The Protection of Aluminium Alloys in Harsh,Corrosive Environments by Oxidized Polyphenylene Sulphide Coatings *

Abstract

A moderate rate of oxidation of the sulphide groups in polyphenylenesulphide (PPS) played a key role in ensuring that PPS coatings adequately protect aluminium (Al) alloys from corrosion in wet, harsh environments. There are three major reasons for a good protective performance: 1) the superior hydrothermal stability of PPS itself, 2) the limited amount of sulphonic acid formed by the oxidation of sulphide, and 3) the formation of a discontinuous, intermediate layer of Al₂(SO₄)₃ as the interfacial reaction product between A1₂O₃ at the top surface of Al, and oxidized PPS. Widespread oxidation of PPS led to an increase in the rate of the interfacial interaction, forming sulphonic acid-enriched A1₂(SO₄)₃ intermediate layers, thereby improving the bond strength at Al-to-PPS adhesive joints. However, an overabundance of these reaction products resulted in an inadequate coating that failed to protect the Al during a long-term exposure in a harsh, corrosive environment because of the susceptibility of these salt products to dissolution in water.