EFFECTS OF CHLORIDE IONS ON THE CORROSION RESISTANCE OF CONDUCTING POLYPYRROLE COATED STEEL IN SIMULATED CONCRETE PORE SOLUTION
Bull., Series B
Epoxy based paint containing conducting polypyrrole as a pigment was applied on low carbon steel sample. By using Tafel polarization technique, corrosion rates of uncoated low carbon steel sample and painted low carbon steel sample, in 3.5 wt% NaCl were determined. The corrosion rate of conducting polypyrrole coated low carbon steel sample was found to be 0.09 mpy which is about 81 times lower than that of uncoated steel sample. A shift of 186 mV in the value of the corrosion potential in the
... potential in the positive direction indicates that the polypyrrole coating imparts corrosion protection by anodic protection. The uncoated and painted steel samples were immersed in simulated concrete pore solution and electrochemical studies were carried out. It was found that the passive film generated on uncoated low carbon steel sample in pore solution gets damaged with addition of chloride ions. As compared to uncoated low carbon sample, polypyrrole coated low carbon steel sample exhibits higher impedance (Zmod) ~6340 KΩ-cm 2 , higher coating resistance (RC) ~1778 KΩ-cm 2 and lower capacitance (CC) ~11.66x10-6 µF just after immersion, in pore solution without chloride contents. Polypyrrole coated steel sample was able to protect low carbon steel for up to 240 hours of immersion in the pore solution containing no chlorides and in the pore solution containing 0.25M NaCl. However, at 0.5M NaCl & higher concentrations, the self healing ability of polypyrrole coating was no longer operating to protect steel sample from corrosion. The novelty of the paint coatings formulated by using polypyrrole pigments is that in case of damage of paint coating in service or handling, a passive film gets generated and protects the underlying metal from further corrosion. Findings in these investigations revealed possibility of using conducting polypyrrole based paint coating system for the protection of rebar in concrete.