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Current Topics in Electrochemistry   Volumes    Volume 5 
Electrical behaviour of different inorganic and organo-inorganic films (uranyl phosphate and uranyl phenylphosphonate films) in electrolyte media by ac and dc measurements: a review
J. Benavente, J. R. Ramos Barrado, A. Cabeza, S. Bruque, M. Martinez
Pages: 119 - 129
Number of pages: 11
Current Topics in Electrochemistry
Volume 5 

Copyright © 1997 Research Trends. All rights reserved

A comparative study of the electrical response of thin films based on differnt uranyl compounds when they are separating solutions of the generating electrolytes is carried out by means of direct and alternating current measurements. The uranyl compounds were: uranyl phosphate (HUP), ammonium uranyl phosphate (NUP), calcium uranyl phosphate (CaUP), all three sell-supported films, and the porous supported uranyl phenylphosphonate (UPP). Self-supported or porous, supported films of the different precipitates were studied by d.c. and a.c. measurements. The rectifier behaviour of the different film/generating electrolyte systems was obtained from direct current measurements, and a minimum level of precipitate ions in the solutions should exist (Cmin≈10-4 M) in order to obtain electrical rectification with the different electrolyte/film systems. These results also permit us to identify the transport mechanisms of the ions across the different thin films. Electrochemical impedance spectroscopy (EIS) permit us to determine the equivalent circuit associated to each system. Concentration dependence for the different circuit elements is also studied (10-4≤c(M)≤10-2). Although HUP, NUP and CaUP films have a similar framework, small chemical and structural modifications provoke important changes in their electrical behaviour. For uranyl phosphate films, a comparison between the electrical resistances of dry and wet samples is made and good concordance between both kinds of results was found. For the uranyl phenylphosphonate film, salt diffusion, concentration potential and electrical resistance for the thin film and the porous support were measured, which permits us to estimate some transport parameters (salt and ionic permeabilities) across the organo-inorganic precipitate. Cationic and anionic permeabilities slightly decrease when the concentration increases but the following sequence of permeabilities was obtained: P(H3O+)<P(NO3-)<P(HO3PC6H5-) <P(UO22+).
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