Corrosion Cell of Cobalt Electrodeposited from Double Salt Type Bath:Studies on Improvement in Corrosion Resistance of Decorative Platings from Cobalt Baths with Insoluble Anode (Part 2)

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For the estimation of corrosion resistance of composite platings, including a cobalt layer, the changes of the following factors with the progress of time were determined. The specimens used were cobalt from double salt type bath, copper from sulfate bath, and bright nickel. The tests were made on the following factors.(a) Spoutaneous electrode potential of each specimen in CASS solution.(b) Mixed potential of a combined specimen in CASS solution.(c) Electromotive force between any two specimens in various accelerated corrosion solutions or in natural water.The following conclusions were drawn from the consideration of experimental results.(1) The Plating order for the most Suitable was as follows: Cu at fast, Co the next, and bright Nickel at last. The order of the Potentials was as follows:Cobalt was least noble, Copper was the next, and bright nickel was noblest(2) In chloride rich surroundings, the electromotive force between bright nickel and cobalt was larger than that detween any other specimens; therefore, copper layer was protected by cobalt layer.(3) In chloride poor surroundings, copper layer was also protected by cobalt layer since copper layer was the noblest in these surroundings.(4) By reasons of the above facts, the composite plating including a cobalt layer was suitable for preparing articles used in various different surroundings.
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