| Since 1950s, plasma spray coating technology is widely used in material surface engineering for its fast forming speed, material variety of coating, good coating performance, low cost and wide application. But the porosity is inevitable in the sprayed coating because of its inherent nature. The presence of porosity would decrease the corrosion resistance of coatings, so it is necessary for sealing treatment to reduce porosity rate and improve the corrosion resistance and of the coatings. There are many ways of sealing treatment, of which sealing agent is used to carry on sealing treatment in this paper, however, organic sealing agent can't used at high temperature and they are liable to volatilize and combust, so the scope of their applications is limited. Therefore, the study of inorganic sealants has been rapidly developed in recent years.In this paper, we developed SiO2-Al2O3 sol sealing agent by sol-gel method, and films were obtained by dip-coating method sealing.Digital viscometer, TG-DSC, XRD and FTIR characterized sol dry gel. The results of TG-DSC showed that sol sealing has good thermal stability. The XRD test results showed that sol dry gel exists as diffuse "steamed bread" peaks and is amorphous state.The FTIR results showed that there are vibrational absorptions of Al-O bonds,Si-O bonds and Si-O-Si bonds, which state that the gel dry gel exists in Si02 and Al2O3.Sol sealing agent was characterized by SEM, XRD, metallurgical microscope, full-immersion corrosion test, electrochemical test and high-temperature oxidation experiment. The SEM and metallurgical microscope results showed that the porosity rate of coating is significantly decreased after the sealing treatment, and the coatings density was significantly increased. What's more, the sealant have excellent permeability and sealing ability. The full-immersion corrosion test of the seal coatings showed that the resistance to acid, alkali and salt is improved compared with that of unsealing coatings. The curve of corrosion medium is basically cyclical trends of "mass loss-mass gain-mass loss". The electrochemical test showed that the corrosion resistance of sealing coatings is better than the unsealing coatings. The corrosion resistance of unsealing P7412 coating is best, unsealing P7418 composite coating is secondary, and unsealing P7418 coating is worst. The best of corrosion resistance is sealing P7418 composite coating, the secondary is sealing P7412 coating, and the worst is sealing P7418 coating. The high-temperature oxidation experiment showed that the oxidation resistance has been greatly enhanced after sealing treatment.Epoxy resin sealing coatings by SEM is dense and smooth surface. The full-immersion corrosion test of the epoxy resin seal coatings showed that the resistance to acid, alkali and salt was improved compared with that of unsealing coatings. The electrochemical test showed that the best of corrosion resistance is sealing P7418 composite coating, the secondary is sealing P7412 coating, and the worst is sealing P7418 coating. The corrosion resistance of sealing coatings is better than the unsealing coatings.
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