Scientific Engineering of Anti-Corrosion Coating Systems based on Organic Metals (Polyaniline)

Dr. Bernhard Wessling
Ormecon Chemie GmbH & Co. KG, Ammersbek
(a subsidiary of Zipperling Kessler & Co.)

5. Conclusions and Outlook

The new Organic Metal polyaniline, almost a noble metal, ennobles steel and other metal surfaces while shifting their surface potential. It furthermore passivates the conventional metals by forming a metal oxide layer of up to 1 µm thickness. This exciting new technology is based on extremely fine dispersions of PAni in coating matrices of special composition.

Many internal and independant tests ^{[4, 8, 20, [24]} have shown that the presence of polyaniline at the metal surface (to be protected) alone in regardless what chemistry form or matrix is by far not sufficient for a reproducible and practically convincing high-performance corrosion protection coating.

As shown, the systematic combination of 4 tests, the measurement of the corrosion potential shift, a new simple scratch test, the Volta potential measurement with the Scanning Kelvin probe, and electrochemical impedance spectroscopy, eventually to be combined with salt spray or climate cycling test according to VDA (Association of German Automobilists) is a productive tool for testing and improving corrosion protection coating systems. In contrast to salt spray and climate cycling tests (3-6 months), useful results from measurements with EIS and the SKP can be obtained within 1-2 weeks (after complete drying of the coatings to be tested), from where accelerated corrosion test results and real-world corrosion prevention performance can be predicted.

CORRPASSIV^TM coating systems for various industrial applications have been developed with this method^[43]. They were specified and are released by several customers; practical industrial reference objects have been realized, e.g. pipelines, bridges, boats, container ships, steel constructions in chemical plants, hydraulic construction in waste water management, hydraulic service center in Airbus manufacturing etc.^[44]. They are performing much better than any other conventional anti-corrosion coating. They can be applied at a 25 to 60% reduced coating thickness compared to conventional systems, without any loss of performance^[45].

Recently, new systems have been developed with the help of these techniques, namely

• a system for coil coating (4500), which is now under first technical tests; this product is designed to replace chromates in coil coating;
• a completely new water-born system comprising a water-born primer and a water-born, or a 100% solids, resp., top-coat; this system will perform at least as well as generally available well performing solvent-borne coatings.

Both systems will soon be presented for independent performance tests.

It might also be of interest, that our CORRPASSIV^TM systems have shown a well advanced performance on structural light metal alloys, like Mg alloys for automotive use. We are following this area, too, whereby we still need to develop our „Scientific Engineering“ method for these metal substrates. Another system for structural Al applications (aerospace) is under development. Here again, the replacement of chromates is the environmentally important goal of the project.

Considering the short time we had for the development, our systematic 4-step method has helped us to develop coating systems of the highest performance at significantly lower coating thickness, because it led to a deep understanding of the phenomena during corrosion attack, ennobling and passivation. We were able to show, that

• our Organic Metal allows for a powerful anti-corrosion technology, and
• the development of corrosion prevention coatings must not necessarily be based only on long-term practical studies with a „trial-and-error-“strategy, but can also be based on systematic scientific tests allowing to gather reliable results within a few weeks only.

It would certainly be of interest to find out, if this method can also be applied on general, non-PAni-coating systems, to predict their performance.

Both, the Organic Metal anti-corrosion technology and our Scientific Enginieering of anti-corrosion coating systems, have the potential to revolutionize corrosion protection. Not only new systems can be quickly developed with a high correlation between short term measurement and long-term performance, but also coatings with about 5 times longer lifetime for the metals to be protected, at 25 - 60% lower coating thickness, replacing chromates and zinc can be provided.

Considering the fact, that corrosion is responsible for the loss of about 4% of each countries Gross National Product per year, and considering, that the repair of the lost values not only requires financial, but even more environmental ressources, our new technology could significantly contribute to reduce costs and to a future ecologically acceptable economy („sustainable economy“).

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