Galvanic coupling effects on the corrosion behavior of the 6061 aluminum alloy used in research nuclear reactors

The 6061 alloy is used in different thermomechanical conditions in research nuclear reactors. Nuclear fuel plates are manufactured by the picture frame technique (PFT) and the 6061 alloy is used as cladding for the nuclear fuel “sandwiches”. After the process, these nuclear plates are placed in a case composed of 6061-T6 alloy. In this work, the galvanic effects of coupling the 6061 alloy in the T6 and PFT conditions on the corrosion behavior was investigated in solutions of different chloride contents. The results showed that galvanic corrosion was favored due to the different microstructural features related to these two thermomechanical conditions of the 6061 alloy. The 6061 alloy in the PFT condition was cathodic to the alloy in the T6 condition. Local electrochemical techniques were useful in characterizing the electrochemical behavior of the coupled alloys

Synthesis and evaluation of anionic schiff bases as pitting corrosion inhibitor for stainless steel 304 in NaCl solution

ECS Meeting Abstracts; Volume MA2019-01The high corrosion resistance of austenitic stainless steel (SS) arises from the formation of a thin, adherent and protective passive film that forms instantaneously on the surface. Unfortunately, in the presence of aggressive ions like chloride anion, the corrosion resistance of passivated stainless steel is limited by local breakdown and pit nucleation [1]. An efficient and economical method to decrease the metal dissolution in aggressive media is the use of corrosion inhibitors. A large number of organic molecules containing electronegative functional groups, such as ¿-electron systems or heteroatoms have been proposed for the inhibition of general metallic corrosion, although the use of organic compounds as pitting corrosion inhibitors in neutral solutions is still rather limited. On the other hand, inorganic-based compounds such as chromates and nitrates are also used as pitting corrosion inhibitors for SS in aggressive media; however the application of these inorganics, especially chromates and phosphates, is not recommended because of their biological toxicity. More recently, Schiff bases have been described as cost effective inhibitors due to their robust and convenient synthesis from inexpensive precursors. They are organic compounds containing the imine (-C=N-) functional group in their structure. Schiff base derivatives with additional heteroatoms, such as N and O, and aryl groups have been used as corrosion inhibitors [2,3], but their application as pitting corrosion inhibitors has not been described. In the present study, three new anionic Schiff bases were synthesized through by reacting para-amino benzoic acid with several aromatic aldehydes containing different functional groups in their para- site. They were designed to improve water solubility, to enhance coordination with Fe atoms by including N and O heteroatoms, two benzene rings and the imine group in their chemical structure, and to be large enough to create heavy hydrophobic complex with Fe+3. The inhibitor efficiency of these compounds as pitting corrosion inhibitor for 304 SS in neutral 0.1 M NaCl was examined using potentiodynamic polarization measurements, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) . Polarization data show the shift of the pitting potential to more positive values with increasing inhibitor concentration. Surface analysis shows chromium enrichment at the metal surface under anodic polarization in the passive region of the metal when the inhibitor compound is present in the test solution, whereas no effect occurs under open circuit conditions. XPS data show that the inhibitor molecules do not adsorb on the clean metal, but on the passive layer instead