Abstract
Structural characterization of compound material coatings is usually achieved using time-consuming and destructive techniques such as optical and electrical microscopy, which require the use of grinding processes not always compatible with the material. This paper reports on the effective use of a theoretical model based on X-ray diffraction to calculate the thickness and composition of thin oxide films formed on the surface of zinc coatings. Zinc coatings are widely used in industrial application as protective layers against the atmospheric corrosion of steel substrates. The thickness of single- and multi-layer coatings is estimated using grazing incidence X-ray diffraction and various incidence angles. The coatings were grown using hot-dip, pack cementation and thermal spray techniques, and their experimental characteristics were compared to the theoretically predicted values of thickness and composition. The results indicate the formation of a thin zinc oxide film on top of each coating, which acts as an isolation layer and protects the surface of the sample against the environmental corrosion. Finally, the penetration depth of the X-rays into the zinc-based coatings for grazing incidence and Bragg–Brentano X-ray diffraction geometries were calculated using theoretical equations and experimentally confirmed.
Highlights
Zinc coatings are technologically important for a wide range of protective applications including anticorrosion layers in wires, tanks and automotive manufacturing components depending on their chemical characteristics [1,2,3,4,5,6,7,8,9,10,11,12]
The samples grown using the hot-dip galvanizing process [1,2,3,4,8,13,14,16,18,19,20], chemical vapor deposition by pack cementation [5,6,7,8,13,14,16,21,22,23,24,25] and wire flame thermal spray [9,10,11,12,13,14,16,26,27,28] were examined using scanning electron microscopy (SEM), Bragg–Brentano and grazing incidence X-ray diffraction (XRD), with specific interest in the composition of the thin zinc oxide layer formed on the surface
Zinc coatings were grown on a commercial hot rolled low carbon steel sheet St-37 (information regarding the chemical composition are provided by the standard alloy numbering system of the regarding the chemical composition are provided by the standard alloy numbering system of the Society of Automotive Engineers (SAE) SAE 1010, Table 2) using three different growth techniques, namely hot-dip galvanizing, chemical vapour deposition by pack cementation and wire flame thermal namely hot-dip galvanizing, chemical vapour deposition by pack cementation and wire flame spraying, to verify the results presented in the previous section
Summary
Zinc coatings are technologically important for a wide range of protective applications including anticorrosion layers in wires, tanks and automotive manufacturing components depending on their chemical characteristics [1,2,3,4,5,6,7,8,9,10,11,12]. The samples grown using the hot-dip galvanizing process [1,2,3,4,8,13,14,16,18,19,20], chemical vapor deposition by pack cementation [5,6,7,8,13,14,16,21,22,23,24,25] and wire flame thermal spray [9,10,11,12,13,14,16,26,27,28] were examined using scanning electron microscopy (SEM), Bragg–Brentano and grazing incidence XRD, with specific interest in the composition of the thin zinc oxide layer formed on the surface. The described methodology is the first approach of a non-destructive theoretical monitoring procedure of zinc coatings after deposition or after exposure to aggressive environments
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