Abstract
The degradation of organic-inorganic hybrid materials based on epoxy resin was characterized electrochemically in aggressive chemical electrolyte. In the present study, the hybrid material as primer was prepared from epoxy resin pigmented by zinc phosphate cured with polyamide (EPZ). The hybrid material was coated on mild steel substrate, and the corrosion behavior was studied by electrode-potential time measurements and mainly by electrochemical impedance spectroscopy (EIS) in 5% NaCl solution. The impedance parameters, namely, coating capacitance (), pore resistance (), charge transfer resistance (), double layer capacitance (), and break point frequency (), corresponding to 45° phase angle as a function of time of exposure were estimated. The observed impedance behavior were compared with the established equivalent electrical circuit represents the coated metal/electrolyte interface. Changes in the values of the circuit components given the information on the stages of degradation and physical phenomenon occurring throughout the degradation of primer coating were also been predicted. In addition, information related to the porous nature of the primer, limited passivation effect, and delamination of coating with longer exposure that resulted in the diffusion controlled corrosion of metal are also recognized. Thus, results indicate that the EPZ coating had good corrosion resistance. This could be a nonpolluting alternative to the traditional chromate like environmentally harmful coatings.
Highlights
Epoxy coatings, generally crosslinked with amines or polyamides, are widely used as heavy duty moisture and chemical resistance, well adhesion, and corrosion-resistive coatings and lining in various environments, since they create a three dimensional protective network [1]
The anticorrosion behavior of different inorganic pigments in epoxy-polyamide [3], degradation of epoxy coating with artificial defect [27, 28], and chemical degradation of novolac coatings [29] has been analyzed by electrochemical impedance spectroscopy (EIS) to obtain information on the corrosion protection
Impedance behavior of mild steel coated with EPZ was studied about 100 days of exposure in 5% NaCl in open-air atmosphere
Summary
Generally crosslinked with amines or polyamides, are widely used as heavy duty moisture and chemical resistance, well adhesion, and corrosion-resistive coatings and lining in various environments, since they create a three dimensional protective network [1]. Though epoxy resins have been widely described for various coating applications with progress of time, water, oxygen, and ions penetrate the coating, which initiates corrosion at metal-coating interface [2, 3] This penetration of species may occur either by diffusion through the polymer or more likely by ingress at local defects. The anticorrosion behavior of different inorganic pigments in epoxy-polyamide [3], degradation of epoxy coating with artificial defect [27, 28], and chemical degradation of novolac coatings [29] has been analyzed by EIS to obtain information on the corrosion protection. The EIS measurement was carried out on steel coated with zinc phosphate-pigmented epoxy-polyamide primer (EPZ) in 5% NaCl in the frequency range 100 KHz to 10 Hz. The impedance data over 100 days of exposure has been analyzed in terms of both Nyquist and Bode plots. The time dependence of Cc, Cdl, Rpo, Rt, fb, and Eoc has been estimated to show a relationship with the observed degradation of coating
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