Phosphorous-based epoxy resin composition as an effective anticorrosive coating for steel

Epoxy resin (ER) is an attractive material for metal protection against corrosion; it can form a strongly adhered film onto a metal surface through its multi coordination sites. In this study, an epoxy resin-based formulation was designed, prepared, and applied onto steel surface with and without a pigment. The anticorrosive formulation (ER–MDA–ZP) was prepared from the ER and the hardener 4,4′-methylene dianiline (MDA) in the presence of the anticorrosive pigment zinc phosphate (ZP). A second standard formulation (ER–MDA) was prepared without ZP. The epoxy and the hardener react to form a 3D cross-linked polymeric network with multicoordination sites (hydroxyl and amino groups) for metals. The characterization of the epoxy resin was performed using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance ( 1 H and 31 P NMR). Both samples exhibited excellent thermal properties as they subjected to thermal analysis using differential scanning calorimetry. The ER–MDA–ZP formulation showed a higher glass transition temperature ( T g ) than ER–MDA. The coated steel specimens were immersed for 1 h in a 3 wt% NaCl solution and their anticorrosive properties were monitored by electrochemical impedance spectroscopy (EIS). The total resistance ( R t ) values obtained by the EIS method for the ER–MDA and ER–MDA–ZP formulations were 21,383 Ω cm 2 and 55,143 Ω cm 2 , respectively. The coated steel samples after the acid treatment were subjected to aging by exposing them to a UV light for 2000 h. The aging caused the R t values to drop to 1621 Ω cm 2 and 7264 Ω cm 2 , respectively. The results indicate the formation of a highly stable film of ER–MDA–ZP formulation on the steel surface that withstands an accelerated corrosive environment of 2000 h exposure to UV light and 1 h of immersion in a 3 wt% NaCl.