A Novel Process of Low Temperature Electrodeposition of Ti-Al Alloys Using Ionic Liquid Electrolytes

This study investigated the species concentration profile and electrical conductivity of the aluminum chloride (AlCl3) and 1-butyl-3-methylimidazolium chloride (BMIC) ionic liquid (IL) mixture, and its application in titanium (Ti)-aluminum (Al) electrodeposition. The species concentration profile was developed at 25°C as a function of AlCl3 mole fraction (X(AlCl3)), and the electrical conductivity of the IL was measured over a temperature range from 70°C to 110°C and X(AlCl3)= 0 to 0.67. Ti-Al alloys were electrodeposited using this IL, with anode as the source of Ti and IL electrolyte as the source of Al. The AlCl3:BMIC electrolyte was maintained at a 2:1 molar ratio (X(AlCl3) = 0.67), as this composition provided the highest concentration of Al2Cl7-, responsible for both Ti and Al deposition.Initial electrodeposition experiments were conducted in a 50 mL electrochemical cell using a single anode-single cathode configuration. These experiments focused on optimizing key deposition parameters, including deposition time under an argon (Ar) atmosphere, temperature, and applied potential under vacuum atmosphere. The results showed that the vacuum atmosphere significantly improved cathode current density compared to Ar. However, in both Ar and vacuum conditions, a passivation layer was formed on the anode, identified as TiCl3, which hindered the redox reactions and thus reduced the cathode current density.Scale-up experiments were then conducted in a 600 mL electrochemical cell with a single anode-single cathode configuration, using the parameters optimized from the 50 mL electrochemical cell setup. The impact of electrode distance was investigated, revealing that reducing the distance between electrodes improved current density by facilitating more efficient ion transport. The effect of stirring speed was also explored, and higher stirring speeds were found to enhance current density by improving ion mobility and reducing concentration polarization.Finally, experiments with three anodes and two cathodes were conducted in a 1000 mL electrochemical cell to assess the feasibility of Ti-Al electrodeposition using AlCl3:BMIC IL at a larger scale. These experiments confirmed the scalability of the Ti-Al electrodeposition process, with optimized parameters. The study highlights the significance of optimizing process parameters to effectively scale up the Ti-Al electrodeposition process for industrial applications.