Leaves on the line are a notorious headache for commuters and train companies alike, causing costly delays. Now scientists say they haven’t chosen why the fallen foliage makes the rails so slippery.
When the sheets are flattened against the tracks, they form a black layer that dramatically reduces friction between the train wheels and rails, a situation that Network Rail has described as “the black ice of the railroad.” But the composition of this slippery layer has been a kind of puzzle.
Now researchers say they have revealed a key ingredient: large molecules found in plants called tannins.
“They are the chemicals that make the wine dry, and they are present in the tea,” said Dr. Michael Watson of the University of Sheffield, co-author of the new research.
The team says the study suggests that the tannins in the sheets adhere to iron that acids from the foliage have dissolved from the rails, forming a layer of black material that reduces friction between steel surfaces.
This substance, Watson added, is very similar to the iron gall ink, a substance used for centuries for everything from sacred texts to drawings by Leonardo da Vinci.
Writing in the Proceedings of the Royal Society magazine, Watson and colleagues report how they made their findings by infusing water with sycamore leaves to produce an acid brown extract.
When a drop of iron chloride in water, representing the dissolved iron in the rails, was added to this leaf extract, a black material containing iron was formed. This was not the case when a tannin-free leaf extract was used.
The researchers then placed their tannin-containing leaf extract between pairs of steel surfaces, and found that the black material that formed significantly reduced friction between them, compared to situations where only water or leaf extract was applied. tannin free.
“The leaf extract alone can cause this extremely low friction,” said Watson.
The team did not compare its black material to material recovered from the train tracks, and cannot rule out other factors that contribute to slippery conditions.
However, Watson said the findings open up new possibilities for reducing the impact of fallen foliage.
Hopefully this leads to some chemical treatments that can stop [the slippery material] to form, “he told the Guardian.
Watson added that the next step is to investigate the tannin content of the leaves of different types of trees, adding that this could help inform Network Rail’s logging operations.
“[We want to explore] which will have the greatest impact if they are cut down, and then they will retain the rest so that we don’t lose that habitat, ”he said.
Zili Li, a professor of railway systems and monitoring at Delft University of Technology who was not involved in the study, appreciated the research.
“This is an interesting finding and worth investigating further in laboratory and rail environments that are closer to the real-life slippery rail phenomenon,” he said.