Technology And Mechanism Of The Electrodeposition Of Cr Alloys From[BMIM]HSO₄

At present,the technology of preparing Cr alloys from water-based trivalent chromium solutions have some problems,such as thin-coating,low chromium content,poor electrical conductivity.However,in contrast to ordinary aqueous solutions,ionic liquids has environmental protection property,stable electrochemical property,etc.As a kind of ideal electrolyte,ionic liquids can prevent hydrogen evolution reaction,improve the quality of deposits.Therefore,the electrodepositing of mental materials has been a worldwide hot spot based on ionic liquid system.However,at present,the electrodepositing of Ni-Cr,Fe-Cr,Fe-Ni-Cr coatings based on ionic liquid are scarcely reported.The1-butyl-3-methylimidazolium hydrosulfate?[BMIM]HSO₄?ionic liquid presents stable chemical and physical properties,its cost is low.Therefore,the technology and electrochemical mechanism of Cr alloy coatings plating in[BMIM]HSO₄ are investigated.The main contents and conclusions as follows:The effects of main salt concentration,electrodeposition potential,electrolyte temperature and electrodeposition time on the coating thickness and Cr content in[BMIM]HSO₄ ionic liquid have been studied.Best parameters for the preparation of Ni-Cr deposits are:0.05M NiCl₂,0.45M CrCl₃,deposition voltage is-1.60 V,time 60 min,temperature55?.The Ni-Cr deposits with the thickness of 18.14?m,Cr content about 26.79%can be prepared under this condition.Best parameters for the preparation of Fe-Cr deposits are:0.06M FeCl₂,0.45M CrCl₃,deposition voltage is-1.90 V,time 45 min,temperature 60?.The Fe-Cr alloy deposits with the thickness of 17.21?m,Cr content about 37.61%can be prepared under this condition.Best parameters for the preparation of Fe-Ni-Cr alloy deposits are:0.06M FeCl₂,0.08M NiCl₂,0.45M CrCl₃,deposition voltage is-2.05 V,time 60 min,temperature 55?.The Fe-Ni-Cr deposits with the thickness of 21.09?m,Cr content about23.57%can be prepared under this condition.The electrodeposits were characterized by SEM,EDS and XRD.SEM analysis shows that the electrodeposits obtained on Cu electrodes were smooth,dense and crack-free.XRD pattern of the electrodeposited layers reveals the crystalline structures of the deposits.The polarization curves revealed that the enhancement of Cr content can significantly increases the corrosion resistance of the coatings.The results from the cyclic voltammetrys showed that all the electrodeposition processes of Cr alloys in[BMIM]HSO₄ were non-reversible diffusion-controlled process.Chronoamperometry results provided direct evidence that Cr alloys electrodeposition took place through an instantaneous nucleation and three-dimensional growth mechanism with diffusion-controlled in[BMIM]HSO₄.