The Preparation Of Aluminum In Ionic Liquid And Its Electrochemical Nucleation Mechanism

Industrial aluminum electrolysis using high temperature molten salt system leads to energy-extensive consumption and high pollution. However, ionic liquids, both room temperature and non-pollution, are becoming the reasearch focus.Based on Cu substrate, aluminum coating was prepared in room temperature ionic liquid [BMIM]Cl-AlCl3 system with direct current electrodeposition and pulse electrodeposition. The optimum parameter of aluminum electrodeposition was determined by orthogonal experiment. The morphology and structure of the electrodeposition were characterized by scanning electron microscope(SEM) and X-ray diffractometer(XRD), respectively; and the elementary composition and the thermostability of the deposite was studied with X-ray photoelectron spectroscopy and thermogravimetric analysis, respectively.The optimum process of aluminum electrodeposition on Cu substrate is as following: the molar ratio of [BMIM]Cl/AlCl3 is 1:2, current density is 20-25mA/cm2, platingbath temperature is 50-55℃, and the additive methylbenzene concentration is 5mL/L. SEM images show that the coatings obtained under the optimum process condition in ionic liquid are composed of uiform and dense particles. XRD pattern indicates that the prepared coatings are of nanocrystalline structure with average crystallities sizes of 55 nm. EDS and XPS analysis suggestes that the mass percentage of aluminum is about 84.12% and oxygen is 15.88% and the surface of plating is oxidized partly into Al2O3.With the classic three-electrode system, the nucleation mechanism of aluminum on Cu substrate was studied in ionic liquid [BMIM]Cl-AlCl3. Chronoamperometry result suggestes that the electrocrystallization of aluminum on Cu electrode follows the three-dimensional instantaneous nucleation mechanism controled by electrochemical polarization.Constant current pulse method was performed to study the electrodeposition of aluminum on Cu substate in ionic liquid. The influence of duty cycle, cycle time and pulse width on electrodeposition morphology was researched. It turned out that duty cycle, cycle time and pulse width have a significant influence on the morphology of the aluminum deposit. The smaller the duty cycle, crystal grain more fine; when the cycle time increase from 20 times to 120 times, the grain size becomes more bigger obviously; the coating becomes more smooth and the grain size becomes more fine when the pulse width changed from 10 s to 5 s.The preparation method of straight through conductive anodic aluminum oxide template electrode is designed to avoid the complicated process by two-step anodic oxidation, which simplifies the preparation process of AAO template electrode.