Doctoral Dissertations

Abstract

"The polarization characteristics of acidified zinc sulfate electrolyte with varying solution chemistries were examined by cyclic voltammetry. An attempt was made to correlate the polarization results with the morphological and current efficiency data in order to develop a better understanding of the more fundamental aspects of impurity and additive behavior during the zinc electrodeposition process.

A statistical screening design program was conducted to determine the effects of certain operating parameters on the nucleation potential of zinc from sulfate electrolyte. The variables studied included: solution temperature, H₂SO₄ and Zn concentration, and scan rate. The solution temperature was found to be the most significant factor followed by scan rate and zinc concentration. Based on the screening design data, mathematical equations were developed to predict the nucleation potential of the addition-free electrolyte.

During the reverse sweep of the voltammogram, the low current density region was examined in detail with emphasis on the effects of antimony and glue on the polarization behavior. The tests were made by potentiostating the electrode during the reverse sweep and monitoring the current change with time. The current was found to increase if an antimony excess was present, with an increase in the hydrogen evolution also being noted to occur simultaneously. The current rise was found to be proportional to the level of antimony present. As expected, higher temperature and acid concentration increased the current rise (i.e., ΔI) and glue additions caused a decrease in the current rise.

The effects of antimony oxidation state (Sb³⁺ vs. Sb⁵⁺) on the nucleation potential and the ΔI values were also investigated. The Sb³⁺ additions caused more depolarization and higher ΔI than Sb⁵⁺ at equivalent concentrations in the solution used.

Based on the current efficiency test results and the zinc deposit morphologies obtained, a correlation has been found to exist between ΔI, current efficiency and deposit morphology. For the given electrolyte, the current efficiency decreases and the resolution of deposit increases as the ΔI increases. Therefore, ΔI can be defined as an electrochemical parameter which reflects the quality of the solution.

Experimental data suggest that the increased ΔI and hydrogen evolution for the excess antimony containing electrolyte is due to the interference of the antimony ions with the zinc adsorption layer in the double layer region of the electrode/electrolyte interface"--Abstract, page iii.

Advisor(s)

O'Keefe, T. J. (Thomas J.)

Committee Member(s)

James, William Joseph
Johnson, James W., 1930-2002
Clark, George Bromley, 1912-

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Metallurgical Engineering

Sponsor(s)

National Science Foundation (U.S.)

Comments

Special acknowledgement is given to the National Science Foundation for financial support under the contracts CPE 800M272 and CPE 8M10867.

Publisher

University of Missouri--Rolla

Publication Date

Fall 1985

Pagination

xxii, 114 pages

Note about bibliography

Includes bibliographic references (page 93).

Rights

© 1985 Rajesh Kumar Singh, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 5256

Print OCLC #

14984246

Electronic OCLC #

1044759770

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