| Stainless steel has been widely used in aerospace,nuclear industry,petroleum,chemical,light industry,food,construction and other fields.The corrosion resistance of stainless steel comes from its stable passivation film on the surface,which can prevent the substrate from being further corroded in general corrosion media.However,in the medium and high temperature non-oxidizing medium,the passivation film on the stainless steel surface is damaged,causing serious corrosion,which causes huge economic losses and serious safety risks to the society.Therefore,how to improve the corrosion resistance of stainless steel in medium and high temperature non-oxidizing media has become a problem that scholars need to solve.In medium and high temperature non-oxidizing media,anodic protection usually has better protection effect and lower resource consumption.Polyaniline coatings are considered one of the most promising conductive polymer anticorrosive coatings.Polyaniline is easy available,simple preparing and non-pollution,and it has good performance in electro-conductivity,thermal conductivity,catalysis,electrochromic property,redox property,proton exchange property and photoelectric characteristics.Due to the anodic protection effect of polyaniline coating on stainless steel,it has attracted much attention in the field of metal anticorrosion.In this thesis,polyaniline materials and polyaniline anticorrosive coatings were prepared by different methods,then tested and evaluated.The effects of test temperature,polyaniline content in the coating and sulfuric acid concentration on the corrosion resistance of the polyaniline coating were investigated,and conductive additives were added to the polyaniline anticorrosive coating,then the anticorrosive performance of composite coating was tested.The works provide theoretical basis and technical accumulation for stainless steel to improve corrosion resistance in medium and high temperature non-oxidizing acid environment.The results show that:(1)Polyaniline materials were prepared by chemical oxidation,and polyaniline anticorrosive coatings were prepared by electrochemical methods,solvent methods,and adding binders.Anti-corrosion performance of these coatings were tested in 1 mol/L sulfuric acid solutions at different temperatures.The experimental results show that PANI coatings prepared by electrochemical method and PANI/PVB composite coatings are not suitable for long-term corrosion protection of stainless steel.PANI/EP composite coatings have good adhesion,physical shielding effects and anodic protection effects,which show the best protection performance on stainless steel in the research system.In addition,experiments show that at 50～60℃,PANI/EP composite coating can provide better corrosion protection for 316L stainless steel in 1 mol/L sulfuric acid solution.(2)DBSA is used as an secondary dopant and epoxy resin is used as a binder to prepare PANI/EP composite coatings.The structure and morphology of the polyaniline and PANI/EP composite coating are characterized by FT-IR,SEM,EDS methods,and the adhesion of composite coatings was tested by the pull-off method.In 50～60℃,1 mol/L H2SO4 solution,the effects of the PANI content in the composite coating and the H2SO4 concentration in the corrosion solution on the corrosion protection effect were investigated.Finally,a scratch immersion test was used to investigate the corrosion protection performance of the coating with minor defects.The experimental results show that in 50～60℃,1 mol/L H2SO4 solution,the PANI/EP composite coating with PANI content of 10 wt.%has the best performance,can provide better physical shielding effect and excellent anode protection effect.PANI/EP composite coating can provide good anodic protection for 316L stainless steel in H2SO4 solution with temperature not higher than 60℃ and concentration not higher than 1.5 mol/L.After being immersed in 50℃ and 60℃,1 mol/L H2SO4 solution for one week,the anodic protection provided by PANI can continue to protect 316L stainless steel from corrosion even if the PANI/EP composite coating has minor defects.(3)Polyaniline was polymerized on the surface of expanded-graphite(G)by in-situ chemical oxidation method,and PANI/G/EP composite coating was prepared by adding epoxy resin as a binder.For a contrast,PANI/GO/EP composite coating was prepared in the same method,then the addition effect was evaluated.By the experimental results,the addition of graphite and graphite oxide can both promote their anodic protection,and the effect of the amount of graphite in the composite coating on the corrosion resistance was explored,and the experimental results showed that the anti-corrosion effect of the PANI/G/EP composite coating sample with G:PANI=2:100 is the most significant.Finally,a scratch immersion test was performed on the composite coating,and the addition effect of PANI/G/EP composite coating samples with with a concentration of G:PANI=2:100 have the best anti-corrosion performance.Scratch immersion test shows that,in the 50℃ and 60℃,1 mol/L H2SO4 solution,the PANI/G/EP composite coating has better anodic protection effect on stainless steel than the PANI/EP composite coating. |
