Filiform Corrosion on Aluminum:
Polyaniline Primer offers superior protection
Test performed by German Institute
"Research Institute for Pigments and Paints, Stuttgart"
(Forschungsinstitut für Pigmente und Lacke, Stuttgart, FPL)
Aluminum is suffering a severe corrosion, especially in humid and salty atmosphere close to sea shore, called "filiform corrosion". There are only few coating systems available, which are offering at least a relatively satisfactory protection, but none does protect perfectly.
The FPL has focussed also on this corrosion field, and has developed a test method (for references, see below [*]).
The test is very severe: the coating system (primer plus top coat) is injured with a cross scratch, the specimen are then subjected first to hydrochloric acid and then to salt fog.
A system consisting of the Zipperling PAni primer CORRPASSIV 900 226/19, specially developed for Aluminum surfaces, and a top coat of a 2-component Epoxy system, showed to be the best system ever tested in this filiform corrosion test. Hardness (fig 1), wet and dry adhesion on the specimen (fig. 2 and 3) was excellent, and undermining was "Zero" after the test (fig 4, left).
A second system with 2-component PUR as top coat did not perform as well, and is not being recommended by us for this purpose.
Full text available (German) (35 K approx.)
[*]
1. J. E. Pietschmann, H. Pfeifer, Filiformkorrosion auf organisch beschichtetem Aluminium, Teil I, Aluminium 69(1993)S. 1019-1023
2. D. C. van Beelen, B. Zweers, J. Glasbergen, K. Zabel, A new technique for monitoring filiform corrosion under anticorrosion primers, Metal Finishing 91(1993)No. 7, S. 51-54
3. G. D. Steele, Filiform Corrosion on Architectural Aluminium - a Review, Corrosion Prevention & Control 40(1993)No. 6, S. 129-134
4. J. E. Pietschmann, H. Pfeifer, Filiformkorrosion auf organisch beschichtetem Aluminium, Teil II, Aluminium 69(1993)S. 1081-1084
5. J. E. Pietschmann, H. Pfeifer, Filiformkorrosion auf organisch beschichtetem Aluminium, Teil III, Aluminium 70(1993)S. 82-85
6. K. Gaszner, M. Heinrich, T. Schuler, Bewitterung von beschichtetem Aluminium, Teil I: Korrosionserscheinungen nach der Freibewitterung im Vergleich zu verschiedenen Laborprüfmethoden, Aluminium 71(1995)S. 562-566