Interfaces of high-protection performance polyaryls-coated zinc phosphated steels.

摘要

To evaluate the ability of polyaryl thermoplastic coatings such as polyphenylenesulfide (PPS) and polyphenyletheretherketone (PEEK), to protect zinc phosphate (Zn(center dot)Ph)-treated steels from corrosion in a wet, harsh environment (1.0 wt % H(sub 2)SO(sub 4), 3.0 wt % NaCl and 96.0 wt % water at temperature from 250 to 200 C), we exposed them in autoclave to determine performance in heating-cooling cyclic fatigue tests (1 cycle = 12 hr at 200 C + 12 hr at 25 C) for up to 90 cycles. Although no changes in appearance were seen in the PEEK specimens after 60 cycles, extension to 90 cycles caused delamination of the coating film from the Zn(center dot)Ph; the major reason was the degradation of the PEEK polymer caused by its hydrothermalcatalyzed esterification. In urea hydrogen peroxide (UHP)-modified PPS-coating systems, chemical reactions at the interfaces between the PPS and Zn in the Zn(center dot)Ph layer led to the formation of a ZnS reaction product, which enhanced the Zn(center dot)Ph-to-PPS adhesive bond; correspondingly, there were no signs of peeling nor separation of the coating after 90 cycles. In addition, because these intermediate reaction products are insoluble at high pH, they minimized the rate of delamination of the PPS coating caused by the cathodic reaction, H(sub 2)O + 1/2O(sub 2) + 2e(sup (-) (yields) 2OH(sup (-), at the corrosion side of a defect in the film. In contrast, PEEK coatings containing non-reactive Zn(center dot)Ph underwent cathodic delamination because of the susceptibility of Zn(center dot)Ph to alkali dissolution.