Improvement of the electrochemical behaviour of Zn-electroplated steel using regenerated Cr(III) passivation baths

Conversion coatings based on trivalent chromium are more sensitive to the presence of zinc and iron impurities than the chromate formulations. This fact contributes to a decrease in the quality of passivation and to the generation of a significant amount of hazardous liquid waste. Recently, a new eco-innovative process based on Emulsion Pertraction Technology (EPT) is being implemented at industrial scale for selectively removing Zn and Fe from spent passivation baths in order to enhance the lifetime of the Cr (III) baths. In this study, the effect of Zn and Fe removal on the electrochemical behaviour of Zn-electroplated steel samples was evaluated by means of polarisation curves and electrochemical impedance spectroscopy measurements at open circuit potential conditions in 3.5 g/L NaCl solutions. The main objective was to assess the benefits brought by EPT using electrochemical methods. Cr (III) passivation baths regenerated using the EPT process have been compared to the bath used in a local industry as well as to fresh and spent baths. According to the results, the samples passivated in the EPT regenerated bath showed a significant improvement in their electrochemical behaviour compared to the samples passivated in the spent baths. This study concluded the suitability of EPT for regenerating Cr (III) passivation baths

Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions

tThe influence of temperature and the effect of aggressive anions on the electrochemical behaviour of UNSN08031 stainless steel in a contaminated phosphoric acid solution were evaluated. Stabilisation of thepassive film was studied by potentiodynamic polarisation curves, potentiostatic tests, electrochemicalimpedance spectroscopy (EIS) measurements, Mott Schottky analysis and X-ray photoelectron spec-troscopy (XPS). The stability of the passive film was found to decrease as temperature increases. The filmformed on the stainless steel surface was a n-type semiconductor and the XPS spectrum revealed thepresence of fluoride ions.Authors express their gratitude to the Ministry of Education of Spain (MHE2011-00202) for its financial support during the stay at University of Manchester, to MAEC of Spain (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09 and D/030177/10) and to the Generalitat Valenciana (GV/2011/093) for the financial support. The authors would also like to acknowledge the support of the School of Materials at the University of Manchester for providing analytical and technical support for the study.Escrivá Cerdán, C.; Blasco Tamarit, ME.; García García, DM.; García Antón, J.; Akid, R.; Walton, J. (2013). Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions. Electrochimica Acta. 111:552-561. https://doi.org/10.1016/j.electacta.2013.08.040S55256111

Passivation behaviour of Alloy 31 (UNS N08031) in polluted phosphoric acid at different temperatures

The influence of temperature (20–80 °C) and chloride concentration (0.06–0.42 wt.% KCl) on the electrochemical behaviour of the UNS N08031 was studied in 40 wt.% polluted phosphoric acid solution. Passivation behaviour was investigated by using potentiostatic tests at different potentials. From the linear regions of the log i vs. log t transients, the parameter n was obtained. The results showed that the applied potential hardly affects on the passivation rate n. However, n values decreased when temperature increased. The values of n demonstrated that the passive film formed on Alloy 31 was compact and highly protective.The authors express their gratitude to the MAEC of Spain (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09 and D/030177/10), to Programa de Apoyo a la Investigacion y Desarrollo de la UPV (PAID-06-09) and to the Generalitat Valenciana (GV/2011/093) for the financial support and to Dr. Asuncion Jaime for her translation assistance.Escrivá Cerdán, C.; Blasco Tamarit, ME.; García García, DM.; García Antón, J.; Guenbour, A. (2012). Passivation behaviour of Alloy 31 (UNS N08031) in polluted phosphoric acid at different temperatures. Corrosion Science. 56:114-122. https://doi.org/10.1016/j.corsci.2011.11.014S1141225

Study of passive films formed on AISI 316L stainless steel in non-polluted and underwater-volcano-polluted seawater

This work studies the semiconducting behavior of passive films formed on AISI 316L (UNS S31603) in two different seawater solutions, non-polluted and polluted, collected from the volcano of El Hierro Island. Polarization measurements, potentiostatic passivation tests, electrochemical impedance spectroscopy, and capacitance measurements were performed. Results show that the polluted seawater worsens passivation kinetics. Additionally, passive films formed on AISI 316L stainless steel in polluted seawater have been found to be less protective than those formed in non-polluted seawater, showing a more defective structure, owing to the acidity of the polluted medium.Fernández Domene, RM.; Sánchez Tovar, R.; Escrivá Cerdán, C.; Leiva García, R.; Garcia-Anton, J. (2014). Study of passive films formed on AISI 316L stainless steel in non-polluted and underwater-volcano-seawater. Corrosion. 70(4):390-401. doi:10.5006/0934S39040170