Electrodeposition Of Copper And Copper Alloys In Imidazolium-based Ionic Liquids

1-Butyl-3-methylimidazole chloride ionic liquid?[BMIM]C1?and 1-butyl-3-methylimidazole hexafluorophosphate ionic]iquid?[BMIM]PF₆?were prepared by 1-chlorobutane,N-methyhmidazole and potassium hexafluorophosphate using as raw materials through two-step method.Using[BMIM]Cl and[BMIM]PF₆ and their mixtures as basic ionic liquids,the electrochemical bahaviors and electrodepositions of copper,copper-tin and copper-silver alloys were studied.The space configuration and functional groups of raw materials and systhetic ionic liquids were studied by Fourier transform-infrared spectroscopy?FT-1R?.The conductivity of ionic liquids was tested by conductivity meter.The electrochemical window of ionic liquids,electrochemical behavior of metal ions,reversibility of redox reaction,reaction control methods and kinetic parameters were studied by cyclic voltammetry?CV?.The electrocrystalization mechanism of copper and copper alloys electrodeposition were studied by chronoamperometry?CA?.The deposition process,micromorphology and element composition were studied by scanning electron microscopy?SEM?coupled with energy dispersive spectrometer?EDS?.The phase compositions of coatings were investigated by X-ray diffraction?XRD?.The mechanism of additive was studied by UV-Vis.The corrosion resistance of the coalings was studied by electrochemical measurement?Tafel curve?.Based on these results,the following conclusions were drawn:The intermediate ionic liquids obtained by the two-step method is 1-butyl-3-methylimidazole chloride and the two-step reaction product is 1-butyl-3-methylimidazole hexafluorophosphate ionic liquids.The density of the synthesized 1-butyl-3-methylimidazole heaxfluorophosphate ionic liquid is 1.032 g/cm³.The conductivity of 1-butyl-3-methylimidazole chloride is lower than that of 1-butyl-3-methylimidazole hexafluorophosphate ionic liquids under the same conditions.The electrochemical window?3.0 V?of 1-butyl-3-methylimidazole chloride is less than that of 1-butyl-3-methylimidazole hexafluorophosphate ionic liquid?4.5 V?.The solubility of mixed ionic liquids to copper chloride metal salt is higher than that of 1-butyl-3-methylimidazole hexafluorophosphate ionic liquids.There exist four reduction peaks in the reduction process of copper in[BMIM]PF₆ ionic liquid,which correspond to the transformation of different anionic groups of copper ions?or cuprous ions?.Among them,the reduction of divalent copper ions to cuprous ions is a reversible reaction,and the conversion of cuprous ions to copper atoms is an irreversible reaction controlled by diffusion.The electrochemical kinetics diffusion coefficient is 3.743×10^-6 cm²/s.The electrocrystallization mechanism of copper in[BMIM]PF₆ ionic liquid follows the three-dimensional instantaneous nucleation growth mechanism,and the micromorphology of the electrodeposition process shows that the growth of speckle-like substances takes place.Copper prepared by electrodeposition in[BMIM]PF₆ ionic liquid is a copper metal with an average grain size of 25.71 nm.1,4-butynediol acts as a leveling agent in this system;and its mechanism is adsorption to the surface of chromophore substances.The initial anion complex of[BMIM]PF₆ electrodeposited copper system is CuCl₄^2-,and its transformation order is as follows:Cucl₄²-?CuCl₄³-?CuCl₃²-?Cu⁺.Copper electrodeposited in[BMIM]Cl-[BMIM]PF₆ mixed ionic liquids follows two steps reduction:the first step is the conversion of copper ion to cuprous ion,and the second step is the reduction of cuprous ion to copper atom.The first step is reversible reaction and the second step is semi-reversible reaction.The electrodeposition of copper in[BMIM]Cl-[BMIM]PF₆ mixed ionic liquids follow different nucleation growth mechanisms at different step potentials,which are three-dimensional nucleation growth at low step potentials and two-dimensional nucleation growth at high step potentials.The electrodeposited copper coating in the mixed ionic liquid system is composed of copper with cellular structure,and the average grain size is 13.92 nm.The improvement of corrosion resistance of copper coating on carbon steel substrates by electrodeposition in mixed ionic liquids system is due to thiner coating obtained from[BMIM]PF₆ ionic liquids system.Different Cu-Sn alloys can be obtained by electrodeposition in[BMIM]Cl ionic liquids.The reduction peak of copper-tin alloy is-0.75 V?1 V,which is an irreversible reaction controlled by diffusion.The electrochemical kinetics diffusion coefficient is 4.673×10-8 cm²/s.When the concentration of copper ions and stannous ions in the system is 0.10 mol/L,the black cypress branched copper-tin alloy with Cu13.7 Sn phase composition can be electrodeposited at different potentials.When the concentration of copper ion and stannous ion in the system is 0.15 mol/L and 0.05 mol/L,the purple copper-tin complex with conical morphology can be obtained by electrodeposition.The phase composition of alloy is Cu₁₀Sn₃,Cu₆Sn₅,CuSn and Cu_3.02Sn_0.98-When the concentration of copper ions and stannous ions in the system is 0.05 mol/L and 0.15 mol/L.the gray-black copper-tin alloy with ice crystal morphology can be prepared by electrodeposition.The phase composition is Sn,SnO,?-CnSn,Cu₃Sn,?-Cu₆Sn₅ and Cu₁₀Sn₃.Among them,the best corrosion resistance the coating is Cu-Sn alloy with single phase composition.The preparation of Cu-Ag alloy with different micromorphology can be obtained in the[BMIM]Cl system by electrodeposition.The reduction of copper-silver alloy has a reduction peak different from that of copper or silver,which is an irreversible reaction controlled by diffusion.The electrochemical kinetics diffusion coefficient is 1.28×10^-7 cm²/s.The electrocrystallization mechanism of Cu-Ag alloy follows the mechanism of three-dimensional nucleation.With the increase of deposition potential.the order of micro-morphology changes is dendritic,bud-like and particulate.Increasing temperature can reduce the micro-size of deposition layer.