Effect Of Modified Zinc Powders On Performance Of Waterborne Zinc-rich Anti-corrosion Coatings

Waterborne zinc-rich anti-corrosion coatings have been widely used in industrial anticorrosion, marine anticorrosion and architrctural anticorrosion due to their excellent corrosion resisrance, zero VOC, strong self-healing ability and reasonable price. Flake zinc powders have gradually become the preferred pigment of zinc-rich coating as their outstanding abilities of cover, shielding and significantly reduce the amount of zinc powders. However, the application of waterborne inorganic silicate alkaline coating were limited by the easily coating degradation, uneven surface of zinc-rich coating resulted from the direct use of the flake zinc powder, which can lead to strong flexicity of zinc powder, poor anti-settling and prone to agglomeration. So the research on overcome the strong flexicity, settlement and poor dispersion of the flake zinc powder has attract more and more attention. To solve the above problems, the author studied on the surface modification of flake zinc powder, and improved the comprehensive performance of the coating.In this paper, flake zinc powders were modified with silane coupling agent and rare earth metal. The optimum process conditions of zinc sheet modification was obtained by using pure zinc sheet replacement of zinc powder to do prophase research. This method was applied to zinc powder modification. The effects of modification on properties of corrosion resistance and anti-settling of zinc powder were analyzed by the sedimentation volume and corrosion appearance. A stable inorganic zinc-rich coating was obtained by the modified potassium silicate solution mixing modified flake zinc pigment and other agents. The effects of modified zinc powders on performance of waterborne zinc-rich anti-corrosion coatings were investigated. Finally, different kinds of silane coupling agent and rare earth metals were used to modify zinc powder, expect to further enhance the effect of the modification. The results show that using silane coupling agent and rare earth metals can successful modified zinc powder. The dispersion and corrosion resistance of zinc powder were improved, because the surface of zinc powders were coated by silane and the protection of rare earth oxides. The best method was use both silane KH570 and lanthanum nitrate to modify zinc powder. Compared with the coating made by unmodified zinc powder, the surface drying time is reduced by 20%, surface cracks are reduced. The corrosion resistance is greatly improved, as shown by the medium stages even after immersing for 9 days in 3.5% NaCl solution. Effect of using silane and lanthanum nitrate to modify zinc powder is superior to use any kind of modification agent alone. The dispersion and corrosion resistance of zinc powder were also improved when the double silane BTSPA, lanthanum nitrate and ytterbium nitrate were used to modify zinc powder, at the same time more Si element was grafted to the surface of zinc powder. Compared with the coating made by zinc powder modified by single silane KH570, the mechanical property of coating was same, surface cracks are reduced. The surface of coating has less obvious corrosion after immersing in NaCl solution for 120 h, the self-corrosion current is reduced an order of magnitude, the coating has stronger corrosion resistance.