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High-Entropy Alloy: A Metallic Alloy That is Tough and Ductile at Cryogenic Temperatures

High-Entropy Alloy: A Metallic Alloy That is Tough and Ductile at Cryogenic Temperatures | Amazing Science | Scoop.it

A new concept in metallic alloy design – called “high‐entropy alloys” – has yielded a multiple-element material that not only tests out as one of the toughest on record, but, unlike most materials, the toughness as well as the strength and ductility of this alloy actually improves at cryogenic temperatures. This multi-element alloy was synthesized and tested through a collaboration of researchers at the U.S. Department of Energy (DOE)’s Lawrence Berkeley and Oak Ridge National Laboratories (Berkeley Lab and ORNL).


“We examined CrMnFeCoNi, a high‐entropy alloy that contains five major elements rather than one dominant one,” says Robert Ritchie, a materials scientist with Berkeley Lab’s Materials Sciences Division. “Our tests showed that despite containing multiple elements with different crystal structures, this alloy crystalizes as a single phase, face‐centered cubic solid with exceptional damage tolerance, tensile strength above one gigapascal, and fracture toughness values that are off the charts, exceeding that of virtually all other metallic alloys.”


“High‐entropy alloys represent a radical departure from tradition,” Ritchie says, “in that they do not derive their properties from a single dominant constituent or from a second phase. The idea behind this concept is that configurational entropy increases with the number of alloying elements, counteracting the propensity for compound formation and stabilizing these alloys into a single phase like a pure metal.” 

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Researchers Grow Single-Walled Carbon Nanotubes with Identical Electronic Properties

Researchers Grow Single-Walled Carbon Nanotubes with Identical Electronic Properties | Amazing Science | Scoop.it

Using custom-made organic precursor molecules, researchers have succeeded for the first time in growing single-walled carbon nanotubes with identical electronic properties.


In future, it will be possible to specifically equip carbon nanotubes with properties which they need for electronic applications, for example. Researchers at Empa in Dübendorf/Switzerland and the Max Planck Institute for Solid State Research in Stuttgart have succeeded for the first time in growing single-walled carbon nanotubes (CNTs) with only a single, prespecified structure. The nanotubes thereby have identical electronic properties. The decisive trick here: The team has taken up an idea which originated from the Stuttgart-based Max Planck researchers and produced the CNT from custom-made organic precursor molecules. The researchers started with these precursor molecules and have built up the nanotubes on a platinum surface, as they report in the latest issue of the scientific journal Nature. Such CNTs could be used in future, for instance, in ultra-sensitive light detectors and very tiny transistors.


For 20 years, material scientists working on the development of carbon nanotubes for a range of applications have been battling a problem – now an elegant solution is at hand. With their unusual mechanical, thermal and electronic properties, the tiny tubes with their honeycomb lattice of graphitic carbon have become the embodiment of nanomaterials. They could be used to manufacture the next generation of electronic and electro-optical components so that they are even smaller and with even faster switching times than before. But to achieve this, the material scientists must specifically equip the nanotubes with desired properties, and these depend on their structure. The production methods used to date, however, always result in a mixture of different CNTs. The team from Empa and the Max Planck Institute for Solid State Research has now remedied the situation with a new production path for single-walled nanotubes.


The researchers have thus proved that they can unambiguously specify the growth and thus the structure of long SWCNTs using custom-made molecular seeds. The SWCNTs synthesized in this study can exist in two forms, which correspond to an object and its mirror image. By choosing the precursor molecule appropriately, the researchers were able to influence which of the two variants forms. Depending on how the honeycomb atomic lattice is derived from the original molecule – straight or oblique with respect to the CNT axis – it is also possible for helically wound tubes, i.e. with right- or left-handed rotation, and with non-mirror symmetry to form. And it is precisely this structure that then determines which electronic, thermo-electric and optical properties of the material. In principle, the researchers can therefore specifically produce materials with different properties through their choice of precursor molecule.


In further steps, Roman Fasel and his colleagues want to gain an even better understanding of how SWCNTs establish themselves on a surface. Even if well in excess of 100 million nanotubes per square centimeter already grow on the platinum surface, only a relatively small fraction of the seeds actually develop into «mature» nanotubes. The question remains as to which processes are responsible for this, and how the yield can be increased.


Publication: Juan Ramon Sanchez-Valencia, et al., “Controlled Synthesis of Single-Chirality Carbon Nanotubes,” Nature 512, 61–64 (07 August 2014) doi:10.1038/nature13607

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Designed Metasurface Is A Thin, Near Perfect Acoustic Absorber

Designed Metasurface Is A Thin, Near Perfect Acoustic Absorber | Amazing Science | Scoop.it

Physicists from the Hong Kong University of Science and Technology have created a thin metasurface material which functions as a near perfect sound absorber tunable to a desired frequency.  Under some conditions more than one frequency is perfectly absorbed.  Unlike conventional sound absorbing material that is sometimes only effective when meters thick, the metasurface is deeply “subwavelength” and therefore much thinner.


Current sound absorption materials must be of a thickness comparable to the wavelength of the sounds, which for human hearing ranges from 17 meters to 17 millimeters for low to high frequencies respectively.   Low frequency sounds are therefore difficult to damp without many meters of absorbent material.


The new metamaterial relies upon a “decorated membrane resonator” (DMR) which resembles a tiny drum membrane embedded in and coupled to a solid support, in the center of which is a platelet.  The dimensions explored by the research team was a membrane 9 cm across, with thickness less than 0.2 mm, holding a platelet in the center 2 cm in diameter.


Crucially, the membrane’s elastic modulus must be very low for the harmonics of the metasurface to correspond to the wavelengths of airborne sounds.  A reflecting backing then sandwiches a sealed gas layer.


The metasurface exhibits resonance at audible wavelengths such that there is near total absorption of sound, and dissipation of the energy along the lossy membrane.


The entire system exhibits “impedance matching” to sound waves in air.  The two consequences of which are that the surface is an excellent absorber of energy and does not reflect waves when absorbing sound of a particular wavelength. Both the sandwiched gas as well as the reflective backing surface are essential for giving rise to the high impedance. The authors show that the resonant frequency (the frequency of sound that is best absorbed) is adjustable by varying the thickness of the gas layer.

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New invisible ink: Stretchy plastics hide secret pictures

New invisible ink: Stretchy plastics hide secret pictures | Amazing Science | Scoop.it

A new invisible ink that reveals secret messages when squeezed could be useful in preventing fraud.


It could be the ultimate stress ball for spies. An invisible ink creates secret messages on bendy plastic that are only revealed when you give it a squeeze.


Previously, Jianping Ge of the East China Normal University in Shanghai, China, and his colleagues created invisible inks that appear when submerged underwater or exposed to a magnetic field. Now they've made an ink you can reveal just by squeezing with your hand. The team first embedded an array of silica crystals in a plastic gel. The crystals reflect light at a certain wavelength depending on their spacing and the angle of viewing, so the relaxed gel appears green, but squeezing or stretching it turns it red or blue.


Next, the team coated the surface with another clear plastic gel, and put a cut-out template of a secret image on top. They shone ultraviolet light on the set-up, which linked the two gels around the cut-out, but left them separate in the parts covered by the template. The linked gels are firmer, so they don't change colours when squeezed. After the cut-out was removed, its silhouette only appeared when the gels were squeezed.


Ge says he is talking to companies about using the technique to protect against counterfeit goods. "These invisible photonic patterns can be potential anti-fake labels," he says. Jon Kellar, a materials engineer at the South Dakota School of Mines and Technology in Rapid City, South Dakota, agrees that the hidden images could help combat fraud, but he thinks that the fabrication process will need to be simplified for commercial use.

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Terminator2: Phase-changing material could allow even low-cost robots to switch between hard and soft states

Terminator2: Phase-changing material could allow even low-cost robots to switch between hard and soft states | Amazing Science | Scoop.it

In the movie “Terminator 2,” the shape-shifting T-1000 robot morphs into a liquid state to squeeze through tight spaces or to repair itself when harmed.


Now a phase-changing material built from wax and foam, and capable of switching between hard and soft states, could allow even low-cost robots to perform the same feat.


The material — developed by Anette Hosoi, a professor of mechanical engineering and applied mathematics at MIT, and her former graduate student Nadia Cheng, alongside researchers at the Max Planck Institute for Dynamics and Self-Organization and Stony Brook University — could be used to build deformable surgical robots. The robots could move through the body to reach a particular point without damaging any of the organs or vessels along the way.


Robots built from the material, which is described in a new paper in the journal Macromolecular Materials and Engineering, could also be used in search-and-rescue operations to squeeze through rubble looking for survivors, Hosoi says.

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Super efficient LEDs could be made from ‘wonder material’ perovskite

Super efficient LEDs could be made from ‘wonder material’ perovskite | Amazing Science | Scoop.it

A hybrid form of perovskite - the same type of material which has recently been found to make highly efficient solar cells that could one day replace silicon - has been used to make low-cost, easily manufactured LEDs, potentially opening up a wide range of commercial applications in future, such as flexible color displays.


This particular class of semiconducting perovskites have generated excitement in the solar cell field over the past several years, after Professor Henry Snaith’s group at Oxford University found them to be remarkably efficient at converting light to electricity. In just two short years, perovskite-based solar cells have reached efficiencies of nearly 20%, a level which took conventional silicon-based solar cells 20 years.

Now, researchers from the University of Cambridge, University of Oxford and the Ludwig-Maximilians-Universität in Munich have demonstrated a new application for perovskite materials, using them to make high-brightness LEDs. The results are published in the journal Nature Nanotechnology.


Perovskite is a general term used to describe a group of materials that have a distinctive crystal structure of cuboid and diamond shapes. They have long been of interest for their superconducting and ferroelectric properties. But in the past several years, their efficiency at converting light into electrical energy has opened up a wide range of potential applications.


The perovskites that were used to make the LEDs are known as organometal halide perovskites, and contain a mixture of lead, carbon-based ions and halogen ions known as halides. These materials dissolve well in common solvents, and assemble to form perovskite crystals when dried, making them cheap and simple to make.


“These organometal halide perovskites are remarkable semiconductors,” said Zhi-Kuang Tan, a PhD student at the University of Cambridge’s Cavendish Laboratory and the paper’s lead author. “We have designed the diode structure to confine electrical charges into a very thin layer of the perovskite, which sets up conditions for the electron-hole capture process to produce light emission.”


The perovskite LEDs are made using a simple and scalable process in which a perovskite solution is prepared and spin-coated onto the substrate. This process does not require high temperature heating steps or a high vacuum, and is therefore cheap to manufacture in a large scale. In contrast, conventional methods for manufacturing LEDs make the cost prohibitive for many large-area display applications.


“The big surprise to the semiconductor community is to find that such simple process methods still produce very clean semiconductor properties, without the need for the complex purification procedures required for traditional semiconductors such as silicon,” said Professor Sir Richard Friend of the Cavendish Laboratory, who has led this programme in Cambridge.


“It’s remarkable that this material can be easily tuned to emit light in a variety of colours, which makes it extremely useful for colour displays, lighting and optical communication applications,” said Tan. “This technology could provide a lot of value to the ever growing flat-panel display industry.”


The team is now looking to increase the efficiency of the LEDs and to use them for diode lasers, which are used in a range of scientific, medical and industrial applications, such as materials processing and medical equipment. The first commercially-available LED based on perovskite could be available within five years.

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A new way to make microstructured surfaces

A new way to make microstructured surfaces | Amazing Science | Scoop.it

A team of researchers has created a new way of manufacturing microstructured surfaces that have novel three-dimensional textures. These surfaces, made by self-assembly of carbon nanotubes, could exhibit a variety of useful properties — including controllable mechanical stiffness and strength, or the ability to repel water in a certain direction.


“We have demonstrated that mechanical forces can be used to direct nanostructures to form complex three-dimensional microstructures, and that we can independently control … the mechanical properties of the microstructures,” says A. John Hart, the Mitsui Career Development Associate Professor of Mechanical Engineering at MIT and senior author of a paper describing the new technique in the journal Nature Communications.


The technique works by inducing carbon nanotubes to bend as they grow. The mechanism is analogous to the bending of a bimetallic strip, used as the control in old thermostats, as it warms: One material expands faster than another bonded to it.  But in this new process, the material bends as it is produced by a chemical reaction. 


The process begins by printing two patterns onto a substrate: One is a catalyst of carbon nanotubes; the second material modifies the growth rate of the nanotubes. By offsetting the two patterns, the researchers showed that the nanotubes bend into predictable shapes as they extend.


“We can specify these simple two-dimensional instructions, and cause the nanotubes to form complex shapes in three dimensions,” says Hart. Where nanotubes growing at different rates are adjacent, “they push and pull on each other,” producing more complex forms, Hart explains. “It’s a new principle of using mechanics to control the growth of a nanostructured material,” he says.


Few high-throughput manufacturing processes can achieve such flexibility in creating three-dimensional structures, Hart says. This technique, he adds, is attractive because it can be used to create large expanses of the structures simultaneously; the shape of each structure can be specified by designing the starting pattern. Hart says the technique could also enable control of other properties, such as electrical and thermal conductivity and chemical reactivity, by attaching various coatings to the carbon nanotubes after they grow.


“If you coat the structures after the growth process, you can exquisitely modify their properties,” says Hart. For example, coating the nanotubes with ceramic, using a method called atomic layer deposition, allows the mechanical properties of the structures to be controlled. “When a thick coating is deposited, we have a surface with exceptional stiffness, strength, and toughness relative to [its] density,” Hart explains. “When a thin coating is deposited, the structures are very flexible and resilient.”


This approach may also enable “high-fidelity replication of the intricate structures found on the skins of certain plants and animals,” Hart says, and could make it possible to mass-produce surfaces with specialized characteristics, such as the water-repellent and adhesive ability of some insects. “We’re interested in controlling these fundamental properties using scalable manufacturing techniques,” Hart says.  

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Technique simplifies the creation of high-tech crystals

Technique simplifies the creation of high-tech crystals | Amazing Science | Scoop.it

Highly purified crystals that split light with uncanny precision are key parts of high-powered lenses, specialized optics and, potentially, computers that manipulate light instead of electricity. But producing these crystals by current techniques, such as etching them with a precise beam of electrons, is often extremely difficult and expensive.


Now, researchers at Princeton and Columbia universities have proposed a new method that could allow scientists to customize and grow these specialized materials, known asphotonic crystals, with relative ease.


"Our results point to a previously unexplored path for making defect-free crystals using inexpensive ingredients," said Athanassios Panagiotopoulos, the Susan Dod Brown Professor of Chemical and Biological Engineering and one of the paper's authors. "Current methods for making such systems rely on using difficult-to-synthesize particles with narrowly tailored directional interactions."


Via Alin Velea
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A noble gas cage: New material traps gases from nuclear fuel better

A noble gas cage: New material traps gases from nuclear fuel better | Amazing Science | Scoop.it

When nuclear fuel gets recycled, the process releases radioactive krypton and xenon gases. Naturally occurring uranium in rock contaminates basements with the related gas radon. A new porous material called CC3 effectively traps these gases, and research appearing July 20 in Nature Materials shows how: by breathing enough to let the gases in but not out.

The CC3 material could be helpful in removing unwanted or hazardous radioactive elements from nuclear fuel or air in buildings and also in recycling useful elements from the nuclear fuel cycle. CC3 is much more selective in trapping these gases compared to other experimental materials. Also, CC3 will likely use less energy to recover elements than conventional treatments, according to the authors.


The team made up of scientists at the University of Liverpool in the U.K., the Department of Energy's Pacific Northwest National Laboratory, Newcastle University in the U.K., and Aix-Marseille Universite in France performed simulations and laboratory experiments to determine how—and how well—CC3 might separate these gases from exhaust or waste.

"Xenon, krypton and radon are noble gases, which are chemically inert. That makes it difficult to find materials that can trap them," said coauthor Praveen Thallapally of PNNL. "So we were happily surprised at how easily CC3 removed them from the gas stream."


Noble gases are rare in the atmosphere but some such as radon come in radioactive forms and can contribute to cancer. Others such as xenon are useful industrial gases in commercial lighting, medical imaging and anesthesia.


The conventional way to remove xenon from the air or recover it from nuclear fuel involves cooling the air far below where water freezes. Such cryogenic separations are energy intensive and expensive. Researchers have been exploring materials called metal-organic frameworks, also known as MOFs, that could potentially trap xenon and krypton without having to use cryogenics. Although a leading MOF could remove xenon at very low concentrations and at ambient temperatures admirably, researchers wanted to find a material that performed better.

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Morphing material could allow robots to switch between hard and soft states

Morphing material could allow robots to switch between hard and soft states | Amazing Science | Scoop.it

A new Terminator T-1000 robot-style material made of wax and foam — and capable of switching between hard and soft states — could be used to build morphing surgical robots that move through the body to reach a desired location without damaging organs or vessels along the way.


Robots built from the material, described in a new paper in the journal Macromolecular Materials and Engineering, could also be used in search-and-rescue operations to squeeze through rubble looking for survivors, says Anette Hosoi, an MIT professor of mechanical engineering and applied mathematics who led the research team.


MIT is working on the project with robotics company Boston Dynamics, who began developing the material as part of DARPA’s Chemical Robots program, the Max Planck Institute for Dynamics and Self-Organization, and Stony Brook University.


Controlling a very soft structure is difficult, compared to a rigid robot. It’s much harder to predict how the material will move and what shapes it will form. So the researchers decided to develop a material that can switch between a soft and hard state by coating a foam structure in wax. Foam can be squeezed into a small fraction of its normal size, but once released will bounce back to its original shape.


The wax coating, meanwhile, can change from a hard outer shell to a soft, pliable surface with moderate heating. This could be done by running a wire along each of the coated foam struts and then applying a current to heat up and melt the surrounding wax. Turning off the current again would allow the material to cool down and return to its rigid state.

In addition to switching the material to its soft state, heating the wax in this way would also repair any damage sustained, Hosoi says. “This material is self-healing,” she says. “So if you push it too far and fracture the coating, you can heat it and then cool it, and the structure returns to its original configuration.”


To build the material, the researchers simply placed the polyurethane foam in a bath of melted wax. They also found that a 3D-printed lattice worked better than the polyurethane foam, which would still be fine for low-cost applications, Hosoi says. The wax coating could also be replaced by a stronger material, such as solder, she adds.


Hosoi is now investigating the use of other unconventional materials for robotics, such as magnetorheological and electrorheological fluids. These materials consist of a liquid with particles suspended inside, and can be made to switch from a soft to a rigid state with the application of a magnetic or electric field.


Reference:

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A graphene replacement made from plastic

A graphene replacement made from plastic | Amazing Science | Scoop.it

Spin-coating a polymer solution (green) to create a carbon nanosheet with characteristics similar to graphene, without the defects (black).


A team of Korean researchers has synthesized hexagonal carbon nanosheets similar to graphene, using a polymer. The new material is free of the defects and complexity involved in producing graphene, and can substitute for graphene as transparent electrodes for organic solar cells and in semiconductor chips, the researchers say. 


The research team is led by Han-Ik Joh at Korea Institute of Science and Technology  (KIST), Seok-In Na at Chonbuk National University, and Byoung Gak Kim at Korea Research Institute of Chemical Technology. The research was funded by the KIST Proprietary Research Project and National Research Foundation of Korea.


Na explains: "Through a catalyst- and transfer-free process, we fabricated indium tin oxide (ITO)-free organic solar cells (OSCs) using a carbon nanosheet (CNS) with properties similar to graphene. The morphological and electrical properties of the CNS is derived from a polymer of intrinsic microporosity-1 (PIM-1), which is mainly composed of several aromatic hydrocarbons and cycloalkanes, can be easily controlled by adjusting the polymer concentration. The CNSs, which are prepared by simple spin-coating and heat-treatment on a quartz substrate, are directly used as the electrodes of ITO-free OSCs, showing a high efficiency of approximately 1.922% under 100 mW cm−2 illumination and air mass 1.5 G conditions. This catalyst- and transfer-free approach is highly desirable for electrodes in organic electronics."

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Metamaterial gives visible light a nearly infinite wavelength

Metamaterial gives visible light a nearly infinite wavelength | Amazing Science | Scoop.it

The new metamaterial is made by stacking silver and silicon nitride nanolayers. It may find applications in novel optical components or circuits and the design of more efficient leds. The work will appear on October 13th in Nature Photonics.


The phase velocity and group velocity of light dictate how light propagates in a material. The phase velocity determines how the peaks and valleys of the wave move in the material, whereas the group velocity describes the transport of energy. According to Einstein’s laws, the transport of energy of light can never be faster than the speed of light. Therefore the group velocity is limited. There are however no physical limitations to the phase velocity. When the phase velocity becomes zero, there is no movement of the peaks and valleys of the wave; when it is infinite the wavelength diverges to very large values. In nature however, no materials with such special properties exist.

Metamaterials
The research team now presents a metamaterial composed of a unit cell structure much smaller than the wavelength of light. By stacking nanoscale layers of silver and silicon nitride a new material is fabricated in which light ‘feels’ the optical properties of both layers. 

The way light travels through matter is dependent on the material permittivity: the resistance of a material against the electric fields of light waves. Because the permittivity of silver is negative and that of silicon nitride is positive, the combined material has a permittivity which is effectively equal to zero. Therefore, it seems that the light experiences zero resistance, and propagates with an infinite phase velocity. The wavelength of the light is nearly infinite.

The researchers fabricated this material using focused ion beam milling, a technique that allows control over the structure of a material on the nanoscale. With a specially built interferometer it was shown that light indeed propagates through the metamaterial with no significant change of phase, corresponding to an almost infinite wavelength. This new material may find applications in novel optical components or circuits and the design of more efficient leds.

Contact
Prof.dr. Albert Polman, +31 (0)20 754 74 00
www.erbium.nl | www.amolf.nl/research/photonic-materials

Reference
Ruben Maas, James Parsons, Nader Engheta and Albert Polman
Experimental realization of an epsilon-near-zero metamaterial at visible wavelengths
Nature Photonics 7, (2013) | DOI: 10.1038/nphoton.2013.256

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A super-stretchable yarn made of graphene

A super-stretchable yarn made of graphene | Amazing Science | Scoop.it

A simple, scalable method of making strong, stretchable graphene oxide fibers that are easily scrolled into yarns and have strengths approaching that of Kevlar is possible, according to Penn State and Shinshu University, Japan, researchers.


“We found this graphene oxide fiber was very strong, much better than other carbon fibers,” said Mauricio Terrones, professor of physics, chemistry and materials science and engineering, Penn State. “We believe that pockets of air inside the fiber keep it from being brittle.”


This method opens up multiple possibilities for useful products, according to Terrones and colleagues. For instance, removing oxygen from the graphene oxide fiber results in a fiber with high electrical conductivity.


Adding silver nanorods to the graphene film would increase the conductivity to the same as copper, which could make it a much lighter weight replacement for copper transmission lines. The researchers believe that the material lends itself to many kinds of highly sensitive sensors.


The researchers made a thin film of graphene oxide by chemically exfoliating graphite into graphene flakes, which were then mixed with water and concentrated by centrifugation into a thick slurry. The slurry was then spread by bar coating — something like a squeegee — across a large plate. When the slurry dries, it becomes a large-area transparent film that can be carefully lifted off without tearing. The film is then cut into narrow strips and wound on itself with an automatic fiber scroller, resulting in a fiber that can be knotted and stretched without fracturing. The researchers reported their results in a recent issue of ACSNano.


“The importance is that we can do almost any material, and that could open up many avenues — it’s a lightweight material with multifunctional properties,” said Terrones. And the main ingredient, graphite, is mined and sold by the ton.”

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Fabric circuit boards that can take bending, washing, stretching and bullets fired at them

Fabric circuit boards that can take bending, washing, stretching and bullets fired at them | Amazing Science | Scoop.it

A pair of researchers at The Hong Kong Polytechnic University, has developed a computerized knitting technology that allows for creating fabric circuit boards (FCBs) that can take a beating and keep on working. In their paper published in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, the two describe how the new technology works and just how strong the resulting products can be.

Making circuit boards that can take more punishment than those currently available would allow for whole new types of products—phones that don't break, wearable devices that are actually part of clothes, tougher police and military gear, etc. To make it happen, scientists have been looking to use new materials and processes for making them. In this latest effort, the two researchers in Hong Kong combined electrically conductive fibrous metal materials with normal fabric materials using new computerized knitting technology. The result is a three-dimensional material that can withstand stretching, being washed in a washing machine and dried in a dryer, being shot by a bullet (when under a bulletproof vest) and twisting—over and over. The team reports that not only can their FCBs take the punishment, they can withstand it over many cycles over long periods of time.


FCBs perform the task of directing electricity from one part of the garment to another, thus they offer mechanical support even as they electrically connect discrete electronic components. They can also be designed as single, double or even multiple layered structures, mimicking their traditional counterparts. To be used as a wearable device, they also have to low resistance, as compared to human skin, to allow for a reasonable degree of comfort and be washable to allow for removing both stains and odors.


The researchers claim their FCBs are ready for use—they're comfortable, durable and will last a long time. They could be used to create an entire shirt, for example, or a vest. Either could be used as a solar collector or as a multiple sensory device, recording heat, perspiration, heart rate, etc. In addition, their new knitting technology allows for stitching, weaving, knitting and embroidery.

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System that prompts objects to ‘float’ in suspension could prove boon to manufacturing with fragile materials

System that prompts objects to ‘float’ in suspension could prove boon to manufacturing with fragile materials | Amazing Science | Scoop.it
Harvard scientists have developed a system for using magnetic levitation technology to manipulate nonmagnetic materials, potentially enabling manufacturing with materials that are too fragile for traditional methods.


While assembly lines have been the gold standard in manufacturing for more than a century, and have put together everything from Model T’s to tablet computers, one aspect of their operation has remained constant: the need for a hand, robotic or human, to manipulate objects.


If Anand Bala Subramaniam, a postdoctoral fellow in chemistry and chemical biology, has his way, however, that could soon change.


Working in the lab of Woodford L. and Ann A. Flowers University Professor George Whitesides, Subramaniam and colleagues, including Dian Yang, Hai-Dong Yu, Alex Nemiroski, Simon Tricard, Audrey K. Ellerbee, and Siowling Soh, have developed a system for using magnetic levitation, or maglev, technology to manipulate nonmagnetic materials, potentially enabling the use of materials that are too fragile for traditional manufacturing methods. The system is described in an Aug. 25 paper published in the Proceedings of the National Academy of Sciences.


“What we’ve demonstrated in this paper is a noncontact method for manipulating objects,” Subramaniam said. “A conventional method for manufacturing is to start with simple components that are easy to manufacture, which are then assembled into more complex objects. Typically, robotic arms grasp the components and twist or turn them during the assembly process. That works very well for hard objects. But soft and sticky materials, which are of interest for building bio-mimetic objects, could easily be damaged.”

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Flexible solar cells woven into fabric could power wearable electronics

Flexible solar cells woven into fabric could power wearable electronics | Amazing Science | Scoop.it

Wearable electronics are quickly becoming the fashion. And there could soon be a way to power those electronics indefinitely, now that scientists in China have developed a solar cell ‘textile’ that could be woven into clothes. The textile retains a power-generation efficiency close to 1% even after been bent more than 200 times, and can be illuminated from both sides.


Scientists have been looking into flexible solar cells for decades, partly for coating irregularly shaped objects but also for integrating into wearable fabrics. One popular line of investigation has been dye-sensitized solar cells, in which a pigment absorbs sunlight to generate electrons and their positive counterparts, holes, before passing on those charges to inexpensive semiconductors. These solar cells are cheap and flexible, but the liquid nature of their pigments means that they must be well sealed. Bend a dye-sensitized solar cell more than a few times and the seals are likely to break, destroying its light-harvesting properties.


That is why Huisheng Peng at Fudan University in Shanghai and colleagues have been exploring another option: polymer solar cells. Although their maximum efficiencies fall below 10% – about half that of crystalline silicon, the most prevalent solar cell – polymer solar cells are lightweight, flexible and easy to manufacture. Peng and colleagues’ solar cell textile consists of microscopic interwoven metal wires coated with an active polymer (to absorb the sunlight), titanium dioxide nanotubes (to conduct the electrons) and another active polymer (to conduct the holes). The researches coated each side of the textile with transparent, conductive sheets of carbon nanotubes, which complete the circuit.


Because of the textile’s symmetry, the cell can be illuminated on either side. In tests it exhibited a maximum efficiency of 1.08%, which varied by less than 0.03% after 200 cycles of bending. However, the textile is currently only about the size of a fingernail. ‘The main difficulties encountered are how to scale up the solar-cell textile while maintaining high energy-conversion efficiencies,’ says Peng.


Materials scientist Anyuan Cao, who was not involved with the work, believes the results are interesting, particularly the use of carbon nanotube sheets to allow illumination from both sides. But he warns that wearable solar cells are still some way off. ‘Current textiles demonstrated in laboratories are too small and have low energy conversion efficiencies,’ says Cao, who is based at Peking University in China.


‘The materials involved and the fabrication processes are still expensive. Practical use not only requires that the textiles should withstand simple bending, but also that they should sustain much more complex deformations such as folding and twisting, even under dynamic conditions.’


Z Zhang et alAngew. Chem., Int. Ed., 2014, DOI: 10.1002/anie.201407688

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‘Shape-memory polymer’ material could help reconstruct faces

‘Shape-memory polymer’ material could help reconstruct faces | Amazing Science | Scoop.it

Injuries, birth defects (such as cleft palates) or surgery to remove a tumor can create gaps in bone that are too large to heal naturally. And when they occur in the head, face or jaw, these bone defects can dramatically alter a person's appearance. Researchers will report today that they have developed a "self-fitting" material that expands with warm salt water to precisely fill bone defects, and also acts as a scaffold for new bone growth.


Currently, the most common method for filling bone defects in the head, face or jaw (known as the cranio-maxillofacial area) is autografting. That is a process in which surgeons harvest bone from elsewhere in the body, such as the hip bone, and then try to shape it to fit the bone defect.


"The problem is that the autograft is a rigid material that is very difficult to shape into these irregular defects," says Melissa Grunlan, Ph.D., leader of the study. Also, harvesting bone for the autograft can itself create complications at the place where the bone was taken. Another approach is to use bone putty or cement to plug gaps. However, these materials aren't ideal. They become very brittle when they harden, and they lack pores, or small holes, that would allow new bone cells to move in and rebuild the damaged tissue.


To develop a better material, Grunlan and her colleagues at Texas A&M University made a shape-memory polymer (SMP) that molds itself precisely to the shape of the bone defect without being brittle. It also supports the growth of new bone tissue.


SMPs are materials whose geometry changes in response to heat. The team made a porous SMP foam by linking together molecules of poly(ε-caprolactone), an elastic, biodegradable substance that is already used in some medical implants. The resulting material resembled a stiff sponge, with many interconnected pores to allow bone cells to migrate in and grow. Upon heating to 140 degrees Fahrenheit, the SMP becomes very soft and malleable. So, during surgery to repair a bone defect, a surgeon could warm the SMP to that temperature and fill in the defect with the softened material. Then, as the SMP is cooled to body temperature (98.6 degrees Fahrenheit), it would resume its former stiff texture and "lock" into place.


The researchers also coated the SMPs with polydopamine, a sticky substance that helps lock the polymer into place by inducing formation of a mineral that is found in bone. It may also help osteoblasts, the cells that produce bone, to adhere and spread throughout the polymer. The SMP is biodegradable, so that eventually the scaffold will disappear, leaving only new bone tissue behind. To test whether the SMP scaffold could support bone cell growth, the researchers seeded the polymer with human osteoblasts. After three days, the polydopamine-coated SMPs had grown about five times more osteoblasts than those without a coating. Furthermore, the osteoblasts produced more of the two proteins, runX2 and osteopontin, that are critical for new bone formation.


Grunlan says that the next step will be to test the SMP's ability to heal cranio-maxillofacial bone defects in animals. "The work we've done in vitro is very encouraging," she says. "Now we'd like to move this into preclinical and, hopefully, clinical studies."

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Eco-friendly ‘pre-fab’ self-assembling nanoparticles could revolutionize nano manufacturing

Eco-friendly ‘pre-fab’ self-assembling nanoparticles could revolutionize nano manufacturing | Amazing Science | Scoop.it

University of Massachusetts Amherst scientists have developed a breakthrough technique for creating water-soluble nano-modules and controlling molecular assembly of nanoparticles over multiple length scales.


The new method should reduce the time nanotech manufacturing firms spend in trial-and-error searches for materials to make electronic devices such as solar cells, organic transistors, and organic light-emitting diodes.


“The old way can take years,” says materials chemist Paul Lahti, co-director with Thomas Russell of UMass Amherst’s Energy Frontiers Research Center (EFRC), supported by the U.S. Department of Energy.


“Another of our main objectives is to make something that can be scaled up from nano- to mesoscale, and our method does that. It is also much more ecologically friendly because we use water instead of dangerous solvents in the process.


“In our recent paper, we worked on glass, but we want to translate to flexible materials and produce roll-to-roll manufactured materials with water,” said chemist Dhandapani Venkataraman, lead investigator. “We expect to actually get much greater efficiency.” He suggests that reaching 5 percent power conversion efficiency would justify the investment for making small, flexible solar panels to power devices such as smart phones.


If the average smart phone uses 5 watts of power and all 307 million United States users switched from batteries to flexible solar, it could save more than 1500 megawatts per year, Venkataraman estimates. “That’s nearly the output of a nuclear power station,” he says, “and it’s more dramatic when you consider that coal-fired power plants generate 1 megawatt and release 2,250 lbs. of carbon dioxide. So if a fraction of the 6.6 billion mobile phone users globally changed to solar, it would reduce our carbon footprint a lot.”


Doctoral student and first author Tim Gehan says that organic solar cells made in this way can be semi-transparent, as well, “so you could replace tinted windows in a skyscraper and have them all producing electricity during the day when it’s needed. And processing is much cheaper and cleaner with our cells than in traditional methods.”

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How to synthesize structurally pure carbon nanotubes using molecular seeds

How to synthesize structurally pure carbon nanotubes using molecular seeds | Amazing Science | Scoop.it

By smoothing nanotube irregularities, a new process could lead to smaller, faster-switching next-generation electronic and electro-optical components. Researchers at Empa and the Max Planck Institute for Solid State Research have succeeded in “growing” single-wall carbon nanotubes (SWCNTs) with a single predefined structure, with identical electronic properties.


The CNTs self-assembled out of tailor-made organic precursor molecules on a platinum surface, as reported by the researchers in the journal Nature.


With a diameter of roughly one nanometer, SWCNTs should be considered as quantum structures; the slightest structural changes, such as differences in diameter or in the alignment of the atomic lattice, may result in dramatic changes in electronic properties.


One SWCNT may be metallic, while another one with a slightly different structure is a semiconductor. So there is a great deal of interest in reliable methods of making SWCNTs as structurally uniform as possible. Such CNTs could help create next-generation electronic and electro-optical components that are smaller than ever before, allowing for faster switching times.


Here’s how the researchers did it:


  1. Transform the flat (2D) starting molecule into a three-dimensional object, the “germling.” This takes place on a hot platinum surface using a catalytic reaction in which hydrogen atoms are split off and new carbon-carbon bonds are formed at very specific locations. The “germ” — a small, dome-like entity with an open edge that sits on the platinum surface — is “folded” out of the flat molecule. This “end cap” forms the “lid” of the growing SWCNT.
  2. Attach more carbon atoms, which originate from the catalytic decomposition of ethylene (C2H4) on the platinum surface. They position themselves on the open edge between the platinum surface and the end cap, and raise the cap higher and higher, causing the nanotube to grow slowly upwards.


Only the germ defines the nanotube’s atomic structure, as the researchers were able to demonstrate through the analysis of the vibration modes of the SWCNTs and scanning tunnel microscope (STM) measurements. Further investigations using the new scanning helium ion microscope (SHIM) at Empa show that the resulting SWCNTs reach lengths greater than 300 nanometers.


The SWCNTs synthesized in this study are mirror-image symmetrical entities. However, depending on the manner in which the honeycombed atomic lattice is derived from the starting molecule (“straight” or “oblique” in relation to the CNT axis), it would also possible be possible to produce helically wound nanotubes, i.e., nanotubes twisting to the right or left, which are not mirror-image symmetrical.


This structure also determines the electronic, thermoelectric, and optical properties of the material. So in principle, the researchers could produce materials with different properties in a targeted manner by selecting the starting molecule.


The project was supported by the Swiss National Science Foundation (FNSNF).

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Underwater self-healing polymer mimics biological self-repair of mussels

Underwater self-healing polymer mimics biological self-repair of mussels | Amazing Science | Scoop.it

A common acrylic polymer used in biomedical applications and as a substitute for glass has been given the ability to completely self-heal underwater by US researchers. The method, which takes inspiration from the self-healing abilities of adhesive proteins secreted by mussels, could allow for longer lasting biomedical implants. Temporary hydrogen bonding network stitches damage as the material fuses together.


'Polymer self-healing research is about 10 years old now and many different strategies have been developed,' says Herbert Waite, who conducted the work with colleagues at the University of California, Santa Barbara. 'None, however, address the need for healing in a wet medium – a critical omission as all biomaterials function, and fail, in wet environments.'


The idea of mimicking the biological self-healing ability of mussel adhesive proteins is not new, and previous attempts have involved polymer networks functionalised with catechols – synthetic water-soluble organic molecules that mimic mussel adhesive proteins – and metal-ion mediated bonding. However, how mussel adhesive proteins self-heal remains poorly understood, which has limited attempts to synthesise catechols that accurately mimic biological self-healing underwater.


Now, Waite and colleagues have discovered a new aspect of catechols after they were simply 'goofing around' in the lab and found a new way to modify the surface of poly(methyl methacrylate), or PMMA, with catechols. This led them to explore the material's properties and discover that hydrogen bonding enables the polymer to self-heal underwater after being damaged. 'Usually, catechols in wet adhesives are associated with covalent or coordination mediated cross-linking. Our results argue that hydrogen bonding can also be critical, especially as an initiator of healing,' he says.


The healing process begins because catechols provide multidentate hydrogen-bonding faces that trigger a network of hydrogen bonds to fix any damage – the interaction is strong enough to resist interference by water but reversible. Acting a bit like dissolvable stitches, hydrogen bonding between the catechols appears to stitch the damaged area, which allows the underlying polymer to fuse back together. After about 20 minutes, the hydrogen bonded catechols mysteriously disappear leaving the original site of damage completely healed. 'We don't know where the hydrogen bonded catechols go,’ Waite says. ‘Possibly back to the surface, dispersed within the bulk polymer, or some other possibility.'


Phillip Messersmith, a biomaterials expert at the University of California, Berkeley, US, says that this is ‘really creative work’. '[This] reveals a new dimension of catechols, which in this case mediate interfacial self-healing through the formation of hydrogen bonds between surfaces, and which are ultimately augmented or replaced by other types of adhesive interactions.'

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Eric Chan Wei Chiang's curator insight, August 5, 2014 1:50 AM

Chemistry is making a comeback with the rise of regenerative medicine. After all, stem cells need a scaffold to grow upon. 

 

Read more scoops on novel therapies here:

http://www.scoop.it/t/biotech-and-beyond/?tag=Novel+Therapies

Team's curator insight, November 2, 2014 1:40 PM

Philippe: Interessant  decrit une synthese depolymer autocicatrisant

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The Motion of the Medium Matters for Self-assembling Particles

The Motion of the Medium Matters for Self-assembling Particles | Amazing Science | Scoop.it

By attaching short sequences of single-stranded DNA to nanoscale building blocks, researchers can design structures that can effectively build themselves. The building blocks that are meant to connect have complementary DNA sequences on their surfaces, ensuring only the correct pieces bind together as they jostle into one another while suspended in a test tube.


Now, a University of Pennsylvania team has made a discovery with implications for all such self-assembled structures.


Earlier work assumed that the liquid medium in which these DNA-coated pieces float could be treated as a placid vacuum, but the Penn team has shown that fluid dynamics play a crucial role in the kind and quality of the structures that can be made in this way.


As the DNA-coated pieces rearrange themselves and bind, they create slipstreams into which other pieces can flow. This phenomenon makes some patterns within the structures more likely to form than others.


The research was conducted by professors Talid Sinno and John Crocker, alongside graduate students Ian Jenkins, Marie Casey and James McGinley, all of the Department of Chemical and Biomolecular Engineering in Penn’s School of Engineering and Applied Science.


It was published in the Proceedings of the National Academy of Sciences.

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Barnacle cement: Nature's strongest glue is a two-component adhesive

Barnacle cement: Nature's strongest glue is a two-component adhesive | Amazing Science | Scoop.it

Over a 150 years since it was first described by Darwin, scientists are finally uncovering the secrets behind the super strength of barnacle glue. 

Still far better than anything we have been able to develop synthetically, barnacle glue – or cement - sticks to any surface, under any conditions.

But exactly how this superglue of superglues works has remained a mystery – until now.


An international team of scientists led by Newcastle University, UK, and funded by the US Office of Naval Research, have shown for the first time that barnacle larvae release an oily droplet to clear the water from surfaces before sticking down using a phosphoprotein adhesive.


Publishing their findings this week in the prestigious academic journal Nature Communications, author Dr Nick Aldred says the findings could pave the way for the development of novel synthetic bioadhesives for use in medical implants and micro-electronics. The research will also be important in the production of new anti-fouling coatings for ships.


Thoracian barnacles rely heavily upon their ability to adhere to surfaces and are environmentally and economically important as biofouling pests. Their adhesives have unique attributes that define them as targets for bio-inspired adhesive development. With the aid of multi-photon and broadband coherent anti-Stokes Raman scattering microscopies, we report that the larval adhesive of barnacle cyprids is a bi-phasic system containing lipids and phosphoproteins, working synergistically to maximize adhesion to diverse surfaces under hostile conditions. Lipids, secreted first, possibly displace water from the surface interface creating a conducive environment for introduction of phosphoproteins while simultaneously modulating the spreading of the protein phase and protecting the nascent adhesive plaque from bacterial biodegradation. The two distinct phases are contained within two different granules in the cyprid cement glands, implying far greater complexity than previously recognized. Knowledge of the lipidic contribution will hopefully inspire development of novel synthetic bioadhesives and environmentally benign antifouling coatings.

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Blackest is the new black: Scientists have developed a material so dark that you can't see it

Blackest is the new black: Scientists have developed a material so dark that you can't see it | Amazing Science | Scoop.it

A British company has produced a "strange, alien" material so black that it absorbs all but 0.035 per cent of visual light, setting a new world record. To stare at the "super black" coating made of carbon nanotubes – each 10,000 times thinner than a human hair – is an odd experience. It is so dark that the human eye cannot understand what it is seeing. Shapes and contours are lost, leaving nothing but an apparent abyss.


If it was used to make one of Chanel's little black dresses, the wearer's head and limbs might appear to float incorporeally around a dress-shaped hole.


Actual applications are more serious, enabling astronomical cameras, telescopes and infrared scanning systems to function more effectively. Then there are the military uses that the material's maker, Surrey NanoSystems, is not allowed to discuss.


The nanotube material, named Vantablack, has been grown on sheets of aluminium foil by the Newhaven-based company. While the sheets may be crumpled into miniature hills and valleys, this landscape disappears on areas covered by it.


"You expect to see the hills and all you can see … it's like black, like a hole, like there's nothing there. It just looks so strange," said Ben Jensen, the firm's chief technical officer. Asked about the prospect of a little black dress, he said it would be "very expensive" – the cost of the material is one of the things he was unable to reveal. "You would lose all features of the dress. It would just be something black passing through," he said.


Vantablack, which was described in the journal Optics Express and will be launched at the Farnborough International Airshow this week, works by packing together a field of nanotubes, like incredibly thin drinking straws. These are so tiny that light particles cannot get into them, although they can pass into the gaps between. Once there, however, all but a tiny remnant of the light bounces around until it is absorbed.


Vantablack's practical uses include calibrating cameras used to take photographs of the oldest objects in the universe. This has to be done by pointing the camera at something as black as possible.

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New germ-killing nanosurface opens up new front in hygiene

New germ-killing nanosurface opens up new front in hygiene | Amazing Science | Scoop.it
Imagine a hospital room, door handle or kitchen countertop that is free from bacteria—and not one drop of disinfectant or boiling water or dose of microwaves has been needed to zap the germs.


That is the idea behind a startling discovery made by scientists in Australia.

In a study published on Tuesday in the journal Nature Communications, they described how a dragonfly led them to a nano-tech surface that physically slays bacteria.


The germ-killer is black silicon, a substance discovered accidentally in the 1990s and now viewed as a promising semiconductor material for solar panels.


Under an electron microscope, its surface is a forest of spikes just 500 nanometres (500 billionths of a metre) high that rip open the cell walls of any bacterium which comes into contact, the scientists found. It is the first time that any water-repellent surface has been found to have this physical quality as bactericide.


Last year, the team, led by Elena Ivanova at Swinburne University of Technology in Melbourne, were stunned to find cicada wings were potent killers of Pseudomonas aeruginsoa—an opportunist germ that also infects humans and is becoming resistant to antibiotics.


Looking closely, they found that the answer lay not in any biochemical on the wing, but in regularly-spaced "nanopillars" on which bacteria were sliced to shreds as they settled on the surface. They took the discovery further by examining nanostructures studding the translucent forewings of a red-bodied Australian dragonfly called the wandering percher (Latin name Diplacodes bipunctata). It has spikes that are somewhat smaller than those on the black silicon—they are 240 nanometres high.


The dragonfly's wings and black silicon were put through their paces in a lab, and both were ruthlessly bactericidal. Smooth to the human touch, the surfaces destroyed two categories of bacteria, called Gram-negative and Gram-positive, as well as spores, the protective shell that coats certain times of dormant germs.


The three targeted bugs comprised P. aeruginosa, the notorious Staphylococcus aureus and the ultra-tough spore of Bacillus subtilis, a wide-ranging soil germ that is a cousin of anthrax. The killing rate was 450,000 bacterial cells per square centimetre per minute over the first three hours of exposure. This is 810 times the minimum dose needed to infect a person with S. aureus, and a whopping 77,400 times that of P. aeruginosa.

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Peter Phillips's curator insight, July 2, 2014 6:48 PM

Learning from nature - dragon fly wings. Minute structures on their surface pop bacteria like balloons. Opening possibilities to reduce antibiotic use in hospitals.

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Hardest Synthetic Diamond Yet Created

Hardest Synthetic Diamond Yet Created | Amazing Science | Scoop.it

A team of researchers based at Yanshan University has produced a new synthetic diamond that’s remarkably robust, outperforming natural diamonds and other synthetic diamonds in both thermal stability and pressure tests. The results have been published in Nature.


Diamond is the hardest natural material known to man and consequently it is used in a wide variety of industrial settings such as aerospace engineering, mining and car manufacture. Its hardness and wear resistance makes it a particularly useful material for cutting tools but unfortunately poor stability at very high temperatures has restricted its applications in industry. Researchers are therefore turning to synthetic diamonds in order to overcome the limits of natural diamonds.


In nature, diamond occurs only as single crystals and while these materials are pretty hardy, they’re expensive and tend to wear unevenly. Synthetic diamonds, however, can either be prepared as single crystals or as a polycrystalline or nanocrystalline material. Polycrystalline diamond (PCD) is formed from tiny grains of diamond, as small as tens of nanometers in diameter, which have been fused together under high-pressure, high-temperature conditions. The smaller the grain, the harder the diamond.


These diamonds offer numerous benefits over natural diamonds given reduced costs, improved hardness and high wear resistance. However, industry is pushing these diamonds to the limits and there has been a need to develop even better diamonds.


In order to produce their super-hard diamond, the researchers subjected carbon nanoparticles that were layered like onions to high pressures and temperatures. The grains were arranged in pairs that were a mere 5 nanometers in size. The resulting “nanotwinned” diamond demonstrated remarkable thermal stability and hardness.


The team applied large pressures to the diamond and found that it was able to endure pressures of up to 200 gigapascals, which is around 1.9 million atmospheres. It would take only around half that pressure to shatter a natural diamond.


Next, they tested temperature resistance by investigating the highest temperature that could be tolerated before the diamond started to oxidize. They found the synthetic started to oxidize at temperatures between 980-1,056oC (1,796-1,932oF), which is around 200oC higher than that of natural diamond.

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