Effect of anticorrosive primer coating on mild steel on the nature of underneath corrosion products

The anticorrosive pigments catalyse the formation of protective corrosion products beneath the coating that also reduce the delamination of paint coating. The nature and composition. of corrosion products formed in presence of anticorrosive pigment present in the primers thus determine its protective action The present paper gives the nature curd composition of the corrosion products formed on mild steel coated with primers containing (i)Micaceous iron oxide (MIO), (ii)MIO + zinc chromate (ZC), (iii)MIO + basic lead silico chromate (BLSC), (iv)MIO + zinc phosphate(ZP) and (v)MIO + red lead(RL) cmd immersed in 3% NaCl for three months. The corrosion products between the metal and coating were removed and studied by Transmission Mossbauer Spectroscopy(TMS) and Fowler Transform Infrared Spectroscopy(FTIR). Mossbauer spectroscopy showed that the corrosion products consisted of non stoichiometric Fe3O4, superparamagnetic (SPM)alpha-FeOOH and gamma-FeOOH except in the case of RL where the formation of SPM alpha-FeOOH and gamma-FeOOH was observed The results also corroborate with FTIR spectral data. Mossbauer data. revealed that the non-stoichiometry of Fe3O4 depends on the type of anticorrosive pigment and was highest in case of chromated pigments. Corrosion spots on the panel were in order of ZC<BLSC<ZP<MIO<RL. It is therefore concluded that anticorrosive pigments which catalyse the formationn of higher non stoichiometric Fe3O4 are capable of giving better protection of steel against corrosion.