GILLETTE – A research team at the University of Wyoming has found a way to use a microwave to turn coal into graphite.
Using copper foil, glass containers and a conventional household microwave oven, UW researchers have demonstrated that pulverized coal powder can be converted into higher-value nano-graphite.
“This method provides a new route to convert abundant carbon sources to high-value materials with ecological and economic benefits,” the research team wrote.
Nano-graphite is used as a lubricant and other items like fire extinguishers and lithium ion batteries.
Previous research has shown that microwaves can be used to reduce the moisture content of coal and remove sulfur and other minerals, but most such methods require specific chemical pre-treatment of the coal, according to a press release from UW.
In the UW experiment, researchers ground Powder River Basin coal into a powder and microwaved it with copper foil.
The research team was led by TeYu Chien, an associate professor in UW’s Department of Physics and Astronomy. Chien said the experiment was inspired by one sentence in one paper where researchers who were microwaving graphene oxide saw a spark when they didn’t use any metal.
Their thought was to force the spark by microwaving metal.
“People kept telling us, ‘Don’t do that,’” Chien said. “We were like, just try it, let’s see how it goes.”
One of his research students went to Walmart and bought a cheap microwave.
The first time they microwaved the metal and coal powder, “we were scared that it would explode,” Chien said.
Christoffer Masi, one of the researchers, called the first attempt “impressively terrifying.”
“I am in a lab with very expensive equipment and this little 900W household microwave, and they want me to do something literally everyone has told you not to do since kindergarten,” Masi said. “Therefore, I had a lot of reservations about it but was confident the process would be safe enough.”
The coal powder was placed on copper foil and sealed in glass containers with a gas mixture of argon and hydrogen before being placed in the microwave.
To the research team’s surprise, it didn’t explode and the metal didn’t spark, Chien said. Instead, “everything we saw just melted.”
“We learned that putting metal inside the microwave will not necessarily induce sparking,” Chien said.
For Masi, this was the most surprising part of the experiment.
In some cases, the glass vials melted, exploded or imploded. And the copper occasionally vaporized.
“It was like having a lightning storm in your microwave,” Masi said.
By cutting the copper into the shape of a fork, they were able to induce sparks with the microwave radiation, “generating an extremely high temperature of more than 1,800 degrees Fahrenheit within a few seconds,” he said.
They experimented with various shapes. The tines of the fork shape allow for sparking and electrical imbalance to take place, Masi said. When they cut the metal into a spoon shape, no sparking occurred.
The sparks caused by the microwave generate the high temperatures necessary to transform the coal powder into polycrystalline graphite, with the copper foil and hydrogen gas also contributing to the process, he said.
While the experiment included microwave time ranging from 3 to 45 minutes, the optimal duration was found to be 15 minutes.
Chien said it took about a year to collect all the data the team needed. And so far, no microwaves have been harmed by the experiment. They’re still on that first Walmart microwave.
“We’re still using it right now. It’s not destroyed,” he said.
The next step is to experiment with other metals, which have different melting points, to see if they can generate a different end result. For example, tungsten has a melting point of nearly 6,200 degrees Fahrenheit, much higher than copper.
Chien said he believes it’s possible to get diamonds out of this process.
They also learned that the microwave method potentially can be used to recycle plastic, food waste and other sources of carbon. They’ve put plastic water bottles through the same process and were able to convert it into something close to graphite. Chien said more research needs to be done on this, however.
The researchers said the new method of coal conversion could be refined and performed at a larger scale to yield both a higher quality and quantity of nano-graphite materials.
“Finite graphite reserves and environmental concerns for the graphite extraction procedures make this method of converting coal to graphite a great alternative source of graphite production,” the scientists wrote.
Being able to mass produce graphite, especially without chemical solutions, “would be phenomenal,” Masi said. “It would release a huge bottleneck in the industry in an economically and environmentally friendly way.”