Influence of Operating Conditions on Deposition Rate and Smoothness of Electrolytic Aluminum Foil Using Chloroaluminate Ionic Liquids

The ionic liquid comprised of anhydrous aluminum chloride (AlCl3) and 1-ethyl-3-methylimidazolium chloride (EMIC) has attracted attention as an electrolyte for Al electrolysis. We have investigated the influence of the operating conditions on the deposition rate and the surface roughness of electrolytic Al foil by using the AlCl3-EMIC melt with/without 20 mmol dm(-3) of an 1,10-phenanthroline anhydrate (OP) additive as the electrolyte. The cross-sectional SIM images revealed that the increase in the operating temperature affected the foil thickness and the OP addition affected the smoothness. At the operating temperature of 50 degrees C and the current density of 52.6 mA cm(-2), the current efficiency was 90% or more and the deposition rate was about 0.9 mu m min(-1) regardless of the OP addition. An AFM image revealed that the surface roughness value of the Al foil obtained on the Ti plate substrate from the melt with the OP additive at 50 degrees C was 45.8 nm at the current density of 52.6 mA cm(-2). The XRD patterns showed that the orientations of the (200) reflections became strong by the OP addition. A smooth Al foil was obtained even at a high current density by increasing the operating temperature and adding OP to the melt.