Water-enhanced dynamic recrystallization and solution transfer in experimentally deformed carnallite |
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| Authors: | Janos L Urai |
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| Institution: | Department of Geological Sciences, State University of New York, Albany, NY 12222, U.S.A. |
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| Abstract: | Cylindrical samples of polycrystalline carnallite (KMgCl3, 6H2O) were deformed in a triaxial apparatus at 60°C, at confining pressures between 0.1 and 31 MPa and at strain rates between 10?4 and 10?8 s?1. In a number of cases, small amounts of saturated carnallite brine were added. Samples without added brine deform by intracrystalline slip, mechanical twinning, cracking, and by frictional sliding on crack surfaces. Stress-strain curves of these samples are strongly dependent on confining pressure. Addition of brine has a dramatic effect on both microstructural development and mechanical properties. Grain-boundary migration is strongly enhanced. At lower strain rates, additional intracrystalline effects start to appear, together with the onset of solution transfer. Rapid compaction in samples deformed with added brine causes high fluid pressures to develop. At higher strain rates addition of brine results in a decrease of the flow stress by a factor of two. This weakening will increase even further at strain rates below about 10?9 s?1, when solution transfer becomes rate controlling. It is argued that deformation of carnallite in nature is adequately described by the flow law found for samples deformed with added brine. |
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