No abstract

The objective of this work was to gain a deeper insight into the behavior of zinc primer, containing either lamellar zinc alone or lamellar zinc mixed with an extender by means of accelerated tests in salt spray (fog) chamber and a 100% relative humidity cabinet. Mica, kaolin, and synthetic calcium silicate were used as extenders.Several series of coatings were designed and manufactured employing the following binders: 20 cP chlorinated rubber, a vinyl copolymer, an unsaturated polymer, or an epoxy resin.A simultaneous analysis of the experimental data was performed taking into account that the best performance is attained at pigment volume concentration (PVC) values equal to or slightly lower than the critical one (CPVC). Results indicate that for every lamellar zinc primer, it is possible to select an extender of high oil absorption as the spacer of the zinc particles attaining both very good blistering resistance and anticorrosive performance.

Lamellar micaceous iron oxide paints are successfully employed to provide longlife corrosion protection for metallic structures when exposed to highly aggressive environments. The aim of this work was to formulate and manufacture lamellar micaceous iron oxide paints, able to be used on the protection of steel structures exposed to water. Several formulation and manufacture variables were taken into account. Many paint films fail when they are saturated with moisture and blistering is a common failure because primers usually are not designed to allow the liquid to dissipate back out through the film. Consequently the film can not resist the formation of projections which result in local adhesion loss. For maximum durability, primers must be properly formulated and manufactured. Film permeability, which depends on paint composition (pigment volume concentration) and micaceous iron oxide dispersion time, seems to be the key characteristic controlling subsequent coating performance. Laboratory results indicated that lamellar micaceous iron oxide is a pigment which provides an anticorrosive action by providing a barrier effect. Film permeability must be compatible so as to attain a satisfactory rusting and blistering resistance.