Electrochemical Aspects in the Failure of Organic Coatings

✍ Scribed by G. Bombara; G. C. Lunazzi; B. Martini

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: German
• Weight: 850 KB
• Volume: 33
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.19820331105

✦ Synopsis

Abstract

With special reference to polybutadiene‐based electroprimers, an electrochemical model is outlined for the decay of coatings applied onto steel substrates. According to this model the driving force for the deterioration is the electrochemical differentiation of the steel substrate induced by local failure of metal‐coating adhesion. The resulting galvanic corrosion, producing high alkalinity at local cathodes and high acidity at local anodes (loss of adhesion), is the rate‐determining process in the decay of both non‐phosphated and phosphated electrocoated systems.

The results of electrochemical measurements of phosphate layer porosity and polarisation resistance of phosphated, polybutadienecoated steel are given for a number of steel samples differing in surface quality. The experimental results are reasonably consistent with the theoretical previsions from the model, indicating that phosphate layer porosities lower than 0.5–1% are required for long‐life coatings.