Abstract
An apparatus for measuring the adherence of zinc electrodeposited from acid zinc sulfate solutions on aluminum cathodes is described. Adherence was recognized as “sheet” or “spot” behavior. Chloride favored increase in sheet adherence and fluoride ion favored spot adherence. Mechanical, thermal, and electrolytic treatments of cathode surface as well as chemical composition of electrolyte were investigated. There was no correlation between surface roughness and adherence. Smaller aluminum crystals in the cathode surface favored stronger adherence.The first stage of deposition was development of ovoid particles 8 × 5 microns, increasing in number until a complete sheet was obtained. Such particles preferred to develop at sharp points and crystal boundaries. Rupture of interface was observed microscopically in the aluminum surface. Zinc diffused into cathode with time, but aluminum on the surface of the zinc electrodeposit was attributed to fracture in aluminum during stripping. Mechanism of adherence was explained as an attachment at a varying number of active spots rather than by mechanical anchoring.
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