Researchers at Rice University, led by chemist James Tour and graduate student Weiyin Chen, developed a process to turn carbon from various sources into valuable forms like graphene or diamond. The technique involves heating the carbon with a flash of electricity, and the transition is instant. The best part is they can “evolve” the carbon through phases, converting it into a final form that’s determined by the flash length. Meaning, they can get the product they want by stopping the flash at designated times.
The team developed the technique, known as flash joule heating (FJH), in early 2020. It involves passing an electrical current through carbon-containing materials, heating them to approximately 2,727°C (4,940°F) to convert the carbon into pristine, turbostratic graphene flakes. The conversion happens in under a second!
The researchers found that by tweaking FJH, they could use the process to create other materials too. So they refined the technique by increasing the duration of the flash and adding organic fluorine compounds and precursors to elemental carbon black. This turned the carbon into several hard-to-get allotropes when flashed, including fluorinated concentric carbon (where carbon atoms form a shell circling a nanodiamond core), fluorinated turbostratic graphene, and fluorinated nanodiamonds. (“Turbostratic” means the layers are not firmly bound to each other, so they’re easier to separate in a solution.)
To make graphene, the flash lasts only ten milliseconds. To make nanodiamond and concentric carbon, the flash goes up to between 10 and 500 milliseconds. The duration determines the final carbon allotrope.
Nanodiamonds are microscopic crystals that display the same carbon-atom lattice as macro-scale diamonds. They are useful in electronic components such as semiconductors. The new FJH process can produce these in bulk, which is traditionally tricky to do.
James Tour, the lead researcher on the study, said:
In industry, there has been a long-standing use for small diamonds in cutting tools and as electrical insulators. The fluorinated version here provides a route to modifications of these structures. And there is a great demand for graphene, while the fluorinated family is newly produced here in bulk. In addition, the concentric-shelled structures have been used as lubricant additives, and this flash method might provide an inexpensive and fast route to these formations.
The team’s next steps are to experiment with other additives like boron, nitrogen, and phosphorus.