Investigation of Preventive Performance of Third Generation Phosphate Based Anti-corrosion Pigments by Use of Electrochemical Experiments

An effective way of reducing the gap between preventive performance of toxic chromate-based compounds and their traditional replacements (zinc phosphate) is using the new generation of phosphate based anti-corrosion pigments. These compounds are product of modified chemical structure of zinc phosphate pigments in cation and anion parts. In this study, our aim is to compare preventive performance of zinc aluminum polyphosphate (ZAPP) as a third generation phosphate and zinc phosphate based anti-corrosion pigments by use of electrochemical and surface analysis tests. For this purpose, uncoated steel samples were immersed inside saturated solution of the pigments in 3.5 percent chloride sodium solution. In addition to surface analysis after 24 hours, electrochemical experiments were carried out on the samples in three time intervals: 1, 4 and 24 hours. The results of electrochemical impedance spectrometer and linear polarization experiments show superiority of the reformed zinc phosphate pigments over its normal form. Generally, timing changes of charge transfer resistance (Rct) resulted from electrochemical impedance experiment and polarization resistance (Rp), current density (Icorr) and corrosion speed resulted from polarization curves as well as spectrum and curve shapes showed a protective film on the surface with presence of ZAPP. Also, images obtained from SEM proved this fact. The elements of the formed layer were identified by use of energy dispersive x-ray microanalysis (EDX)