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Why you can't use water to make cryoporometric measurements of the pore size distributions in meteorites - or in high iron content clays, rocks or concrete.

By J. Beau W. Webber, Philip A. Bland, John H. Strange, Ross A. Anderson and Bahman Tohidi

Abstract

Many porous materials have high susceptibility magnetic gradients in the pores, due to\ud the presence of iron or other magnetic materials. Thus if probe liquids are placed in the\ud pores they exhibit fast decaying signals with a short T2*. Usually the actual T2 of the\ud liquids is also reduced, due the presence of paramagnetic ions in the pore walls. The\ud usual solution in NMR is to measure an echo (or echo train) at short times. However,\ud recent work [J. Phys.: Condens. Matter 19, 415117, 2007.] has shown that water/ice\ud systems near a pore wall form rotator phase plastic ice, with T2 relaxation times in the\ud region of 100 to 200 ms. Thus if a NMR cryoporometric measurement is attempted\ud with a measurement time significantly less than 1 or 2 milli-seconds, the result is to\ud make a measurement based on the phase properties of the brittle to plastic ice phase\ud transition, not that of the brittle ice to water phase transition. This gives rise to\ud artefacts of small pore sizes that may not actually be present. This work successfully\ud uses a-polar liquids instead

Topics: QC807, QB, QC176.8.N35, QC
Year: 2009
OAI identifier: oai:kar.kent.ac.uk:23117

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