Abstract
Zinc-rich primers (ZRP) offer good anti-corrosive behaviour, and are an ecologically acceptable solution, when applied on carbon steel substrates that are rusted and contaminated with soluble salts (chlorides and sulphates), provided certain critical contamination thresholds are not exceeded. The use of phosphate-type co-pigments in ZRP formulations, could lead to an increase in tolerable critical levels for soluble salts. This work discusses the results of a comparative study carried out with ZRP and non-ZRP systems incorporating various types of co-pigments in several concentrations, applied on substrates contaminated with different chloride and sulphate levels. The study considers the results of atmospheric exposure test (24 months in Madrid atmosphere) and of accelerated humidity condensation tests.
Highlights
One of the most frequent causes of premature failure of anticorrosive paint coatings applied on steel structures is the presence of soluble salts, mainly chlorides and sulphates, at the metal/paint interface
The best behaviour is provided by zinc phosphate and calcium phosphate. This does not occur with the non-Zinc-rich primers (ZRP) systems, where the behaviour of the co-pigmented primers is very similar to that of the red lead primer, selected as reference, presenting notable problems after the level of [200-300] mg/m^
Worse behaviour is seen with the non-ZRP systems than with the ZRP systems, and there is a notable improvement in the case of the latter with the co-pigmented systems compared to the ZRP reference system
Summary
One of the most frequent causes of premature failure of anticorrosive paint coatings applied on steel structures is the presence of soluble salts, mainly chlorides and sulphates, at the metal/paint interface. Ecological criteria make it impossible to use the pigments tested in these early studies, since they contained Cd, Ba and Cr. there are other pigments, such as calcium phosphate, zinc phosphate and zinc-iron phosphate, which do not present these limitations and whose use as co-pigments in ZRPs may improve the anticorrosive behaviour of the latter, permitting an increase in the allowable critical levels of Cl~ and SO4 ~ at the metal/paint interface. Specimens of 1 2 . 5 x 8 cm were cut from carbon steel plate and degreased with acetone
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