polyphenylene ether washcoats on metal surfaces

We have found that polyphenylene ether (PPE) (also called polyphenylene oxide or PPO) applied directly to metal surfaces forms an adherent and protective coating.  This effect is seen in both electrochemical and salt fog (ASTM B117) testing.

We propose that the origin of the effect is electrochemistry between the PPE and substrate metal, as summarized in this scheme:

The effect is evident in DC potentiodynamic scans of Al2024T3 coated with clear epoxy resin (upper curve) or coated with PPE (lower curve).  Both surfaces were scored before testing.

Our method of measuring the effects of organic coatings on the passivity of metal surfaces is illustrated in this figure and explained in the literature citations listed below.

Literature

P. Spellane, A DC electrochemical method for studying the inhibition of metal corrosion by chromate-containing paint, Prog. Org. Coatings 1999, 35,  277

P. Spellane, Poly(2,6-dimethylphenylene Ether): an Electroactive Anticorrosion Coating for Aluminum," p. 136 in Corrosion and Corrosion Prevention of Low Density Metals and Alloys, R. G. Buchheit, B. A. Shaw, J. P Moran, eds., PV 2000-23, The Electrochemical Society Inc., Pennington NJ.

Patents

U S Patent 6,004,628: Metal corrosion protection with wash coat of polyphenylene oxide.

U S Patent 6,376,021: Heat treatment of polyphenylene oxide-coated metal.

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