Steel corrosion protection by means of alkyd paints pigmented with calciumacid phosphate

The use of classic anticorrosive pigments is becoming more and more restric ted by increasing environmental concerns; they are gradually being replaced by zinc phosphate and related compounds. Other anticorrosive pigments such as surface-exchanged silicas were also proposed. The object of this resear ch is to study the anticorrosive properties of calcium acid phosphate as an inhibitive pigment, introducing a careful selection of complementary pigme nts in order to achieve an efficient anticorrosive protection. Several alky d paints were prepared and evaluated through accelerated and electrochemica l tests. The nature of the passive film formed was also studied. Paint cont aining zinc oxide and calcium carbonate (50/50) as complementary pigments s howed the best performance in the salt spray test. Zinc oxide and calcium c arbonate decreased film permeability and improved steel passivation. The pa ssive film was composed of ferric oxyhydroxide, the pores of which became p lugged by ferric phosphate.