Date of Award
Master of Science in Ocean Engineering
Robert H. Heidersbach
Electroplated cadmium is currently used as· an effective hydrogen diffusion barrier on ferrous based alloys . Many of these alloys are susceptible to hydrogen embrittlement, and cadmium electroplating has been shown to Be a very efficient method of reducing hydrogen induced failures. However, industrial cadmium plating wastes are toxic and expensive to process for proper disposal. Current government regulations regarding this waste disposal have encouraged commercial platers away from cadmium as an amphoteric coating . Zinc is frequently used and aluminum looks encouraging as an alternative to cadmium electroplates. In order to accurately assess the effectiveness of these alternative coatings to cadmium, it is first necessary to quantitatively determine the permeation rate of hydrogen through cadmium electroplated coatings.
Hydrogen permeation experiments can be done in an electrochemical cell with electronically generated hydrogen using a technique known as the electrochemical hydro-gen permeation method. Previous work at th_e University of Rhode Island, using this method, has determined the necessity for a controlled sample preparation te technique in order to get reproducibility of data. It has also been determined that it is necessary to coat the inlet and exit surfaces of the sample membrane with an inert coating to prevent reaction of the test sample material or coating with either th.e inlet or exit electrolyte . Also , this inert coating must not be the rate determining step for the hydrogen permeation rate. In this project, an electroplating bath and technique was developed that would provide a thin flash of palladium over the inlet and exit surfaces of the sample membrane. Electron microscopy was used to check the integrity of these inert coatings.
The base metal chosen for this project was a high purity "Ferrovac E" iron. The first phase of the tests was to replicate earlier experiments on a pure palladium-iron palladium membrane in order to confirm the proper functioning of the experimental technique .
After this, it was necessary to determine the rate controlling step of the sample membrane with a cadmium electroplate just inside the palladium coating on the inlet side of the membrane. Cadmium should be rate controlling , and this is determined by varying the thickness of the iron substrate and observing the variations in steady state permeation rates .
Finally, the effects of various thicknesses of cadmium electroplated coatings was determined by observing the changes in steady state permeation rates .
The results of tests with samples without cadmium coating closely resembled those of earlier researchers at University of Rhode Island , which confirmed the proper function of the equipment . The tests per.for.med with a constant cadmium plating thickness and various iron substrate thicknesses showed a relatively small difference in steady state permeation rate, which proved the cadmium layer to be the rate controlling step. The tests with various thicknesses of cadmium on a constant iron substrate thickness proved again that the cadmium was rate controlling.
Allen, Ben G., "A Hydrogen Permeation Study of Electroplated Cadium on an Iron Substrate" (1982). Open Access Master's Theses. Paper 1098.