Chromium electrodeposition from [BMIm][BF4] ionic liquid

摘要

The electrodeposition of black chromium coatings from ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate with chromium chloride, and the chemical composition of the deposits are discussed in this article. The UV-Vis spectra recorded for chromium(III) species in 1-butyl-3-methylimidazolium tetrafluoroborate suggest that along with the chromium(III) complexes containing three ligands, there are some amounts of chromium species containing four ligands in the bath employed. The cathodic process of chromium electrodeposition in the employed ionic liquid is complicated by the electrochemical reduction of water molecules, which is followed by chemical disintegration of tetrafluoroborate ions. The surface morphology of black chromium films deposited potentiostatically (-1.5 to -2.0 V) at 85 °C shows nodules and microcracks increasing in size with cathodic potential. Analysis of the X-ray photoelectron spectra recorded from surface to depth of the deposit has shown that the black oxide-rich chromium coating consists of chromium in both oxide and metallic states with small impurities of other elements (fluorine, boron, carbon and nitrogen) and the surface is covered with a thin layer of organic substances. The results of this study show that 1-butyl-3-methylimidazolium tetrafluoroborate may be considered as a promising substitute of toxic Cr(VI) baths for black chromium plating.