Dr. Bernhard Wessling
Ormecon Chemie GmbH & Co. KG, Ammersbek
(a subsidiary of Zipperling Kessler & Co.)
We began our research in this area 1986 and prepared the first dispersed polyaniline (PAni) containing coating in 1987. [1] Our goal was to find out, if corrosion protection was possible on just normal steel, without any pretreatment, especially without previous passivation in acid or under electrochemical conditions. We wanted to know, if corrosion protection was feasable using a PAni dispersion in a coating, hence without any electrochemical deposition of PAni. Our research was motivated by the publication of deBerry in 1985 [2] according to which polyaniline, electrochemically deposited on pre-passivated stainless steel in strong acid environment, was enhancing the corrosion protection of this metal. Similar observations, however with a composition not identical with polyaniline, had previously been made by Mengoli et al. [3] Both authors favoured the conclusion, that PAni, if electrodeposited on pre-passivated steel, was capable of maintaining the passive state.
This was the only public knowledge available, when we first began our work with the goal to find out about anti-corrosion effects based on PAni. Our proprietary knowledge at that time was how to disperse polyaniline, although still at a relatively low performance level, as we had succeeded with first dispersions of polyaniline only some 2, 3 years before (mainly in thermoplastic polymers). It was completely unknown, if a PAni dispersion coating (with the PAni-free insulating matrix around) would have any effect, and if, what the effect would be based on, and if not, how to make it to be an anti-corrosion coating. Nothing at all was known about any anti-corrosion effect of PAni, if applied non-electrochemically and on a non pre-passivated steel (or iron or any other metal) surface, and nothing at all was to be expected in this direction at that time.
In 1987, we surprisingly found some corrosion protection [1], and we also found that an oxide was formed, but this could have been any oxide or hydroxide, or even a first sign of rust, as we had not yet been able to see any improvement over state-of-the-art coatings. We followed these first findings in the next years, partially together with other groups, and also published another patent application [4] with some improvements in corrosion protection, but still not at all convincing for corrosion experts, still not performing reproducibly, and not performing any better than conventional coatings, but worse.
At that time, we had no idea, what mechanism was active if there was any beneficial and remarkable anti-corrosion effect of polyaniline deposited by other than electrochemical means on other than pre-passivated metal surfaces (stainless steel) under other than passivating conditions. The conductive polymer research community, and moreover the corrosion experts outside it, did not believe in the possibility to realize an anti-corrosion technique using polyaniline, especially not with a PAni dispersion. Also Allied and Americhem, with which together we had made the study leading to the second patent [4], stopped their work on this question and left the cooperation, as a success of the research was not at hand.
