Study On Anti-corrosion Materials On Gas Condensing Exchanger And The Process Of Ceriume Coverson Coating

The purpose of this paper is to solve the problem of the condensing heat exchanger corrosion. Through metallographic analysis, SEM, EDS and electrochemical methods researched on different silicon content in aluminum silicon alloy for the corrosion resistant substrate selection. The optimum techniques parameters of rare earth cerium conversion coating on the aluminum silicon alloy surface were obtained by orthogonal and single factor experiment, and studied the effects of technical parameters in detail. At the same time, the microstructure, element composition and elemental composition of cerium conversion coating hade been examined by SEM. EDS and XRD. The corrosion resistance of cerium-based conversion coating was evaluated by polarization curve, electrochemical impedance spectroscopy (EIS) and immersion corrosion experiment.and the electrochemical corrosion behavior and corrosion mechanism of conversion coating were studiedThe pitting corrosion occurs on Al-Si alloy in the gas condensate of60℃.When the silicon content is low, local corrosion can easily be formed at the intergranular of the Al-Si alloy. When the silicon content is high, the content of eutectics was gradually reduced and a amount of primary silicon appeared, accelerating the local corrosion of Al-Si alloys. When the content of Si is13%, more fibrous eutectics (α+Si) were formed in the Al-Si alloy and evenly distributed in the aluminum, enhancing the pitting corrosion resistance of Al-Si alloy in flue gas condensate. The prepared Al-Si alloy can be used as a candidate corrosion resistant material applied in flue gas condenser.The optimum techniques parameters were obtained by orthogonal and single factor experiment as follows:Ce(NO3)3:14g/L; KMnO4:1.5g/L; K2S2O8:1.0g/L:NaF:0.8g/L; pH value of solution:2.0, immersing60min at room temperature. These parameters are too high or too low that is adverse effection for formation of conversion coating on the surface of aluminum silicon alloy, furthermore makes the corrosion resistance decrease.Results of the SEM, EDS and XRD indicate, Ce-Mn conversion coating closes to the matrix, the coating is composed of a matrix film and different sizes particles adhesive on it.; the coating thickness is about10-15μm. consisting essentially of the oxide or hydroxide of Ce and Mn, The content of Ce and Mn in particles is higher than matrix film; The coating is amorphous structure, with the same direction, can inhibit the generation of micro-battery electrolyte. Polarization curve test results show that:the Ce-Mn conversion coating corrosion potential is higher, the corrosion current density decreases. The corrosion potential of aluminum silicon alloy with the conversion film increace210mV, Inhibiting the anodic dissolution and charge diffusion, the corrosion current density decreases to1/10.than the previous.EIS electrochemical testing results show:Ce-Mn conversion coating has higher layer resistance and charge transfer resistance, the lower layer capacitor and electric double layer capacitor, higher dielectric constant. Coating resistance reached33656Ω·cm2much more than the natural oxide film, Ce-Mn conversion film is more compact, less surface defect, uniformly covering on the surface of aluminum silicon alloy.it has a good protective effect in flue gas condensate.Immersion experimental results show that:with immersion time increasing, aluminum silicon alloy surface Ce-Mn conversion coating gradually dissolved, white particles by the small and large disappeared gradually.At the first Ce and Mn content increase and then decrease.