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Percolation Treatment of Charge Transfer in Humidified Smectite Clays
Author(s) -
Hunt Allen G.,
Logsdon Sally D.,
Laird David A.
Publication year - 2006
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2005.0044
Subject(s) - clay minerals , percolation threshold , soil water , analytical chemistry (journal) , chemistry , conductivity , spectral line , relative humidity , water content , percolation (cognitive psychology) , mineralogy , electrical resistivity and conductivity , materials science , soil science , thermodynamics , geology , environmental chemistry , physics , geotechnical engineering , astronomy , neuroscience , biology , electrical engineering , engineering
Bulk electrical conductivity of soil is generally assumed to be dominated by the electrical conductivity of the soil solution, with perhaps a small contribution from surface charges associated with soil solids. Soils high in smectites often exhibit high electrical conductivity due to water associated with the clays. These charges are either associated with the exchangeable cations or with proton migration in the clay‐associated water. The purpose of this study was to use percolation principles to elucidate mechanisms of charge transfer in humidified smectites. The theory predictions were compared with electrical conductivity spectra measured for mono‐ionic humidified smectites. The measured spectra were consistent with a percolation model of proton hopping in the maximum interlayer spacing beyond a threshold water content, plus an offset term for some samples. The threshold water content for percolation in the maximum interlayer spacing was 0.07 m 3 m −3 , which was assumed the same for all basal spacings. The spectra should converge at the phonon frequency ( v ph ), but for some samples at the higher humidity levels, the spectra were offset. The samples with this offset were determined by examining the spectra for the same mono‐ionic smectite at different humidity levels. The mean offset level was 0.015 m 3 m −3 and was likely related to charge transfer on external surfaces. The phonon frequency fitted across all samples was 3.54 × 10 8 Hz, lower than the 10 12 Hz often assumed. These results are generally consistent with the idea that water associated with smectite clays generated the observed electrical conductivity.