Evaluation of coating performance using break point frequency

Abstract

Break point frequency values were used to evaluate the degradation of alkyd and epoxy coatings on rolled steel panels. Panels of size 6'' x 4'' were given the following coatings. 1. Alkyd primer(35 mu m) 2. Phosphating (10 mu m) + Alkyd primer (35 mu m) 3. Phosphating (10 mu m) + Alkyd primer (35 mu m) + Alkyd top coat (35 mu m) 4. Epoxy primer (50 mu m) 5. Phosphating (10 mu m) + Epoxy primer (50 mu m) 6. Phosphating (10 mu m) + Epoxy primer (50 mu m) + Epoxy top, coat (50 mu m) Corrosion of these panels was accelerated by exposing the coated panels to a neutral salt spray of 5% NaCl solution for long exposure times and impedance measurements were carried out at various intervals of time. The break point frequency values were found to increase with the time of exposure to the corrosive environment. There was a correlation between the number of blisters, the average blister area and the break point frequency. Various coating systems were ranked on the basis of break point frequency values.