Aluminum is a very important material because of its distinctive features of a bright silvery appearance, light weight and high corrosion resistance. Also, it is used as a base in light-emitting diodes owing to its high reflectance of more than 90% in the visible light region. We have been investigating Al electrodeposition in a magnetic field. The surface morphology changed remarkably in the presence of a magnetic field, where the large grains with tabular-face were created [1]. This is explained by MHD convection induced by Lorentz force.

We consider that the MHD convection can act more effectively as compared with an aqueous solution system, since an ionic liquid consists of only ion species. In this report, Al films were electrodeposited in EMIC-AlCl₃ ionic liquid under a superconducting magnet. Their morphology and crystal orientation were analyzed by scanning electron microscopy and X-ray diffractometry.

2. Experimental

Electrodeposition was carried out with a three-electrode system. The electrolyte used was EMIC-AlCl₃ (1:2). The cathode was a Cu plate and the anode was an Al plate. All experiments were conducted in a glove box purged using by Ar gas at 60°C. The Al electrodeposition was conducted galvanostatically until the amount of electrical charge reached 29 C cm⁻², which corresponds to a deposition 10 µm thick. A superconducting magnet up to 5 T was applied parallel to the electrode surface. The surface morphology of the electrodeposited Al films was observed using SEM, while the crystal orientation was measured by XRD using the Cu-Kα line.

3. Results and discussion

Figure 1 shows the SEM image of the Al electrodeposited surface without a magnetic field and with a magnetic field of 5 T. When no magnetic field is applied, there were many grains on the surface and the deed groove was seen (Fig. 1 (a)). On the other hand when 5 T was applied parallel to the electrode surface, the grooves between the grains were buried and a very smooth surface was observed (Fig. 1 (b)). Because the MHD convection was generated by the magnetic field, the ions were supplied to the vicinity of the trench between the grains. This was attributed to the uniform electrodeposition.

In order to evaluate the crystal orientation of the Al films obtained by electrodeposition, XRD measurement was carried out. When the magnetic field was not applied, the (200) plane showed a very strong orientation compared with other crystal faces. In the magnetic field, the orientation of the (200) plane decreased with the increase of the magnetic flux density, while the crystal growth of the (111) and (220) planes were progressed.

[1] H. Takahashi, H. Matsushima and M. Ueda, J. Electrochem. Soc., 164, H5165 (2017).