Electrodeposition of Al-Ti Alloys from Emimcl-AlC3 Ionic Liquid Containing TiCl4

Abstract

Electrodeposition of Al-Ti alloys from EmImCl-AlC3 ionic liquid containing TiCl4 using cathodic-anodic pulse techniqueTakahiro Kizawa1, Taisuke Nozawa2, Takehiko Kumagai3, Hisayoshi Matsushima3,and Mikito Ueda3 (Graduate School of Engineering, Hokkaido University1, NIPPON STEEL CORP.2 Faculty of Engineering, Hokkaido University3)To improve the pitting corrosion resistance of aluminum in chloride environment, alloying with transition metals is conducted. Titanium is one of candidate of the transition metals for improvement of the corrosion resistance of aluminum, and Al-Ti alloys with high titanium concentration has better corrosion resistance1). The electrodeposition of Al-Ti alloys from EmImCl(1-ethyl-3-methyl-imidazolium chloride)-AlCl3 containing TiCl4 or TiCl2 has been widely investigated for enhancement of titanium concentration in the electrodeposits2, 3). However, the electrodeposition of Al-Ti alloys by pulse electrolysis has not been investigated. Cathodic-Anodic Pulse deposition (CAP deposition), which combines Al-Ti deposition and Al dissolution, is considered to be one of the effective techniques to increase the Ti concentration in the electrodeposits. In this study, we investigated the electrodeposition of Al-Ti alloys by the CAP deposition in EmImCl-AlCl3-containing TiCl4 at 338 K.EmImCl-AlCl3 ionic liquid (molar ratio of 1 : 2) with 50 mM TiCl4 was prepared in the glove box with Ar atmosphere. Voltammogram measurement was recorded at a potential range from -0.3 V to 1.5 V (vs. Al / Al (III)) and scan rate was 20 mV s-1. Electrodeposition experiments of constant current, current pulse and CAP electrolysis were carried out. In the constant current and current pulse electrolysis, current density was from 3 to 10 mA cm-2 and duty ratio was 0.83 (ton = 1.0 s, toff = 0.2 s). In the CAP electrolysis, the cathodic current density was 5 mA cm-2, the anodic current density was from 0.50 to 2.0 mA cm-2. The charge density was 20 C cm-2 in the all experiments. The electrodeposits were washed with distilled water and ethanol, then dried, and weighed. After observing the surface of the electrodeposits by SEM, the electrodeposits were dissolved in an HF solution and the Ti concentration were measured by ICP-AES.In the voltammogram measurement, three cathodic current waves at 0.95 V (vs, Al / Al (III)), 0.35 V, and 0.06 V were observed. The waves are considered to correspond to reduction reaction of Ti (IV) / Ti (III), Ti (III) / TI(II) and Ti(II) / Ti, respectively. At a potential lower than 0 V, the cathodic current increased due to electrodeposition of the Al-Ti alloys. During the positive potential sweep, oxidation waves corresponding to the three reduction waves were observed at 0.25 V, 0.55 V, and 1.1 V, respectively. In the voltammogram measurement, dissolution potential of Al-Ti alloy shifted to the noble side compared to the it of pure aluminum. It was found that the potential shift is an effect of titanium.In the constant current electrolysis, the maximum Ti concentration in the electrodeposit was 11 at% at 5 mA cm-2. Since the potential of electrodeposition of Al and Ti is close and the concentration of Al ions in the ionic liquid is much higher than the concentration of Ti ions, the electrodeposition of Al occurs preferentially during the electrolysis. In the current pulse electrolysis, the maximum Ti concentration in the electrodeposits was 20 at% at 5 mA cm-2. It is considered that the Ti ions decrease at the electrode surface during the electrolysis, then recovery of the Ti ions occurs at off-time of the pulse, therefore Ti concentration in the electrodeposit increases compare to it of the constant current electrolysis. In the CAP electrolysis, the maximum Ti concentration was 21 at% at the anodic current density of 1.5 mA cm-2. Comparing this result with the current pulse electrolysis, the increase in Ti concentration is small. It is indicating the dissolution reaction of only Al from Al-Ti alloys is difficult to occur.1) J. R. Davis, Corrosion of Aluminum and Aluminum Alloys, ASM International,Materials Park,OH (1999).2) R. T. Carlin, R. A. Osteryoung, J.S. wiles, and J. Rovng, Inorganic Chemistry, 29, 3003 (1990)3) T. Tsuda, C. L. Hussey, G. R. Stafford, and J. E. Bonevich, J. Electrochem. Soc., 150, C234 (2003)