Evaluation of corrosion protection of carbon black filled fusion-bonded epoxy coatings on mild steel during exposure to a quiescent 3% NaCl solution

Carbon black (CB) was mixed with fusion-bonded epoxy (FBE) coatings to generate a series of formulations with 0.5-4% by weight of carbon black. The degradation of these FBE coatings on mild steel exposed to a quiescent 3% NaCl solution was monitored using electrochemical impedance spectroscopy (EIS). The experimental results showed that the electrochemical behaviour of coated systems changed dramatically when the CB concentration reached 3% by weight. This phenomenon was relevant to the formation of the percolation regime in the coating, at which a sharp drop in the electrical resistance of the coating was achieved by the generation of a continuous conducting network. A comparison of the protective properties of the FBE coatings filled with various CB loadings, along with the inspection of view underneath the coatings, indicated that the protective performance of the FBE coating was significantly improved when the CB loading exceeded the threshold concentration. This conclusion was confirmed by the results obtained from Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) measurements.