DIFFUSION OF H THROUGH PD MEMBRANES EFFECTS OF NON-IDEALITY ON DH AND ED

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H diffusion constants, D{sub H}, have been obtained from steady-state fluxes across Pd membranes with the downstream side maintained at p{sub H2} {approx} 0. Good linearity of plots of H flux versus (1/d), where d is the thickness, attests to the H permeation being bulk diffusion controlled in this temperature (423 to 523K) and p{sub H2} range ({le} 0.2 MPa). D{sub H} values have been determined at constant p{sub up} and also at constant (H/Pd)=r conditions. H fluxes through Pd membranes with three different surface treatments have been investigated (polished (un-oxidized), oxidized, and palladized) in order to determine the effects ... continued below

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Shanahan, K March 9, 2007.

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H diffusion constants, D{sub H}, have been obtained from steady-state fluxes across Pd membranes with the downstream side maintained at p{sub H2} {approx} 0. Good linearity of plots of H flux versus (1/d), where d is the thickness, attests to the H permeation being bulk diffusion controlled in this temperature (423 to 523K) and p{sub H2} range ({le} 0.2 MPa). D{sub H} values have been determined at constant p{sub up} and also at constant (H/Pd)=r conditions. H fluxes through Pd membranes with three different surface treatments have been investigated (polished (un-oxidized), oxidized, and palladized) in order to determine the effects of these pretreatments. The palladized and oxidized membranes give similar D{sub H} values but the polished membranes give values about 12% lower. For diffusion in a concentration gradient D{sub H}*(c{sub H}/RT)(d{mu}{sub H}/dx) is the more proper description, where c{sub H} is the H concentration, rather than D{sub H}(dc{sub H}/dx) where D{sub H} and D{sub H}* are the concentration-dependent and independent diffusion constants. D{sub H}* can be obtained from D{sub H} using the thermodynamic factor, D{sub H}(r) = D{sub H}*({partial_derivative}lnp{sub H2}{sup 1/2}/{partial_derivative}lnr){sub T} = D{sub H}*f(r). In the commonly employed situation where there is a large difference in concentrations between the upstream and downstream sides of a membrane, the thermodynamic factor varies with distance through the membrane and this should be allowed for in obtaining D{sub H}*. Procedures are given and utilized for using D{sub H}(c{sub H}) to determine D{sub H}* values when there is a large concentration gradient through the membrane. Activation energies for diffusion, E{sub D}(c{sub H}), have been determined. E{sub D} is found to increase with c{sub H} which can be attributed to the thermodynamic factor. D{sub H}* values have been found to increase with H content.

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  • Journal Name: J. of Alloys and Compounds or J. of Membrane Science

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  • Report No.: WSRC-STI-2007-00125
  • Grant Number: DE-AC09-96SR18500
  • Office of Scientific & Technical Information Report Number: 901095
  • Archival Resource Key: ark:/67531/metadc887900

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  • March 9, 2007

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  • Sept. 22, 2016, 2:13 a.m.

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  • Dec. 12, 2016, 3:39 p.m.

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Shanahan, K. DIFFUSION OF H THROUGH PD MEMBRANES EFFECTS OF NON-IDEALITY ON DH AND ED, article, March 9, 2007; [Aiken, South Carolina]. (digital.library.unt.edu/ark:/67531/metadc887900/: accessed October 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.