London / Hamburg - The coveted rare earths could be even more in demand in the future. Experiments show that these substances are water-repellent even under extreme conditions. They retain this property over a wide temperature range and even in the event of abrasion, write Kripa Varanasi and his colleagues from the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts. in the specialist magazine "Nature Materials".

This means that rare earths could be used for corrosion-resistant surfaces or for aircraft coatings to prevent icing there. "We attribute their water-repellent properties to their unique electronic structure, which prevents hydrogen bonding with adjacent water molecules," write Kripa Varanasi and his colleagues.

Rare earths are of great importance in entertainment, energy and telecommunications technology. They are needed for the manufacture of computers, cars, semiconductors, cell phones and wind turbines, among other things. The economy has been complaining about a shortage for years: the main supplier China had cut its export of special raw materials. Europe is now pursuing a new strategy of extracting rare earths.

Two hours at 1000 degrees

In order to make materials water-repellent, they are usually coated with plastics so far. However, these weaken under extreme conditions. Rare earths, on the other hand, remain water-repellent even when worn, as shown in the new study. In an experiment, the researchers ground the rare earth metal cerium as well as aluminum and stainless steel. Here, the wear rate of cerium was much lower than that of aluminum and comparable to that of stainless steel. In addition, Cer retained its water-repellent property even after the abrasion.

Condensation tests revealed that droplets on the surface of rare earths are smaller than in other water repellent materials. An impinging water droplet even completely bounced off a cerium surface. In another experiment, the researchers expose Cer and a piece of plastic coated with silicon to 1000 degrees Celsius of hot air for two hours. The plastic dissolved, the silicon became water-attracting. Cerium, on the other hand, remained water-repellent.

With the exception of the radioactive element promethium, the MIT scientists tested all the rare earth metals in the form of their oxides. They received similar results for all.