Electrodeposition of Ti Alloy from Emic-AlCl3 Ionic Liquid Electrolytes

Abstract

In this work, Ti-Al alloys were electrodeposited from the ionic liquid electrolyte containing a mixture of 1-ethyl-3-methylimidazolium chloride (EMIC) and aluminum chloride (AlCl3). The constant potential electrolysis was performed by two-electrode configuration at a constant potential with the copper electrode as cathode and the Ti electrode as an anode at optimized temperature and electrolyte composition (AlCl3 mole fraction). The density, viscosity, electrochemical potential window, and conductivity are important physical properties that determine the suitability of ionic liquid electrolytes for electrochemical applications. Therefore, before performing the Ti-Al alloy electrodeposition, the conductivity values of electrolytes and the diffusion coefficient of electroactive anion species (e.g., Al2Cl7 -, Al3Cl10 -) were determined as a function of temperature (343-383 K) and electrolyte compositions (0.6 to 0.71-mole fractions of AlCl3) using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), chronoamperometry (CA), and chronopotentiometry (CP) techniques. The conductivity (k) values of EMIC-AlCl3 electrolytes varied from 2.65 to 5.58 S m–1. The concentration of Al2Cl7 − anions in the electrolyte at a given composition and temperature decide the formation of Ti-complex ([Ti(Al2Cl7)4]2−) with Ti ions dissolved from Ti anode and its two-electron reduction to Ti, along with three-electron reduction of Al2Cl7 − to Al at the cathode electrode. The alterations in conductivities are due to the differences in concentration of electroactive anion species, the molecular structures, cation-anion interactions, and the viscosity of ionic liquid melts. The diffusion coefficient values of Al2Cl7 − and Ti-complex species were determined to be 0.259 ´ 10–10 and 6.36 ´ 10–10 m2 s–1, respectively. Homogeneous and compact Ti-Al alloy with Ti content ranging from 12 to 40 at.% was obtained under optimized conditions. The applied potentials, electrolyte composition, and temperature were critical in controlling the alloy compositions and surface morphologies of the resultant Ti-Al alloys.