Coloring the Aluminum Surface with Dye Emulsions and Pigment Colloids in Plasma Electrolytic Oxidation

Abstract

Coatings of plasma electrolytic oxidation (PEO) can be colored during its oxide growth through electrophoretic deposition, with an electrolyte containing dye emulsion or pigment colloid. We perform the coloration in two steps; growing a white barrier layer first, then depositing the colorful layer. Despite the strong similarities in processing, addition of dye or pigment results in different effects on the electrolytic system. The dye emulsion increases the system impedance and reduces the positive current. Conversely, the pigment plus surfactant increase the positive current, since the negatively charged pigment particles enhances the electrolyte conductivity. Often the enhancement effect is so large that we have to operate PEO in the constant current mode.