Evaluation of hydrogen diffusivity in mild steel from electropermeation transients under conditions of galvanostatic charging

• Published in: Surface & coatings technology 1986-07, Vol.28 (3), p.261-280
• Main Authors: Chaudhari, B.S., Radhakrishnan, T.P.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Diffusion in solids; Diffusion of impurities; Exact sciences and technology; Materials science; Metals, semimetals and alloys; Physics; Specific materials; Transport properties of condensed matter (nonelectronic)
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/0257-8972(86)90084-8

The diffusivity of hydrogen in mild shim steel has been determined by an electropermeation method under conditions of galvanostic charging. Normalized experimental rise-decay curves have been obtained for shim steel subjected to pretreatments such as vacuum annealing, hydrogen annealing and presaturation with cathodic hydrogen. Theoretical permeation transients are given for (i) a constant hydrogen concentration and (ii) a step function in hydrogen flux at the input side of the membrane. A comparative study of the normalized experimental curves with dimensionless theoretical curves helps to identify the appropriate boundary conditions prevailing at the entry face of steel during galvanostatic charging. Phenomenological hydrogen diffusivity in pretreated steel membranes has been computed from experimental data for the breakthrough time, time lag, time for half-rise or half-decay and also for the time constant for the rise-decay curves. The diffusivity of hydrogen in vacuum-annealed shim steel increased with increase in charging current density, although it remained nearly constant for hydrogen-annealed or hydrogen-presaturated membranes.