Category Archives: Materials
Making Complex Composite Materials to Order
A sample of a co-continuous polymer composite material produced in the lab by a team including MIT postdoctoral researcher Lifeng Wang. Device in background is used to test the strength of the material. (Credit: Melanie Gonick)
A team of researchers at MIT has found a way to make complex composite materials whose attributes can be fine-tuned to give various desirable combinations of properties such as stiffness, strength, resistance to impacts and energy dissipation.
composites is a “co-continuous” structure of two different materials with very different properties, creating a material combining aspects of both. The co-continuous structure means that the two interleaved materials each form a kind of three-dimensional lattice whose pieces are fully connected to each other from side to side, front to back, and top to bottom.
The research — by postdoc Lifeng Wang, who worked with undergraduate Jacky Lau and professors Mary Boyce and Edwin Thomas — was published in April in the journal Advanced Materials.
The initial objective of the research was to “try to design a material that can absorb energy under extreme loading situations,” Wang explains. Such a material could be used as shielding for trucks or aircraft, he says: “It could be lightweight and efficient, flexible, not just a solid mantle” like most present-day armor.
In most conventional materials — even modern advanced composites — once cracks start to form they tend to propagate through the material, Wang says. But in the new co-continuous materials, crack propagation is limited within the microstructure, he says, making them highly “damage tolerant” even when subjected to many crack-producing events.
Some existing composite materials, such as carbon-carbon composites that use fibers embedded in another material, can have great strength in the direction parallel to the fibers, but not much strength in other directions. Because of the continuous 3-D structure of the new composites, their strength is nearly equal in all dimensions, Wang says.
Story Continues -> Making Complex Composite Materials to Order
Invisibility Cloak: Scientists Achieve Optical Invisibility in Visible Light Range of Spectrum
Electron micrograph of an invisibility cloak structure. The polymer-air metamaterial (“logs”) is colored blue, the gold-coated areas are colored yellow. (Credit: CFN)
“Seeing something invisible with your own eyes is an exciting experience,” say Joachim Fischer and Tolga Ergin. For about one year, both physicists and members of the team of Professor Martin Wegener at KIT’s Center for Functional Nanostructures (CFN) have worked on refining the structure of the Karlsruhe invisibility cloak to such an extent that it is also effective in the visible spectral range.
In invisibility cloaks, light waves are guided by the material such that they leave the invisibility cloak again as if they had never been in contact with the object to be disguised. Consequently, the object is invisible to the observer. The exotic optical properties of the camouflaging material are calculated using complex mathematical tools.
These properties result from a special structuring of the material. It has to be smaller than the wavelength of the light that is to be deflected. For example, the relatively large radio or radar waves require a material “that can be produced using nail scissors,” says Wegener. At wavelengths visible to the human eye, materials have to be structured in the nanometer range.
The minute invisibility cloak produced by Fischer and Ergin is smaller than the diameter of a human hair. It makes the curvature of a metal mirror appear flat, as a result of which an object hidden underneath becomes invisible. The metamaterial placed on top of this curvature looks like a stack of wood, but consists of plastic and air. These “logs” have precisely defined thicknesses in the range of 100 nm. Light waves that are normally deflected by the curvature are influenced and guided by these logs such that the reflected light corresponds to that of a flat mirror.
Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Karlsruhe Institute of Technology.
Journal Reference:
- J. Fischer, T. Ergin, M. Wegener. Three-dimensional polarization-independent visible-frequency carpet invisibility cloak. Optics Letters, 2011; (in press)
Story Continues -> Invisibility Cloak: Scientists Achieve Optical Invisibility in Visible Light Range of Spectrum
Space “Egg,” Meteorite Yield All-New Minerals
Minerals date to birth of solar system
Richard A. Lovett
Published May 19, 2011
Two new minerals that formed during the birth of our solar system have been found inside meteorites, new research shows.
The new discoveries—krotite and wassonite—are particularly exciting for scientists, who have found only about 60 minerals that can be traced to the solar system’s beginnings 4.5 billion years ago.
“These 60 primary minerals are the beginning of mineral evolution in our solar system,” said Chi Ma, a mineralogist at the California Institute of Technology who led the study on krotite.
“They are our … starting materials, which evolve under different physical, chemical, and biological conditions until now—on our own planet we have about 4,500 minerals.”
(See “Oldest Material in Solar System Found.”)
Krotite Found in “Cracked Egg” Meteorite
Krotite, named for pioneering cosmochemist Alexander Krot of the University of Hawaii, was discovered in a meteorite collected about eight years ago in North Africa.
While recently examining the meteorite, scientists spotted an odd material that looked like a cracked egg and was about the size of a grain of rice.
Laboratory analyses revealed that krotite contains a type of calcium aluminum oxide (CaAl2O4) that forms only when there’s a combination of low pressure and high temperatures above 2,700 degrees Fahrenheit (1,500 degrees Celsius). These were also the conditions during the dawn of the solar system—which is why the minerals’ discoveries are so interesting to scientists.
The same material is well known in the field of synthetic materials science, and is sometimes used in concrete. “But this is the first time [it] was found in nature,” said Ma, who describes krotite in the May issue of American Mineralogist.
(Also see “Oldest Rocks on Earth Discovered?”)
Antarctic Meteorite Reveals Wassonite
Wassonite—named for John Wasson, a pioneer in meteorite mineralogy at the University of California, Los Angeles—was found in a meteorite known as Yamato 691.
Several years ago, UCLA scientists noticed strange, microscopic crystals inside the Yamato meteorite, which was collected in Antarctica 42 years ago, said Keiko Nakamura-Messenger, a mineralogist at NASA’s Johnson Space Center in Houston, Texas.
But the crystals, which measured only 50 by 450 nanometers—about a hundredth the width of a human hair—were too tiny to analyze until recently.
(Related pictures: “Best Micro-Photos of 2010.”)
Using an instrument called a focused ion beam, a team led by Nakamura-Messenger prized the crystals out of the rock.
The team then analyzed the crystals’ chemical structures, which revealed that they were composed of just two elements, titanium and sulfur.
Those elements occurred in a 1:1 ratio—an extremely simple formula for a never before seen mineral.
The crystal structure itself, however, is a bit more complex, said Nakamura-Messenger, whose paper on wassonite is pending publication. “You’d expect a cube. But it isn’t.” Rather, “it has an elongated rhombohedral structure.”
In other words, the crystal resembles an office tower that’s been shoved slightly out of plumb.
Photograph courtesy Chi Ma, Caltech
Story Continues -> All new Minerals
New Nanolens Breaks Resolution Record
A new kind of lens reaches an unprecedentedly sharp focus by giving up on being perfect. The lens is the first ever to help take visual light images of structures smaller than 100 nanometers (four one-millionths of inch), which could make it useful for nanotechnology and probing the insides of cells.
Ordinary lenses, like those used in magnifying glasses, have curved surfaces that bend light to a single point. A small object sitting at that point appears larger and sharply focused, helping myopic readers discern fine print and old-school detectives search for fingerprints. But conventional lenses need to be almost perfect to work. Scratches and roughness destroy the clear image.
“Every deviation from the perfect surface results in a deteriorated focus,” said Elbert van Putten, a graduate student at the University of Twente in the Netherlands. “And in practice you’ll always see surface defects.”
The smallest object on which physicists have managed to focus a single conventional lens is 200 nanometers across, just larger than the smallest known bacteria (although more complicated microscopy systems have reached down to 50 nanometers). But a lot of structures that physicists and chemists are interested in, like subcellular structures, nanoelectric circuits and photonic structures, are less than half that size.
Story Continues -> New NanoLens
China''''s Rare-Earth Monopoly
An attractive material: Neodymium (shown here) is one of the rare-earth elements that are key to making very strong magnets for compact electric motors. Credit: Hi-Res Images of Chemical Elements
The rest of the world is trying to find alternatives to these crucial materials.
By Adam Aston
For three weeks, China has blocked shipments of rare-earth minerals to Japan, a move that has boosted the urgency of efforts to break Beijing””s control of these minerals. China now produces nearly all of the world””s supply of rare earths, which are crucial for a wide range of technologies, including hard drives, solar panels, and motors for hybrid vehicles.
In response to China””s dominance in rare-earths production, researchers are developing new materials that could either replace rare-earth minerals or decrease the need for them. But materials and technologies will likely take years to develop, and existing alternatives come with trade-offs.
China apparently blocked the Japan shipments in response to a territorial squabble in the South China Sea. Beijing has denied the embargo, yet the lack of supply may soon disrupt manufacturing in Japan, trade and industry minister Akihiro Ohata told reporters Tuesday.
Rare earths are comprised of 17 elements, such as terbium, which is used to make green phosphors for flat-panel TVs, lasers, and high-efficiency fluorescent lamps. Neodymium is key to the permanent magnets used to make high-efficiency electric motors. Although well over 90 percent of the minerals are produced in China, they are found in many places around the world, and, in spite of their name, are actually abundant in the earth””s crust (the name is a hold-over from a 19th-century convention). In recent years, low-cost Chinese production and environmental concerns have caused suppliers outside of China to shut down operations.
Alternatives to rare earths exist for some technologies. One example is the induction motor used by Palo Alto, California-based Tesla Motors in its all-electric Roadster. It uses electromagnets rather than permanent rare-earth magnets. But such motors are larger and heavier than ones that use rare-earth magnets. As a rule of thumb, in small- and mid-sized motors, an electromagnetic coil can be replaced with a rare-earth permanent magnet of just 10 percent the size, which has helped make permanent magnet motors the preferred option for Toyota and other hybrid vehicle makers. In Tesla””s case, the induction motor technology was worth the trade-off, giving the car higher maximum power in more conditions, a top priority for a vehicle that can rocket from zero to 60 mph in 3.7 seconds. “The cost volatility going into the rare-earth permanent magnets was a concern,” says JB Straubel, Tesla””s chief technology officer. “We couldn””t have predicted the geopolitical tensions.”
More manufacturers are following Tesla””s lead to shun the rare-earth materials, although the move means sacrificing space and adding weight to vehicles. A week after the China dust-up began, a research team in Japan announced they had made a hybrid vehicle motor free of rare-earth materials, and Hitachi has announced similar efforts. BMW””s Mini E electric vehicle uses induction motors, and Tesla is supplying its drive trains to Toyota””s upcoming electric RAV 4. Given the volatility of rare-earth supplies, and the advantages induction motors offer in high performance applications, “It makes sense for car companies to give serious thought to using induction motors,” says Wally Rippel, senior scientist at AC Propulsion. Rippel previously worked on induction motor designs at Tesla and GM, where he helped to develop the seminal EV1.
Article Continues -> http://www.technologyreview.com/energy/26538/?p1=A2
Glass roof tiles let a little sunshine in to cut heating bills
Soltech Energy glass tiles help cut energy bills. Click image for more pictures.
By Darren Quick
Swedish company, Soltech Energy, recently received the gold medal for this year’s hottest new material at the Nordbygg 2010 trade fair in Stockholm, Sweden. The award was fitting because it was for the company’s home heating system that features roof tiles made out of glass. The tiles, which are made from ordinary glass, weigh about the same as the clay roof tiles they replace but allow the sun to heat air that is then used to heat the house and cut energy bills.
Thankfully, although the tiles themselves are transparent, they are backed by a special black absorption fabric so sticky beaks won’t be able to sit on the roof and watch what’s going on inside. This fabric absorbs the sun’s rays, which heats the air underneath, with the air formed into columns by beams within the roof to ensure it is heated sufficiently.
The most common way to connect the system to a house’s existing heating system would be to a water based heating system via an accumulation tank but the system is also designed to be integrated with both air and water based systems, such as a ground source heat pump, air heat pump, pellet boiler or electric boiler – the only requirement is some form of central heating system.
This setup allows the system to heat the house during winter and transfer the heat absorbed in summer to a ground heating system through a heat convector and a fluid based system to help achieve a cooling effect.
Depending on factors such as climate, roof angle and house direction, the system should generate around 350 kWh heat per square meter (3 square ft).
If your roof isn’t suited to tiles, Soltech Energy also offers glass wall panels that can be tailored to individual houses and benefit from the lower angle of the incoming rays of sunlight during the winter.
Via inhabitat
http://www.gizmag.com/soltech-energy-glass-tiles/16660/
New graphene-based single-transistor amplifiers are a triple threat
The new triple-mode, single transistor amplifier could replace many traditional transistors
By Darren Quick
Graphene has already brought us the world’s smallest transistor – twice – and now the one atom thick form of carbon that recently won its discoverers the Nobel Prize has been used to create a triple-mode, single-transistor amplifier. The new transistor has the potential to replace many traditional transistors in a typical integrated circuit and its developers say the device could become a key component in future electronic circuits.
Aside from being very strong, nearly transparent and being a very good conductor of electricity, graphene is also ambipolar, meaning it is able to switch between using positive and negative carriers on the fly depending on the input signal. In comparison, traditional silicon transistors usually only use one or the other type of carrier, which is determined during fabrication. It is graphene’s ambipolar property that has allowed the researchers from Rice University and the University of California, Riverside, to develop the new three-terminal single-transistor amplifier.
The triple-mode transistor can be changed during operation to any of three modes at any time using carriers that are positive, negative or both. This provides opportunities that are not possible with traditional single-transistor architectures, said Kartik Mohanram, an assistant professor of electrical and computer engineering at Rice.
Mohanram likened the new transistor”s abilities to that of a water tap. “Turn it on and the water flows,” he said. “Turn it off and the water stops. That”s what a traditional transistor does. It”s a unipolar device – it only opens and closes in one direction. But if you close a tap too much, it opens again and water flows. That”s what ambipolarity is – current can flow when you open the transistor in either direction about a point of minimum conduction.”
This means a graphene-based transistor can be “n-type” (negative) or “p-type” (positive), depending on whether the carrier originates from the source or drain terminals, which are effectively interchangeable. When the input from each carrier is equal, a third function appears with the transistor becoming a frequency multiplier. By combining the three modes, the Rice-Riverside team demonstrated such common signaling schemes as phase and frequency shift keying for wireless and audio applications.
“Our work, and that of others, that focuses on the applications of ambipolarity complements efforts to make a better transistor with graphene,” Mohanram said. “It promises more functionality.” The research demonstrated that a single graphene transistor could potentially replace many in a typical integrated circuit, he said. Graphene”s superior material properties and relative compatibility with silicon-based manufacturing should allow for integration of such circuits in the future, he added.
However, technical roadblocks still need to be overcome before that happens. Fabrication steps such as dielectric deposition and making contacts actually disturb graphene’s lattice structure, scratching it and introducing defects, which immediately limits its signal gain and degrades its performance. This means the team has to exercise a lot of care when making the transistors.
But Mohanram is confident these problems can be overcome, saying, “the technology will mature, since so many research groups are working hard to address these challenges.”
A paper detailing the triple-mode transistor appears in the online journal ACS Nano.
http://www.gizmag.com/triple-mode-graphene-based-transistor/16646/
Genetically Engineered Silkworms Spin Like Spiders
The new silk alone could shake up the textile industry by creating a softer and stronger fabric that still looks like silk. Click to enlarge this image. Hemera
Silkworms have been modified to produce spider silk, creating a fabric that could be used in everything from bulletproof clothing to artificial tendons.
By Eric Bland
- Silkworms have been genetically engineered to spin spider silk.
- The new hybrid silk is finer and tougher than ordinary silk.
- The development could lead to wound-healing, lighter body armor as well as artificial tissue.
If Spider-Man ever ran out of webs, he could now enlist an army of silkworms to spin extra high-tensile spider silk.
Scientists have created a genetically modified silkworm that spins a new kind of silk: a hybrid of silkworm silk and spider silk.
The new material alone could shake up the textile industry, while future silk hybrids could be used in everything from bulletproof clothing to artificial tendons.
“Compared to normal spider silk, it””s not as strong,” said Malcolm Fraser, a scientist from the University of Notre Dame. “But we are confident that, this being our first attempt, that we will be able to tweak the system to bring the system closer to the strength of true spider silk.”
Fraser, along with professor Randy Lewis from the University of Wyoming, developed the spider-silk-spinning silkworms.
Silkworms have helped clothe people for thousands of years by reliably producing large quantities of a soft, supple and luxurious material.
Spider dragline silk is significantly stronger than silkworm silk — so strong that it can best steel wire — but it is hard to make.
“They just don””t produce enough silk,” said Fraser, who notes that a golden cloth on display at the American Museum of Natural History in New York City required more than one million spiders to produce. “One million silkworms can produce considerably more silk than one million spiders.”
The new silk is a hybrid of spider silk and silkworm silk. It is stronger and finer than silkworm silk, but not quite as strong as spider silk. “It would definitely be stronger (than a normal silk shirt),” said Lewis. “But it wouldn””t flow like silkworm silk does.”
“It””s a fabulous accomplishment,” said Cheryl Hayashi, a spider silk expert and a professor at the University of California, Riverside.
Other groups have produced spider silk protein in plants, in bacteria and even in goat””s milk. But spider silk protein is not the same as spun spider silk. The silkworms have the necessary body parts to spin the protein into silk threads — and to produce it in large quantities.
The new silk alone could shake up the textile industry by creating a softer, stronger fabric that still looks like silk.
Fraser and his team, however, have bigger plans in mind.
In this work the Notre Dame and University of Wyoming scientists replaced only one of multiple silk-producing genes in silkworms with spider silk genes. Eventually they want to replace multiple silkworm silk-producing genes with spider silk genes.
In particular, they hope to insert genes from the newly discovered Darwin””s Bark Spider (Caerostris darwini), which produced silk twice as strong as any other. That””s more than 10 times stronger than Kevlar, a fabric commonly found in bulletproof vests.
Mass produced, stronger-than-steel spider silk will also have a range of biomedical applications, said Fraser and Lewis. Hybrid silk could be speed wound-healing, eliminate or reduce the need for cadaver-derived tendons and ligaments.
http://news.discovery.com/tech/spider-silk-silkworms-genetic-engineering.html
A Touch Screen with Texture
Subtle sensation: In this TeslaTouch demonstration, one finger is stationary while the other experiences the sensation of friction as it moves. Credit: Disney Research
Electrovibration could make for a better sensory experience on a smooth touch surface.
By Kate Greene
Touch screens are ubiquitous today. But a common complaint is that the smooth surface just doesn”t feel as good to use as a physical keypad. While some touch-screen devices use mechanical vibrations to enhance users” experiences of virtual keypads, the approach isn”t widely used, mainly because mechanical vibrations are difficult to implement well, and they often make the entire device buzz in your hand, instead of just a particular spot on the screen.
Now, engineers from three different groups are proposing a type of tactile feedback that they believe will be more popular than mechanical buzzing. Called electrovibration, the technique uses electrical charges to simulate the feeling of localized vibration and friction, providing touch-screen textures that are impossible to simulate using mechanical actuators.
One of these groups, composed of researchers from Disney Research in Pittsburgh, Carnegie Mellon University, and the University of Paris Sud, presented a paper earlier this month at the User Interface Software and Technology (UIST) symposium in New York City. In the paper, they described their approach to electrovibration, called TeslaTouch, in which they modified a commercial touch panel from 3M that uses capacitive sensing — the approach used in most mobile phones and in the iPad.
The touch panel is made of transparent electrodes on a glass plate coated with an insulating layer. By applying a periodic voltage to the electrodes via connections used for sensing a finger”s position on the screen, the researchers were able to effectively induce a charge in a finger dragged along the surface. By changing the amplitude and frequency of the applied voltage, the surface can be made to feel as though it is bumpy, rough, sticky, or vibrating. The major difference is the specially designed control circuit that produces the sensations.
It”s a challenge, says Ivan Poupyrev of Disney Research, to vibrate a screen in a way that makes sense for a user. When an entire device buzzes, it can be more annoying than helpful. There are also technical hurdles and extra costs in making a touch screen mechanically move. The goal, then, was to create a tactile sensation without using any mechanical motion. “It sounds crazy,” Poupyrev says, “but that”s what we”ve done with TeslaTouch.”
Electrovibration was first proposed for touch screens in the 1950s, but the approach didn”t see widespread use because the screens didn”t achieve commercial success until recently. Now, with many researchers looking for ways to improve the now-popular screens, other groups have also rediscovered electrovibration. Nokia recently announced a smartphone prototype that uses the approach. And a Finnish company called Senseg has also implemented electrovibration in touch screens, having closed deals with three companies to incorporate the technology into products that could be available in 2011.
Story Continues -> http://www.technologyreview.com/computing/26506/?p1=A3
Clearing the Way for Cheap, Flexible Solar Panels
Solar protection: This polymer film seals out water far better than other plastics—it can protect solar panels for decades. Credit: 3M
A new polymer film protects panels from water so they can last for decades.
By Ucilia Wang
For years solar companies have wanted to make lightweight, flexible panels that are cheap to ship and easy to install (by unrolling them over large areas). But they””ve been held up by a lack of good and affordable glass substitutes.
Now 3M thinks it””s found a solution. This week the company unveiled a plastic film that it says can rival glass in its ability to protect the active materials in solar cells from the elements and save money for manufacturers and their customers.
The protective film is a multilayer, fluoropolymer-based sheet that can replace glass as the protective front cover of solar panels, says Derek DeScioli, business development manager for 3M””s renewable energy division. Manufacturers laminate the sheets onto the solar panels to seal them tight and shield them from moisture and other weather elements that can be deadly to the solar cells inside.
The film is 3M””s answer to demand by solar-panel makers–particularly manufacturers of certain thin-film solar cells–for an alternative to glass. Glass has been the armor of choice because it””s cheap, weather-resistant, and durable enough to last decades. The vast majority of the solar panels made today rely on glass as the top cover. But glass also adds weight and bulk to solar panels, and it must be packaged carefully to keep it from breaking, adding to shipping costs. By replacing glass, the new film can do away with the need for supporting racks, which is particularly useful on roofs that can””t bear a lot of weight. Blending solar panels into roofs also can overcome aesthetic objections by homeowners.
“Flexible solar panels have all these great-sounding benefits, but then you come to the question of how you encapsulate them. For many years people didn””t appreciate this problem,” says Steven Hegedus, a scientist at the Institute of Energy Conversion at the University of Delaware.
Using plastic to protect solar cells isn””t a new idea. You can find plastic-covered solar cells in camping gear and novelty gadgets such as backpacks with built-in solar-energy chargers. But this type of plastic film isn””t designed to withstand continuous outdoor exposures for 20 to 25 years, which is how long solar panels are supposed to last, Hegedus says.
Several other companies have recently started to market plastic front covers for flexible solar panels, but 3M””s material has orders of magnitude higher performance in terms of keeping out moisture, which is key to long life.
United Solar Ovonic is the only major thin-film maker that has been shipping flexible panels for years. The Michigan company uses amorphous-silicon, which also isn””t as sensitive to moisture as other emerging compounds. Its amorphous-silicon solar panels can only convert about 7 percent of the sunlight that falls on them into electricity, a low efficiency rate that has rendered Uni-Solar””s products less desirable. Uni-Solar uses a fluoropolymer-based resin from DuPont as the top coat for its panels.
Story Continues -> http://www.technologyreview.com/energy/26494/?p1=A1
