Electrodeposition of Al–Ni intermetallic compounds from aluminum chloride- N-( n-butyl)pyridinium chloride room temperature molten salt

Abstract

Electrodeposition of aluminum–nickel intermetallic compounds (particularly Ni 3Al) has been carried out onto platinum and mild steel cathodes from a 2:1 (mole ratio) aluminum(III) chloride- N-( n-butyl)pyridinium chloride (BPC) molten bath saturated with nickel(II) chloride at room temperature. A single phase of Al–Ni alloy is difficult to obtain by controlled-potential and controlled-current methods; however, it can be obtained by pulse current plating. The electrodeposition of nickel from an AlCl 3–BPC–NiCl 2 (6.14:3.07:0.09 mole ratio) molten bath occurs via an instantaneous nucleation mechanism in the very initial stage of the crystal growth. The deposition reaction mechanisms of nickel in this molten bath are revealed by electrochemical analysis. The experimental Tafel slope of 42 mV dec −1 and the calculated transfer coefficient α → c of 1.5 suggest that the rate determining step is a charge transfer reaction of an adsorbed bare monovalent cation to the metallic state. The effect of the cycle regime on the electrodeposition of Al–Ni alloys has been investigated. The current efficiency for the deposition of alloys is about 99%.