エタノール−エチレングリコール混合溶媒電解液中でのチタンの電解研磨

概要

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Using a rotating disc electrode, electropolishing behavior of titanium (Ti) was studied in mixed ethanol (EtOH) -ethylene glycol (EG) solvents dissolving metal chlorides. Effects of the electrolyte composition on the anodic behavior of the rotating titanium were discussed in terms of the balance in ionic conductivity and solution viscosity. A mirror surface of Ti was obtained by anodic polarization in a mixed alcohol system of EtOH and propan-2-ol (i-PrOH), which dissolves ZnCl2 and AlCl3. However, substitution of i-PrOH by EG with lower vapor pressure did not proceed to anodic oxidation of Ti when ZnCl2 was used as the co-electrolyte of AlCl3 in the mixed solvent system. The use of LiCl with AlCl3 with a proper mole ratio produced a mirror surface of Ti in the mixed solvent system of EtOH and EG. The polarization behavior of the system was almost identical to that in the mixed alcohol system of EtOH and i-PrOH dissolving ZnCl2 with AlCl3. The best electropolishing result was obtained for a solution containing 0.225 M AlCl3 and 1.8 M LiCl (M = mol dm−3). Results of conductivity and viscosity measurements for the electrolyte solution suggest that anodic dissolution of Ti coupled with the formation of a viscous surface layer would be balanced in EtOH+EG mixed solvent systems containing LiCl+AlCl3 with moderate values of Waldens product.