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Persistent URL http://purl.org/net/epubs/work/54194
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Record Id 54194
Title The use of neutron diffraction in studies of planetary ice-rock analogue mixtures
Abstract We have carried out rheological experiments on planetary ice-rock analogue mixtures in the ENGIN-X beamline at the pulsed neutron source ISIS in Oxfordshire, UK. Neutron diffraction has previously been used to study the deformation of geologically relevant polyphase materials [e.g. 1], as it allows the strain in each phase to be determined, and hence (via the elastic constants) the stress partitioning between each phase to be calculated, whereas traditional deformation tests only allow bulk properties of the whole sample to be obtained. We demonstrate for the first time the application of neutron diffraction to the deformation of icy planetary materials at conditions relevant to large icy bodies such as Europa, Ganymede and Titan. Experiments were conducted on samples with fluorite fraction 0.09 and 0.27, at strain rates of 5 x 10-7 - 5 x 10-6, temperatures of 233 and 253K, and confining pressures of 50MPa. This pressure is equivalent to depths of 30-40 km in the largest icy satellites, therefore allowing us to explore the P,T conditions throughout the thickness of Europa's icy crust [2], and much of Titan's outermost ice shell [3], however, strain rates are necessarily faster than planetary rates to allow for results on laboratory timescales. In order to obtain these conditions, we adapted a previously used pressure vessel design [4] to allow study of cylindrical polycrystalline D2O ice + fluorite samples of diameter 25mm, length 65mm. This vessel was designed to fit within the beamline cryogenic chamber [5]. Our preliminary results suggest that the ice phase may be experiencing localised melting during higher temperature runs, possibly due to stress increases around the fluorite grains. We suggest that this is due to the irregular ('pointy') shape of our rock grains, and would not be seen if our grains were spherical. This would have important ramifications for planetary ice analogue experiments, as using spherical rock particles [e.g. 6] may not well represent the actual situation in icy bodies, and it may, therefore, be important that interactions between the ice and rock grains are accounted for when considering these polyphase mixtures. We will present these results, along with further analysis of the strain partitioning between the ice and fluorite phases.
Organisation ISIS , ISIS-ENGIN-X , STFC
Keywords SSTD 2009-2010 , planetary ice-rock , neutron diffraction , engineering
Funding Information
Related Research Object(s): 10.5286/ISIS.E.24079177
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Language English (EN)
Type Details URI(s) Local file(s) Year
Paper In Conference Proceedings In International Mineralogical Association, 20th General Meeting, Budapest, Hungary, 21-27 Aug 2010, (2010). 2010