Dr. Bernhard Wessling
Ormecon Chemie GmbH & Co. KG, Ammersbek
(a subsidiary of Zipperling Kessler & Co.)
When we started our primer and coating system development, we were aware of the fact, that we had no practical experience in corrosion phenomena, and even less in coatings. On the other hand, corrosion and coatings experts did not believe in our findings, and we were unable to convince them to combine their experience in coatings with ours in the Organic Metal polyaniline, its synthesis and dispersion, and in „ennobling and passivation“ by it.
We
realized very soon [5c, 15], that a polyaniline containing primer
alone was not sufficient as a practically convincing coating system,
but that it needed a top coat. This top coat (or eventually an
intercoat between primer and final top coat) had to fulfill certain
requirements in order to be compatible with the primer. The primer
itself had to meet the following demands:
The top coat (or the intercoat, resp.) had to offer
Having no practical experience and not enough time for the development of such coating systems, which should not only to be competitive, but moreover out-performing generally used state-of-the-art products, we had no other chance than to follow a scientific systematic route, in contrast to a „trial-and-error“ strategy.
We started with the open circuit potential (and corrosion current density) measurement as described in [5b] in combination with a wheel-driven alternating immersion test according to DIN 50905 T4 as a 2-step screening tool. Systems which passed our test[29] were subjected to other laboratory tests, salt spray and outside weathering corrosion tests (cf. [16]). We found an acceptable correlation in performance and decided to let one of our systems be tested by a neutral paint research institute, the „Forschungsinstitut für Pigmente und Lacke“ in Stuttgart.
Two studies were performed by them on our behalf. The first study was a comparison between a system composed of our primer 900 226/32 plus our selected epoxy top coat („2-C EP“) and 2 comparative systems having the same primer, but different top coats („2-C AY“ and „1-C AY“, resp.). The study comprised measurement of dry and wet adhesion, and salt spray test performance. The system /32 + „2-C EP“ performed by far at best[30], and the performance was in accordance with our previous internal results and [16]. This system is a first model system for our commercial product CORRPASSIVTM 4900, introduced in late 1996 [15].
The second study involved a system we had developed for aluminum, which requires a different primer (internal number: 900 226/19) used with the same „2-C EP“ top coat. Here, the filiform corrosion was tested, both in laboratory as in an outside weathering site at Netherlands. Also this system performed very well, as documented by FPL[31]. This system has been further developed by us to the commercial product CORRPASSIVTM 4901.
In parallel, the FPL investigated some other properties[32] of some systems comparable to those evaluated in the first study. They confirmed the immense potential shift found by us earlier [5] and found comparable potential values. The formation of the iron oxide Fe2O3 was confirmed, too. They also confirmed a link between barrier properties, stability of potential shift and corrosion protection performance.
However, for further development of more and different systems for different corrosion environments, we needed a tool which was not only capable of screening between „good“ and „bad“, but was moreover capable of delivering quantitative data enabling us to predict corrosion test results, both of accelerated and real-time tests and practical behaviour.
