Hull cell technique for evaluating zinc sulfate electrolytes

Abstract

An electrochemical procedure has been developed to monitor active species present in a zinc sulphate electrolyte such as antimony, glue, and MnO 4−. The technique employs a Hull cell for the electrolysis configuration to take advantage of the unique current density distribution. An expression called the stabilizing current density (SCD) is introduced to represent the results. An increase in the SCD means a higher current density is necessary to prevent a deterioration in the stability of zinc deposits or that hydrogen evolution is the preferred reaction. The results indicate that the SCD's correlate very well with the plating parameters, such as acid to zinc ratio and temperature. The SCD values increase with increasing antimony addition to an electrolyte. The effect of the antimony oxidation state (Sb +3 vs. Sb +5) on the SCD values has been investigated. The Sb +3 additions cause a relative increase in SCD values over those for Sb +5 at equivalent concentrations in the electrolyte. Glue decreases the SCD values for electrolytes containing Sb +3 and/or Sb +5. The technique developed provides a simple, fast, and reliable method for the evaluation of zinc sulphate electrolytes, i.e., serves as an indirect measure of the current efficiency.