In-Situ Study of Single and Double Loop Reactivation Methods During the Characterisation of the Degree of Sensitisation of a Duplex Stainless Steel (UNS 1.4462) Using a Minicell and a Confocal Microscope

[EN] The aim of this work is to study the evolution of the electrode surface during the single and double reactivation methods at microscopic scale. The tested material has been a duplex stainless steel (UNS 1.4462) in its as-received state and heated at 825 degrees C for 1 hour in an inert atmosphere. Tests have been carried out in an electrochemical minicell that can be put in the stage of a confocal microscope. These devices allow the in-situ observation of the electrode surface at microscopic scale during the tests. Differences in the evolution of the electrode surface have been observed between the single and the double loop methods. Furthermore, the sensitised sample shows different evolution during the electrochemical tests than the as-received sample. These differences are due to the formation of new phases during the heat treatment. Therefore, the minicell permits obtaining additional information during the electrochemical characterisation of the degree of sensitisation in duplex stainless steels.We wish to express our gratitude to MICINN (CTQ2009-07518), to FEDER, to the Generalitat Valenciana for its help in the CLSM acquisition (MY08/ISIRM/S/100), and to Dr. Asunción Jaime for her translation assistance.Leiva García, R.; Muñoz-Portero, M.; Garcia-Anton, J. (2011). In-Situ Study of Single and Double Loop Reactivation Methods During the Characterisation of the Degree of Sensitisation of a Duplex Stainless Steel (UNS 1.4462) Using a Minicell and a Confocal Microscope. International Journal of Electrochemical Science. 6(3):830-846. http://hdl.handle.net/10251/61142S8308466

Influence of sensitisation on the corrosion behaviour of Alloy 926 (UNS N08926) in concentrated aqueous lithium bromide solutions at different temperatures

[EN] The aim of this work is to study the influence of sensitisation to intergranular corrosion on a highly alloyed austenitic stainless steel, Alloy 926 (UNS N08926). Some specimens of this steel have been heated in an argon atmosphere at 825 degrees C during 1 hour. The degree of sensitisation has been characterised by means of SEM, etching (with oxalic acid), and electrochemical reactivation methods (single and double loop tests). The corrosion behaviour of sensitised and unsensitised Alloy 926 has been analysed in a concentrated aqueous lithium bromide (LiBr) solution of 992 g/L by means of cyclic potentiodynamic curves at different temperatures. The results indicate that chromium carbide precipitates reduce the pitting potential value of Alloy 926. Besides, the pitting potential decreases with temperature. On the other hand, the corrosion potential and open circuit potential values increase with temperature and sensitisation.We wish to express our gratitude to MICINN (CTQ2009-07518), to FEDER, to Dr. Helena Alves from Krupp VDM for supplying the materials, and to Dr. Asunción Jaime for her translation assistance.Leiva García, R.; Muñoz-Portero, M.; Garcia-Anton, J. (2011). Influence of sensitisation on the corrosion behaviour of Alloy 926 (UNS N08926) in concentrated aqueous lithium bromide solutions at different temperatures. International Journal of Electrochemical Science. 6(2):442-460. http://hdl.handle.net/10251/61141S4424606

Effects of Hydrodynamic Conditions and LiBr Concentration on the Corrosion of Copper in LiBr Absorption Machines

Refrigeration absorption machines are again considered as suitable refrigeration systems and they are replacing compression machines due to the ban of chlorofluorocarbons (CFCs) and the strict regulations of hydrochlorofluorocarbons. Lithium Bromide (LiBr) is one of the most widely used absorbents in refrigeration technology. However, the operating conditions of absorption machines (high concentration and high temperature) can cause serious corrosion problems in the structural materials. Corrosion problems can be enhanced by the hydrodynamic conditions of the system. The present work studies of the influence of hydrodynamic conditions on copper corrosion under different LiBr conditions. Polarisation potentiodynamic curves obtained following ASTM G-5 were used to study the influence of the LiBr concentration and hydrodynamic conditions. Parameters such as corrosion current density and corrosion potential were obtained from the potentiodynamic curves. A rotating disk electrode (RDE) was used to determine the hydrodynamic conditions. Three LiBr solutions of different concentration (400 g/l, 700 g/l, and 850 g/l) at 25 degrees C and different rotation rates (0 r.p.m. - 3000 r.p.m.) were used during the tests. Results show that an increase of the bromide concentration and rotation rate favours copper corrosion and enhances anodic dissolution. The effects of the hydrodynamic conditions are smaller at higher LiBr concentrations.Leiva García, R.; Muñoz-Portero, M.; Garcia-Anton, J.; Sánchez Tovar, R. (2012). Effects of Hydrodynamic Conditions and LiBr Concentration on the Corrosion of Copper in LiBr Absorption Machines. International Journal of Electrochemical Science. 7(2):1332-1347. http://hdl.handle.net/10251/61162S133213477

Study of the sensitisation process of a duplex stainless steel (UNS 1.4462) by means of confocal microscopy and localised electrochemical techniques

When duplex stainless steels are heated, they can become sensitised and intermetallic phases can appear. In this work, samples of duplex stainless steel, UNS 1.4462, have been heated (850 degrees C for 1 and 2 h) in a heating unit that can be accommodated to a confocal microscope in order to study the morphological changes in-situ. The electrochemical behaviour of the samples has been analysed by means of conventional and localised electrochemical techniques. According to the results, there is a general decrease in the steel resistance to localised corrosion; this decrease can be related to defects in the formed passive film.We wish to express our gratitude to MICINN (CTQ2009-07518), to Universitat Politecnica de Valencia (CEI-01-11), to the Generalitat Valenciana for its help in the CLSM acquisition (MY08/ISIRM/S/100), to Professor Alda Simoes and Andreia Marques for the help on LEIS measurements and to Dr. Asuncion Jaime for her translation assistance.Leiva García, R.; Fernandes, JS.; Muñoz-Portero, M.; Garcia-Anton, J. (2015). Study of the sensitisation process of a duplex stainless steel (UNS 1.4462) by means of confocal microscopy and localised electrochemical techniques. Corrosion Science. 94:327-341. https://doi.org/10.1016/j.corsci.2015.02.016S3273419

Study of the sensitisation of a highly alloyed austenitic stainless steel, Alloy 926 (UNS N08926), by means of scanning electrochemical microscopy

The feedback mode of a scanning electrochemical microscope (SECM) was applied to study differences in the reactivity of a highly alloyed austenitic stainless steel, Alloy 926 (UNS N08926), in its unsensitised and sensitised state. Alloy 926 was heated at 825 °C for 1 h in an inert atmosphere in order to produce a sensitised metallurgical condition. Sensitisation was due to chromium carbide formation at the grain boundaries. The oxygen reduction reaction was used as an indicator to monitor the effect of the sensitisation process on the corrosion activity of the Alloy 926 surface in a 35 g l−1 NaCl solution. Higher oxygen consumption was observed above the sensitised sample than above the unsensitised sample due to differences in the oxide films of the two alloy conditions