This false-color scanning electron microscope image shows the fractured surface of a sequentially bonded graphene sheet.
An international research team led by scientists from Beihang University in China and The University of Texas at Dallas has developed high-strength, ultra-tough carbon sheets that can be fabricated cheaply at low temperatures.
The team chemically stitched together small pieces of graphitic carbon, similar to the graphite in the soft core of an ordinary pencil. The manufacturing process produces materials with mechanical properties that exceed those of carbon fiber composites currently used in various commercial products.
"These sheets could eventually replace expensive carbon fiber composites in everything from aircraft and car bodies to windmill blades and sports equipment," said Dr.
Today's carbon fiber composites are expensive, in part because carbon fibers are produced at extremely high temperatures, which can exceed 2,500 degrees Celsius (about 4,500 degrees Fahrenheit).
"In contrast, our process can use cheap graphite, dug out of the ground and processed at temperatures below 45 degrees Celsius (113 degrees Fahrenheit)," said a professor of chemistry at Beihang University. "The strength of these sheets in all in-plane directions is comparable to that of laminated carbon fiber composites, and they can absorb higher mechanical energy before the carbon fiber composite fails."
Graphite consists of small flakes made up of stacked graphene layers. Graphene is just a layer of carbon atoms arranged in a way that looks like barbed wire, with each hexagon in the grid made up of six carbon atoms.
"While scientists can continuously fabricate large sheets of graphene through high-temperature processing and demonstrate the extraordinary strength of these sheets, it is impractical to create thick graphite sheets simply by stacking large-area graphene sheets," said Dr. "A human would need to stack about 150,000 graphene sheets to make a sheet of graphite about the thickness of a human hair."
The researchers found inspiration in natural mother-of-pearl, also known as mother-of-pearl, which gives shells strength and toughness. Nacre consists of parallel sheets held together by thin layers of organic material, similar to how mortar holds bricks to a wall.
"Instead of mechanically stacking large-area graphene sheets, we oxidized micron-scale graphite sheets so that they could be dispersed in water, and then filtered this dispersion to manufacture aligned graphene oxide sheets at low cost," the researchers said. Similar to making paper by hand by filtering fiber pulp.
"At this stage, the sheets are neither strong nor tough, which means they can't absorb much energy before they rupture," he said. "The trick we use is to stitch together the platelets in these sheets using sequential permeation bridging agents that connect overlapping adjacent platelets to each other and convert the oxidized graphene oxide to graphene. The key is our Bridging agents by forming covalent chemical bonds and van der Waals bonds".
According to a doctoral student of Beihang University, the strength of bed sheets with bridging agent is 4.5 times and 7.9 times that without bridging agent. "Unlike carbon fiber composites, no polymer matrix is required," he said.
"While expensive carbon fiber composite sheets can provide similar strength in all sheet plane directions, they are able to absorb about one-third as much energy as our sequentially bridged graphene sheets before fracturing," said the professor . Our sheets are manufactured at low temperatures and are therefore inexpensive, and in addition to their high sheet strength, toughness, and fatigue resistance, they are also highly conductive and capable of shielding electromagnetic radiation, properties that make these sequentially bridged graphene Sheets are very attractive for possible future applications. "