Study On The Anodic Behavior Of Austenite Stainless Steel In AlCl₃-EMIC Ionic Liquid And Its Mechanism

Since the technological maturity of stainless steels,i.e.advanced fabrication routes,welding technologies and general industrial experience,they were also employed as structural materials for ITER test blanket modules.In fusion reactor,the permeability of hydrogen isotopes for stainless steel is generally high in the operational temperature range.In order to handle radioactive tritium,the use of coatings on the surface of stainless steel as tritium permeation barriers(TPB)was found to be an efficient method.Recently,an Al-electroplating ionic liquid process has shown to be an effective method to fabricate a homogeneous TPB with efficient reduction of tritium permeation on the complex geometries surface of stainless steel.The electrolytic etching of the stainless steel in acidic AICl3-EMIC was found to be an effective pretreatment to improve adhesion of deposited Al.However,the underlying mechanism of the stainless steel electrochemical etching in acidic AICl3-EMIC has not been clearly revealed yet.Therefore,it is necessary to study the anodic behavior of austenite stainless steel and it's mechanism in ionic liquid.At the same time,it is an important topic in the research area of electrochemical in ionic liquid.In the present paper,anodic behavior of Cr,Fe and austenite stainless steel were studied by LSV,chonopotentiometry,SEM,EDS,XRD,XPS,UV-vis and Raman.The mechanism of general broken of oxide film on stainless steel was studied using the electrochemical in situ Raman.At last,based on the above research,the aluminide coatings was prepared on the inner surface of 316 stainless steel tube.The results showed that the native oxide film on the Cr electrode showed great effects on the anodic dissolution.During the OCP test,the native oxide film on the Cr electrode can be partially broken.After two subsequent LSV in ionic liquid,the native oxide film on the Cr electrode can be completely removed.The Cr electrode without oxide film exhibited active dissolution and then passivation during the anodic polarization process,attributed to the oxidation of Cr to Cr(?)and to the formation of CrCl3,respectively.The latter acts as a passive film on the electrode surface,consisting of particles with average diameter of about 50 nm.The Fe electrode showed active dissolution and then passivation during the LSV test.The passive film is composed by the FeCl2 particle with average diameter of about 500 nm.The formation of FeCl2 film is attributed to the variation of the electrolyte Lewis acidity from acidic to neutral at the interface during the dissolution process of Fe.The reason for the variation of the electrolyte Lewis acidity may be due to the consumption of Al2Cl7-by coordinating with dissolved Fe ion in acidic AlCl3-EMIC ionic liquid.The oxide film of 304 and 316 stainless steel can be partially broken after first andic scan in ionic liquid.After two subsequent LSV in ionic liquid,the oxide film on the stainless steel can be completely removed.The stainless steel without oxide film showed active dissolution and then passivation behavior in the following LSV test.The homogeneous dissolution of stainless steel can be obtained after twice chonopotentiometry test.There is a critical potential(2.5 V)during the breakdown of oxide film on 316 stainless steel in ionic liquid.When the potential is samller than the critical potential,the location breakdown of oxide film occurred.On the contrary,the general breakdown of oxide film occurred.The general breakdown of oxide film is attribute to the produced Cl-,which come from the window reaction of ionic liquid,permeaing the oxide film.The structure of aluminide coating can be regulated by the thickness of Al coating before heat treatment.The aluminide coating of 1 ?m-Al sample was FeAl and Fe3Al.When the thickness of Al coating increased to 5 ?m,the structure of aluminide coating was Fe3Al/FeAl/Fe2Al5.The aluminide coating changed into Fe3Al/FeAl/Fe2Al5/FeAl3 with a 10 ?m-Al coating.