ELECTRODEPOSITION OF CO-NI ON ALUMINUM PLATE FROM CHLORIDE BATH

Adherent and compact deposits of cobalt, nickel and cobalt-nickel allo ys were obtained from a chloride bath at pH 4, on aluminum cathodes, u sing direct and pulsed current. Pretreatment of the aluminum consisted of a 5 min immersion in 3.6 M H2SO4 at 60 degrees C, followed by rins ing with distilled water. The electrodes were used immediately after t he last rinsing. Pulse rime was 5 min at a current density of 20 mA cm (-2) followed by current interruption for 20 tns. The thickness of the deposit was 3 mu m. The addition of surfactants to the bath was inves tigated. The polarization curves with surfactants SDS, SOBS and BRIJ78 leading to the best deposits were similar to those recorded in their absence. Whereas the following surfactants promoted the formation of a dherent deposits: CTAB, FORAFAC1179 and sodium saccharinate reduced th e adherence of the deposit. The morphology of the deposits was observe d using scanning electron microscopy and X-ray diffraction was used to analyze the deposit. At Ni alloy content lower than 18%, alpha-Co pha se was identified. Higher Ni content in the alloy resulted in the pres ence of alpha-Co and beta-Ni. Copyright (C) 1996 Canadian Institute of Mining and Metallurgy.