Self-repairing poly(phenylenesulfide) coatings in hydrothermal environments at 200 °C

Abstract

Usefulness of hydraulic calcium aluminate (CA) fillers, containing monocalcium aluminate (CaO.Al 2O 3) and calcium bialuminate (CaO.2Al 2O 3) reactants as the major phases, in healing and repairing micro-sized cracks generated on the surfaces of poly(phenylenesulfide) (PPS) coating was evaluated by exposing the cleaved coatings to a simulated geothermal environment. CA fillers with a grain size of <40 μm were incorporated into the PPS coatings. The cleaved PPS coatings containing fillers then were exposed for up to 20 days in a 200 °C CO 2-laden brine. The decalcification–hydration reactions of the CaO.Al 2O 3 and CaO.2Al 2O 3 reactants disclosed in the cracks led to the rapid growth of boehmite crystals, while the crystalline calcite phase formed by the carbonation of these reactants was leached out of cracks because of the formation of water-soluble calcium bicarbonate. During exposure for 24 h, the block-like boehmite crystals, ∼4 μm in size, densely filled and sealed the open cracks; this was reflected in an increase in pore resistance to two orders of its magnitude compared with that of cleaved coatings without fillers. Extending the exposure time to 20 days resulted in no change in pore resistance, suggesting that the sealing of the cracks by boehmite crystals played an essential role in reconstituting and restoring the function of the failed coatings as corrosion-preventing barrier. Therefore, CA-filled PPS coatings are able to self-heal and -repair cracks generated on the surfaces of coating films in hydrothermal environments.