| Phosphating treatment refers to that the workpiece contacts with acid phosphate solution and reacts to form a layer of insoluble phosphate film on its surface.Phosphating is one of the common chemical treatment methods to improve the corrosion resistance of carbon steel.In the past,the phosphating solution mostly contained substances such as nitrite and nickel ions,toxic gases are generated during the phosphating reaction,which polluted the environment,and had the disadvantages of excessive sedimentation and poor phosphating effect.Therefore,it is imperative to find a new phosphating accelerator and upgrade the traditional phosphorus chemical technology.Black phosphorus nanosheets have attracted widespread attention due to their large specific surface area,stable chemical properties,and excellent ion adsorption energy.In this paper,the performance of the composite phosphating film prepared by the introduction of black phosphate nanosheets into a phosphating solution was studied.Q235 steel was used as the matrix.Firstly,the formulation and process parameters of the phosphating solution were optimized through single-factor experiments.The effects of the components of the phosphating solution and the conditions of the phosphating process on the performance of the phosphating film were analyzed.Through orthogonal experiments,the optimal formula of the basic phosphating solution and the phosphating process parameters were determined:zinc dihydrogen phosphate 55 g/L,phosphoric acid 8g/L,zinc nitrate 50 g/L,Sodium chlorate 4 g/L,hydroxylamine sulfate 3 g/L,sodium fluoride 1.8 g/L,phosphating solution p H 2.5,phosphating temperature 40°C,phosphating time 20 minutes,drying naturally.The surface morphology,phase composition,and thickness of the black phosphorus nanosheets were characterized by scanning electron microscope,X-ray diffraction,and atomic force microscope tests.The results show that the black phosphorus nanosheets used in this paper had micron-scale lateral dimensions,the surface was smooth,there were no impurities,the crystallinity was high,and the thickness was about 2 nm.Black phosphorus nanosheets with different addition amounts were added to the basic phosphating solution,and the phosphate treatment of Q235 steel was performed.The effects of the addition of black phosphorus nanosheets on the morphology,chemical composition and corrosion resistance of phosphating film were analyzed by means of film weight,film thickness,X-ray diffraction,X-ray photoelectron spectroscopy,scanning electron microscopy,salt water immersion test and electrochemical test.The results show that after the introduction of the black phosphorus nanosheets,the chemical composition of the phosphating film didn't change,and the main components were still Zn3(PO4)2·4H2O and Zn2Fe(PO4)2·4H2O,but the morphology changed.The introduction of black phosphorus nanosheets increased the number of nucleation sites and reduced the grain size,and the structure of the phosphating film became more compact and complete.When the concentration of black phosphorus nanosheets was 0.1 g/L,the phosphating effect was the best.At this time,the densest and most uniform phosphating film was obtained,and the weight and thickness of the film were the highest.At the same time,the dropping time of copper sulfate reached330 s,which was an increase of 175%over the phosphate film without the black phosphorus nanosheets,the time when yellow rust appeared in salt water immersion experiment was more than 4 hours.The corrosion current density decreased from1.595×10-5A/cm2to 1.809×10-6A/cm2,and the corrosion rate decreased from 1.875mm/year to 0.2126 mm/year.Electrochemical impedance spectroscopy show that the film resistance increased from 1.467×103?·cm2to 5.249×103?·cm2.It is shown that the addition of black phosphorus nanosheets effectively improved the corrosion resistance of the phosphating film. |
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