Anticorrosive Zn Free Pigments: their performance

 
Anticorrosive pigments are key compounds in coating formulations to protect the metallic substrates on which coatings are applied. As these products are subjected to an increasing demand for more sustainable products, new ranges of zinc-free anticorrosive pigments are being developed. Their activity and protection mechanism are based on the combination of selected inorganic and organic compounds and they consist in a specially tailored core part based on silicate and phosphate chemistries with an organic surface treatment. Their anticorrosive mechanism is based on the precipitation of phosphate and oxide-like compounds that provide anodic and cathodic protection of the metal substrate, while the organic part increases the barrier effect and the compatibility with the resin, enhancing the anticorrosive performance of the paint. The methodology used to develop new pigments and to verify their anticorrosive properties involves both formulating and testing through the use of accelerated tests. The most common are the evaluation of coatings by means of the salt fog spray and prohesion tests, which require very long exposure times and only a qualitative evaluation of the rusting, adhesion, blistering or cracking in the different exposed zones. In the present work the development of anticorrosive pigments by means of classic accelerated tests but also fast electrochemical techniques is presented as an alternative to the traditional methodology.