Hydrogel-Based Coating Prevents Limescale Adhesion
A research team from ETH Zurich and University of California, Berkeley, are currently developing a new coating to repel limescale in places from household water tanks to thermal power stations.
Led by former ETH professor Thomas Schutzius, researchers looked at the interactions among individual growing limescale crystals, water flow and the surface at the microscopic level.
The study was recently published in the journal Science Advances.
According to the university, limescale forms in domestic appliances that encounter hot water, especially in areas where the water is hard and high in calcium.
In thermal power stations that generate electricity, the problem becomes much more expensive as fouling collects in heat exchangers and affects the efficiency of systems. A layer of limescale just one millimeter thick reportedly reduces the efficiency of electricity production by approximately 1.5%, meaning an additional 8.7 million tons of hard coal would have to be burned to compensate for the loss.
The team says now they have found a possible solution to the problem in the form of a limescale-repellent coating with microscopically small ridges to prevent the adhesion of limescale crystals. Doctoral student Julian Schmid and other team members reportedly developed several coatings from various soft materials to test.
Wherever hot water flows, #Limescale is never far away. In households, this is a nuisance; in thermal power stations, it’s an expensive problem. Now researchers at ETH Zurich have found an answer. ???? https://t.co/awvKovRiNk @eth_dmavt @tomschutzius @UCBerkeley— ETH Zurich (@ETH_en) February 9, 2024
The most effective coating, ETH says, turned out to be a polymer hydrogel, which is covered in tiny ridges thanks to microtextured molds that were fabricated using photolithography. The microstructure is reportedly similar to shark scales that are ribbed to suppress fouling on the animal’s skin.
These “riblets” ensure that limescale crystals have less contact with the surface, preventing adhesion and making it easier to remove. Water flowing over the hydrogel and through the ribbed structure reportedly carries them away.
However, the team notes that the coating can’t fully prevent limescale crystals from forming. That said, a constant passive removal of the microscopic crystals can stop them growing together to form a tenacious layer.
The researchers reportedly varied the polymer content when creating the different coatings. The lower the polymer content and the higher the water content, the less well the calcium carbonate crystals adhere to the surface, the study says.
Additionally, tests with model particles made of polystyrene showed that the coating’s surface structures must be smaller than the particles that are deposited on it. This reduces the contact surface and, consequently, the adhesive force.
“We varied the material’s surface structure to achieve the greatest efficiency, then carried out the crystal experiments with this optimum structure size,” Schmid said.
When testing the water flow across the hydrogel-coated surface, on which limescale crystals with a size of around 10 micrometers had previously been grown, up to 98% of the crystals were reportedly removed.
The researchers emphasized in the study that their solution is more eco-friendly and more efficient than existing approaches to descaling, some of which involve toxic and aggressive chemicals. In contrast, the hydrogel is considered biocompatible and environmentally friendly.
The team adds that the technology behind this solution should also be scalable, as the coating could be applied in various ways that are already in use in industry today.
ETH says that the scientists have deliberately decided in favor of publication in a scientific journal rather than applying for a patent. This reportedly will allow all interested parties to further develop and utilize the new coating.