Carbyne may turn out to be the strongest of a new class of microscopic materials ever, if scientists can determine an effective way to produce it in bulk. Researchers at Rice University (Houston) have studied carbyne nanorods or nanoropes that could have a host of remarkable and useful properties, which are described by Rice University theoretical physicist Boris Yakobson and his group in a paper published in the American Chemical Society journal ACS Nano.
Carbyne, a chain of carbon atoms held together by either double or alternating single and triple atomic bonds, is a true one-dimensional material, unlike atom-thin sheets of graphene that have a top and a bottom or hollow nanotubes that have an inside and outside. In calculations by Yakobson and his group, carbyne’s tensile strength—the ability to withstand stretching—surpasses “that of any other known material” with twice the tensile stiffness of graphene and carbon nanotubes, and nearly three times that of diamond.
Stretching carbyne as little as 10% alters its electronic band gap significantly, the Rice researchers noted. If outfitted with molecular handles at the ends, it can also be twisted to alter its band gap. With a 90° end-to-end rotation, it becomes a magnetic semiconductor. Carbyne chains also can take on side molecules that may make the chains suitable for energy storage, according to the researchers, and it is stable at room temperature, largely resisting crosslinks with nearby chains.
That’s a remarkable set of qualities for a simple string of carbon atoms, said Yakobson, Rice’s Karl F. Hasselmann Professor of Mechanical Engineering and Materials Science, a professor of chemistry and a member of the Richard E. Smalley Institute for Nanoscale Science and Technology. “You could look at it as an ultimately thin graphene ribbon, reduced to just one atom, or an ultimately thin nanotube,” Yakobson said.
The material could be useful for nanomechanical systems, in spintronic devices, as sensors, as strong and light materials for mechanical applications or for energy storage. “Regardless of the applications,” Yakobson noted, “academically, it’s very exciting to know the strongest possible assembly of atoms.”
Based on the calculations, carbyne might be the highest energy state for stable carbon, he said. “People usually look for what is called the ‘ground state,’ the lowest possible energy configuration for atoms,” Yakobson said. “For carbon, that would be graphite, followed by diamond, then nanotubes, then fullerenes. But nobody asks about the highest energy configuration. We think this may be it, a stable structure at the highest energy possible.”
Scientific theories about carbyne first appeared in the 19th century, and an approximation of the material was first synthesized in the USSR in 1960. Carbyne has since been seen in compressed graphite, has been detected in interstellar dust and has been created in small quantities by researchers. “I have always been interested in the stability of ultimately thin wires of anything and how thin a rod you could make from a given chemical,” Yakobson said. “We had a paper 10 years ago about silicon in which we explored what happens to silicon nanowire as it gets thinner. To me, this was just a part of the same question.”
The Rice researchers, led by Rice graduate student Mingjie Liu and postdoctoral researcher Vasilii Artyukhov, set out to detail carbyne with computer models using first-principle rules to determine the energetic interactions of atoms, Artyukhov said. “Our intention was to put it all together, to construct a complete mechanical picture of carbyne as a material,” Artyukhov said. “The fact that it has been observed tells us it’s stable under tension, at least, because otherwise it would just fall apart.”
Yakobson said the researchers were surprised to find the band gap in carbyne was so sensitive to twisting. Another finding of great interest was the energy barrier that keeps atoms on adjacent carbyne chains from collapsing into each other. “When you’re talking about theoretical material, you always need to be careful to see if it will react with itself,” Artyukhov said. “This has never really been investigated for carbyne.”
Rice graduate student Fangbo Xu and former postdoctoral researcher Hoonkyung Lee, now a professor at Konkuk University in South Korea, are co-authors of the paper. The Air Force Office of Scientific Research and the Welch Foundation supported the research, and calculations were performed on the National Science Foundation-supported DaVinCI supercomputer, administered by Rice’s Ken Kennedy Institute for Information Technology. For more information, see www.rice.edu or read the abstract at http://tinyurl.com/Carbyne. ME
New Solvent Aimed at Creating Low-Cost Electronics
Researchers at the University of Southern California (USC; Los Angeles) have devised a new solvent that will dissolve semiconductors safely and cheaply, and allow them to be applied as a thin film for creating a new generation of low-cost electronics devices.
Technology exists to “print” electronics using semiconductor inks at room temperature, which is a cheaper process for making electronics than low-pressure vapor deposition. Until now, the problem has been that the only substance that dissolves semiconductors to form these inks was hydrazine, a highly toxic, explosive liquid used in rocket fuel.
New research by Richard Brutchey and David Webber of the USC Dornsife College of Letters, Arts and Sciences mixed two compounds to create a solvent that dissolves a class of semiconductors, known as chalcogenides, at room temperature. Brutchey and Webber call the solvent, which they’ve patented, an “alkahest” after a hypothetical universal solvent that alchemists attempted to create to dissolve any and all substances. They presented their findings in a paper presented to the Journal of the American Chemical Society.
The researchers showed how a mixture of 1,2-ethanedithiol and 1,2-ethylenediamine is able to dissolve a series of nine semiconductors made from combinations of arsenic, antimony, bismuth, sulfur, selenium and tellurium. Such semiconductors are often used in lasers, optics, and infrared detectors. The solution was then applied as a thin film to substrates like glass and silicon and heated, evaporating the solvent and leaving only a high-quality film of crystalline semiconductor for use in electronics. For more information, see www.usc.edu. ME
Solutions to Springback Challenges Span Decades
Springback is a long-time challenge of stamping technology that can be addressed successfully once properly understood. Several SME Technical Papers typify the attention given to this topic for over the years.
In Richard Agricola’s 1967 paper (TP67PUB170), five different alloys were used for research into forming shallow shapes such as gore segments of large domes. For this fabrication, stretching must be somehow enhanced to maximize plastic deformation and reduce springback. A technique for positive edge restraint was used to maximize tensile strains by pretensioning the blank before explosive deformation, and by completely restraining the edges, thus forcing the blank to stretch as well as bend.
Ninety-degree V-die bending of hot-rolled high-strength, low-alloy (HSLA) steel and AISI 1045 steel plate is researched in TP79PUB159, one of many forming papers by the late Klaus J. Weinmann, PhD, FSME. For both materials, the angular error in the final bend geometry due to elastic springback can be eliminated by coining in some cases, most easily for small punch radii in relation to die width and sufficiently high coining forces. Elimination of springback errors is generally more difficult for 1045 steel than for HSLA steel, presumably because of the different tensile strengths of the steels, although this was not investigated in this paper.
Eric Kam, product manager at AutoForm Engineering USA (Troy, MI) and co-chair of SME’s stamping and dies tech group, provides an overview in TP09PUB116 of how to clear the springback hurdle. There is no single “right” springback compensation, only some discrete steps to innovate solutions for materials with higher and higher strengths to fabricate thinner and stronger parts delivered under tighter tolerances. Using multiple, statistically relevant simulations to stabilize the springback response, determine countermeasure and compensation methodology and verify process capability, the needs of tomorrow’s products can likely be met. ME
Manufacturing practitioners are encouraged to send submissions for possible publication as SME Technical Papers. SME membership is not required. Learn more at www.sme.org/techpapers.
Eric Kam’s paper highlighted above, presented at FABTECH in 2009, received the 2010 Forming & Fabricating Community Technical Paper Excellence Award. Some previously honored papers cover: the effect of work hardening on bending of hydroformed parts (TP07PUB200), phased-array ultrasonic inspection of pipe welds (TP07PUB135), new classes of AHS and UHS steels (TP06PUB161) and aqueous cleaning of tubes (TP05PUB240).
The SME Rapid Technologies & Additive Manufacturing Community also honors outstanding papers with the Dick Aubin Distinguished Paper Award. SME’s North American Manufacturing Research Institution (NAMRI) recognizes research implementation, best papers and outstanding student presenters associated with its annual research conference. For more information, visit www.sme.org/awards. ME
TechFront is edited by Senior Editors Patrick Waurzyniak, firstname.lastname@example.org, and Ellen Kehoe.
This article was first published in the January 2014 edition of Manufacturing Engineering magazine. Click here for PDF.
Published Date : 1/1/2014