Abstract:

The mechanism, protective properties, microstructure, phase composition of coats on steel have been investigated. According to the developed method, the coats were deposited potentiodynamically and potentiostatically in an aqueous solution of sodium tripolyphosphate. Based on the results of electrochemical studies, it has been established, that on potentiodynamic curves, characterizing the corrosion behavior of low-carbon steel in an aqueous sodium TPP solution, up to three passivation plateaus can be observed. The multi-stage formation mechanism of tripolyphosphate coat has been proposed. The mechanism includes three stages: at the start the adsorptive film is formed, that afterwards is modified two times, accompanied by a change of properties and composition. By using the methods of optical and scanning electron microscopy, X-ray diffraction, it has been established that the coat formed in an aqueous Na TPP solution by the potentiodynamic method under conditions of complete passivation, is composed of two layers: first – thin, compact layer, that contains a crystalline phase of phosphate nature, and second – thick hydrophilic layer, capable of drying. Such coat possesses the best protective properties in 0.1 N Na2SO4 solution, that models conditions of atmospheric corrosion. The nature of the electrochemical formation mechanism of tripolyphosphate coats and features of their structural and phase composition have been established. The further studies will be directed at the development of effective deposition methods of tripolyphosphate coats with estimated set of properties for the protection of metal goods from atmospheric and high-temperature gas corrosion. Author Biographies Elena Vlasova, SHEI «National Metallurgical Academy of Ukraine» Gagarina ave., 8, Dnepr, Ukraine, 49005 PhD, Associate Professor Department of coating, composite materials and metal protection from corrosion. 

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