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. Experimental performance of the coating in immersion indicated the coating resistance as acquired by electrochemical noise methods (ENM), electrochemical imped ance spectroscopy (EIS), and direct current resistance (R-DC) measurements decreased in an Arrhenius manner with increasing temperature up to the glass transition temperature (T-g) of the immersed coating 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 differential scanning calorimetry (DSC) experiments, T-g was shown to be that of the water-plasticized film and not of the dry film. Calculation 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 expected for use at lower temperatures.