the dissociation temperatures for CO2 clathrate hydrates formed in saline solutions are depressed by 10–20 K relative to those formed in pure water, depending on the nature of the salt and the CO2 pressure. We suggest that the inhibiting effect that salts such as MgCl2, CaCl2 and NaCl have on clathrate hydrate formation could also be related to the salts’ effect on the formation of the low temperature phase.

Citation

Safi, E., Thompson, S. P., Evans, A., Day, S. J., Murray, C. A., Baker, A. R., …Van Loon, J. T. (2019). X-ray powder diffraction study of the stability of clathrate hydrates in the presence of salts with relevance to the Martian cryosphere. Geochimica et Cosmochimica Acta, 245, 304-315. https://doi.org/10.1016/j.gca.2018.10.034

• Journal Article Type: Article
• Acceptance Date: Oct 31, 2018
• Online Publication Date: Nov 9, 2018
• Publication Date: Jan 15, 2019
• Publicly Available Date: May 26, 2023
• Journal: Geochimica et Cosmochimica Acta
• Print ISSN: 0016-7037
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 245
• Pages: 304-315
• DOI: https://doi.org/10.1016/j.gca.2018.10.034
• Keywords: Freezing brines, Chlorides, CO2 clathrate hydrates, X-ray, powder diffraction, Martian cryosphere, Mars
• Publisher URL: http://doi.org/10.1016/j.gca.2018.10.034