Permeation transients

Bockris and Subramanyan during studies of the permeation of hydrogen through pure Fe and Fe-SNi alloy found that a normal permeation transient was obtained (Fig. 20.21), providing the overpotential was less than a critical value, and when the overpotential was less than it was possible to reproduce the normal permeation curve, i.e. apply the polarising current at a constant rj < t , allow J to attain a steady value, switch off, reapply... 

Figure 26. Rising permeation transient based on a solution to Pick s second law of diffusion.

Fig. 7 Theoretical permeation transients showing the increase in flux, J(L, t) — J[L, 0), as a fraction of the overall increase,...

Fig. 8 Permeation transients for a type 410 stainless steel membrane (thickness of 0.5 mm) in acidified NaCi at 23 °C [90]. The steel was discharged after each...

Fig. 13 Comparison of experimental (solid curve) and theoretical permeation transients for Armco iron [102], Experimental data ...

By assuming hydrogen diffusion through metal is the rate-determining step, hydrogen permeation transients are obtained by Pick s laws in one-dimensional form ... 

T is dimensionless time t is time, s D is the difEision coefficient, cm s and L is thickness of the membrane, cm. The hydrogen difFusivity in the metal membrane is determined by fitting the theoretical solution to the experimental permeation transients. 

Fig. 8.3 Atomic hydrogen permeation transients through a HY-130 steei membrane as a function of time for different appiied cathodic potentiais in a cathoiyte containing 1 M NaS04,0.4 M NaCi, and 1 M H3BO3. The thickness of the membrane =0.15 mm [16]. Reproduced by the permission of The...

Case Study 8.1—Evaluation of the Atomic Hydrogen Permeation Transients Through an AISI 4340 Membrane... 

IPZ analysis of the experimentally measured steady state hydrogen permeation rates through AISI 4340 steel are used to estimate hydrogen kinetic diffusion constants and hydrogen diffusivity within the ahoy. Atomic hydrogen permeation transients through an AISI 4340 membrane for different appHed potentials were studied in an electrolyte... 

In Eq. (8.43), aj and 2 are transfer coefficients for reactions (8.41) and (8.42), is the cathodic current density and a = F/RT. If ai = 2. the hydrogen permeation current is directly proportional to the cathodic current. This expression is consistent with experiment [16] for atomic hydrogen permeation transients through a HY-130 steel membrane as a function of time for different appHed potentials and other experimental data [20-27]. 

Fig. 8.18 Hydrogen permeation transients through an AISI 4340 steel membraneat = 0.6 Vvs. SCE in the absence and presence of underpotential deposited lead. Cp, 2. =2x 10 M, membrane thickness=0.45 mm [3]. Reproduced by the permission of The Electrochemical Society.

Fig. 8.19 Hydrogen permeation transients through type 4340 steel membrane at = — 0.60 V vs. SCE in the presence and absence of bismuth on the substrate (L=0A5 mm) 185]. NACEInternational 1995.

Figure 5. Theoretical permeation transients showing the increase in flux, /(L, /) — /(L, 0), as a fraction of the overall increase, /(L, oo) —/(L, 0), with t. Input boundary conditions assumed for the transients (C) constant concentration, (F) constant flux, and (DF) flux decreasing with time. Data used to obtain DF curves were taken from Ref. 38. (After Ref. 48. Reprinted with permission from Scripta Metall., Copyright 1980, Pergamon Press pic.)...

Figure 14. Permeation transients for a AISI 410 stainless steel membrane (L = 0.5 mm) in acidified NaCl at 23 The steel was discharged after each transient, which is numbered according to its position in the sequence. — Theory - - - Range of uncertainty in fit to experimental data, which are shown as points. (After Ref. 62. Reprinted with permission from Acta MetalLy Copyright 1989, Pergamon Press pic.)...

Figure 17. Comparison of experimental (solid curve) and theoretical permeation transients for Armco iron. (After Ref. 48. Reprinted with permission from Scripta MetalL, Copyright 1980, Pergamon Press pic.) Experimental data (a) Potentiostatic charging in 0.5 M H2SO4. (After Ref. 96. Reprinted by permission of the publisher, The Electrochemical Society, Inc.) (b) Galvanostatic charging at 2mAcm in 0.1 M NaOH. (After Ref. 97. Reprinted with permission from Metall Trans., The Minerals, Metals, and Materials Society.)...

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