Ii. Physical Electronics and Surface Physics Academic and Research Staff A. Permeation of Hydrogen through Metals Joint Services Electronics Program (contract Daab07-71-c-0300)

The absorption and permeation of hydrogen in metals occurs in a variety of technological processes and systems, and in some cases the results are extremely detrimental (e. g., hydrogen embrittlement, stress corrosion, degradation of electrical and magnetic properties, undesired loss (or gain) of hydrogen, etc.). In an increasing number of applications the hydrogen pressure, p, is extremely low, falling considerably below the range of existing permeation data. In these cases it is usually assumed that the permeation rate, J, may be estimated by extrapolation of experimental data obtained at higher pressures. As pointed out elsewhere, the common extrapolation based on 1/2 the relation Jc p/2 is not valid at extremely low pressures because there are various gas phase and surface processes that become increasingly important with decreasing pressure. Consequently, the present practice of estimating permeation rates by the common extrapolation method may lead to serious errors. This report summarizes our attempts to provide more reliable data on the permeation of hydrogen through various materials. We shall concentrate on our current theoretical investigation of permeation at low pressures and present our most recent experimental results concerning the permeation of hydrogen through niobium. The results of our earlier investigations have been described in previous publications.2-6