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Persistent URL http://purl.org/net/epubs/work/12189139
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Record Id 12189139
Title Molecular hydrogen diffusion in the interlayer pores of Laponite by quasi-elastic neutron scattering
Abstract The swelling clay minerals, such as smectites and vermiculites, have negatively charged interlayer surfaces which form two-dimensional pores of a height that is on a scale comparable to a hydrogen molecule. We have investigated the molecular diffusion dynamics of hydrogen molecules absorbed into sub-mono-layer hydrated synthetic laponiteTM, which acts as a representative example of the smectite class of swelling clays. Data obtained from adsorption isotherms and quasi-elastic neutron scattering (QENS) experiments show that H2 intercalates into the interlayers of Ca-exchanged LaponiteTM (Ca-laponite). Jump diffusion analysis of QENS spectra obtained on the IRIS spectrometer at the ISIS pulsed neutron source has provided an estimate for the interlayer diffusion coefficient (DCa-laponite) of H2 in Ca-laponite expanded with 3 wt% D2O at a range of temperatures from 40 to 100 K. We find that DCa-laponite = 8.73 x 10-5 cm2/s at 100 K, which is an order of magnitude slower than in bulk liquid at the same temperature (Dbulk = 8.13 x 10-4 cm2/s). Using the activation energy for diffusion obtained at lower temperature yields a value at 400 K of DCa-laponite = 2.11 x 10-4 cm2/s. Our results therefore demonstrate that QENS can be used to understand whether hydrated swelling clays will act as a barrier to molecular diffusion of hydrogen over repository timescales.
Organisation ISIS , ISIS-IRIS , STFC
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Language English (EN)
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Paper In Conference Proceedings Clays in natural and engineered barriers for radioactive waste confinement -- 5 International meeting (2012): 923. http://inis.iaea.…eRecord&RN=44060525# 2012