Methodology for zinc phosphate pigment incorporation into polypyrrole matrix

In this work, the incorporation of a commercial zinc phosphate pigment into polypyrrole (PPy) matrix during its electrochemical synthesis on mild steel was studied in order to produce PPy/zinc phosphate composite films as a protective layer against corrosion. Potassium nitrate, oxalic acid, tosylic acid and sodium salicylate solutions were used as electrolytes in cyclic voltammetry and galvanostatic polarisation studies. The influence of synthesis parameters such as nature, concentration, pH and stirring of the electrolyte on the degree of incorporation of the pigment was investigated, as well as time and current densities of the electropolymerisation process. Their influence on current efficiency was also evaluated. Sodium salicylate was the only electrolyte to show a high current efficiency in the polymerisation reaction and to yield a composite film with a reasonable amount of zinc phosphate. In this electrolyte medium, X-ray photoelectron spectroscopy (XPS) analysis showed that zinc phosphate may be found in the polymeric matrix: (i) as a conductive ionic minority form and (ii) as a non-conductive non-ionic majority one for higher incorporation levels. Scanning electron microscopy (SEM) showed that zinc phosphate is heterogeneously distributed on the surface of the polymer.