Electrochemical Measurement of Tritium and Hydrogen Permeation through Iron Membranes

Abstract

trolyte. Tritium and hydrogen were introduced from one side of a specimen by cathodic polarization with a constant current density, while at the other side of the specimen the permeated tritium and hydrogen were extracted by potentiostatical ionization. Nearly all of the potentiostatic current of the extraction side stands for the ionization of hydrogen, because the concentration of tritium in the cathodic electrolyte is very small. The amount of permeated hydrogen was obtained by integrating the anodic current, and that of tritium was determined by measuring the radioactivity of the electrolyte sampled from the extraction side. The separation factor for permeation obtained under steady state conditions (the ratio of permeation rates of hydrogen to tritium divided by the ratio of the concentration of hydrogen to tritium in the charging electrolyte) is 12 at 288K. This value is independent of cathodic current density. Diffusion coefficients of tritium (DT) and hydrogen (DH) in iron were determined from the time lag of

Quantum–Thermal Crossover of Hydrogen and Tritium Diffusion in α-Iron

“…Notice that this value is close to the square root of the tritium–hydrogen mass ratio of 3.0, in agreement with the classical mechanics. In addition, this result is comparable with experiments in the range of error at room temperature. − , …”

“…As far as we are aware, there has been only one report on the experimental diffusion coefficients for T; Hagi and Hayashi have estimated the diffusion coefficients for T and H in Fe at T = 286 K to be D T = 0.09 × 10 −8 m 2 s −1 and D H = 0.4 × 10 −8 m 2 s −1 using an indirect electrochemical permeation method. 56 It seems that this value of H diffusion coefficient seems to be underestimated since it is almost one-half of our CMD and RPMD values (0.83−0.84 × 10 −8 m 2 s −1 at T = 300 K) as well as other experimental values reported in the literature (0.74−0.89 × 10 −8 m 2 s −1 at T = 300 K; see Table 1). 8−15 In general, measurements of diffusion coefficients in Fe−H system strongly depend on the purity of the specimen, that is, concentration of vacancies and impurities, while the specimen of Hagi and Hayashi contains somewhat more impurities (>0.1 mass %) than in other measurements.…”

“…[8][9][10][11][12][13][14][15]56 Thus, it might be due to the trapping effects that the estimated tritium diffusion coefficient is underestimated in the study of Hagi and Hayashi. 56 Their experimental D T value is also about one-half of our CMD, and RPMD calculations give D T at T = 300 K to be 0.17 × 10 −8 and 0.18 × 10 −8 m 2 s −1 , respectively, although the temperature is slightly different from the experimental temperature. However, the ratio for D T and D H is in agreement between the computational and experimental results.…”

“…In addition, this result is comparable with experiments in the range of error at room temperature. [8][9][10][11][12][13][14][15]56 Figure 4 displays a representative three-dimensional perspective plot of the nuclear distribution function for the H/T (gray color) in Fe (purple color) obtained from the PIMD simulation at T = 300 K. In Figure 4a, a large fluctuation can be seen for a H atom. In particular, we can see that the hydrogen is distributed around not only the paths between Tsites via S-sites but also around the O-sites.…”

“…8−15 In general, measurements of diffusion coefficients in Fe−H system strongly depend on the purity of the specimen, that is, concentration of vacancies and impurities, while the specimen of Hagi and Hayashi contains somewhat more impurities (>0.1 mass %) than in other measurements. [8][9][10][11][12][13][14][15]56 Thus, it might be due to the trapping effects that the estimated tritium diffusion coefficient is underestimated in the study of Hagi and Hayashi. 56 Their experimental D T value is also about one-half of our CMD, and RPMD calculations give D T at T = 300 K to be 0.17 × 10 −8 and 0.18 × 10 −8 m 2 s −1 , respectively, although the temperature is slightly different from the experimental temperature.…”