The effect of additions of anticorrosive pigments on the cathodic delamination and wear resistance of an epoxy powder coating

Abstract

The cathodic delamination and wear resistance of epoxy powder coatings were evaluated after adding 3 % (by wt.) of calcium ion exchanged micropigments from amorphous synthetic silica. The materials were manufactured through the innovative and economical hot mixing method, and three different coatings were considered: commercial epoxy, epoxy without micropigments submitted to the hot mixing treatment, and epoxy with micropigments. The curing kinetics of the powder coatings was studied in order to evaluate the possible effects of the micropigments on the epoxy, using differential scanning calorimetry (DSC). In addition, mechanical properties of coatings (hardness and scratch resistance) and their wear resistance (reciprocal tribometer tests) were assessed. After provoking a controlled mechanical failure in the coatings, their delamination resistance was analyzed by scanning Kelvin probe (SKP). The delamination front was calculated after adding a drop of 3.5 % NaCl solution and taking measurements for 26 days. The results show that the corrosion attack progresses through a cathodic delamination mechanism. The addition of corrosion inhibitors in epoxy powder coatings has not only allowed a considerable improvement in delamination resistance, but has also led to greater mechanical and wear resistance. At the same time, it has simultaneously reduced the chances for mechanical failure of the coating and decreased the progression rate of damage, if it occurs. The study has also been completed with electrochemical impedance spectroscopy and polarization measured of fully-immersed defective coatings in 3.5 % NaCl.