Polytetrafluoroethylene-Blended Polyphenylenesulphide Coatings for Mitigating Corrosion of Steel in Geothermal Environments *

Abstract

To improve the ability of polyphenylenesulphide (PPS) coatings to protect cold-rolled steel against corrosion in a low pH, hypersaline brine geothermal environment at 200°C, polytetrafluoroethylene (PTFE) was blended into the PPS. Not only does PTFE inhibit hot brine-induced oxidation of PPS surfaces, it provides a less susceptible surface to moisture because of its hydrophobic characteristics, reducing the rate of infiltration of corrosive ionic species through the coating film. However, blending an excessive amount of PTFE into PPS creates two undesirable features, causing the failure of the coatings as corrosion-preventingbarriers. One is the development of porous microstructure in the coating layer; the other is the formation of a weak boundary region at the interphase between the blended topcoating and the zinc phosphate precoating. The reason for the latter is the phase separation of PTFE from PPS.