Graduation Year

2014

Document Type

Thesis

Degree

M.S.M.E

Degree Name

MS in Mechanical Engineering (M.S.M.E.)

Department

Mechanical Engineering

Degree Granting Department

Mechanical Engineering

Major Professor

Wenjun Cai, Ph.D.

Committee Member

Delcie Durham, Ph.D.

Committee Member

Alex A. Volinsky, Ph.D.

Keywords

cyclic voltammetry, FIB, Potentioamperometry, SEM

Abstract

Aluminum-nickel (Al-Ni) alloys and Al/Ni bilayers were successfully electrodeposited from AlCl3-EMIM-NiCl2 electrolyte at room temperature. Dissolution of NiCl2 was shown to be favorable in Lewis basic (with molar ratio of AlCl3 < 0.5) AlCl3-EMIM solution. The use of electrochemically active Cu working electrode as opposed to inert W induced additional Cu oxidation and dissolution in the cyclic voltammetry scan. The reduction potentials of Al and Ni were found to be ~ – 0.3 and 0.15 V vs. Al/Al3+ respectively. Increasing [NiCl2] in the electrolyte leads to an increase of Ni concentration in the deposited structures. Dense and well-adherent Al-Ni alloys with Ni concentration up to 17.7 at.% were deposited by potential control. XRD analysis revealed that the deposited Al-Ni exhibit a supersaturated fcc crystalline structure. The visual appearance of the deposits ranged from bright silver, dull silver, grey, to black, where the darker shade typically indicated higher Ni content. SEM analysis revealed that the surface morphology of the deposits ranged from nodular to flake-like structures. Al-Ni alloy typically showed nodular morphology with cauliflower structure. Flake structures, which were independent of substrate roughness, were found to develop under pulsed potential deposition with 1:1 duty ratio.

The concentration of Ni in electrodeposited Al-Ni alloys increases nonlinearly with the increase in molarity of NiCl2. Al and Ni contents increase with increasing the time of positive and negative cycle of the pulse respectively. Decreasing the frequency by half resulted in almost double the amount of Ni in the deposited alloy. A smoother substrate increased Ni concentration from 6 to 17.7 at.%. Al/Ni bilayer was successfully deposited in 1.5:1 AlCl3-EMIM containing 0.026 M NiCl2. Deposition of Al on Ni was achieved using constant potential and pulse potential control. The deposition of Ni on Al is complicated since the deposition potential of Ni lies in the vicinity of Al stripping potential thus inducing competition between Ni deposition and Al stripping.

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