Research On The Preparation And Corrosion Resistance Of Composite Film On Zinc Surface

Zinc is widely used in steel anti-corrosion coating because it has high corrosionresistance in the atmosphere. Zinc coating is corroded fast when it is applied tomarine atmosphere or other harsh environments. The passivation coating is usuallyprepared on the surface in order to improve the corrosion resistance of zinc coating.Chromate is used traditionally. But it has high toxicity and carcinogenicity. Countriesaround the world impose restrictions on the use of chromate and wastewateremissions in the environmental protection laws and regulations. It is necessary tostudy the surface pollution-free processing method. So the non-toxic pollution-freezinc coating surface processing method has very important significance.A zinc oxide/cerium oxide (ZnO/CeO2) composite film has been fabricated onzinc surface by electrochemical oxidation method. The corrosion resistance of thecomplex film influenced by chitosan is also studied. The elementary composition andsurface appearance of the film are studied to discuss the corrosion theory. The digitalmicroscope, scanning electron microscope (SEM) and energy dispersive spectrometer(EDS) are used to analyze the surface morphology and elementary composition of thefilm. The X-ray photoelectron spectrometer (XPS) is used to analyze element valencestate. Corrosion resistance is analyzed through polarization curves, electrochemicalimpedance spectroscopy (EIS) and neutral salt spray test (NSS).The main conclusions are as follows:1. XPS result shows that the film comprises ZnO and CeO2. The increase incerium content in the film is beneficial to improve its ability of corrosion resistance.Within a certain range, cerium content increases with the increase of current densityand the preparation time. The membrane layer structure becomes more uniform as thetemperature becomes lower within the scope of the film can be fabricated on zincsurface. With the temperature increasing, the surface appearance of the films becomesroughly.2. Compared with the bulk sample, the Icorrof the film under the conditions of12mA cm-2,1200s and40℃decreases an order of magnitude. The result shows that thecorrosion resistance of film has improved significantly. Compared with the bulk sample, the smaller corrosion current density of the oxide film indicates that theexistence of the oxide film mainly inhibits the cathodic process of zinc corrosionreaction.3. The influence on composite membrane surface morphology and corrosionresistance is studied. In addition to ZnO and CeO2, the film also contains chitosan.The thickness of the composite membrane increases and the film hinders the contactsof zinc with oxygen, water and other corrosive medium, so as to improve thecorrosion resistance of the film.4. The influence of the current density on the corrosion resistance ofZnO/CeO2/chitosan composite membrane is explored preliminary. Tafel curve testresult shows that under different current densities of the composite membrane Icorrarein the same order of magnitude and corrosion potential Ecorris at-1.0V or so. Bycomparing the two kinds of composite membranes, the neutral salt spray test resultshows that the resistance to salt fog time of ZnO/CeO2/chitosan composite membrane(192h) is longer than ZnO/CeO2composite membrane (168h), which suggests thatthe former has better annicorrosion performance.