Stripping behavior of zinc cathodes with focus on their adherence to aluminum blanks

Abstract This work describes the stripping behavior of zinc cathodes with focus on the effect of current density, fluoride ion concentration in the electrolyte and acidity on their adherence to the aluminum blanks. The adhesion strength was measured using a customized stripping device that reproduces the loading submitted to the deposit in the conventional stripping operations. The force versus displacement plots exhibited a similar behavior: initial increase of the force to a peak value, followed by its gradual decline to a nearly stable value, and by a final increase until the required value to detach the deposit is reached. This increase registered at the final stage was associated with the relatively higher thickness of the metal deposit. Around the corners of the aluminum plate, which represent sites with a relatively higher charge density, the product exhibits a higher thickness and crystallites with a smaller grain size. The adhesion strength was estimated from the force registered at the intermediate stage, which comprises (i) the component required to bend the sample, (ii) the component related to the adhesion between the deposit and the aluminum plate and (iii) the component associated with the friction between the deposit and the steel blade of the stripping device. The measurements revealed an increase of the adhesion strength and energy required for stripping by increasing the current density and fluoride ion concentration, but the effect of acidity on both the parameters was found to be negligible. The effects of fluoride ion and current density were related to the observed decreases in the average sizes of the first grains of the zinc deposits due to high nucleation rates.