The researchers, who published their findings in the journal Nano-Structures & Nano-Objects, used copper foil, glass containers, and a conventional household microwave oven to demonstrate that pulverized coal powder can be converted into high-value nano-graphite.
Cooking up some nano-graphite
As the use of coal for energy declines, converting it into the highly valuable nano-graphite could provide a new lease of life to many coal providers. Nano-graphite is a high-demand material used as a lubricant in items ranging from lithium-ion batteries to fire extinguishers.
"This method provides a new route to convert abundant carbon sources to high-value materials with ecological and economical benefits," wrote the research team, led by associate professor TeYu Chien, in UW’s Department of Physics and Astronomy.
Though previous research shows that microwaves can be used to remove sulfur and other minerals from coal and reduce moisture, chemical pre-treatment of the coal is usually required.
In their paper, the researchers from UW explain how they simply ground raw Powder River Basin coal into powder before placing it on copper foil and sealing it in glass containers with a gas mixture of argon and hydrogen.
Following this, the researchers placed the substance in a microwave oven — chosen for its convenience, the team explained.
Optimal microwave settings
The microwave provided the desired levels of radiation. By cutting the copper foil into a fork shape, sparks were induced by the microwave radiation that generated a temperature of over 1,800 degrees Fahrenheit (approx 982 degrees celsius) within a few seconds.
The high temperature and the interaction with the copper foil and hydrogen provided the necessary conditions to transform the coal powder into polycrystalline graphite. The ideal time duration for the transformation period was found to be 15 minutes.
Next, the scientists aim to hone the method to yield higher quality and quantity of nano-graphite materials. They also hope to scale their method of coal conversion for mass production.