Metal pretreatments play a crucial role in the long-term performance of metals. Hexavalent chromium has been a state of the art metal pretreatment, but it is being phased out due to human health and environmental concerns. Therefore, the need for environmentally friendly pretreatment coatings has emerged. 2-D nanomaterials such as graphene have gained interest in this regard because of their ability to act as physical barriers to corrosion-causing agents, yet graphene's deposition is not always scalable or sustainable. Adding to the complexity, the corrosion inhibiting ability of 2-D graphene nanosheets has exhibited differing results in the past. Here, we present reduced graphene oxide-polyvinyl alcohol (PVA) nanocomposite coatings on branched polyethylenimine (B-PEI)-coated aluminum alloy 2024-T3, where B-PEI, acts as an adhesion promoting layer, realized by a high throughput airbrushing process of a graphene oxide-polymer ink followed by reduction. For the first time, a water-stable dispersion of reduced graphene oxide and polyvinyl alcohol (PVA) is prepared and quickly sprayed to yield a smooth pinhole-free coating, where reduced graphene oxide sheets act as bricks and PVA as mortar. It is shown that the coating is an exceptional oxygen barrier, similar in performance to SiO_x. The reduced graphene oxide sheets may also provide an alternative electronic pathway that prevents electrons from reaching the cathodic site, thereby hindering the corrosion cycle. Coatings with varying compositions on aluminum alloy 2024-T3 were evaluated in 0.2 M NaCl solution for 30 days period. The alloy coated with 60 to 70 wt% reduced graphene oxide exhibited the best performance, with little to no corrosion. Coatings with higher or lower reduced graphene oxide content exhibited corrosion due to increased oxygen permeability and swelling, which may explain conflicting prior reports.

中文翻译：

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环保型喷刷还原型氧化石墨烯-聚乙烯醇涂料的腐蚀行为

金属预处理在金属的长期性能中起着至关重要的作用。六价铬一直是最先进的金属预处理技术，但由于人类健康和环境问题，六价铬已被淘汰。因此，出现了对环境友好的预处理涂层的需求。二维纳米材料（例如石墨烯）在这方面引起了人们的兴趣，因为它们能够充当导致腐蚀剂的物理屏障，但是石墨烯的沉积并不总是可扩展的或可持续的。过去，二维石墨烯纳米片材的腐蚀抑制能力增加了复杂性，显示出不同的结果。在这里，我们介绍了在支化聚乙烯亚胺（B-PEI）涂层铝合金2024-T3上还原的氧化石墨烯-聚乙烯醇（PVA）纳米复合涂层，其中B-PEI，通过对氧化石墨烯-聚合物墨水进行高通量喷枪处理，然后进行还原，可以起到粘合促进层的作用。首次制备了还原性氧化石墨烯和聚乙烯醇（PVA）的水稳定分散体，并迅速喷涂以产生光滑的无针孔涂层，其中还原性氧化石墨烯片用作砖，PVA用作砂浆。结果表明，该涂层是一种特殊的氧气阻隔层，其性能与SiO相似_X。还原的氧化石墨烯片还可以提供可替代的电子路径，该电子路径防止电子到达阴极部位，从而阻碍腐蚀循环。在0.2 M NaCl溶液中对铝合金2024-T3上具有不同成分的涂层进行了30天的评估。涂覆有60％至70％（重量）的氧化石墨烯的合金表现出最好的性能，几乎没有腐蚀。降低或降低氧化石墨烯含量的涂层由于增加的氧气渗透性和溶胀而显示出腐蚀，这可能解释了先前的报道相互矛盾。