Chemical vapor deposited hexagonal boron nitride sheets as little as one atom thick can protect metals in harsh environments at up to 1,100°C, according to Rice University scientists. From top: micrographs of uncoated nickel after exposure in a high-temperature oxidizing environment; nickel with a 5-nm h-BN layer after exposure; four electron micrographs of h-BN deposits of various thicknesses; and (bottom) the hexagonal arrangement of nitrogen (bright) and boron atoms. (Credit: Z. Liu/Rice.)
Corrosion annually costs the world economy about 3% of global GDP—about $2.2 trillion, according to a report from the World Corrosion Organization (pdf). Particularly difficult are applications that require protection from corrosive substances at high temperatures.
Now researchers from Rice University, Houston, Tex., say they have discovered a new protective coating for high-temperature corrosion applications—hexagonal boron nitride.
According to this news release, h-BN sheets only one atom thick can protect metal substrates in corrosive environments at up to 1,100 degrees Celsius. The scientists say the chemical vapor deposition method they have developed for making layers of “white graphene” can be scaled up to make the coatings practical for industrial use.
“We think this opens up new opportunities for two-dimensional material,” says Jun Lou, associate professor of mechanical engineering and materials science, in the release. “Everybody has been talking about these materials for electronic or photonic devices, but if this can be realized on a large scale, it’s going to cover a broad spectrum of applications.”
Lou and colleague Pulickel Ajayan led a research team that produced h-BN sheets via CVD, depositing the material on nickel foil. They found the coating improved corrosion resistance in oxidizing environments at high temperature. According to the paper, published last week online in Nature Communications, a layer of h-BN a few atoms thick also protected its chemical cousin graphene under similar conditions. The scientists also were able to transfer sheets of h-BN grown on graphene to copper and steel substrates, according to the news release.
Potential applications for CVD h-BN include gas turbines, jet engines, oilfield equipment, chemical processing, and other harsh environments, Lou says in the release. The coating is transparent, which may allow its use, for example, in solar photovoltaic applications. Wear and abrasion could be issues, and optimal h-BN thickness would need to be determined for specific applications, Lou says.
The Nature Communications paper is “Ultrathin high-temperature oxidation-resistant coatings of hexagonal boron nitride” (DOI: 10.1038/ncomms3541).