Dr. Bernhard Wessling
Dr. Joerg Posdorfer
Ormecon Chemie GmbH & Co. KG, Ammersbek
(a subsidiary of Zipperling Kessler & Co.)
Keywords: Polyaniline, Organic Metal, Conductive Polymer, Corrosion Protection, Ennobling, Passivation, Metal Oxide, Coatings, Electrochemical Impedance Spectroscopy (EIS), Scanning Kelvin Probe (SKP), Volta Potential, Open Circuit Potential, Potential Shift, Scratch Test, Accelerated Corrosion Tests.
Abstract
published online in a modified form in JCSE
The new corrosion protection technology with polyaniline, the Organic Metal (conductive polymer) is presented. It is based on an immense surface ennobling and the formation of a passivating metal oxide. The requirements for efficiently working coating systems, comprising the dispersed Organic Metal containig primer, eventually an intercoat, and a top coat, are characterized. An integrated 4-step-method („scientific engineering") has been developed and is successfully used for the systematic development of such coating systems. The combination of the measurement of the open circuit potential, an new scratch test, EIS and SKP together are a powerful tool for predicting the results of accelerated corrosion tests and real-time corrosion prevention performance. Organic Metal coating systems are out-performing even the best conventional anti-corrosion coating systems.
| Content | Figures | |
| We began research directed to polyaniline containing anti-corrosion
coatings in 1986 and realized the first dispersion coatings 1987. Prior to that, only
electrochemically deposited PAni on pre-passivated stainless steel was known to maintain,
but not create a passive state. No anti-corrosion effect of PAni itself on untreated metal surfaces, coated by non-electrochemical means, was known or to be expected. Our early work showed some effects, but no superior performance, and did not convince any corrosion or coating expert. |
1. Early Work | |
After 5 years of intensive research, we discovered two new phenomena
enabling us to provide excellent corrosion protection:
We also revealed the reaction mechanism for the passive oxide layer formation, which involves a catalytic action of PAni including a reduction In consequence, the Organic Metal is providing corrosion protection
It became evident, that only our dispersion technology allowed to realize sgnificant corrosion protection (ennobling and passivation), while „soluble PAni" and other approaches did not. |
2. Breakthrough | |
| We succeeded very early to develop the first well performing
coating systems, and we realized the importance of a barrier top coat. But we also felt
the need for a systematic, scientific approach for the development of benchmarking coating
systems in contrast to a "trial and error" strategy. We defined the requirements for a) primer and b) top coat (or eventually an intercoat) and especially their compatibility. We found a first screening method by open circuit potantial and a new in-house scratch test. Further development led to a 4-step systematic and scientific method. |
3. The need for a systematic, scientific development tool | |
| The new method is composed by the following steps: 1. Open circuit potential measurement using our impedance spectrometer This experiment shows us, if a new coating provides the necessary potential shift and maintains it over time. 2. A scratch test developed by us This simple test proves the far-reaching ennobling and passivation effect even in broad uncoated areas (scratches); only those new systems will become commercial products, which prevent rust formation even in 1 - 2 mm wide open scratches. 3. Scanning Kelvin potential measurement (SKP) By scanning the Volta potential, we detect surface composition and potential changes under the coating, and we measure underfilm corrosion propagation velocity, which we want to be < 3µm per hour 4. Electrochemical impedance spectroscopy (EIS), using a new routine FFT technique developed by us this technique allows to measure changes in the capacitance behaviour of intact coatings; we want them to be stable over > 2 weeks compared to an internal standard (CORRPASSIV 4900) These 4 elements of our new method enable us to predict the performance of our coating systems in accelerated corrosion tests like those required by the industry. Real-time and real-world corrosion protection performance is in absolute accordance with these results. |
4. "Scientific
Engineering": a new development tool for anti-corrosion coatings
spec: D V » 800 mV spec: no rust in open scratch of 1 - 2 mm width spec: underfilm corrosion < 3 µm/h spec: stable for > 2 weeks at an internal standard level or higher 4.5 Climate cycling, cyclic immersion or salt spray test spec: no blistering, no underfilm corrosion after 2000 hrs |
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