Development Of Environment-friendly Passivation Solution Used In Galvanizing And The Mechanism Of Corrosion Resistance

Recently,our country has made higher demands on the environmental protection in industrial production.Due to the application of traditional passivation liquid which contains chromium in batch hot-dip(steel tube)galvanizing,worsen the environment seriously.And there are several problems with the domestic environmentally-friendly passivation liquid for batch hot-dip galvanizing: the corrosion resistance of domestic products cannot meet the requirements of the industry,the price of imported goods is in on the high side.Therefore,the development of an environmentally-friendly compound passivation solution is an important direction for the batch hot-dip galvanizing.This paper mainly adopts neutral salt spray test,damp heat test,scanning electron microscope observation,Electrochemical impedance spectroscopy,X-ray photoelectron spectroscopy and other test means to study the corrosion resistance,passivation mechanism and coating liquid formulation.The corrosion resistant performance of different waterborne acrylic emulsion on the hot-dip galvanized steel plates were compared,and the waterborne acrylic emulsion with relatively good film forming properties was selected the main organic component for the development of environmentally friendly composite passivation solutions.The content of silane crosslinking agent,gas phase nano-silica and other fillers was determined by the method of orthogonal experimental analysis.Vanadate was selected as the main salt of compound passivation solution,and the inorganic salt component of the passivation solution was prepared with molybdate and borate as the promoter.The optimum film ratio of inorganic salts was determined by orthogonal experiment,and the film forming mechanism was studied.The process of nucleation and growth of vanadate conversion coating was observed by scanning electron microscopy;the film weight was analyzed by chemical method;the corrosion resistance of the coating was tested by neutral salt spray test;the corrosion behavior of the coating in 5%NaCl was analyzed by electrochemical workstation.The results indicate that sodium perborate improved the content of vanandium compound in the transformation film,and it helped to create a thick and dense transformation film,sodium molybdate can promote the nucleation of conversion film and accelerate the initial growth rate of the film.The conversion film is composed of vanadium oxide,phosphate,hydroxide and so on.In the corrosion environment,mixed valence compound of vanadium can protect the zinc layer by inhibiting the reduction of oxygen in the cathode area.The basic formula of the environmentally friendly compound passivation solution was obtained by combining organic and inorganic components.The results show that the corrosion resistance of the compound passivating solution is better than that of domestic passivating solution and has a certain market potential.