Herein, the dissolution behaviors of Al-Si casting alloy and cold rolled alloy anodes in AlCl3-NaCl-KCl molten salt were investigated at 423 K to produce high-purity Al from Al-Si alloys. All the Al-Si alloys were purified to more than 99.4 wt% by electrorefining. In particular, the purity of the AC4C and Al-11%Si alloys was 99.9 wt% each. It was confirmed from linear sweep voltammetry (LSV) measurements that anodic dissolution did not occur in the Si molten salt electrolyte. The dissolution of Al occurred preferentially on the anode surface of the ADC12 alloy during electrolysis, while the undissolved Si formed an enriched layer on the surface. In the ADC12 and AC4C casting alloys, a microstructure identical to that of the bulk metal was observed on the surface after electrolysis. On the contrary, the Si microstructure in the cold-rolled Al-11%Si alloy was fine, and adhesion was weak and did not remain firmly on the surface. In addition, the Si-enriched layer on its surface did not significantly affect the outcome of the 50-h electrorefining experiment.

To produce high-purity Al from Al–Cu alloys, the dissolution behaviors of various Al–Cu binary alloy anodes in EmImCl–AlCl3 ionic liquid have been investigated at 323 K. In the anodic polarization measurements, anodic current density peaks were observed at potentials of approximately 0.3 and 0.8 V vs. Al/Al(III) for the Al–5.0%Cu casting alloy. In the constant potential electrolysis of the Al–5.0%Cu casting alloy and cold-rolled plate at 0.3 V, Al atoms in the matrix phase were preferentially dissolved followed by the formation of Al2Cu surface species. The dissolution of both Al2Cu and Al in the alloy matrix occurred during electrolysis at 0.8 and 1.2 V. Moreover, a Cu-rich layer derived from Al2Cu was formed on the cold-rolled plate surface at a potential of 0.8 V. Additionally, Cu was co-deposited on the cathode at the potentials at which Al2Cu dissolved. The dependence of the anodic dissolution behavior of the Al−Cu alloys on the potential in the EmImCl–AlCl3 ionic liquid was analyzed. By controlling the anodic dissolution potential, the dissolution of Cu in Al2Cu into the electrolyte can be suppressed, thus considerably increasing the purity of electrorefined Al.

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To improve the reduction efficiency of chlorine electrodes in aluminumchlorine cells, this reports a circular cone type graphite cathode, with an electrochemical cell consisting of an aluminum anode and the graphite cathode evaluated in EMIC-AlCl 3 ionic liquid. The current density in the circular cone type cathodes with different cone angles exhibited a maximum value at 40 ∘ , and the current density at cell voltage of 0.5 V was about 25 mA cm −2 . This value is about 80% larger than that of a cylindrical type graphite cathode. In a circular cone type cathode with a 40 ∘ angle, the maximum power density recorded was 15.3 mW cm −2 .

Bright white plasma electrolytic oxidation (PEO) films with uniform maze-like structures were obtained by anodizing Al in an ammonium tetraborate solution. High-purity Al plates were galvanostatically anodized in 0.3-2.4 M ammonium tetraborate solutions at 303-343 K and 10-100 Am-2. A PEO film consisting of an outer porous layer consisting of amorphous alumina and crystalline alumina with α- and γ-phases and an inner amorphous barrier alumina layer was obtained on the Al surface. An extremely uneven PEO film with various pore sizes and many cracks was formed in a 0.3 M ammonium tetraborate solution, whereas a relatively uniform porous PEO film with similar pore sizes was obtained in 0.9-2.4 M solutions. This difference in the PEO film morphology was due to the plasma generation behavior while anodizing. The lightness of the PEO film increased with increasing anodizing time and PEO film thickness; thus, a bright white PEO film measuring 87.5 in lightness (L*) was formed on the Al surface. The water wettability of the PEO film exhibited weak hydrophilicity. Moreover, a superhydrophobic PEO film with a contact angle of 154° was easily fabricated by self-assembled monolayer modification. Similar bright white PEO coatings were successfully fabricated on various industrial alloys.