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The electrodeposition of metallic molybdenum thin-film coatings, from aqueous electrolytes containing molybdate ions

University of British Columbia

Electrodeposition of metallic molybdenum from aqueous electrolyte has in most cases previously yielded poor results due to the extremely high rate of the secondary hydrogen evolution reaction occurring at the cathode. This results in low current efficiencies and thin brittle films. The use of a highly concentrated aqueous-acetate based electrolyte containing molybdate ions has been used to deposit thick (~50 μm) adhered, mirror like metallic molybdenum coatings. Plating variables were investigated to determine the optimum deposition conditions; it was seen that current density was the most influential factor for the successful deposition of the refractory metal. The coating surface was analysed using SEM and EDX. XRD analysis confirmed the deposits were amorphous in nature with broad peaks in the (110) orientation. The deposition mechanisms were studied through electrochemical techniques such as PDP and CV. It was concluded that metallic molybdenum is deposited in a two-step reduction process, with the formation of an intermediate coating of molybdenum oxide, requiring hydrogen gas to fully reduce. Corrosion studies have shown the coatings stability in a chlorinated environment however active uniform corrosion in alkaline conditions resulted in film failure. Exposure to strong acidic conditions result in oxidation and delamination of the coating. Up-scaling of the process was seen to be successful and large deposits of well adhered and uniform metallic molybdenum were formed under high applied currents.

Text

2015-11-05

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/55131

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/