The use of silver decoration technique in the study of hydrogen transport in metallic materials

Abstract

The silver decoration technique proposed by Schöber and Dieker^[10] for revealing local hydrogen flux in terms of microstructural characteristics is reinterpreted. The results of decoration tests in polycrystalline nickel and palladium with and without hydrogen charging show that hydrogen flux is not solely responsible, nor even a prerequisite, for the deposition of silver crystals on metal surfaces. There is, consequently, no one-to-one correspondence between escaped hydrogen atoms and deposited silver atoms during the decoration process as reported previously. It is the oxidation film formed during electropolishing that prevents silver deposition. Any damage to the film and any factor which reduces its stability may result in spontaneous silver deposition in the absence of hydrogen. With this new interpretation, one can use the silver decoration technique to obtain qualitative information regarding hydrogen transport along grain boundaries in metallic materials.