Study On Mechanism Changes On The Alkyd Varnish Coatings/Steel Interface Influenced By Atmospheric Plasma Treatment And Carbon Nanotubes

In the natural environment, the material will be occurring corrosion and failure, losing their original role of mechanical and structural, which would cause potential safety hazard and economic losses. In all kinds of environment corrosions, the marine corrosion is the most serious and this question needs to be researched and conquer urgently. In the aspect of Marine corrosion protection, coating protection possess a high proportion, which makes the research of coating failure in sea water environment to be a hot topic. So it is very necessary to improve the service life of the coating and the protective quality of coating.The modification of the coating and the base material is adopted in this article mainly to prolong the service life of coating and improve the quality of coating protective effect. Alkyd varnish coatings(AVCs) with defects are coated onto the surface of the Q235 steel and all samples with AVCs are immersed in 3.5 wt% NaCl solution. Characterization methods such as the Depth from Defocus method, Electrochemical impedance spectroscopy(EIS) and scanning kelvin probe testing(SKP) are adopted to characterize and analysis the coating failure process.1. Air plasma treatment on substrateCompared to traditional modification strategies, air plasma treatment has many advantages such as maintaining the overall performance of the substrate, low chemical consumption, high reliability, wide applicability, safety, etc. After air plasma treatment, the substrate has been added some functional groups,such as hydroxyl(-OH), carbonyl(-CO). These functional groups can act with some functional groups in alkyd resin, including-C=C-, R-OH, R-OOH, R-OOR and other functional groups,which can improve the bonding force between the coating and substrate and enhance the roughness of the surface. So the plasma treatment can enhance the protective performance of coating and delay coating failure. 2. Mix multi-walled carbon nanotubes with varnishIn order to improve the water and corrosion resistance performance of coating, we mix multi-walled carbon nanotubes with varnish. Carbon nanotubes in the coating act as a waterproof fillers and make the coating film more dense, blocking the infiltration channel of water molecules. Which can increase the penetration time of water from the coating surface to the substrate surface, delay the coating failure and increase the service life of the coating. 3. Effects of carbon nanotubes on the water penetration through coatingsIn order to compare influence of the addition of carbon nanotubes on water penetration rate, infrared spectrometer has been used to test the water infiltration in the coating. According to the change of infrared absorption peaks whose wave number is 3300 and 1650, water penetration rate is calculated. The results show that the addition of carbon nanotubes make water penetration rate much smaller than the original coating, which indicate that the adding of carbon nanotubes can enhance the ability of water resistance.4. Molecular simulation of the relationship between the failure of coating and themetal interfaceMaterials Studio 7.0 has been used by establishing the model, optimization of structure and dynamics simulation from the side of molecular mechanics. Through comparing the influence of plasma treatment on the surface of the iron substrate on the adsorption between alkyd resin and substrate, we get a result that plasma treatment on the surface of the substrate can play a promoting role in the adsorption on the surface of the substrate.Basing on the Mean Square Displacement(MSD) curve of water molecules in the different degree of polymerization of alkyd resin crystal cell, water diffusion coefficient in different cells can be got. Then add different sizes of Carbon Nanotube(CNT) to the same degree of polymerization of alkyd resin in the cell. Through their respective MSD curve, we can get water diffusion coefficient of different sizes of CNT in crystal cells. The results show that with the increasing of the degree of polymerization of alkyd resin, water diffusion coefficient in alkyd resin crystal cell increases gradually; After adding different sizes of CNT, with the increasing of sizes of CNT, the water diffusion coefficient will decrease firstly and decrease later.By analyzing impact of plasma treatment and the adding of CNTs on the coating failure, we can improve protective effect of the coating and increase the coating life.