Details of the mechanism of dissolution of iron–zinc coatings based on the δ-phase in acidic media

• A.I. Biryukov¹, O.A. Kozaderov², R.G. Galin³, D.A. Zakharyevich¹ and V.E. Zhivulin^4,5

¹ Chelyabinsk State University, 129 Br. Kashirinykh str., 454001 Chelyabinsk, Russian Federation
² Voronezh State University, 1 Universitetskaya pl., 394018 Voronezh, Russian Federation
³ Vika Gal Ltd., 7 Molodogvardeytsev str., 454138 Chelyabinsk, Russian Federation
⁴ South Ural State University (Research University), 76 Lenin pr., 454080, Chelyabinsk, Russian Federation
⁵ South Ural State Humanitarian Pedagogical University, 69 Lenin pr., 454080 Chelyabinsk, Russian Federation

Abstract: The anodic corrosion behavior of diffusion zinc coatings, the main component of which is the delta phase, was studied in acidic media. Diffusion zinc coatings were obtained by heating in zinc powders, the surface of the particles of which is coated with zinc oxide. Gravimetric measurements, potentiometry, scanning electron microscopy and X-ray structural analysis have been used to study the characteristics of anodic corrosion as well as the evolution of surface morphology. The concentrations of zinc and iron ions were determined in acidic corrosive media by atomic absorption spectroscopy. The concentrations of zinc and iron in the diffusion zinc coatings were determined using X-ray fluorescence spectroscopy. The data obtained were used to calculate the selectivity coefficients of dissolution of elements. It is shown in the work that the dissolution rate nonlinearly depends on the concentration of zinc and the thickness of the coating. It was found that the corrosion of the zinc-rich δ-phase is accompanied mainly by the dissolution of zinc in it. Dezincification is accompanied by surface morphological development and the formation of multiple cracks and pores, which, in turn, initiate galvanic corrosion. Prolonged acidic corrosion of the iron–zinc coating leads to deep dezincification with phase transformation.

Keywords: diffusion iron–zinc coatings, selective dissolution, structurally selective corrosion, sherardizing

Int. J. Corros. Scale Inhib., 2020, 9, no. 4, 1477-1489 PDF (975 K)
doi: 10.17675/2305-6894-2020-9-4-18

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