Preparation And Corrosion Resistance Behavior Of Anti-corrosion Materials On Flue Gas Condenser

With the implementation of strategy of global sustainable development and emergence of energy sources optimizing trend, natural gas has been regarded as a high efficienct and environmental friendly cleaing source, which has been wide utilized in many fields. Novel flue gas condenser is taken as an efficient gas utilizing equipment. However, low temperature condenser surface suffers from severe corrosion due to the production acdic flue gas condensate. So, anticorrosion and heat transfer measures are the key technique for the development of novel equipment for thermal energy reclaimtion.Firstly, the corrosion resistant properties of electrolessly deposited Ni-Cu-P、Ni-Mo-P and Ni-W-P alloys were investigated. It shows that the addition of metallic element and change of pH value of plating solution. Ni-P and Ni-Cu-P coatings are smooth and possess amorphous structures, and Ni-Mo-P and Ni-W-P coatings are rough and display polymorphous structures. In contrast, the anticorrosion property of Ni-Cu-P coating is most superior among the prepared alloys, which may be used as a potential protective coating material.Secondly, various process parameters including stabilizer, concentration of Na3PO2and CUSO4, temperature of condensate, heat treatment on the structure, composition and anticorrosion properties were investigated as well. The results show that the increase of CUSO4concentration resulted in the increase of Cu content and the decrease of Ni and P content in Ni-Cu-P coating. Meanwhile, the crystal structure tends to transform from amorphous to crystalline one, consequently resulting the degradation of corrosion resistance properties of coating. When Na2MoO4served as stabilizer, the corrosion resistance of coating is the most superior. The increase of Na3PO2concentration induced the increase of P elemental composition, thus resulting in the enhancement of corrosion resistance of Ni-Cu-P coating. In addition, the introduction of Ce4+can refine the grain size, resulting in the production of smooth and corrosion resistant coatings. However, excess addition of Ce4+is detrimental to the electroless deposition of Ni-Cu-P coating. It should be noted that heat treatment apparently affacts the corrosion resistance of Ni-Cu-P coating. The coating is of amorphous structure after heat treatment below300℃for1h. Ni-Cu solid solution and Ni5P2phase emerge after heat treatment at400for1h, thus resulting in the degradation of corrosion resistance of the coating. After heat treatment at500℃, the emergence of Ni3P phase results in the occurrence of micro galvanic corrosion, further decreasing the corrosion resistance of Ni-Cu-P coating.Thirdly, the corrosion resistant mechanism of Ni-Cu-P coating was elucidated by investigating the effects of various factors including anion nature and condensate temperature and composition on the corrosion behavior of Ni-Cu-P coatings It shows that the anticorrosion property of the coating is due to the P enrichment induced passivation of coating surface, which is caused by selective dissolution of Ni in coating. The addition of little Cu element not only accelerate the enrichment of P element on coating surface, but also enhance the hydrogen evolution potential, thus resulting in the decrease of corrosion resistance of Ni-Cu-P coating. Besides, the chemical nature of anions also plays very important roles in the passivation of Ni-Cu-P coating. NO3-oxidation dorminatcs the coating passivation process at low anion concentration. Conversely, Cl-and SO42-mainly act on the passivation of the coating.Lastly, the aluminium silicon alloy was prepared by adding a certain content of silicon into melted Al substrate,and meanwhile various process parameters on structure and properties of cerium oxide conversion coatings was investigated as well. The result showed that when silicon content approach to13%,eutectic (α+Si) tends to uniformly form in Al substrate, resulting in the enhancement of pit corrosion resistance of aluminium silicon alloy. When silicon content is far beyond the eutectic arrest, the liquidus silicon forms and the number of eutectic (α+Si) decrease.Liquidus silicon induces the occurrence of galvanic corrosion, thus accerating the pit corrosion of aluminium silicon alloy.The optimum process parameters for preparation of conversion coating on aluminium silicon alloy is obtained as follows: Ce(NO3)3:14g/L; KMnO4:1.5g/L: K2SiO8:1.0g/L; NaF:0.8g/L; pH:2; T:60min; room temperature. The prepared Ce-Mn conversion coating which consist of oxide and hydroxide of Ce and Mn elements, is compact and of amorphous structure. The coating tends to suppress the formation of micro galvanic corrosion cell and shows the superior corrosion resistance properties in flue gas condensate.