Paint systems formulated with ion-exchange pigments applied on carbon steel: Effect of surface preparation

Ion exchange pigments are a scientifically very interesting alternative to chromates that have not yet been fully explored. This study considers the following candidate anticorrosive pigments: calcium-exchanged silica (Si/Ca), hydrotalcite/vanadate (HT/V) and calcium bentonite (Bentonite/Ca).Paint systems manufactured with these ion exchange pigments have been subjected to adhesion, permeability and accelerated corrosion laboratory tests (humidity condensation (HC) and salt fog (SF)), simulating environments of low and high corrosivity, in order to assess their anticorrosive behaviour in comparison with a zinc chromate reference system. For this purpose the degree of coating degradation has been monitored: blistering, underfilm corrosion and delamination from scribe.This paper focuses on the effect of several parameters of interest when designing a paint system: (a) sanding treatment of the base steel prior to application of the primer paint; (b) pigment concentration in the primer paint coating; and (c) application of a topcoat layer over the primer coating.