Date of Award

Spring 1961

Document Type

Thesis

Degree Name

Master of Science in Chemical Engineering - (M.S.)

Department

Chemical Engineering

First Advisor

C. L. Mantell

Second Advisor

Joseph Joffe

Third Advisor

George C. Keeffe

Abstract

The quality of electrodeposited coatings is to a great ex- tent determined by cleaning or surface-conditioning methods employed in preparing the basis metal for plating. Cleaning pro- cedures are usually established empirically, by trial and error. Little or no experimental work was devoted to a quantitative stu- dy of measurable parameters that are influenced by the relative effectiveness of individual cleaning processes. The present ex- periment was designed in an attempt to establish a correlation between one such parameter (namely, the single-electrode poten- tial of polarized cathode) and the quality of subsequent plating.

High-carbon steel cathodes, -a material that is often noto- riously difficult to electroplate,- were used in the experiment. Each sample cathode was carried through one of 21 selected clean- ing cycles, consisting of one or more individual steps. After cleaningsamples were placed into cell containing Or03 electro- lyte and their potential was measured at various densities of po- larizing current. When Plotted in juxtaposition, all 21 Cathode Potential vs Current Density curves were found to posess a sim- ilarity of shape. Curves did, however, differ in their position with respect to the ordinate (used as the current density axis). The entire family of curves thus had the appearance of a band with a considerable and variable width in the direction of the abscissa. The possible significance of this horizontal shift was investigated by test-plating several samples. These samples were prepared by means of cleaning cycles that corresponded to most widely separated Potential-C.D. curves.

An examination of Plated samples revealed that the quality of the deposit did, indeed, vary from sample to sample. The cleaning Procedure corresponding to curve most distant from the ordinate produced sample surface that easily accepted the electrodeposit, while procedure corresponding to curve located near the ordinate produced a surface that was definitely more difficult to plate.

Thus, the experiment shows that 1) there is a one-to-one correlation between the cleaning method employed in preparing metal surface for plating and the quality of subsequent electro-deposit on this surface, 2) the single-electrode potential of the basis metal is a measurable parameter that can be used to evaluate the relative effectiveness of various metal cleaning methods, and 3) when plating chromium on polished hardened high-carbon steel, best results are obtained when basis metal is cleaned mechanically, by wet-scouting with a mildly abrasive slurry.

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