Study On Blackishgreen Colored Passivation Of Zinc Coating

Steel is the most widely used metallic materials in our daily life,however,its corrosion impose a great loss to the word.Resently,the common technology corrosion protection for steel is galvanization followed by chemical conversion treatment.Unfortunately,because the cyanide has severe horrible torture and caustic soda break the balance of solid's PH seriously those are both used to electroplating handicraft,they impose immense injuries for the people health and environment,so that environmentally friendly conversion anti-corrosion treatment is urgently needed. The passivation handicraft that gone into probes is just assorted to the potassium chloride zinc plating handicraft for being put into use.Only this handicraft is one of the green environmental protection handicraft in few number being in electroplating produces,it is harmonious friendship,all the time is praised highly fully,can be termed as green electroplating with the environment.Blackishgreen colored passive film was prepared by dipping galvanized steeI in solution made of foue types of acid with certain stabilizer and toner.A series of tests was taken to select best experimental procedure parameter,such as the solution's concentration,bath temperature,solution's PH and dipping time.As a result,the best parameters of technological process of preparing Blackishgreen colored passivation film formed on galvanized steel were selected.Scanning electron microscopy was used to observe the morphology of the film. Elements of passive film are conformed by using EDS.Moreover,x-ray photoelectron spectroscopy was also used to study Ire formation mechanism of the blackishgreen colored passive film with the organic amine.Phase composition of the blackishgreen colored passive films was identified by X-ray diffraction.Influence of an organic amine addictive on anti-corrosion performance and principle of blackishgreen colored passive film formed on galvanized steel was investigated by pctenriodynamic polarization,electrochemical impedance measurements and neutral salt spray test.In order to find the optimization passivation craft,we firstly do passivation liquid component and technological conditions optimizing test.Results show that: CrO₃30 g/L,H₃PO₄11ml/L,H₂SO₄6ml/L,HNO₃4ml/L,stabilizer is 4ml/L,toner is 10ml/L,pH1～1.5,temperature is 20～30℃and passivation time is 35～60s.SEM showed that the surface of the film was even.Cr,O,P,S,N,Zn and a small amount of Fe were found in the film by the test of EDS.XPS showed that there are Cr,O,P,N,Zn in the film,they probably exist in Cr(OH)₃,CrOOH,Cr₂O₃,CrO₃,ZnO,Zn₃(PO₄)₂·4H₂O and H₂O.XRD also showed that except the Zn crystal(zinc plating tier),other substances have appeared,they include CrPO₄,Cr(OH)₃,CrOOH,Cr₂O₃,Zn(OH)₂, 2ZnO·CrO₃·H2O,Zn₃(PO₄)₂·4H₂O,H₂O and Ag.Potentiodynamic polarization showed that marked passivating characteristic was found in anodic polarization curve.The oxide thickening processes played an important role on the corrosion protection mechanism.The corrosion potential of the film was higher than that of matrix,and corrosion current of the film was smaller than that of matrix.EIS showed that Nyquist picture was characterized as a complete capacitive impedance curve,corrosion process was controlled by the electrical chemical mechanism.In a word,the appearance of galvanized sample treated by the optimization passivation craft is blackishgreen,color and luster is uniform.The scanning microscopic examination indicated that the passivation films form on the galvanized steels are homogeneous.The passivation films can endure neutral salt spray test for 400h.The corrosion rates of passivation films reduced greatly comparaed with rainbow passivation film.Its adhesion test time reached 100,this far exceeds the national standard demand.The technological process is so simple that the unfamiliar operators can manipulate it.Furthermore,the consumption of expenses in small during passivation process.Accordingly,it is a kind of perfect passivation technique. It has promising prospect in industrial applications.