Deposits formed on iron during cathodic polarization in the presence of arsenic and their effect on hydrogen permeation

Deposits produced on iron and steel during cathodic polarization in the presence and absence of arsenic in acid and alkaline solutions have been studied microscopically, by electron microprobe analysis, and by double layer capacity measurements. The results of these studies are compared with permeation rates of hydrogen through rotating membranes. It is shown that the compactness of the deposits and their effect on the permeation depend on following major factors: surface condition and pre‐treatment of the cathode, pH of the electrolyte, As concentration, electrode potential. Elemental arsenic deposited on the cathode does not promote the permeation of hydrogen. On the contrary, adherent and compact films impede the entry of hydrogen into the metal phase. Arsine adsorbed on the metal surface is the main promoting species.