Molybdenite was one of the rare earth oxides tested.
Molybdenite was one of the rare earth oxides tested.

Generally speaking, ceramics tend to be hydrophilic (water-attracting) rather than hydrophobic. However, the unique electronic structure of rare earths improves the water-repellence of the material.

The MIT reseachers used powder oxides of 13 of the 14 rare earth elements and made pellets by compacting and heating them to nearly their melting point in order to fuse them into solid, ceramic form. When tested, all 13 of the rare earth oxide ceramics displayed strong hydrophobic properties.

“We showed, for the first time, that there are ceramics that are intrinsically hydrophobic,” said associate professor Kripa Varanasi, who led the research. “[Rare earth oxides] are exotic materials and, interestingly, their wetting properties have not been studied. This paper also gives a whole host of the properties of rare-earth oxides.”
The research also investigated the morphology, surface chemistry, crystallographic structure, grain structure, sintering temperature and density about the oxides.The MIT researchers also showed that the materials have greater hardness than many others currently used in rough industrial settings.
The ceramic forms of rare earth oxides could be used either as coatings on various substrates, or in bulk form. Because their hydrophobicity is an intrinsic chemical property, even if they are damaged, they can sustain their hydrophobic properties.
The team has also coated nanotextured surfaces with the ceramics at MIT’s Microsystems Technology Laboratories, making them equally as hydrophobic. These materials, therefore, provide a pathway to make durable superhydrophobic surfaces as well, and these coatings can be fabricated using existing processes. Such extreme non-wetting properties, coupled with durability, could find applications in steam turbines and aircraft engines, for example.
Varanasi said that most prior research on hydrophobic materials and coatings has focused on surface textures and structure rather than on their intrinsic chemical properties. “No one has really addressed the key challenge of robust hydrophobic materials,” he explained. “We expect these hydrophobic ceramics to have far-reaching technological impact.”