アミン類を主剤とする防食剤の研究 (第43報)

Niの陽極挙動に及ぼすプロトン提供性インヒビターの影響

抄録

In our previous reports, it was presumed that there were two types of water molecules adsorbed on metal surface. One was adsorbed by donating an electron-pair of its oxygen atom to metal and the other by hydrogen-bridging with metal. When the former was desorbed from the metal surface because of being attracted with electron-donating inhibitors, organic inhibitors would be immediately adsorbed by sharing an electron-pair with metal on the site where the former was desorbed.
In this report, the latter type of water was concerned. To verify existence of the latter type of water, some preliminary experiments were carried out by means of examining the adsorption of inhibitors with and without an active hydrogen atom on metal oxide. These experiments were anodic polarization curve measurements and others to confirm the influence of inhibitors on the induction period of passive film breakdown which would be observed on nickel in 1N H₂SO₄ by adding some amounts of KCl. Infrared absorption spectrum was also adopted to determine the amounts of inhibitors adsorbed on nickel oxide.
The induction period of breakdown for electrochemically prepared nickel oxide was prolonged by addition of inhibitors with active hydrogen atom, such as, n-octylamine, butyl alcohol, and butyric acid. No prolongation in the induction period was, however, detected by inhibitors without active hydrogen atoms, such as N, N-dimethyloctylamine, and dibutyl ether.
These showed that inhibitors were adsorbed by two ways, one by electron donation and the other by protonation. The adsorption of inhibitors by protonation suggested the possibility of the water which was hydrogen-bridged with metal surface.