Organic collaborative passivation of aluminum tubes used for evaporators in refrigerators and freezers

Organic passivation film, obtained through vinyl-tri-β- methoxyethoxy)silane collaborative passivating with dodecyl phosphate (VSDP), was quickly deposited on the surface of aluminum tubes. According to the bluestone drips test (BDT), hydrogen evolution test (HET), and neutral salt spray test (NSS), VSDP film was recommended for its good corrosion resistance, which is better than that of conventional chromate passivation film. As the electrochemical results obtained from the Tafel polarization curves and electrochemical impedance spectroscopy (EIS) show, the resistance of Al was enhanced significantly and corrosion current density was obviously decreased, resulting in the decreased corrosion rate of Al by the VSDP film. In adhesion and bending experiments, the VSDP film showed good performance. The surface structure and composition were analyzed using metallographic microscopy, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). It was found that the surface of VSDP film, mainly consisting of Al, C, O, Si, and P elements, was smooth, uniform, and dense, which indicated that the synergistic passivation reactions were carried out on the surface of aluminum tubes in the passivation solution. The formation mechanism of the organic collaborative passivation was also discussed.