In our previous paper, we suggested that organic corrosion inhibitors could be adsorbed on metal by two ways. One was carried out by electron-donation of the central atom of the adsorbate, and the other by proton-donation. The latter was brought about only when inhibitor molecules had active hydrogens as their constitutional atoms. As the suggestion was derived mainly from weight loss tests conducted in inhibited acid media, more detailed experiments such as from electro-chemical methods were shown in this paper.
As results, dodecylamine which had active hydrogens were more effective than N, N-dimethyldodecylamine which was prepared from dodecylamine by displacing its active hydrogens with methyl radicals. Cetylmercaptan was more effective than methylcetyl sulfide even at room temperature. Generally, S-containing compounds could hardly be adsorbed on metal at room temperature because of their deficient electron donation ability, while cetylmercaptan was more inhibitive than methyl-cetyl sulfide. For this difference, we supposed that mercaptan could be adsorbed on metal by its proton-donating as we could see in hydrogen-bridged compounds.
Dodecylamine and cetylmercaptan could be adsorbed on metal surface both by electron-donation and by proton-donation, but N, N-dimethyldodecylamine and methyl-cetyl sulfide could only by electrondonation. So, the metal surface filmed by N, N-dimethyldodecylamine (or the sulfide) had areas to be adsorbed by dodecylamine (or the mercaptan) by means of their hydrogen-bonding ability, but dodecylamine-filmed surface had no areas to be adsorbed by N, N-dimethyldodecylamine (or the sulfide).
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