| We often use chromate for chemical conversion of galvanized steel to improve its corrosion resistance.However,hexavalent chromium in chromate conversion is a highly toxic substance,which has carcinogenic,teratogenic and mutagenesis effects,and is a serious threat to the environment and human health.Among alternative technologies for chromate conversion,organic-inorganic composite conversion has received much attention.In this paper,the four inorganic salts(molybdate,tungstate,metavanadate,fluorozirconate)commonly used in the chemical conversion treatment of galvanized steel were screened by single factor experiment method,and the fluorozirconate with the best corrosion resistance is selected as the film-forming main salt.On this basis,seven kinds of corrosion inhibitors(sodium polyaspartate,phytic acid,disodium edetate,sodium gluconate,sodium citrate,sodium tartrate,acetanilide)were used to compound with fluorozirconate to prepare organic-inorganic composite conversion coating on the surface of galvanized steel,and the fluorozirconate-acetanilide composite conversion film is obtained.The main conclusions include:(1)Potassium fluorozirconate and acetanilide were used as the main film-forming salt,and boric acid was used as a buffer to prepare a composite conversion film on the surface of galvanized steel.The optimum film formation conditions were determined by studying the composition of the conversion solution(potassium fluorozirconate,acetanilide,boric acid)and the reaction conditions(pH,temperature,reaction time):4g/L potassium fluorozirconate,0.9-1.2 g/L-acetanilide,0.6 g/L boric acid,pH 3.6,temperature 40°C,reaction time 40 min.(2)The results of scanning electron microscopy,energy spectrometer,infrared spectrometer,neutral salt spray test and electrochemical workstation on the morphology,composition and corrosion resistance of the composite film show that the composite film is amorphous,uniform and dense,and the thickness is up to 7?m;the conversion film is mainly composed of Zr O2,Zr F4 and a complex of acetanilide and zinc,and its elemental composition is:73.10%Zn,9.33%Zr,8.26%C,6.68%O,2.63%F.Compared with galvanized steel,the corrosion potential of the composite film increased by 97m V(from-1.254V to-1.157V);the corrosion current density decreased by an order of magnitude(from 1.748×10-5A·cm-2 to 3.606×10-6A·cm-2);the impedance value of the low frequency region(0.01 Hz)is expanded by 15 times(730?·cm2and11008?·cm2,respectively).The neutral salt spray time of the composite film reached96h,and the corrosion resistance was significantly enhanced. |
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