Research On The Preparation And Corrosion Resistance Of Nano-coating Paint

Coating is the most important and economical method of all anticorrosive methods. Although there are all kinds of coatings with corrosion resistance, anticorrosive results are not very good because mechanics and chemistry cause lifetime problem. As a result, it is very significant to study a coating with high corrosion resistance. Through co-mixing, nanometer carbon black and silicon dioxide composite coatings can be prepared. Immersion corrosion testing, anodic polarization and electrochemical impedance spectroscopy (EIS) are employed to study the corrosion behavior of nanometer composite coating. The effects of ultrasonic field and nanometer-particle content on corrosion resistance of the coatings are studied. Through surface graft modification, polymethyl acrylate and polyvinyl alcohol are introduced on the surface of carbon black. Then oil-soluble carbon black nanometer particles are synthesized. SPM image and TEM picture show that the particle size is about 63nm and 74nm. Nanometer carbon black dispersion system using alkyd resin paint thinner as diluting agent is got in the ultrasonic field, and then nanometer composite coating is got through ultrasonic field and mechanical agitation. Coating of carbon black grafting polyvinyl alcohol, increasing weight corrosion experiment shows that corrosion resistance of the coating in 3.5% NaCl solution is better normal coating without carbon black grafting polyvinyl alcohol and the weight is reduced by 3/4 of the original. Anode polarization curves show that its anodic corrosion current is reduced to about 1/10 of the former, and its corrosion potential increases by about 400mV. Losing weight corrosion experiment and electrochemical impedance spectroscopy (EIS) get the same results. Through chemical modification, silane coupling agent (A858) reacts with hydroxide radical on the surface of nano-SiO2 reducing or removing hydroxide radical content. Then nano-SiO2 becomes hydrophobic, and its compatibility with coatings is improved. The SPM image shows that the particle size is about 98nm. In the ultrasonic field, modified SiO2 is dispersed in acetone. SiO2 dispersion system is added into coating, and then nanometer SiO2 composite coating is got through ultrasonic field and mechanical agitation. Corrosion experiments show that modified SiO2 improves corrosion resistance of coating in 3.5% NaCl solution greatly. Coatings with different nanometer particles content is compared, and the result is got that when nanometer particle content is low, corrosion resistance become better with the increase of nanometer particle content. But when nanometer particle content is high, the result is contrary. For the coating of carbon black grafting polyvinyl alcohol, corrosion resistance of 1wt% is the best; for the coating of carbon black grafting polymethyl acrylate, corrosion resistance of 0.68wt% is the best; for the coating of nano-SiO2, corrosion resistance of 0.91wt% is the best. Through analysis of surface graft modification, ultrasonic field and nanometer particle content effects on nanometer carbon black dispersion in coating and corrosion resistance, the composite coating corrosion resistance mechanism is studied. The corrosion resistance can be effectively improved when the nanometer carbon black can be dispersed uniformly without agglomeration. The nanometer carbon black has small grain diameter, can move in coating freely. The nanometer particles fill the defect area in coatings, improve its flexibility, and prevent ions from penetrating coating to corrode the substrate. Nano-SiO2 not only have such effects on corrosion resistance as nanometer carbon black, but also have the thixotropy that after it is dispersed, it can recombine with each other which prevents nano-SiO2 from stratifying and makes adhesion strong. In addition, modified nano-SiO2 becomes hydrophobic, which prevents corrosive things from immersing the coating film. When nano-SiO2 content is low, the nano-SiO2 can be dispersed uniformly without agglomeration, can move in coatings freely and fill the defect area in coatings, so it improves corrosion resistance. But when nano-SiO2 content is high, nano-SiO2 agglomerates and its size becomes bigger. So it can not move in coatings freely, stress concentration increases and bigger particles fall off easily, which makes corrosive things touch metal directly and corrosion resistance become worse.