| Waterborne coatings have been widely used in recent years because of their environmental friendliness.However,compared with solvent-based coatings,the corrosion resistance of waterborne coatings needs to be further improved.In this paper,the effects of iron red pigments and zinc phosphate pigments with different ratios on the corrosion resistance of waterborne epoxy coatings containing 3%nano-oxides were studied by polarization curve test,electrochemical impedance test,Machu test,infrared spectroscopy and SEM test.The main results are as follows:(1)The corrosion resistance of waterborne epoxy coatings containing nano-oxides was modified by iron red and zinc phosphate respectively,the results show that the corrosion resistance of waterborne epoxy coatings containing nano-oxides can be greatly improved by adding iron red pigments or zinc phosphate pigments with any mass ratio of pigments/epoxy(0.8,1,1.2).(2)The mechanism of the difference in corrosion resistance of several kinds of coatings was studied.It was found that the corrosion resistance of waterborne coatings without anti-rust pigments decreased significantly after being immersed in solution for tens of days,while the waterborne coatings with anti-rust pigments maintained good corrosion resistance after being immersed for hundreds of days.Through impedance simulation and SEM analysis,it can be known that the high shielding ability of alumina to corrosion products in iron red pigments at the later stage of immersion and the blocking of corrosive channels between coatings and substrates by complex substances formed by the complexation of zinc phosphate and corrosion products in zinc phosphate pigments are the main reasons for the two coatings to maintain good corrosion resistance(3)When the mass ratio of pigments/epoxy is 1,the coating containing iron red and zinc phosphate pigments has the best corrosion resistance,which may be related to the curing of waterborne epoxy coatings.When the mass ratio of pigments/epoxy is less than 1,the protective effect of pigments progresses with the increase of the mass ratio.However,if the pigments are added too much(the mass ratio of pigments/epoxy is more than 1),a large number of pigments will exist in the gap between epoxy latex particles.It makes it more difficult for curing agent to contact with epoxy particles,which leads to the decrease of crosslinking degree of epoxy coatings.Therefore,the coating exhibits the best corrosion resistance when the mass ratio of pigments/epoxy is 1.(4)The corrosion resistance of the coating containing zinc phosphate pigment with the mass ratio of pigment/epoxy 1 is better than that of the coating containing iron red pigment.There may be two reasons:first is that iron red pigments exist in spherical form in coatings,while zinc phosphate pigments exist in flake form.Generally,the shielding performance of flake material is better than that of spherical material.Secondly,the protection principle of the two kinds of pigments is different.Iron red pigments mainly shield the matrix and surround the corrosion products separately.In addition,zinc phosphate pigments can also complex with corrosion products to form complex insoluble substances to block corrosion channels.(5)The corrosion resistance of coatings containing iron red and zinc phosphate pigments with the same mass which the mass ratio of pigments/epoxy 1 is also greatly improved compared with waterborne coatings without anti-rust pigments.However,compared with iron red pigments and zinc phosphate pigments which the mass ratio is 1,the corrosion resistance of the coatings is roughly the same,and there is no further significant improvement.(6)The corrosion resistance of solvent-based epoxy coatings was compared with that of waterborne epoxy coatings.It was found that the corrosion resistance of solvent-based epoxy coatings was better than that of coatings without anti-rust pigments.greatly improved by adding anti-rust pigments,which is better than that of ordinary solvent coatings.This also provides a basis for further application of waterborne coatings. |
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