Hydrogen permeation into aluminium AA1060 as a result of corrosion in an alkaline medium. Influence of anions in solution and of temperature

Aluminium AA1060 corroding in 0.01 mol dm −3 KOH solution is permeated by hydrogen whose diffusion can be monitored by recording the hydrogen ionization current on the other face of the metal sample. The effect of small concentrations of nitrite, sulphide and cyanide on the corrosion rate of Al has been investigated using such an experimental arrangement. Results have shown that corrosion is enhanced in the sequence OH − < NO 2 − < S 2− < CN − as a consequence of double layer effects on hydrogen discharge operated by specifically adsorbed anions. The influence of temperature has also been investigated. The apparent activation energy of the steady-state permeation current is shown to result from contributions of (i) hydrogen diffusivity, (ii) corrosion process and (iii) electrocatalysis. The advantage of monitoring corrosion processes in real time by recording the hydrogen permeation current is stressed.