The role of fluoride in the adherence of electrodeposited zinc to aluminum cathodes

“The influence of fluoride ion on zinc adherence to aluminum cathode blanks was determined. The studies have shown a direct correlation between the fluoride content of zinc electrolyte and the degree of adherence of deposited zinc to aluminum. With higher fluoride contents, the number of initial nuclei was proportionally increased and the surface of the aluminum was rougher after zinc stripping, illustrating that the higher adherence of zinc was due to increased chemical and physical bonding of zinc to aluminum substrate. Even in solutions containing low fluoride, the cyclic usage of an aluminum cathode showed a similar effect to that of high fluoride, eventually resulting in strong adherence of zinc. SEM examinations revealed that the fluoride effect was accumulated during repetitions. Electrochemical tests demonstrated the instability of the oxide layer of aluminum in fluoride containing solution, which appeared to be the cause of zinc adherence. Electrolytes containing antimony showed less tendency for zinc adherence and in turn fluoride counteracted the lowering of current efficiency related to antimony. The decreased adherence is thought to be related to enhanced hydrogen evolution and the simultaneous zinc dissolution caused by the intrinsic antimony effect”--Abstract, page iii