Zinc tripolyphosphate:: An anticorrosive pigment for paints

The aim of this paper was to study the efficiency of zinc tripolyphosphate as an anticorrosive pigment for paints. A procedure to prepare the pigment was outlined and its anticorrosive properties evaluated following the electrochemical behaviour of a steel electrode in pigment suspensions. In a second stage, solvent-borne paints containing barium sulphate, talc and titanium dioxide together with 30 or 10% v/v (by volume) of zinc tripolyphosphate, with respect to the total pigment content, and PVC/CPVC (pigment volume concentration/critical pigment volume concentration) ratio 0.8 were formulated. Two resins were chosen as film-forming materials: an alkyd and an epoxy-polyamide (1:1) resin. The performance of the resulting anticorrosive paints was assessed by accelerated (salt-spray and humidity chambers) and electrochemical tests (corrosion potential, ionic resistance and polarisation resistance). It was demonstrated that zinc tripolyphosphate inhibited corrosion when incorporated into a paint film. It showed an excellent performance when employed with the alkyd resin. Good correlation was obtained between accelerated and electrochemical tests.