Behaviour of Activated Iron in Sodium Hydroxide Solutions

Abstract

AFTER it had been shown that strong corrosion of iron may occur in alkaline solutions in the presence of special reagents¹, the question arose regarding the corrosion conditions in the absence of the organic reagent, that is, in solutions of pure alkali hydroxide. The literature on this point is rather meagre. It has now been found that in this case also there is a decided difference between activated and non-activated iron, which, however, is generally not visible during the first days after activation but appears very slowly. After about a week, the surface of the activated iron assumes a dull lead-like appearance, thereafter turning darker and darker. After a rather long time the surface finally turns brownish, rust-like. The time needed for the whole procedure seems to vary widely with the conditions of the experiment, but several months may pass before the final state is reached. Oxidizing substances, added to the alkaline solution at the time when the surface of the iron shows a lead-like colour, rapidly oxidize the lead-coloured substance to a brownish one, whereas they have no visible effect on iron not activated. The difference between activated and non-activated iron can, of course, be shown immediately after the activation by the addition of a suitable organic reagent, such as nitrosoguanidine. However, it can also be shown by the addition of an alkaline copper tartrate solution, which produces a brilliant coating, often in several colours, on the activated metal.