THERMAL TRANSITION EFFECTS AND ELECTROCHEMICAL PROPERTIES IN ORGANIC COATINGS - PART 1 - INITIAL STUDIES ON CORROSION PROTECTIVE ORGANIC COATINGS

Thermal effects in a high performance fusion-bonded epoxy (FBE) powder coating on, steel were measured by electrochemical means. Experimenta l performance of the coating in immersion indicated the coating resist ance as acquired by electrochemical noise methods (ENM), electrochemic al imped ance spectroscopy (EIS), and direct current resistance (R-DC) measurements decreased in an Arrhenius manner with increasing tempera ture up to the glass transition temperature (T-g) of the immersed coat ing film Coating resistance then abruptly decreased more rapidly. The abrupt change in film resistance (a coating transport property) at T-g was seen in all three film resistance measures. Using independent dif ferential scanning calorimetry (DSC) experiments, T-g was shown to be that of the water-plasticized film and not of the dry film. Calculatio n of film capacitance values from EIS indicated increased water uptake with temperature consistent with water-plasticization as seen in T-g measurements. Data implied that use of coatings above their T-g values will lead to much lower barrier protection properties than would be e xpected for use at lower temperatures.