Electric-Arc and Electrochemical Texturing of Surfaces

Electric arcs and electrochemical etching can be used to impart microscopic textures to surfaces of metals. In electric-arc texturing, one strikes an arc between a water-cooled electrode and a substrate that one seeks to texture. As the arc is moved across the substrate surface, a condensate from the plasma consisting of a mix of electrode and substrate species becomes redeposited on the substrate, forming an extremely rough surface layer that is intimately mixed with, and attached to, the substrate. The thermal emittances of arc-textured surfaces are considerably greater than those of the corresponding untreated surfaces. Unlike high-thermal-emittance oxide coatings, arc-textured surfaces are integral with substrates and are thus less likely to spall because of differential thermal expansion over wide ranges of operating temperatures. Arc texturing shows promise for enhancing the performances of metal components that must radiate heat; for example, anodes of x-ray tubes used in computer-assisted tomography, or waste-heat radiators on spacecraft.