High performance alkyd paints based on platy kaolin for corrosion protection of steel

Calcination of kaolin presents an easy route to obtain high performance and eco-friendly anticorrosive filler. The objective of the present work was to prepare a new ecologically friendly inorganic filler, based on thermal treatment of kaolin to be used as an anticorrosive. This work studied the corrosion protection of medium oil-modified alkyd paints based on thermally treated kaolin at different temperatures. Paints were formulated with different pigment volume concentrations (PVCs) and critical pigment volume concentrations (CPVCs). The prepared paints were formulated with increasing content of kaolin, with PVC ranging from 10 to 30%. The physical and chemical properties of kaolin were evaluated at different temperatures. Particle shapes of thermally treated kaolin were characterized using scanning electron microscopy. The physico-mechanical properties of dry films, water vapor transmission and their corrosion properties using accelerated laboratory corrosion test were tested. The thermal treatment of kaolin enhanced both the oil absorption and the alkalinity. This led to alkyd results in saponification and consequently passivation of the substrate. Good wetting with alkyd resin gave homogeneous films without defects which resisted water and oxygen permeation and protected steel against corrosion. The results revealed that thermally treated kaolin at 400°C was the best at protecting steel substrates for all PVCs.