{"id":7810,"date":"2013-06-02T19:51:46","date_gmt":"2013-06-03T02:51:46","guid":{"rendered":"http:\/\/cafe.foundation\/blog\/?p=7810"},"modified":"2013-06-02T19:51:46","modified_gmt":"2013-06-03T02:51:46","slug":"making-graphene-and-carbon-fibers-even-lighter-and-stronger","status":"publish","type":"post","link":"http:\/\/cafe.foundation\/blog\/making-graphene-and-carbon-fibers-even-lighter-and-stronger\/","title":{"rendered":"Making Graphene and Carbon Fibers Even Lighter and Stronger"},"content":{"rendered":"

While scientists at Columbia University have used chemical vapor deposition (CVD) to create large sheets of stronger-than-average graphene, a research team at Massachusetts Institute of Technology (MIT) has found ways to weave stronger carbon nanotubes.<\/p>\n

James Hone and Jeffrey Kysar, professors of mechanical engineering at Columbia University, learned that the enormous strength of graphene is usually achieved in only small patches.\u00a0 The \u201cgrain boundaries\u201d for larger sheets were often far weaker than the theoretical strengths of which the material is capable.<\/p>\n

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Only one atom thick, graphene sheet could withstand an elephant tug-of-war. \u00a0\u00a0Illustration by Andrew Shea for Columbia Engineering<\/em><\/p><\/div>\n

That strength is phenomenal.\u00a0 Hone explains, “It would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap.”<\/p>\n

Results of their study were published in the journal Science<\/em><\/a>.<\/p>\n

The paper’s lead author, Gwan-Hyoung Lee, a postdoctoral fellow in the Hone lab, says, “Our findings clearly correct the mistaken consensus that grain boundaries of graphene are weak. This is great news because graphene offers such a plethora of opportunities both for fundamental scientific research and industrial applications.”\u00a0 The team found that they can grow television-sized sheets of graphene using CVD on copper substrates in a high-temperature furnace.<\/p>\n

Kysar notes that \u201c\u2026CVD graphene is ‘stitched’ together from many small crystalline grains — like a quilt — at grain boundaries that contain defects in the atomic structure.”\u00a0 The research team has found that they can achieve 90-percent of \u201cideal crystal\u201d strength at sizes practical for use in real-world applications.<\/p>\n

“This is an exciting result for the future of graphene, because it provides experimental evidence that the exceptional strength it possesses at the atomic scale can persist all the way up to samples inches or more in size,” says Hone. “This strength will be invaluable as scientists continue to develop new flexible electronics and ultrastrong composite materials.”<\/p>\n

The team concludes that, \u201cWith appropriate processing that avoids surface damage, grain boundaries in 2D materials, especially graphene, can be nearly as strong as the perfect, defect-free structure.”<\/p>\n

The study was supported by grants from the Air Force Office of Scientific Research and the National Science Foundation.<\/p>\n

Apropos of \u201cstitching\u201d and \u201cquilting\u201d, Dr. Brien Seeley, President of the CAFE Foundation, shared this item<\/a> from Jennifer Chu in the MIT news office.\u00a0 Her article, \u201cPlanes, trains and automobiles: faster, stronger, lighter,\u201d looks at a technique Brian Wardle, an associate professor of aeronautics and astronautics, and his doctoral and post-doctoral students conceived to strengthen carbon fiber, probably not a close second to graphene for overall strength.<\/p>\n

Airplanes such as the Boeing 787 and Airbus 380 use advanced carbon-fiber composites to reduce aircraft weights by 20 percent.\u00a0 Ever desiring even stronger, lighter materials, though, \u201cResearchers are looking to even stronger and lighter materials, such as composites made with carbon fibers coated with carbon nanotubes \u2014 tiny tubes of crystalline carbon. When arranged in certain configurations, nanotubes can be hundreds of times stronger than steel, but only one-sixth the weight, making such composites attractive for use in airplanes, as well as cars, trains, spacecraft and satellites.<\/p>\n

\u201cBut a significant hurdle to achieving such composites lies at the nanoscale: Scientists who have tried growing carbon nanotubes on carbon fibers have found that doing so significantly degrades the underlying fibers, stripping them of their inherent strength.\u201d<\/p>\n

Wardle and his team have found the root cause of this, and came up with ways to maintain the native fibers\u2019 strength.\u00a0 Coating carbon fibers with nanotubes not only made the fibers stronger, but also more electrically conductive.\u00a0 They can also fit into current manufacturing processes.<\/p>\n

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Postdoc Stephen Steiner (right) and graduate student Richard Li are part of the research team. \u00a0Photo by David Castri-Olmedo\/MIT<\/em><\/p><\/div>\n

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Wardle sounds a hopeful note.\u00a0 \u201cUp until now, people were basically improving one part of the material but degrading the underlying fiber, and it was a trade-off, you couldn\u2019t get everything you wanted.\u00a0 With this contribution, you can now get everything you want.\u201d<\/p>\n

A paper\u00a0detailing the results<\/a>\u00a0by Wardle and his colleagues is published in the journal ACS Applied Materials and Interfaces<\/em>. \u00a0Co-authors are postdoc Stephen Steiner, who contributed to the research as a graduate student, and Richard Li, a graduate student who was an undergraduate in Wardle\u2019s lab.<\/p>\n

Visiting carbon-fiber manufacturers in Japan, Germany and Tennessee, Wardle\u2019s team saw how fibers are stretched near breaking at high temperatures, in sharp opposition to the low-tension approach to growing nanotubes on carbon fibers.<\/p>\n

Li and Steiner made a small graphite apparatus, across which they strung individual carbon fibers, and hung tiny weights from each fiber to tauten it. \u00a0 According to their news item, \u201cThe group then grew carbon nanotubes on the fibers, first covering the fibers with a special set of coatings, and then heating the fibers in a furnace. They then used chemical vapor deposition to grow a fuzzy layer of nanotubes along each fiber.\u201d<\/p>\n

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Finding a happy medium – MIT’s just-right relationship between temperature and tension in making stronger carbon nanotubes<\/p><\/div>\n

After many attempts to find a proper catalyst to ease this growth of \u201chairy\u201d fibers, the group found that a layer of alumina ceramic helped \u201cdisguise\u201d the carbon fiber, enabling an iron catalyst to stick \u2013 but the layer of alumina flaked off instead.<\/p>\n

The team developed\u00a0 a polymer coating called K-PSMA to keep the alumina in place, and which worked like a hair conditioner in reverse.<\/p>\n

According to MIT, \u201cHair conditioners have two seemingly opposite chemical features: a water-absorbent component that allows the conditioner to stick to hair, and a waterproof component that keeps hair from getting frizzy. Likewise, K-PSMA has hydrophilic and hydrophobic components, but its waterproof feature sticks to the carbon fiber, while the water-absorbent component attracts the alumina and the metal catalyst.\u201d<\/p>\n

In their tests, the team found that they could reduce the need for tension and drop process temperatures by 300 degrees Celsius than typical and avoid damage to the underlying fiber.<\/p>\n

\u201cThis process reduces not only the amount of energy and volume of gas required, but the amount of extraneous substances you have to put on the fiber,\u201d Steiner says. \u201cIt\u2019s actually pretty simple and cost-effective.\u201d<\/p>\n

The researchers have filed a patent for the two strategies, and envision advanced fiber composites incorporating their techniques for a whole range of applications.<\/p>\n

Both these studies could lead to lighter, stronger structures – \u00a0and in the realm of electric aircraft those are highly desirable properties.\u00a0 That the materials have potential as either battery materials or even as structures that can act as batteries is part of a trend that we may see in future aircraft designs.<\/p>\n