Corrosion Characteristics And Mechanism Of E52100 Steel In Imidazolium Ionic Liquids

Ionic liquids (ILs) is used as a new type of green solvent in many fields and have received increasing interest both in academic and industrial fields over the past decade. The corrosion of ionic liquids is a common and critical problem in basic research and industrialized process, and also is one of the main problems of blocking industrialization of ionic liquids. In recent years, the research results show that ILs is expected to applied in field of tribology. However, the corrosion results of ILs on related materials is unclear. So it is important to do some research on these vital corrosion problems prior to the extensive application of ionic liquids. Corrosion characteristics and mechanism of E52100 bearing steel in imidazolium ionic liquids were studyed in this paper, which provide theoretical basis for the further application of ionic liquids.Corrosion characteristics of E52100 steel in 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim]BF4) ionic liquid, 1-ethyl-3-methyl imidazolium tetrafluoroborate ([emim]BF4) and 1-octyl-3-methyl imidazolium tetrafluoroborate ([omim]BF4) in three different conditions (oxygen, temperature and water content) have been studied. Electrochemical tests (open-circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization curves) were performed in order to characterize the corrosion resistance of the steel samples in three ionic liquids. Their morphology and chemical composition were investigated using SEM microscopy coupled with ED AX microanalysis and X-ray diffraction. Moreover, surface analysis techniques were used to investigate the corrosion behavior of E52100 steel in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6) and chloride 1-butyl-3-methyl imidazolium ([bmim]Cl).The results showed that E52100 steel could corrode in 1-butyl-3-methylimidazolium tetrafluoroborate, and the presence of oxygen, the increasing of temperature and moisture could accelerate the corrosion rate of E52100 steel in the ionic liquid, while among these factors, the water content had the most significant influence on the corrosion. The surface corrosion product composition analysis showed that the main corrosion products might be iron fluoride compounds and iron oxides.The electrochemical impedance spectroscopy showed that with the increase of carbon lengths, capacitive loop radius increases, as well as electrochemical impedance increase. The fitting results indicted that the main reason for this phenomenon was the increase of the charge transfer resistance. At the same time, with the existence of oxygen, the corrosion behavior of E52100 steel in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid was different from the other two kinds of ionic liquids, which the results of surface analysis reflected. The surface analysis results also showed that the corrosion products were different in three ionic liquids with the presence of water.The type of corrosion products was also associated with the anion type. In [bmim]PF6 and [bmim]Cl ionic liquids, with the existence of oxygen, the surface of steel samples appeared pitting corrosion. With the presence of water, phosphide and chloride exist among the corrosion products.