Center for Neutron Research , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States.
Department of Physics , Carnegie Mellon University , Pittsburgh , Pennsylvania 15213 , United States.
Langmuir. 2018 Aug 21;34(33):9634-9644. doi: 10.1021/acs.langmuir.8b01646. Epub 2018 Aug 6.
The search continues for means of making quick determinations of the efficacy of a coating for protecting a metal surface against corrosion. One means of reducing the time scale needed to differentiate the performance of different coatings is to draw from nanoscale measurements inferences about macroscopic behavior. Here we connect observations of the penetration of water into plasma polymerized (PP) protective coatings and the character of the interface between the coating and an oxide-coated aluminum substrate or model oxide-coated silicon substrate to the macroscopically observable corrosion for those systems. A plasma polymerized film from hexamethyldisiloxane (HMDSO) monomer is taken as illustrative of a hydrophobic coating, while a PP film from maleic anhydride (MA) is used as a characteristically hydrophilic coating. The neutron reflectivity (NR) of films on silicon oxide coated substrates shows that water moves more readily through the hydrophilic PP-MA film. Off-specular X-ray scattering indicates the PP-MA film on aluminum is less conformal with the substrate than is the PP-HMDSO film. Measurements with infrared-visible sum frequency generation spectroscopy (SFG), which probes the chemical nature of the interface, make clear that the chemical interactions between coating and aluminum oxide are disrupted by interfacial water. With this water penetration and interface disruption, macroscopic corrosion can occur much more rapidly. An Al panel coated with PP-MA corrodes after 1 day in salt spray, while a similarly thin (∼30 nm) PP-HMDSO coating protects an Al panel for a period on the order of one month.
人们一直在寻找快速确定金属表面涂层防腐效果的方法。一种缩短不同涂层性能差异的测试时间的方法是从纳米级测量结果推断宏观行为。在此，我们将等离子体聚合（PP）防护涂层的水渗透观察结果以及涂层与涂覆有氧化物的铝基底或模型氧化物涂覆硅基底之间界面的特性与这些系统的宏观可观察腐蚀联系起来。六甲基二硅氧烷（HMDSO）单体的等离子体聚合膜被用作疏水性涂层的实例，而马来酸酐（MA）的 PP 膜则用作典型的亲水性涂层。涂覆有硅氧化物基底的薄膜的中子反射率（NR）表明，水更容易通过亲水性的 PP-MA 膜移动。非镜面 X 射线散射表明，与 PP-HMDSO 膜相比，PP-MA 膜在铝上的附着性较差。用红外可见和频产生光谱（SFG）进行的测量表明，涂层与氧化铝之间的化学相互作用被界面水破坏。由于这种水的渗透和界面的破坏，宏观腐蚀会更快地发生。涂有 PP-MA 的 Al 板在盐雾中腐蚀 1 天后就会发生腐蚀，而类似厚度（约 30nm）的 PP-HMDSO 涂层可保护 Al 板约一个月。
