In a new study, scientists at the University Of Wyoming have generated an environment in a microwave oven to convert raw coal powder into nano-graphite successfully. They have done this by using copper foil, glass containers, and a conventional household microwave oven.
The study offers a whole new approach that could represent a simple and relatively inexpensive coal-conversion technology. The method also provides a new route to convert abundant carbon sources to high-value materials with ecological and economic benefits.
The resultant nano-graphite can be used as a lubricant and in items ranging from fire extinguishers to lithium-ion batteries.
Past studies had shown that microwaves could be used to reduce the moisture content of coal and remove sulfur and other minerals. But, such methods need specific chemical pretreatment of the coal.
In this new study, scientists just ground raw Powder River Basin coal into powder. They then placed the powder on copper foil and sealed it in glass containers with a gas mixture of argon and hydrogen before being placed in a microwave oven.
Chris Masi, a lead author of the paper, said, “By cutting the copper foil into a fork shape, the sparks were induced by the microwave radiation, generating an extremely high temperature of more than 1,800 degrees Fahrenheit within a few seconds. This is why you shouldn’t place a metal fork inside a microwave oven.”
“The sparks caused by the microwaves generated the high temperatures necessary to transform the coal powder into polycrystalline graphite, with the copper foil and hydrogen gas also contributing to the process.”
While the experiment included microwave durations ranging from 3 to 45 minutes, the optimal duration was 15 minutes.
Scientists noted, “This 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.”
- Christoffer A. Masi et al. Converting raw coal powder into polycrystalline nano-graphite by metal-assisted microwave treatment. DOI: 10.1016/j.nanoso.2020.100660