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Issue 57, 2018
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Chemistry of black leaf films synthesised using rail steels and their influence on the low friction mechanism

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Abstract

Fallen leaves are the main issues for train operations in the autumn season due to their low friction coefficient (COF), leading to signals being passed dangerously and amended timetables. The main aim of this study was to elucidate the mechanism of low friction due to black leaf films, which are often seen on leaf-contaminated rails. A black material was successfully synthesised in the laboratory with water extracts from sycamore leaves and a plate of R260 rail steel. The black powder made from the extracts of brown leaves (BBP) was identified as the key material of low friction by the pin-on-flat tribological test, giving a COF between 0.08 and 0.14, which was lower than the COF of commercial engine oil (approximately 0.14). X-Ray fluorescence showed that the black material was a mixture of iron and leaf-organics. Laser Raman spectroscopy revealed that graphite-like carbon was likely to be formed on iron oxides. Fourier transform infrared spectroscopy showed that the formation of iron carboxylate was likely in bulk, which possibly transformed into iron oxides on the surface. Moreover, X-ray photoelectron spectroscopy detected a relatively high concentration of phosphates only in BBP. Hence, the low friction is presumably due to graphitic carbon, iron oxides and phosphate compounds in the black leaf films, as well as mechanical separation effects of bulk leaves. This black material could be a product of the Maillard reaction or reaction between iron and organic acids, such as tannic acids.

Graphical abstract: Chemistry of black leaf films synthesised using rail steels and their influence on the low friction mechanism

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Publication details

The article was received on 17 Jul 2018, accepted on 12 Sep 2018 and first published on 19 Sep 2018


Article type: Paper
DOI: 10.1039/C8RA06080K
RSC Adv., 2018,8, 32506-32521
  • Open access: Creative Commons BY-NC license
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    Chemistry of black leaf films synthesised using rail steels and their influence on the low friction mechanism

    K. Ishizaka, S. R. Lewis, D. Hammond and R. Lewis, RSC Adv., 2018, 8, 32506
    DOI: 10.1039/C8RA06080K

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