Microscopically small ribs: Researchers develop coating against limescale

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Lime crystals a few micrometers in size on the grooved surface

Photo: Julian Schmid / ETH Zurich

We know the problem with kettles or irons. Every household appliance that comes into contact with hot water becomes calcified. In the home it's just a nuisance, but on a larger scale it's an expensive problem. In thermal power plants that convert heat into electricity, limescale deposits cause high energy losses.

According to ETH Zurich, a lot of limescale forms in the heat exchangers of power plants in particular: a layer of just one millimeter in the heat exchanger pipes makes electricity production around 1.5 percent more inefficient, they say. In order to compensate for the Europe-wide loss caused by these deposits, millions of tons of additional hard coal would have to be burned. A research team from ETH Zurich and the University of Berkeley has now developed a lime-repellent coating that is intended to prevent deposits. The scientists report this in the journal “Science Advances”.

More environmentally friendly than chemicals against limescale

The team led by Julian Schmid, a doctoral student in the laboratory for multiphase thermofluidics and surface nanoengineering, looked at the solution to the problem from nature. The researchers provided a polymer hydrogel with microscopic ridges that resemble those on shark scales. According to the researchers, these ensure that lime crystals have less contact with the surface, cannot settle and can therefore be removed more easily.

The coating cannot therefore prevent some lime crystals from forming. But water flowing over the hydrogel wears away the crystals and prevents them from growing together to form a stubborn layer. In the experiments, up to 98 percent of all lime crystals up to around 10 micrometers that had previously grown on a hydrogel-coated surface were removed.

Until now, the lime has been dissolved with sometimes toxic and aggressive chemicals. According to the researchers, their approach is more environmentally friendly and efficient. The technology is biocompatible and scalable.

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