Date of Award

Spring 1995

Project Type

Dissertation

Program or Major

Engineering

Degree Name

Doctor of Philosophy

First Advisor

Dale P Barkey

Abstract

An experimental and theoretical investigation on pattern formation in electrochemical deposition from copper and zinc binary sulfate electrolyte in two dimensional cells was carried out in this study. Aggregates were produced by electrochemical deposition. An interferometric setup was developed to measure the concentration boundary layer around the aggregates produced during growth.

Convection is observed during electrodeposition from binary sulfate solution of zinc and copper with the concentration of 0.04M and higher in horizontal cells. The theoretical and experimental investigation indicates that natural convection is much stronger in a horizontal cell than that in a vertical cell. Channel growth is observed in our experiment for both zinc and copper deposition from binary sulfate solution. Zinc channel growth is produced under conditions where natural convection is suppressed by deposition in a vertical configuration; however, zinc dendrites are observed in a horizontal cell under the same experimental conditions. In contrast to zinc deposition, channel growth from copper deposition is produced in either the horizontal or vertical configuration. Therefore, the role of natural convection is of primary importance in morphological selection for deposition from $ZnSO\sb4$. However, no effect of natural convection is found on pattern selection for deposition from $CuSO\sb4$.

Electrokinetic streaming was identified as a morphology determining process. The preliminary theoretical results show that the electric force acting at the double layer close to the tip of copper aggregates is much larger than is the case with zinc aggregates. The dependence of morphology selection for zinc and copper deposition on the vertical or horizontal configuration of cells is due to the interaction of natural convection and electrokinetic effects.

Theoretical models of velocity selection developed in solidification were translated to the systems of electrochemical deposition. However, numerical simulations based on this theory for both diffusion controlled and the ohmic controlled growth are not consistent with the experimental results.

An adiabatic cell model was developed to quantify the effect of ohmic heating in the deposition experiments. The predicted temperature increases during electrodeposition in two dimensional cells are much higher than the experimental values, indicating that the cells efficiently shed the heat generated by the passage of current. Analysis based on this adiabatic model shows that the errors for the interferometric concentration measurement due to temperature rises are negligible for electrochemical deposition in two dimensional cells at moderate applied potential.

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