Electrodeposition of Bright Al Coatings from Dimethylsulfone-AlCl3 Baths with the Addition of Tetraethylenepentamine

Abstract

Electrodeposition of bright Al coatings from dimethylsulfone-AlCl3 baths was demonstrated using tetraethylenepentamine (TEPA) as an additive. While the Al coatings electrodeposited from the bath without TEPA were lusterless, bright coatings with a mirror-like appearance showing high specular-reflectance were obtained in the presence of TEPA. Comparative examinations of the coatings revealed that the addition of TEPA changed the Al deposits from randomly-oriented, relatively-large crystals to (100)-oriented fine ones, and markedly decreased the surface roughness of the coatings. Cathodic polarization curves indicated that TEPA increased the overvoltage for the deposition of Al. Specific adsorption of TEPA on the Al deposits was considered to be the origin of the formation of the bright, leveled surface of the coatings.