Improvement of the anticorrosive properties of an alkyd coating with zinc phosphate pigments assessed by NSS and ACET

The effect of the addition of two anticorrosive phosphate pigments, standard zinc phosphate and modified zinc phosphate (zinc molybdenum phosphate modified with a surface treatment) on the corrosion protection of an alkyd coating on steel, has been investigated by means of a traditional accelerated test (salt fog spray test) and an electrochemical technique (accelerated cyclic electrochemical technique). Solvent-based alkyd coatings based on phenolic modified resins were formulated with different anticorrosive pigment concentrations (3%, 4.5% and 6%, expressed as anticorrosive pigment volume concentration in dry film volume, PVC) and finally characterised. An improvement in the anticorrosive properties is obtained with the addition of both pigments, the coatings formulated with modified zinc phosphate having better performance. Both techniques showed results that can be correlated.