MECHANISM OF ELECTROCHEMICAL PIGMENT FILM FORMATION ON ALUMINUM SUBSTRATES USING AQUEOUS SURFACTANT MEDIA

The mechanism of pigment film formation by the aqueous coating method was studied. This method is based on the electrochemical reduction of an Al substrate in aqueous pigment-dispersed surfactant systems. The e lectrode reactions of the Al substrate, the effect of the salt on the stability of the dispersion, the effect of the electrolytic conditions and the surfactant type on film growth, the film and dispersion compo sitions, and the growth of pigment particles during deposition were in vestigated. It was found that the pigment films grow on the Al substra te in the following consecutive steps: (1) a hydrogen evolution reacti on occurs at the Al cathode, resulting in an increased concentration o f OH- ions; (2) the OH- ions cause clouding of the surfactant adsorbed on pigment particles; (3) the pigment-surfactant aggregates are made non-dispersible by the clouding effect and are deposited onto the Al s ubstrate, leading to formation of the pigment film.