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An Investigation of the Electrode Kinetics and Electrochemistry of Refractory Metal Deposition.

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Final rept. 26 Apr 82-30 Jun 85,

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Electrochemical methods represent important ways in which the refractory metal coatings can be applied to the more active metals and alloys to take advantage, at the new surface, of their superior properties to provide erosion and corrosion protection. Currently, of the refractory metals, only chromium can be plated from aqueous solution, albeit in a form that is not entirely free of cracks and pores. These aberrations in the coating can lead to protection failure under severe conditions. The remaining metals can be plated from molten fluoride electrolytes at temperatures in excess of 700 C. It is clear that less severe operating conditions are required for the plating of these metals, to take advantage of their properties in coatings upon as wide a range of materials as possible. The plating process involves the transport of ionic species, established in an ionic medium, to the solution electrode interface at which these species undergo electron transfer reactions and ligand removal to form metal atoms at favored sites. The aggregation of these atoms into clusters of nuclei, their growth into crystallites, and the accumulation of crystallites into a coherent polycrystalline metal coating, represents the final stages of the complex process of metal plating. This program of work has explored some aspects of each of these contributing processes to develop a scientific basis for the design of new plating baths and techniques which can be operated for chromium and molybdenum at substantially lower temperatures.

Subject Categories:

  • Physical Chemistry
  • Coatings, Colorants and Finishes
  • Fabrication Metallurgy

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