Research On The Service Behavior Of Polyimide Anticorrosive Coating

Corrosion of metals can lead to the increase of energy consumption,the decrease of product quality,the pollution of environment.Severe metal corrosion can also endanger personal safety.There are many methods for the protection of metal materials,and the application of anti-corrosion coatings to metal surfaces is one of the most economical,effective,and widely used methods.As a plastic with excellent strength,heat resistance,corrosion resistance and impact resistance,engineering plastics are widely used in the corrosion-resistant fields of electronics,electrical,automotive,construction,aerospace and other industries.As an excellent high-performance special engineering plastic,polyimide has great application prospects in the severe chemical environment and mechanical damage conditions,due to its prominent characteristics in performance and synthesis.Since the research on polyimide in China is still in the initial stage of theoretical research and application development,there are not many reports on polyimide coating in the field of anticorrosion.The research reports of polyimide anticorrosive coating are rarely both at home and abroad.In this paper,a kind of polyimide anticorrosive coating was prepared on the surface of N80 steel by electrostatic powder spraying method.The service conditions and corrosion resistance of the coating in different corrosion environments were evaluated by salt spray test and immersion test.The degradation process of the coating was studied by infrared spectroscopy,electrochemical impedance spectrum(EIS)measurement,scanning electron microscopy(SEM)and energy dispersive spectrometer(EDS).The coating showed good corrosion resistance during 3080 hours salt spray test.Only the non-penetrated micro-cracks were found on the surface and some corrosion products appeared in artificial scratches.The coating in 3.5wt.%NaCl,25wt.%HC1 and 25wt.%H2SO4 solutions had excellent corrosion resistance and their electrochemical performance did not change significantly over time,but some micro defects could be found on its surface.The coating also displayed a great mechanical property.The service behavior of the coating at different temperatures and in different corrosive media was evaluated by high temperature immersion test.The mechanical properties of the coating were evaluated by adhesion test and impact test.The failure process of the coating was studied by EIS testing and SEM.The experimental results show that the corrosion resistance of the coating in a 3.5wt.%NaCl solution is better than that in a 25wt.%HC1 solution at high temperature.The higher the temperature of the corrosive medium,the faster the corrosion resistance declines and the mechanical properties also decrease.The service performance of the coating under thermal loading and force loading was evaluated by cyclic thermal shock test and erosion corrosion test.Electrochemical EIS testing,SEM morphology observation,thermal analysis and other methods were used to evaluate the thermal shock resistance,corrosion resistance and wear resistance of the coating.The results of TGA analysis showed that the initial thermal decomposition temperature(Td5)of the polyimide coating was 518℃.The EIS test results and SEM topography observations show that the electrochemical performance of the coating after the cyclic thermal shock at different temperatures is improved,and the surface is free from detachment and damage.The coating has excellent thermal shock resistance.The coating was eroded in 3.5wt.%NaC1 solution for a long time.The electrochemical performance did not change significantly with time.The coating microscopic surface had only slight scratches,no cracks,and no corrosion products.Erosion resistance and wear resistance of the coating are good.