Case Study 1 - XPS Analysis of Railhead Residue

“Leaves on the line” can be responsible for the slow running or cancellation of train services here in the UK, can be mocked by an unappreciative public - and yet is also the focus of much detailed research by the railway companies and interested academics. 

The issue is the formation of a low friction, low adhesion layer between the rail and the wheel which can lead to wheel slippage and reduce the effectiveness of braking. Ongoing research is consequently in three areas i) understanding the formation of the intermediate layer in order to prevent it, ii) methods to remove the layer in a cost effective environmentally friendly manner, and iii) methods to improve braking to counteract the influence of the layer.

X-ray Photoelectron Spectroscopy studies carried out here in Sheffield have contributed to the on-going work of Professor Roger Lewis and Dr Joseph Lanigan. Simple analyses of swab samples before and afterwards have confirmed the effectiveness of a novel layer removal system (reference 1) as well as looking at the composition of the tribological layer. Similarly, swab samples have been analysed from “real life” rails suffering from the low adhesion layer and a proposed low-cost track test simulation of the problem to show the similarities and limitations of an artificially made layer (reference 2).

Railhead swab sample before cleaning

Railhead swab sample after cleaning

XPS Survey scan from swab before cleaning

XPS Survey scan from swab after cleaning

The "before" analysis shows the tribological layer includes iron oxide and organic residue. The "after" analysis is largely that of the filter paper used to carry out the swabbing. This is confirmed by the high resolution spectra.


1.    Development and implementation of novel cryogenic railhead cleaning technology.

Peter Krier, Joseph Lanigan, Paul Ferriday, Roger Lewis (2020)

Permanent Way Institution Journal, 138 (2020). pp. 35-39. ISSN 2057-2425


2.    Field trials of a methodology for locomotive brake testing to assess friction enhancement in the wheel/rail interface using a representative leaf layer

Joseph L Lanigan , Peter Krier, Luke Buckley Johnstone, Benjamin White , Paul Ferriday and Roger Lewis

Proc IMechE Part F: J Rail and Rapid Transit 2021, Vol. 235(9) 1053–1064