Preparation And Corrosion Resistance Of Polycarbosilane-derived Coating

As one of the pillar industries of national economic development,steel plays an important role in all stages of national economic development.However,due to the active chemical properties of steel,its annual waste is amazing.Polymer precursor derived coating has attracted wide attention due to its low preparation temperature,simple equipment requirements,good coating uniformity and suitable for mass production.However,the polymer precursor derived coating has the problems of large shrinkage and poor interfacial bonding.In order to solve this problem,polycarbosilane-derived coatings were prepared by dip-coating method.The effects of crosslinking methods(oxidative crosslinking and DVB crosslinking)and pyrolysis temperature on the coatings were studied.On this basis,SiC inert filler was used to improve the shrinkage of polycarbosilane-derived coatings.The effects of filler content,particle size and morphology on the structure,surface morphology and corrosion resistance of the coatings were studied,and the corrosion mechanism of the coatings was analyzed.The main results of this paper are as follows:(1)Polycarbosilane-derived coatings were prepared on the surface of steel by dip-coating method.The effects of crosslinking method and pyrolysis temperature on the morphology,bonding strength and corrosion resistance of the coatings were studied.The average microcrack width and surface roughness of the coating pyrolyzed at 600℃ are higher than those of the coating pyrolyzed at 400℃ or unpyrolyzed,and the average microcrack width of the oxidized cross-linked coating is smaller than that of the DVB cross-linked coating.The degree of crosslinking of the oxidized cross-linked sample was 0.289,which was larger than that of the DVB cross-linked sample.The TG-DSC curve showed that the weight loss rate of the oxidized cross-linked sample was 27%.The coating with oxidation cross-linking and pyrolysis temperature of 400℃ has better corrosion resistance due to its small average microcrack width,low surface roughness and high degree of ceramicization.(2)The effects of SiC filler content on the surface morphology,interface bonding and corrosion resistance of polycarbosilane-derived coatings were studied.The results show that the SiC filler has an inhibitory effect on the shrinkage of the coating during pyrolysis.With the increase of SiC filler content,the average crack width of the coating decreases first and then increases.Excessive filler is not conducive to the improvement of the bonding strength of the coating.When the 30 nm SiC particle filler with a filler ratio of 0.0125 is added,the surface crack width of the coating can be reduced to 0.19 μm.(3)The effect of particle size of SiC filler on the coating was studied.The results show that compared with the SiC filler with an average particle size of 0.5 μm,the filler with a small particle size(30 nm SiC)not only has less dosage but also can obtain a coating with a smaller surface crack width.The corrosion resistance of the coating is mainly affected by the surface micro-crack width and bonding strength.When the ratio of 30 nm SiC filler is 0.025,the coating has the best corrosion resistance,and its self-corrosion current density is 9.53×10-8 A/cm2(4)The effects of fiber filler and filler morphology on the coating were studied by using SiC fiber as inert filler.The SiC fiber filler has a good effect on inhibiting the cracking of the coating.When the filler ratio is 0.0125,the surface micro-crack width of the coating can be reduced to 0.14 μm.The SiC fiber filler has a significant effect on the improvement of the corrosion resistance of the coating.