片层蒙脱土对溶胶-凝胶涂层防腐蚀性能的影响

Effect of Lamellar Montmorillonite on Corrosion Protection of Sol-Gel Coating

为改善无机涂层脆性大、成膜性差的问题,以正硅酸四乙酯为原料,片层蒙脱土为填料,采用溶胶凝胶法在AA2024铝合金表面制备了蒙脱土溶胶-凝胶涂层。利用扫描电镜(SEM)、能谱仪(EDS)和傅里叶红外光谱仪((FT-IR))分析了涂层的微观形貌和聚合原理。通过动电位极化和电化学阻抗谱测试,研究了所制备的涂层在3.5%NaCl溶液中的电化学行为,并与纯硅溶胶涂层和基体进行比较。结果表明:制备的蒙脱土纳米片,其厚度最小约为10nm,直径最小约为500nm;蒙脱土在涂层中分布较为均匀,在溶胶聚合过程中,蒙脱土在溶胶中引导溶胶粒子有序聚合,提高了涂层的致密度,减少了固化时涂层产生的缺陷;蒙脱土溶胶-凝胶涂层试样的腐蚀电流密度(1.04×10^(-8)A·cm^(-2))比纯硅溶胶涂层试样(1.22×10^(-7)A·cm^(-2))低1个数量级,蒙脱土溶胶-凝胶涂层具有较高的涂层阻抗,且蒙脱土溶胶-凝胶涂层的Rct始终远高于纯硅溶胶涂层,表明蒙脱土溶胶-凝胶涂层具有更持久的防护效果。

In order to improve the brittleness and poor film-forming property of the inorganic coating,a montmorillonite sol-gel coating was prepared on the surface of AA2024 aluminum alloy by sol-gel method with tetraethyl orthosilicate as raw material and lamellar montmorillonite as filler.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and Fourier transform infrared spectroscopy(FT-IR)were used to analyze the micro-morphology and polymerization principle of the coating.The electrochemical behavior of the coating in 3.5%NaCl solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy test,and compared with pure silica sol coating and substrate.The results showed that the lowest thickness of montmorillonite nanosheets was about 10 nm and the diameter was about 500 nm.Montmorillonite was evenly distributed in the coating.In the process of sol polymerization,montmorillonite guided the ordered polymerization of sol particles in the sol,which improved the density of the coating and reduced the defects of the coating during curing.The corrosion current density of montmorillonite sol-gel coating was 1.04×10^(-8) A·cm^(-2),about one order of magnitude lower than that of pure silica sol coating which was 1.22×10^(-7) A·cm^(-2).The resistance of montmorillonite sol-gel coating was higher than that of pure silica sol coating,and the Rct of montmorillonite sol-gel coating was always much higher than that of pure silica sol coating,which indicated that montmorillonite sol-gel coating had longer protective effect.