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(Construction Europe) The start of 2012 marked the introduction of another tranche of emissions legislation in Europe and the U.S. - an extension of the EU Stage IIIB and U.S. Tier 4 Interim laws that came into force at the start of 2011 for the 130kW to 560kW power band. As of Jan. 1, 2012, the strict emissions limits - which call for a 90 percent reduction in particulate matter along with a 50 percent drop in nitrogen oxides (NOx)—also apply to the 56kW to 129kW power categories. These laws take emissions down to near-zero levels - in fact, some manufacturers say that in certain areas and inner cities, the requirements are so strict that their Tier 4 Final engines will act as air cleaners. To achieve this next step, engine manufacturers will have to use all the tools in their emissions reduction armoury. Depending on the engine size, this could mean a combination of cooled exhaust gas recirculation, selective catalytic reduction and diesel particulate filters.
Energy Secretary Steven Chu, speaking at an innovation conference organized by Oak Ridge National Lab, told industry leaders about the opportunity to use DOE’s supercomputing capabilities to accelerate the development and design of new products and to improve industrial competitiveness. Some of the country’s top technology CEOs were in attendance, including AMD’s Rory Read, Cray’s Peter J. Ungaro, NVIDIA’s Jen-Husn Huang and others. Through the national laboratories, DOE operates several of the fastest, most powerful supercomputers in the world and allows industry to use its facilities and expertise to for advanced computational modeling to accelerate product development. Chu says the supercomputers can aid the design of everything from advanced nuclear reactors to more efficient automobile engines.
Inspired by nature’s ability to shape a petal, and building on simple techniques used in photolithography and printing, researchers at the University of Massachusetts Amherst have developed a new tool for manufacturing three-dimensional shapes easily and cheaply, to aid advances in biomedicine, robotics and tunable micro-optics. To date, the UMass Amherst researchers have made a variety of simple shapes including spheres, saddles and cones, as well as more complex shapes such as minimal surfaces.
Neutron testing of the Japanese-made superconducting cable for the central solenoid magnetic system for US ITER begins next Tuesday, says Ke An, lead instrument scientist for the VULCAN Engineering Materials Diffractometer at SNS. The 3-meter-long cable, mounted in a specially designed cryostat, can be cooled down to 80 K (-193.5°C). The mapping experiment will be performed at both room temperature and cryogenic conditions, for one week. U.S. ITER is contributing 100% of the design, R&D, and fabrication of the central solenoid for the giant ITER tokamak experimental fusion reactor. The CS is one of three magnet systems that will contain the burning plasma inside the tokamak. Past tests showed cable degradation under cyclic power loading conditions
A technique for creating a new molecule that structurally and chemically replicates the active part of the widely used industrial catalyst molybdenite has been developed by researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). This technique holds promise for the creation of catalytic materials that can serve as effective low-cost alternatives to platinum for generating hydrogen gas from water that is acidic. Christopher Chang and Jeffrey Long, chemists who hold joint appointments with Berkeley Lab and UC Berkeley, led a research team that synthesized a molecule to mimic the triangle-shaped molybdenum disulfide units along the edges of molybdenite crystals, which is where almost all of the catalytic activity takes place. Since the bulk of molybdenite crystalline material is relatively inert from a catalytic standpoint, molecular analogs of the catalytically active edge sites could be used to make new materials that are much more efficient and cost-effective catalysts.
NIST researchers have done a mash-up of two very different experimental techniques - neutron scattering and electrochemical measurements - to enable them to observe structural changes in nanoparticles as they undergo an important type of chemical reaction. Their recently published technique allows them to directly match up particle size, shape and agglomeration with the “redox” chemical properties of the particles. The measurements are important both for the design of nanoparticles for particular applications and for toxicology studies. The NIST team was interested in the redox properties of zinc oxide nanoparticles, which are used or being considered for a wide variety of applications ranging from sunscreens and antibacterial coatings to semiconductor and photoelectronic devices.
(Gizmag) California-based Envia Systems claims to have broken the world record for energy density in a rechargeable lithium-ion cell, with an automotive-grade battery that reportedly has a density of 400 Watt-hours/kilogram. Not only is that figure two to three times higher than what is currently possible with commercially-available cells, but Envia also claims that its battery should cost less than half the price of existing li-ion batteries. Testing of the battery was performed by the Electrical Power Systems Department at the Naval Surface Warfare Center in Crane, Ind. Envia uses a high-apacity manganese-rich cathode based on technology created at Argonne National Laboratory. It consists of nickel, cobalt, manganese and Li2MnO3. Envia has introduced a patented nanocoating process to that mix, to enhance cycle life and safety. The HCMR is said to have twice the capacity of regular cathodes, and should be available for use in pilot vehicle projects later this year. A low-cost silicon-carbon nanocomposite acts as the anode. The composition of the Envia-developed electrolyte isn’t being revealed, although it is reportedly able to remain stable at higher voltages than currently used materials.
The steady march to grid parity for solar energy devices continues: A Santa Clara, Calif., maker of gallium arsenide photovoltaic panels, Alta Devices, announced Tuesday that the NREL verified that its top-line panels operate at 23.5% efficiency. The ability to deliver an entire high-efficiency panel is a big step forward for the company’s business, which last year achieved verified record-setting efficiencies as high as 28.2% with a single, single-junction PV cell.
This looks to be a record efficiency-level for PV panels. Although, as the chart above indicates, NREL has verified higher efficiencies in other PV arrangements, these have been for a single or small sets of PV cells, not full panels. (It should probably be noted that Sanyo asserts that its in-production silicon heterostructure (HIT) panels come near to the numbers achieved by Alta, but this has not been verified by NREL.)
In a news release, Alta Devices explains a little bit about its interest in GaAs-based devices. The company says, “Alta chose to focus on GaAs because of its intrinsic efficiency advantages as well as its ability to generate electricity at high temperatures and in low light. This means that Alta’s panels have substantially higher energy density than other technologies, generating more kilowatt–hours of energy over the course of a year in real life conditions.”
Some investors have been cautious about GaAs-based solar technologies because they generally have appeared to require higher-priced materials than, for example, silicon. But the company says, “though GaAs is known for being expensive to produce, Alta has invented a manufacturing technique that enables extremely thin layers of GaAs that are a fraction of the thickness of earlier GaAs solar cells. Alta’s cells are about one micron thick… In utilizing very thin devices that have the highest energy density possible, the cost of the material needed in Alta panels remains low and the potential costs of an entire solar energy system based on Alta’s technology could be dramatically reduced.”
Alta deposits the GaAs on a thin, flexible film substrate. By focusing on this form factor, Alta says its film “has the potential to be integrated in wholly unique ways and into a variety of applications, including roof and building materials, and numerous military, consumer and transportation products.”
The company was cofounded by two well known California scientists engaged in academic-based energy research, CalTech’s Harry Atwater and University of California at Berkeley’s Eli Yablonovitch. Atwater is director of the Energy Frontier Research Center on Light-Matter Interactions and director of the Resnick Institute for Science, Energy and Sustainability, and Yablonovitch is director of the NSF Center for Energy Efficient Electronics Science, at their respective schools. Alta has received venture capital funding from high profile groups, such as August Capital and Kleiner Perkins Caufield & Byers.
In a recent story on the Lawrence Berkeley National Lab website, Yablonovitch offered a fundamental defense of GaAs. He said, “Gallium arsenide absorbs photons 10,000 times more strongly than silicon for a given thickness but is not 10,000 times more expensive,” says Yablonovitch. “Based on performance, it is the ideal material for making solar cells.”
But the trick is to extract the high efficiency from GaAs. In a June 2011 release, Yablonovitch explained, “Up until now it was understood that to increase the current from our best solar materials, we had to find ways to get the material to absorb more light. But, the voltage is a different story. It was not recognized that to maximize the voltage, we needed the material to generate more photons inside the solar cell. Counterintuitively, efficient light emission is the key for these high efficiencies.”
How are these efficiencies and energy density being achieved? For one thing, it required some open-mindedness. The LBL story describes that a leap in logic had to occur: “Past efforts to boost the conversion efficiency of solar cells focused on increasing the number of photons that a cell absorbs. Absorbed sunlight in a solar cell produces electrons that must be extracted from the cell as electricity. Those electrons that are not extracted fast enough, decay and release their energy. If that energy is released as heat, it reduces the solar cell’s power output. [LBL's Owen Miller] calculated that if this released energy exits the cell as external fluorescence, it would boost the cell’s output voltage. ‘This is the central counter-intuitive result that permitted efficiency records to be broken,’ Yablonovitch says.”
“In the open-circuit condition of a solar cell, electrons have no place to go so they build up in density and, ideally, emit external fluorescence that exactly balances the incoming sunlight. As an indicator of low internal optical losses, efficient external fluorescence is a necessity for approaching the [theoretical efficiency] limit,” Miller said.
In other words, the Alta Devices PV panels achieve high efficiency by emitting certain light while converting solar energy, instead of allowing excess electron energy to build up internal heat.
On the processing side of things, the company says it “is making substantial progress on the build-out of its pilot manufacturing line, which uses mostly off–the–shelf equipment with some proprietary optimizations unique to Alta’s process. Moreover, Alta is starting to plan for full–scale production, with activities such as building strategic manufacturing partnerships and selecting its first large, commercial manufacturing site.”
Experimental setup shows an IR free-electron laser light source and perovskite superlens consisting of BiFeO3 and strontium titanate SrTiO3 layers. Imaged objects are strontium ruthenate patterns (orange) on a SrTiO3 substrate. The near-field probe is shown in blue and the evanescent waves in red. Credit: Kehr, et. al.
The DOE’s Lawrence Berkeley National Lab and Ramamoorthy Ramesh are in the news again. A new release from the Berkeley Lab announces a novel mode of fabricating a superlens for the infrared spectrum using, for the first time, perovskite-based oxides.
Ramesh is the leader of this research and senior author of a recent Nature Communications paper titled, “Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling” (doi:10.1038/ncomms1249).
The innovation is an alternative to super-resolution imaging approaches that are based on metamaterials. In brief, metamaterials are tough to make and absorb a lot of precious light energy.
According to the release, “The perovskite-based oxides on the other hand are simpler and easier to fabricate and are ideal for capturing light in the mid-infrared range. This opens the door to highly sensitive biomedical detection and imaging. It is also possible that the superlensing effect can be selectively turned on/off, which would open the door to high dense data writing and storage.”
The group says it able to achieve an imaging resolution of λ/14 at the superlensing wavelength.
One of the biggest challenges for the researchers according to the report was finding the right combination of perovskites that would make an effective superlens. What they landed on was a layer of bismuth ferrite and a layer of strontium titanate with thicknesses of 200 and 400 nanometers, respectively. These thin-films were grown by pulsed-laser deposition.
In the lab’s release, Susanne Kehr, formerly with Ramesh’s Berkeley research group and now with the University of St. Andrews (Scotland) and Yongmin Liu, a metamaterials expert at Berkeley’s NSF Nanoscale Science and Engineering Center, provide additional information about the advantages of perovskites. “The bismuth ferrite and strontium titanate material feature a low rate of photon absorption and can be grown as epitaxial multilayers whose highly crystalline quality reduces interface roughness so there are few photons lost to scattering,” they say. “This combination of low absorption and scattering losses significantly improves the imaging resolution of the superlens.”
This research was carried out by an international collaboration of scientist, including ACerS member Lane Martin at the University of Illinois, Champaign-Urbana.
Because of thickness and related wavelength issues, these investigators sought and found a way to gain detailed control over the superlens, selective tuning sections or toggling the effect via an external electric field.
“The ability to switch superlensing on and off for a certain wavelength with an external electric field would make it possible to activate and deactivate certain local areas of the lens,” Kehr says. “This is the concept of data-storage, with writing by electric fields and optical read-outs.”
Liu says that the mid-infrared spectral region at which their superlens functions is prized for biomedical applications. “Compared with optical wavelengths, there are significant limitations in the basic components available today for biophotonic delivery in the mid-infrared. Our superlens has the potentials to eliminate these limitations.”
Liu suggests there the world is full of opportunities for these materials, saying, “Perovskites display a wide range of fascinating properties, such as ferroelectricity and piezoelectricity, superconductivity and enormous magnetoresistance that might inspire new functionalities of perovskite-based superlenses, such as nonvolatile memory, microsensors and microactuators, as well as applications in nanoelectronics.”
Investigators in the field of high-temperature superconductors have been stumped for some time about what is occurring between when the temperature of a material drops to the point (T*) where electrons begin to form Cooper pairs and the critical temperature (Tc) for full superconductivity. Heretofore, this odd transitional region has been dubbed a “pseudogap,” but now a collaborative research project has revealed that three different tests suggest the pseudogap is actually a distinct phase.
The collaboration included scientists from the Lawrence Berkeley National Laboratory, the University of California at Berkeley, Stanford University and the SLAC National Accelerator Lab and their results have just been published in Science (doi:10.1126/science.1198415).
Led by Zhi-Xun Shen, director of the Stanford Institute for Materials and Energy Science at SLAC and a professor of physics at Stanford University, the group focused only on Pb-Bi2201 (a lead bismuth strontium lanthanum copper oxide) because of the materials relatively wide range between T* and Tc.
Previous research supported two separate theories about the odd pseudogap: One theory is that it is just a range of gradual transition to superconductivity, and the other is that it is a state of material distinct from both superconductivity and normal “metallicity” with a quantum critical point.
“Promising as the ‘quantum critical’ paradigm is for explaining a wide range of exotic materials, high-Tc superconductivity in cuprates has stubbornly refused to fit the mold. For 20 years, the cuprates managed to conceal any evidence of a phase-transition line where the quantum critical point is supposed to be found,” says Joseph Orenstein in a news release from the Berkeley Lab. Orenstein works in the lab’s Materials Sciences Division and is a professor of physics at UC Berkeley, whose group conducted one of the research team’s three experiments.
As is always the case in these kinds of situations, the question becomes, so what?
According to the release, the hope is that once scientists can wrap their thinking around the concept of a quantum critical point (Xc), new routes to superconductivity can be found. ”This is a paradigm shift in the way we understand high-temperature superconductivity,” says Ruihua He, lead author with Makoto Hashimoto. “The involvement of an additional phase, once fully understood, might open up new possibilities for achieving superconductivity at even higher temperatures in these materials.” These two worked with Shen at SIMES and also worked at Stanford’s Department of Applied Physics and Berkeley Lab’s Advanced Light Source.
One of the tests they conducted involved angle-resolved photoemission spectroscopy to track the kinetic energy and momentum of the emitted electrons over a temperature range.
In another test, investigators measured changes in rotations of the plane of polarization light reflected from the same Pb-Bi2201 sample under a zero magnetic field (magneto-optical Kerr effects). The rotations are proportional to the net magnetization of the sample at different temperatures.
Orenstein’s group performed the third test, a study of time-resolved reflectivity of the Pb-Bi2201 sample.
None of these tests were particularly novel — except that this time they were conducted on the same material and all yielded results consistent with what they expected if there indeed is a phase transition at the pseudogap phase boundary at T*.
Looking ahead, members of the group hope to exploit their discovery that the electronic states dominating the pseudogap phase do not include electron Cooper pairs found in a superconducting phase, yet seem to influence the motion of Cooper pairs in a way previously overlooked.
“Instead of pairing up, the electrons in the pseudogap phase organize themselves in some very different way,” says He. “We currently don’t know what exactly it is, and we don’t know whether it helps superconductivity or hurts it. But we know the direction to take to move forward.”
On the SLAC website, He outlines a plan, saying, “First to-do: uncover the nature of the pseudogap order. Second to-do: determine whether the pseudogap order is friend or foe to superconductivity. Third to-do: find a way to promote the pseudogap order if it’s a friend and suppress it if it’s a foe.”
In the SLAC story, Shen also confidently notes, “Our findings point to management and control of this other phase as the correct path toward optimizing these novel superconductors for energy applications, as well as searching for new superconductors.”
Ashby map of the damage tolerance of materials. Arrow indicates the combination of toughness and strength potentially accessible to metallic glasses extends beyond the traditional limiting ranges towards levels previously inaccessible to any material. Filled star: data for new metallic glass. X: data for other metallic glasses (three Fe-based glasses, two Zr-based glasses a Ti-based glass and a Pt-based glass). O: data for ductile-phase-reinforced metallic glasses. Yield-strength data shown for oxide glasses and ceramics represent ideal limits. (Credit: Nature Materials/Robert Ritchie.)
If you do a Google search (admittedly not very scientific) for “world’s strongest material” and “world’s toughest material,” among the results graphene and spider silk tend to rank the highest, respectively. If you expand your efforts to search for materials that are both strong and exhibit fracture toughness, you start finding a variety mentioned, including silicon carbide (and several other engineering ceramics), Ni/Ti alloys (and other engineering metals) and metallic glasses.
Engineering ceramics are hard to beat on the strength scale. They are scratch resistant and difficult to bend. However, they suffer from a tendency to brittleness. Some engineering metals tend to have higher numbers for combination of both strength and fracture toughness than engineering ceramics. However, even these metals’ toughness come with a price: a tendency to malleability.
But now a group of researchers from Caltech, Lawrence Berkeley National Lab and University of California, Berkeley report in a new paper in Nature Materials that they have found a new composition for a highly damage-tolerant glass — a metallic glass — that is tougher and stronger than Ni and Ti alloys – that apparently make it the toughest, strongest material ever made. Furthermore, their insights suggest even stronger, tougher materials aren’t too far down the road.
The search for materials that suppress fractures while maintaining high strength can be difficult because these two properties are, generally speaking, mutually exclusive. Fracture-tough crystalline materials resist crack expansions because of plastic shielding (think of tiny areas of “shear” bands of the material sliding by each other) ahead of the crack. But, because this shielding doesn’t require much energy, its easy for it to occur, thus decreasing its overall strength.
Conversely, noncrystalline (i.e., amorphous or glass) materials tend to strongly resist the development of openings, but lack the mobile microstructures to employ plastic shielding. So, once an opening does develop, a crack can readily expand to the point of failure (brittleness).
As a result, scientists and engineers are faced with the dilemma of the trade-off between strength and toughness. Previously, metallic glass compositions had been investigated and found to have shear band-forming properties, but under strain a single shear band would often form and grow extensively, resulting in major material failure.
That’s what is so important about this group’s work: They achieve higher strength and higher toughness, successfully dodging the trade-off, by using a composition and process that creates a glass capable of multiple microscale shear bands when subjected to stress.
The important component of this new material is palladium. Researchers leverage the high bulk-to-shear stiffness ratio of palladium. ACerS Fellow Rob Ritchie, a professor at the university and materials scientist at LBL, explains, “Because of the high bulk-to-shear modulus ratio of the palladium containing material, the energy required to form shear bands is much lower than the energy required to turn these shear bands into cracks. The result is that glass undergoes extensive plasticity in response to stress, allowing it to bend rather than crack.”
Ritchie acknowledges that finding this combination is a little counterintuitive. “You know,” he says, “who would have really imagined that we’d find these rare combinations of properties in a glass? It’s neither the strongest material nor the toughest material, but its the combination of toughness and strength, or damage tolerance, that’s key and that goes beyond the benchmark ranges established by the toughest and strongest materials known until now.”
Besides palladium, the glass contains phosphorous, silicon, germanium and silver (Pd79Ag3.5P6Si9.5Ge2). Marios Demetriou, one of the paper’s coauthors, has been able to make rods of the glass with diameters of six millimeters.
The researchers think this is only the beginning. Ritchie tells me that they know “this is a compositional thing, not a structural thing. We are looking at a lot of other compositions. We are fairly certain we didn’t just get lucky with our first composition. We are sure extensive plasticity can be induced in other metallic glasses and that even higher levels of damage resistance are accessible.”
But, don’t look for these materials in applications anytime in the near future. “Right now, these glasses are phenomenally expensive to make, and even so, we can only make them in small quantities. This is going to be an immature field for quite some time, and, as with a lot of potential structural materials, they will probably take decades to perfect and mature.”
Micrograph of deformed notch in palladium-based metallic glass shows extensive plastic shielding of an initially sharp crack. Inset is a magnified view of a shear offset (arrow) developed during plastic sliding before the crack opened. (Credit: Nature Materials/Maximilien Launey.)
Nature has a video of the shear bands/plastic shielding here.