Microwave Synthesis Of Ionic Liquids And Its Application In Electrodeposition Of Al And Al-Zn Alloys

The concept of ionic liquids is based on green chemistry and efficiency and electrodeposition of aluminium (Al) and its alloys from chloroaluminate ionic liquid has been studied for many years, but the conventional synthesis of this ionic liquid is often time consuming and needs a lot of solvent to get reasonable yield. It is necessary to explore a new and efficient synthesis method about chloroaluminate ionic liquid. Although Al and various of its alloys have been electrodeposited from chloroaluminate ionic liquid, the studies about electrodeposition mechanism is still not sufficient, the structure of double layer and the anode and cathode reaction kinetics is still unclear, further analysis of influencing factors is still needed for high-quality Al and its alloys deposits.A new microwave synthesis of bromo-chloroaluminate ionic liquid was described in our work and its physical and chemical characteristics were tested. Results indicated that the reaction time of the new microwave synthesis of chloroaluminate ionic liquid was drastically reduced as compared to the conventional methods and chloroaluminate ionic liquid with high properties was achieved;2AlCl3/[EMIM]Br (the molar ratio of AlCl3/[EMIM]Br is 2:1) ionic liquid was used as the electrolyte in Al electrodeposition. Electrochemical techniques of cyclicvoltammetry, electrochemical impedance spectroscopy, chronoamperometry and potentiodynamic polarization technology (tafel) were used to investigate the mechanism of Al electrodeposition. Constant potential electrodeposition of Al was conducted on Copper substrates at room temperature and the morphology, structure and anti-corrosion behavior analysis of the deposits was performed using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and electrochemical methods, respectively. Results revealed that Al electrodeposition from this ionic liquid was not a simple linear diffusion controlled process, but a quasi-reversible process with complex kinetic limitations, a slight capacitance dispersion occurred in the chloroaluminate ionic liquid, three different regions occurred on the chronoamperometric curve are responding to the three different polarizations and the different periods of Al nucleation and growth process, instantaneous nucleation growth of Al electrodeposition was proved; Al deposits obtained at different potential were mainly about three typical morphology and the reason for the three typical morphology and their characteristics were analyzed.Co-deposition of Al-Zn alloy was performed from electrolyte that was prepared by directly dissolving of ZnCl2 into 2AlCl3/[EMIM]Br ionic liquid. Cyclicvoltammetry was used to investigate the mechanism of co-deposition of Al-Zn alloy, co-deposits obtained from different molar ratio of ZnCl2/AlCl3/[EMIM]Br were measured by XRD and the surface morphology and the composition of the co-deposits were measured by SEM and Energy Dispersive Spectrometer(EDS), respectively. Results indicated that bare Zn deposition occurred at the potential of-0.42 V (vs. Al), and Al-Zn coating begin to be co-deposited at the potential of-0.63 V; Zn was solidified as the second phase in the alloys, the co-deposits obtained at higher molar ratio of Zn appears bigger 20 shift, broader reflection centered around a 20 and lower reflections intensity; The applied potential has significantly effects on the composition of Al-Zn alloy, the deposition rate of Zn was more quick than that of Al at less negative potential and was limited when the potential getting more negative.