Influence of preliminary mechanical and thermal treatment on the steady-state creep of metals
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INHIBITION OF CORROSION BY A MIXTURE OF NONCHROMATE PIGMENTS IN ORGANIC COATINGS ON GALVANIZED STEEL V. I. Pokhmurs’kyi, I. M. Zin’, and S. B. Lyon
UDC 621.193: 678.643
We consider several possible substitutes for toxic chromate pigments. Among the most promising compositions for the corrosion inhibition of galvanized steel with a protective organic coating, we should mention a mixture of phosphate- and calcium-containing pigments. As was shown earlier, such a mixture possesses a high efficiency under conditions of the corrosion of zinc and galvanized steel sheet; however, it is less efficient for the protection of carbon steels. This pigment mixture forms an adsorbed phosphate film on the metal and hinders the course of anodic and cathodic reactions. Zinc ions play an important role for obtaining a synergistic protective effect, increasing the coherence and decreasing the porosity of the deposited film. Traditional and local electrochemical methods (EIS and SVE) were used for studying the corrosion of galvanized steel with coatings in acid rain solution. The data obtained corroborated the high anticorrosive efficiency of a pigment mixture in an organic coating on galvanized steel. In addition, we established some specific features of its inhibiting action near defects in the coating.
Organic coatings on a metal do not form a completely impenetrable barrier for corrosive media. In the course of operation in a corrosive medium, they lose protective properties due to the formation of local defects. It is customary to introduce inhibiting anticorrosive pigments into the first ground coat of an organic coating in order to protect the metal surface at the moment of penetration of the corrosive medium into it. Chromates are the most efficient anticorrosive pigments, which favor the passivation of steel substrate at the sites of through defects of the coatings [1]. Chromates represent inhibitors of mixed type, which protect the metal against corrosion in a wide range of pH values (from 4 to 9) [2] and can also function as cathodic inhibitors in the case of low concentrations (less than 10 mg / liter). They protect metals well in a subacid industrial atmosphere. However, there is an urgent need to replace toxic chromate pigments by other, less harmful agents for the environment. Nontoxic phosphate pigments can serve as an alternative for chromates. Phosphate compounds used as anticorrosive pigments are poorly soluble, although their extracts protect steel weaker than chromates. However, when these pigments are dispersed in the mass of an organic binder, they possess satisfactory protective properties [3, 4]. They protect better in subacid media owing to ion exchange with binder molecules. Calcium-containing pigment based on silicon oxide is also recommended for application in anticorrosive prime coats as a substitute for chromates [5]. It inhibits predominantly the cathodic reaction, and its protective properties can improve as a result of combination with other inhibiting compounds. In the present work, we study the co
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