The protection of aluminium alloys in harsh, corrosive environments by oxidized polyphenylene sulphide coatings
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: l) 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 Al 2 (SO 4 ) 3 as the interfacial reaction product between Al 2 O 3 at the topsurface of Al, and oxidized PPS. Widespread oxidation of PPS led to an increase in the rate of the interfacial interaction, forming sulphonic acid-enriched Al 2 (SO 4 ) 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.