Department of Chemical Engineering technical papers, 1900-1935
Traub, Walter G.
Electroplated zinc and the diffusion of electrodeposits into zinc, pp. [unnumbered]-62
DISCUSSION. little extent upon the thickness of the copper plate, since the diffusion rate will be materially lowered as the surface of the zinc metal under the coating becomes richer in the constituent which is being absorbed. Thus we noted from our experiments that our heaviest plated coatings were not absorbed after heating at 1000 C. for over one month. As would be expected, the rate of absorption is greatly influenced by the temperature. At a higher temperature, absorption of the thinner coatings was completed in some instances within a few minutes. From our examinations of actual plated articles which had previously been flashed with a coating of copper, we could find no indication that peeling was due to any absorption of the under- lying copper plate. In many instances, where the plated coating could be peeled off, the underlying copper flashing was found to have peeled from the zinc base and to be tightly adherent to the outer coating. It is apparent, also, that trouble resulting from diffusion of plated coatings can be overcome to a considerable extent by increasing the thickness of the copper flashing which is usually deposited preparatory to the finished plating. The writer has recently examined microscopically a number of nickel plated zinc sheets of German origin, which were several years old, in which the "flash" coat of copper is still clearly visible. This material carried a copper coating of 0.024 g./sq. dm. over which had been deposited a nickel coating of 0.204 g./sq. drn. 62
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