An anonymous reader writes: CLEVELAND--Instead of having to use tons of crushing force and volcanic heat to forge diamonds, researchers at Case Western Reserve University have developed a way to cheaply make nanodiamonds on a lab bench at atmospheric pressure and near room temperature.
The nanodiamonds are formed directly from a gas and require no surface to grow on.
Their investigation is published today in the scientific journal "Nature Communications".
"This is not a complex process: ethanol vapor at room temperature and pressure is converted to diamond," said Mohan Sankaran, associate professor of chemical engineering at Case Western Reserve and leader of the project. "We flow the gas through a plasma, add hydrogen and out come diamond nanoparticles. We can put this together and make them in almost any lab."
The other researchers involved were postdoctoral researcher Ajay Kumar, PhD student Pin Ann Lin, and undergraduate student Albert Xue, of Case Western Reserve; and physics professor Yoke Khin Yap and graduate student Boyi Hao, of Michigan Technical University.
"At the nanoscale, surface energy makes diamond more stable than graphite," Sankaran explained. "We thought if we could nucleate carbon clusters in the gas phase that were less than 5 nanometers, they would be diamond instead of graphite even at normal pressure and temperature."
They first create a plasma, which is a state of matter similar to a gas but a portion is becoming charged, or ionized. A spark is an example of a plasma, but it's hot and uncontrollable.
To get to cooler and safer temperatures, they ionized argon gas as it was pumped out of a tube a hair-width in diameter, creating a microplasma. They pumped ethanol—the source of carbon—through the microplasma, where, similar to burning a fuel, carbon breaks free from other molecules in the gas, and yields particles of 2 to 3 nanometers, small enough that they turn into diamond. In less than a microsecond, they add hydrogen. The element removes carbon that hasn't turned to diamond while simultaneously stabilizing the diamond particle surface.
The group's process produces three kinds of diamonds: about half are cubic, the same structure as gem diamonds, a small percentage are a form suspected of having hydrogen trapped inside and about half are lonsdaleite, a hexagonal form found in interstellar dust but rarely found on Earth.
"Maybe we're making diamond in the way diamond is sometimes made in outer space," Sankaran proposed. "Ethanol and plasmas exist in outer space, and our nanodiamonds are similar in size and structure to those found in space."
