An investigation was made of the effect of copper oxide in pro-moting the adherence of vitreous coatings to AISI type 321 stainless steel. It was found that copper ions in the coating produced a signifi¬cant increase in adherence on both pickled and sandblasted surfaces but that the effect of the copper decreased with increased firing tempera¬ture and increased firing time for the pickled specimens. X-ray examination of specimens revealed that the copper ions are reduced to metallic, copper near the interface during firing; however, examination of sections with the metallographic microscope showed no selective corrosion of the stainless-steel surface.nIt was observed that the curve obtained when plotting copper oxide content of the coating against adherence index was of the same type as that obtained for cobalt oxide on ingot iron. The similarity of these curves, when combined with other observations, was believed to imply that, in the case of 18-8 stainless steel, surface roughness^ is relatively unimportant to the development of bond between vitreous coatings and the metal.
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