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Innovative coating prevents limescale formation

Innovative coating prevents limescale formation

 


A test setup in which researchers tested how lime crystals adhere to different surfaces.Credit: Julian Schmid / ETH Zurich

Hot water tanks, washing machines, kettles: Limescale forms in all household appliances that come into contact with (hot) water, especially in areas where the water is hard, i.e. high in calcium. Often, the only solution is to use vinegar or a special descaler to dissolve rock-hard deposits and restore functionality to your appliance.

This is a nuisance in homes and, for example, in thermal power plants producing electricity, limescale formation is an expensive problem known as fouling.

Heat exchangers are particularly prone to limescale, which significantly reduces the efficiency of the system. Just 1 millimeter of limescale in heat exchanger pipes reduces power generation efficiency by about 1.5 percent. To make up for these losses, an additional 8.7 million tonnes of hard coal will need to be burned. This has a negative impact on carbon emissions and the climate, and is costly for power producers.

Innovative scale-repellent surface

A research team from ETH Zurich and the University of California, Berkeley has discovered a potential solution to this problem. It is a special limescale-repellent coating with microscopically small ridges that prevent the adhesion of limescale crystals. The research team's study was published in the journal Science Advances.

Little basic research has been conducted on the development of surfaces that repel limescale. So researchers led by former ETH professor Thomas Szczius took a closer look at the interactions between individual growing calcareous crystals, surrounding water flow, and surfaces at a microscopic level.

Based on this, Schutzius' PhD student Julian Schmidt and other team members developed several coatings from different soft materials and tested them in their laboratory at ETH Zurich.

Test polystyrene beads on a grooved surface.Credit: Julian Schmid / ETH Zurich

Microstructured hydrogels are the most effective

The most effective coating was found to be a polymer hydrogel. Its surface is covered with tiny bumps thanks to a microtextured mold that the researchers created using photolithography.

The microstructure of the hydrogel is reminiscent of natural models such as shark scales, and it also has a ribbed structure to reduce dirt on shark skin.

In kettles and boilers, riblets reduce the chance of calcareous crystals coming into contact with the surface, preventing them from sticking and making them easier to remove. Water flowing over the hydrogel and through the rib structure carries away the hydrogel. Although the coating cannot completely prevent the formation of limescale crystals, the continuous passive removal of microscopic crystals prevents them from growing together and forming a tenacious layer.

In producing the various coatings, the researchers primarily varied the polymer content. Lower polymer content and higher moisture content make it difficult for calcium carbonate crystals to adhere to the surface.

Tests using model particles made of polystyrene show that the surface structure of the coating must be smaller than the particles deposited on it. This reduces the contact surface and reduces adhesion. “We modified the surface structure of the material to achieve maximum efficiency and performed crystal experiments with this optimal structure size,” says Schmidt.

The research team's experiments showed that the hydrogel coating was highly effective. When water flowed over the hydrogel-coated surface, limescale crystals around 10 micrometers in size had already grown on the surface, and up to 98 percent of the crystals were removed.

When observed under an electron microscope, only a few micrometers of lime crystals are found on the grooved surface.Credit: Julian Schmid / ETH Zurich

environmentally friendly solution

The researchers emphasize that their solution is environmentally friendly and more efficient than existing descaling approaches that use toxic and aggressive chemicals. In contrast, hydrogels are biocompatible and environmentally friendly. The technology behind this solution also needs to be scalable. Coatings can be applied using a variety of methods already used in today's industry.

The researchers made a conscious decision to support publication in a scientific journal rather than apply for a patent for their development. This means that all parties are free to further develop and utilize new coatings.

Further information: Julian Schmid et al., Imparting scale aversion through rational microtexturing of soft materials, Science Advances (2023). DOI: 10.1126/sciadv.adj0324

Citation: Innovative coating prevents limescale formation (February 12, 2024) from https://techxplore.com/news/2024-02-coating-limescale-formation.html on February 12, 2024 acquisition

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