IIT Madras researchers have found a simpler method to produce graphene platelets from graphite. The researchers have found that when graphite is suspended in an appropriate fluid and subjected to intense shearing force of machining, the layers of graphite separate into graphene platelets.
The Research was led by Dr. Sathyan Subbiah, Associate Professor, Department of Mechanical Engineering, IIT Madras and his research student Mr. Wazeem Nishad. Their work was also published in the reputed peer-reviewed international journal Manufacturing Letters.
Graphene is a form - an allotrope, to use the technical term - of carbon, that shot into fame in 2010 through the Nobel Prize it earned for Sir Andre Geim and Sir Kostya Novoselov of the University of Manchester. The idea of graphene is, however, not new. The history of this two-dimensional honeycomb shaped carbon spans more than a century of worldwide research. Graphene is the building block of the more commonly known graphite; a one millimetre-thick sheet of graphite is made of 3 million layers of graphene.
"Superior quality Graphene is commonly prepared by the exfoliation method", says Dr. Subbiah, adding that the Nobel-winning work at Manchester involved peeling off layers of graphene from graphite using scotch tape. Since then, laboratories all over the world have been developing various forms of chemical and mechanical methods to produce graphene.
Dr. Subbiah looked at exfoliation from an unconventional angle. "Graphite is a lubricant because it is made of layers of carbon that slide over one another. The lubricating action itself would shear the layers off, and cause separation of the 2-D graphene sheets", Dr. Subbiah explains. With research scholar Mr. Wazeem, he set out to see if his conjecture was right.
The researchers suspended graphite in a lubricant liquid containing sodium cholate to prevent the graphite particles from clumping together and subjected the suspension to machining of mild steel using oscillations of a carbide tool. As Dr. Subbiah had expected, the oscillations trapped the graphite to produce graphene flakes as a by-product of the lubricant with thicknesses in the range of a few nanometers - a nanometre being one billionth of a metre; to put this in perspective, a single human hair is about 60,000 nanometres in diameter.
"Graphene is considered a super material of the century", says Dr. Subbiah.
Graphene is one of the strongest materials known; puncturing a pristine single layer of graphene with a pen would require the pen to be pushed by a large car in fifth gear. In addition, it conducts electricity thirteen times better than copper, forms an excellent barrier layer and has an extremely high surface area - 6 grams of graphene could cover an entire soccer field, a property that makes it extremely useful in applications like catalysis.
The IIT Madras team's experiments showed that increasing the time of machining induces defects and disorders in the layers.
"We are now focusing on controlling the stresses and machining parameters to produce defect-free few-layer graphene" says Dr. Subbiah on future directions of his research.
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