The protective action of lead compounds

Abstract

AbstractIt has been shown that distilled water may be rendered non‐corrosive by contact with lend powder, litharge and red lead, whilst under the same conditions little or no inhibition was obtained from lead peroxide, lead sulphate, lead chromate, basic lead sulphate, basic lead carbonate, iron oxide and titanium oxide. The inhibition was associated with the passage of lead into solution. Atmospheric carbon dioxide removed the lead from solution by precipitating it as basic lead car be unto. In certain cases, therefore, protection broke down, and the results were not very reproducible. Paints have been prepared from the majority of the pigments mentioned above, by grinding them in a drying oil, and it had been found that so long as the lead pigment was sufficiently basic to form lend soaps it yielded a paint film which was capable of making water non‐corrosive. It was concluded, that inhibition was brought about the soluble lead compounds produced by the hydrolysis of lead soaps, and this was confirmed an examination of the behaviour of a commercial sample of lead linoleate, Tins inhibition was obtained even in the presence of small quantities of electrolytes and atmospheric carbon dioxide. It would seem that the ideal vehicle should contain sufficient acid to ensure adequate soap formation, and should yield a film of maximum water resistance, in order that the soluble inhibitive ingredients may be retained as long as possible. The possible ways in which such a vehicle could be developed are discussed in the paper. The mechanism by which the products of hydrolysis of lead linoleate cause inhibition has been examined, and it is concluded that the soluble lead compounds are adsorbed on the bare metal, and act as anodic adsorption inhibitors. The nature of the adsorbed substance has not been clearly established. The paper contains suggestions for future work.