Preparation and characterization of electrolytic alumina deposit on austenitic stainless steel

Conversion coating modified by alumina has been studied as a way for improving the resistance to thermal oxidation of an austenitic stainless steel. Conversion coating, characterized by a particular morphology and strong interfacial adhesion with the substrate, facilitate the electrochemical deposition of ceramic layers and enhance their adhesion to the substrate. The influence of the current density and treatment time on alumina deposit was studied using statistical experimental designs like Doehlert uniform shell design. After heating, coatings present a continuous composition gradient with refractory compounds at the surface. The behavior at high temperature (1000 8C) of the alumina coating was investigated. The presence of alumina increases the oxidation resistance of an austenitic stainless steel at 1000 8C. The morphology and the chemical composition of the deposit are analyzed. Results on the thermal stability of coating on austenitic stainless steel are presented

Effect of Temperature on Galvanic Corrosion of Non-Welded/Welded AISI 316L Stainless Steel in H3PO4

[EN] Galvanic corrosion of non-welded/welded AISI 316L SS at different temperatures (25 degrees C to 60 degrees C) at a Reynolds number of 1456 in phosphoric acid has been studied using polarization curves (by the mixed potential theory) and zero resistance ammeter (ZRA) measurements. Imposed potential measurements provide more active predicted coupled potentials and higher Galvanic current densities than those obtained using ZRA measurements. Polarization curves show that the anode of the pair is the non-welded AISI 316L. Galvanic current density values obtained from polarization curves increase with temperature. ZRA tests present the highest i(G) values at 60 degrees C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluate the Galvanic phenomenon importance. Both techniques present the most positive potentials at the highest temperature.The authors would like to express their gratitude to the Spanish MAEC (PCI Mediterráneo C/018046/08).Sánchez Tovar, R.; Montañés, M.; Garcia-Anton, J.; Guenbour, A. (2010). Effect of Temperature on Galvanic Corrosion of Non-Welded/Welded AISI 316L Stainless Steel in H3PO4. ECS Transactions. 25(37):63-81. https://doi.org/10.1149/1.3407548S6381253

Corrosion Behaviour of a Highly Alloyed Austenitic Alloy UB6 in Contaminated Phosphoric Acid

The influence of temperature (20-80°C) on the electrochemical behaviour of passive films anodically formed on UB6 stainless steel in phosphoric acid solution (5.5 M H3PO4) has been examined by using potentiodynamic curves, electrochemical impedance spectroscopy, and Mott-Schottky analysis. UB6 stainless steel in contaminated phosphoric acid is characterised by high interfacial impedance, thereby, illustrating its high corrosion resistance. The obtained results show that the films behave as n-type and p-type semiconductors in the potential range above and below the flat band potential, respectively. This behaviour is assumed to be the consequence of the semiconducting properties of the iron oxide and chromium oxide regions which compose the passive film

Effect of potential formation on the electrochemical behaviour of a highly-alloyed austenitic stainless steel in contaminated phosphoric acid at different temperatures

The electrochemical behaviour of the highly alloyed austenitic stainless steel UNS N08031 (Alloy 31) in a contaminated phosphoric acid solution is studied using potentiodynamic curves, EIS and Mott–Shottky. The relative stability of the films formed on Alloy 31 has been studied after a pre-passivated treatment at 0.3, 0.5, 0.8 and 1 VAg/AgCl, potentials within the passive domain. The protection of Alloy 31 was provided by the inner oxide film, while the outer film was more defective. The electronic-semiconducting properties of the passive films have been correlated to corrosion resistance. Passivated Alloy 31 at 0.8 VAg/AgCl showed lower concentration of charge carriers, which beneficially affects the protecting and electronic properties of the passive oxide film.The authors wish to 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), to the Generalitat Valenciana (GV/2011/093) for the financial support and to Dra. Asuncion Jaime for her translation assistance.Escrivá Cerdán, C.; Blasco Tamarit, ME.; García García, DM.; García Antón, J.; Guenbour, A. (2012). Effect of potential formation on the electrochemical behaviour of a highly-alloyed austenitic stainless steel in contaminated phosphoric acid at different temperatures. Electrochimica Acta. 80:248-256. https://doi.org/10.1016/j.electacta.2012.07.012S2482568

Galvanic Corrosion of the Base AISI 316l/Micro-Plasma Arc Welded AISI 316l in Polluted Phosphoric Acid Media at Different Temperatures

[EN] In this work, the galvanic corrosion of the base AISI 316L stainless steel/micro-plasma arc welded AISI 316L stainless steel in phosphoric acid solutions polluted with sulphuric acid and chlorides was studied by means of the Zero-Resistance Ammeter technique. Experiments were performed at different temperatures (25, 40 and 60 degrees C) under flowing conditions (Reynolds number of 1456). Galvanic current density values are negative during the first hour of the test indicating that the welded alloy is corroding; then, they shift towards positive values indicating that the base stainless steel corrodes. Galvanic current density values reached stable values from the third hour of the tests performed at 25 and 40 degrees C, and during the last two hours of the test at 60 degrees C indicating passivation of the base alloy. Uniform corrosion processes occur for the AISI 316L alloy in polluted phosphoric acid solutions. Galvanic current densities increase with temperature according to Arrhenius plot. Impurities seem to increase galvanic corrosion and hinder passivation processes.This work was supported by the Spanish MAEC (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09, D/030177/10). The authors also wish to express their gratitude to Dr. Asuncion Jaime for her translation assistance.Sánchez Tovar, R.; Montañés Sanjuan, MT.; Garcia-Anton, J.; Guenbour, A. (2011). Galvanic Corrosion of the Base AISI 316l/Micro-Plasma Arc Welded AISI 316l in Polluted Phosphoric Acid Media at Different Temperatures. International Journal of Electrochemical Science. 6(8):3656-3670. http://hdl.handle.net/10251/61144S365636706

Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures

[EN] This paper studies the general corrosion behaviour of the micro-plasma arc welded AISI 316L stainless steel in phosphoric acid at different temperatures (25-60°C) and at a Reynolds number of 1456. Galvanic corrosion has been studied using zero-resistance ammeter (ZRA) measurements and polarization curves (by the mixed potential theory). Results show that the microstructure of the stainless steel is modified due to the micro-plasma arc welding procedure. Coupled current density values obtained from polarization curves increase with temperature. ZRA tests present the highest iG values at 60°C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluates the importance of the galvanic phenomenon. Both techniques present the most positive potentials at the highest temperature. This study reveals that micro-plasma arc welded AISI 316L stainless steels are appropriated working in the studied H3PO4 media from a corrosion point of view for all the temperatures analysedThe authors would like to express their gratitude to the Spanish MAEC (PCI Mediterráneo C/8196/07, C/018046/08, D/023608/09) and to Asuncion Jaime for her translation assistance.Sánchez Tovar, R.; Montañés Sanjuan, MT.; García Antón, J.; Guenbour, A.; Ben Bachir, A. (2011). Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures. Corrosion Science. 53(4):1237-1246. https://doi.org/10.1016/j.corsci.2010.12.017S1237124653

Effect of Welding on The Corrosion Behaviour of a Highly Alloyed Austenitic Stainless Steel UNS N06027 in Polluted Phosphoric Acid Media

[EN] The objective of this work is to study the effect of welding on the corrosion resistance of the austenitic stainless steel Alloy 59 (UNS N06027) as well as the galvanic corrosion generated by the base/weld pair estimated from the polarisation curves according to the mixed potential theory. The materials have been exposed to polluted phosphoric acid at several temperatures. The microstructure of the samples was studied by SEM and EDX analysis. The results show that the welding process shifts the corrosion potential values to more anodic potentials. The corrosion current densities and the passive current densities also increased by the effect of welding. This effect is aggravated with the increase in temperature. Open circuit potential values were located in the passive zone of the potentiodynamic curves, which means that the materials passivated spontaneously.The galvanic corrosion of the pair is not severe in the studied conditions. The ratio between the galvanic current density of the pair and the corrosion current density of the uncoupled anode is less than 5, which implies compatibility of the members in the couple.The authors acknowledge the Spanish Ministerio de Asuntos Exteriores y Cooperacion "MAEC" (PCI Mediterraneo C78196/07, D/023608/09, D/030177/10 and D/030177/10) for its financial support to the Krupp VDM Group (Germany) for the supplied alloys and to Dr. Asuncion Jaime for her translation assistance.Bakour, S.; Guenbour, A.; Bellaouchou, A.; Escrivá Cerdán, C.; Sánchez Tovar, R.; Leiva García, R.; Garcia-Anton, J. (2012). Effect of Welding on The Corrosion Behaviour of a Highly Alloyed Austenitic Stainless Steel UNS N06027 in Polluted Phosphoric Acid Media. International Journal of Electrochemical Science. 7(11):10530-10543. http://hdl.handle.net/10251/61163S105301054371

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