Diamonds full of microscopic holes have been made in the lab by a team of U.S. and Canadian researchers, who believe they could be used as a material for extra-robust membranes or filters.
The diamonds, which are about a millimetre in diameter, are transparent and resemble raw, yellowish or brownish natural diamonds when viewed under a light microscope, said Kai Landskron, a chemist at Lehigh University in Bethlehem, Pa., who led the study published online Monday in the Proceedings of the National Academy of Sciences Early Edition.
Landskron sent the diamonds to be analyzed by Neil Coombs, director of the Centre for Nanostructure Imaging at the University of Toronto, the university where he himself was a postdoctoral researcher from 2001 until 2005.
Viewing the diamonds under an electron microscope and analyzing them with related instruments revealed they were made up of interconnected nanocrystals, each about five to 10 nanometres in diameter, and that they are mesoporous — that is they are full of tiny pores.
Many mesoporous materials are used to make membranes for filtration, but such membranes are typically flimsy, Landskron said: "If you punch holes into something, then it becomes mechanically weaker."
However, diamond is the hardest material known, he added.
"So even if you make it porous, you can still expect a high mechanical stability in such a system."
Landskron and his team made the diamond by heating up a special form of carbon called periodic mesoporous carbon — a black material that resembles powderized coal — under very high pressures.
It formed transparent mesoporous diamonds at just 1300 C — a relatively low temperature for diamond formation.
Because the diamonds are transparent and shiny, they can be used in optics — and they can, in theory, also be polished and cut, and set in jewelry.
"You would just need to grow perhaps a little bit larger pieces … then you would have a porous diamond gemstone."
However, Landskron acknowledged that most jewelry shoppers might not be thrilled about the idea of having a diamond full of holes, even if they're far too small to see.
The researchers are now trying to make diamonds from other porous starting materials and are also trying to look at the material's hardness, strength and other mechanical properties in more detail.