MÖSSBAUER EFFECT INVESTIGATION OF FE-C STEEL ELECTROLYTIC GALVANISATION

Autor/autori: Ion BIBICU, Caius BULEA, Vasile RUS

Abstract: Galvanizing is a very well known industrial process for anticorrosive and protection coatings. At first sight, galvanizing should not need any further important research and development involvement but many reasons contradict this appreciation: the constant emergence of new sophisticated steel grades, the sustainable requirement of strictly controlled microstructure, new designed surface treatment, etc. There are, relatively, few studies dedicated to electrogalvanizing, most of these are dedicated to hot-dip galvanizing. The Mossbauer effect allows nondestructive superficial studies for iron compounds and remains today as the only technique to reliably monitor in situ the Fe–Zn phase composition from the interface steel-zinc coating. Samples of industrial Fe-C steel with low C concentrations (up to 0.04 wt. %) were electrogalvanized. We were interested mainly to investigate the influence of the sample preparation procedure before galvanization and the interface between steel and Zn coating. It is possible to obtain new information about mechanism and the kinetics of the coating formation.The Mossbauer measurements were performed in two geometries: transmission and backscattering. By transmission geometry, which imply a sample preparation, were obtained sample volume information. By backscattering geometry, which do not imply sample preparation, were obtained surface data before and after electrogalvanizing. Surface measurements were realized by detection of conversion electron (CEMS) and conversion X-ray (CXMS). The maximum studied depths are: 200 nanometres by conversion electrons and 20 microns by X-rays. The CEMS spectra of the sample prepared for deposition reveals a magnetic anisotropy: a preferred direction of the magnetic moments of the iron nuclei. By contrast the transmission spectra and the CXMS spectra (with an exception) show that the magnetic moments inside the sample are practically in a random arrangement. CEMS spectrum for a sample shows the presence of an additional compound without magnetic ordering where Fe has +3 valence. CXMS spectra of the interface are very close to that obtained before galvanizing and do not put in evidence a new compound at interface steel-Zn coating

Keywords: low carbon steel, electrolytic galvanization , Mössbauer effect

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