Every autumn rail networks across the world suffer delays, accidents and schedule changes due to low friction problems caused by leaves landing on the rails. These leaves form a layer that can reduce the friction between the wheel and the rail to a similar level as that between ice and an ice-skate (μ=0.01–0.05). Previous works have generated several hypotheses for the chemical reactions and low friction mechanism associated with these layers. In this work, the reaction between an aqueous extract of sycamore leaves and metallic iron is investigated. This reaction has been shown to produce a black precipitate, which matches field observations of leaf layers, while friction tests with these extracts produce characteristic ultra low friction. The reaction is investigated through FTIR, XPS, CHNS and ICP-MS analysis as well as wet chemical testing. The impact of the reaction on friction is investigated through three rounds of tribological testing. The results indicate that the black precipitate produced is iron tannate, formed by complexation of tannins with dissolved iron ions. Friction testing showed that eliminating tannins from the leaf extract resulted in a significant increase in the friction coefficient compared with the control.

中文翻译：

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叶层的组成和减摩性能


每年秋季，由于树叶落在铁轨上造成的低摩擦问题，世界各地的铁路网都会遭受延误、事故和时刻表变更的情况。这些叶子形成一层，可以将车轮和轨道之间的摩擦力降低到与冰和溜冰鞋之间的摩擦力相似的水平（μ=0.01-0.05）。之前的工作已经对与这些层相关的化学反应和低摩擦机制提出了几种假设。在这项工作中，研究了梧桐叶的水提取物和金属铁之间的反应。该反应已被证明会产生黑色沉淀物，与叶层的现场观察相匹配，而这些提取物的摩擦测试产生了特有的超低摩擦力。通过 FTIR、XPS、CHNS 和 ICP-MS 分析以及湿化学测试对该反应进行了研究。通过三轮摩擦学测试研究反应对摩擦的影响。结果表明，产生的黑色沉淀物是单宁酸铁，是单宁与溶解的铁离子络合形成的。摩擦测试表明，与对照相比，从叶子提取物中消除单宁导致摩擦系数显着增加。