Materials
A chamber of graphene in Dr Sorenson’s lab after a planned explosion process has been carried out.
force the materials to turn into the graphene. Our materials do it all by themselves; the precursors bring their energy with them.” This means Sorensen’s approach is not only environmentally benign, but also economically viable on a large scale – all it requires are the right gases. “Right now,” Sorensen explains, “we use either acetylene or ethylene – these are industrially available gases – and oxygen, which is easy to obtain.” Sorensen and the team at HydroGraph (the company established to commercialise his detonation process) are well aware that they are not alone in their endeavour. As Kjirstin Breure, president of HydroGraph, explains: “We’re not the only company that has effectively solved standardised production – there are other companies who are producing very high quality and consistent graphene […] The industry at large is improving.”
potential. Although the material itself had been discovered, the question remained as to how it could be manufactured at scale, economically and with repeatable quality. But all that is about to change – or so Sorensen believes. “I came upon graphene, not as a graphene person. I was trying to do something else,” he explains. While studying the formation of fractal aggregates and trying to create an aerosol gel, he filled a chamber with acetylene and oxygen. “I detonated it with a spark plug and after the detonation, I had a cloud of smoke,” he recalls. “A couple of minutes later, when I opened the chamber […] we had a very dark, black, angel food cake – something that I call an aerosol gel. I was really quite pleased with that.”
An explosive discovery Serendipity was in the soot-stained air. When Sorensen and his team looked under the electron microscope, he realised that the soot was not in the typical little round balls of amorphous carbon – they were little flakes. Sorensen had created graphene – but he was reticent to get swept up in the hype that surrounded this novel material. He took a low-key approach, moving slowly to be sure that what he had produced was the genuine article. When the patent finally came through in 2016, it became clear that Sorensen had hit upon a remarkable process. “It’s simple”, he explains. “All you’ve got to do is put hydrocarbon gas and oxygen in a chamber and ignite it with a spark. And notice it’s exothermic, not endothermic. In every other process to make graphene, you have to add energy to your precursor materials, you have to cook them in some manner or another – either chemically or electronically, or whatever – to
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One such company is Universal Matter Inc., who’s commercial method is based on the Flash Joule Heating (FJH) process discovered by Dr James Tour, professor of organic chemistry and nanotechnology at Rice University in Houston. “Graphene is generally made by pulling graphite sheets apart,” Tour explains, “which is energy intensive and damages the graphene sheets; or by building the graphene sheets one atom at a time, which makes high-quality graphene sheets but on a miniscule scale.
“So, the industry must sacrifice quality for quantity, and both methods are very expensive ($60,000– $200,000 per ton). Our method of Flash Joule Heating is able to produce very high-quality graphene sheets, in bulk quantities, synthesised within seconds.”
Quick as a flash Unlike Sorensen’s process, FJH is endothermic, operating on the highly efficient conversion of electric current directly into thermal energy when it passes through a resistor. Yet, as Tour notes, “unlike other methods for synthesising graphene, which require highly pure gases, graphite, large amounts of solvent, or very hot furnaces, our method uses no solvents, furnace or reactive gases.” Key advantages to this method, as Tour outlines, include: “scalability, ability to convert waste materials into graphene, high efficiency and low impacts”. What is more, Tour notes, “our method was determined to use 80–88% less energy, 93–97% less water and emits 80–85% less greenhouse gases to synthesise one kilogram of graphene, as compared to current graphene production methods.” Already, Tour says, “Universal Matter is scaling the FJH process to be able to produce tons of graphene per day.” In fact, as Tour explains, graphene is already being used at scale in some industries. “Ford Motor Company has included graphene in all of their late-model cars in the form of a polymer reinforcing agent – so, graphene
Medical Device Developments /
www.nsmedicaldevices.com
Hydrograph
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