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Metallic Glass
- Posted at 10:48 AM on Mar. 18, 2010 by ausetute in Chemistry Update Ordinary metallic materials have an ordered, crystalline structure. Metallic glass has a disorganized structure which can improve some properties of the material because boundaries between crystal grains in an ordered structure lead to weaknesses in the structure. Metallic glass is often stronger and more durable than other metals. Metals have a structure in which the atoms are closely packed together. For a long time it has been thought that subjecting metals to higher pressures will not cause them to become more closely packed, reducing their volume and therefore becoming more dense. Cerium-rich metallic glasses such as Ce75Al25, however, do become more dense under pressure. Changes in the electronic structure of the cerium atoms in which 4f electrons bound to specific cerium atoms under low pressure become delocalised under high pressure cause the bond between atoms to shrink, allowing the atoms to pack together more closely. Qiao-shi Zeng, Yang Ding, Wendy L. Mao, Wenge Yang, Stas. V. Sinogeikin, Jinfu Shu, Ho-kwang Mao, and J. Z. Jiang. Origin of Pressure-Induced Polyamorphism in Ce75Al25 Metallic Glass. Physical Review Letters, 2010; 104 (10): 105702 DOI: 10.1103/PhysRevLett.104.105702 0 Comments - Post Comment - Permanent Link
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Strength of Silk
- Posted at 12:57 PM on Mar. 16, 2010 by ausetute in Chemistry Update Silks are among the toughest materials known. Weight for weight, silks are stronger and less brittle than steel. Massachusetts Institute of Technology Scientists have been studying these remarkable properties of silks. Silks are made up of proteins, some of which are thin, planar sheets called beta-sheets. Hydrogen-bonds connect one beta-sheet to another forming a structure like a stack of pancakes but with the crystal structure within each pancake alternating in their orientation. This allows hydrogen-bonds to work cooperatively, reinforcing adjacent chains against external forces which leads to the outstanding strength of silks. When the crystal size of the beta-sheets is about 3nm the silk is ultra-strong and ductile, but if the crystals are just 2nm larger at 5nm, the silk becomes weak and brittle. This sort of research could lead to the synthesis of new materials that are like silks but using different molecules such as carbon nanotubes. Sinan Keten, Zhiping Xu, Britni Ihle and Markus J. Buehler. Nanoconfinement controls stiffness, strength and mechanical toughness of beta-sheet crystals in silk. Nature Materials, 2010; DOI: 10.1038/nmat2704 |
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AUS-e-NEWS
- Posted at 12:27 PM on Mar. 14, 2010 by ausetute in AUS-e-NEWs The March 2010 issue of AUS-e-NEWS, AUS-e-TUTE's quarterly newslettter, has been emailed out to members and subscribers. Please contact AUS-e-TUTE if you have not received your copy. |
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Silicon and Solar Cells
- Posted at 10:38 AM on Mar. 8, 2010 by ausetute in Chemistry Update A solar cell is composed of two separate layers, one with an abundance of electrons that functions as a negative pole, and one with an abundance of electron holes, or positively-charged spaces, that functions as a positive pole. Energy from the absorption of photons from the sun is used to create electron-hole pairs separated at the interface between the two layers and collected as electricity. Silicon is a popular choice for the semiconductor used in solar cells because of its excellent photo-electric properties, but because solar-cell production to date has required very pure silicon, it has been an energy intensive and expensive choice. Berkeley Lab scientists are developing a new approach to trapping sunlight using thin films of ordered arrays of vertical silicon nanowires that could reduce the costs and improve efficiency. These vertical arrays use radial p-n junctions in which a layer of n-type silicon forms a shell around p-type silicon nanowire core. The photo-excited electrons and holes only move very short distances to the electrodes compared to more traditional planar p-n junctions, so efficiency and light-trapping ability should be enhanced. Erik Garnett and Peidong Yang. Light Trapping in Silicon Nanowire Solar Cells. Nano Letters, 2010; 100202130154041 DOI: 10.1021/nl100161z |
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Organic Molecules Found in the Orion Nebula
- Posted at 9:41 AM on Mar. 5, 2010 by ausetute in Chemistry Update ESA's Herschel Space Observatory has observed numerous organic molecules (carbon-containing compounds) in the Orion Nebula using the Heterodyne Instrument for the Far Infrared (HIFI). The HIFI spectrum recorded a pattern of spikes, each spike representing the emission of light from a specific molecule in the Orion Nebula which is known to be one of the most prolific chemical factories in space. Molecules of water, carbon monoxide, formaldehyde (methanal), methanol (methyl alcohol), dimethyl ether, hydrogen cyanide, and sulfur dioxide have been identified. University of Cologne - Universitaet zu Koeln (2010, March 5). Precursors of life-enabling organic molecules in Orion Nebula unveiled by Herschel Space Observatory. ScienceDaily. Retrieved March 5, 2010, from http://www.sciencedaily.com /releases/2010/03/100304102320.htm |
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Entropy and Water
- Posted at 11:00 AM on Mar. 1, 2010 by ausetute in Chemistry Update Water, H2O, is a very unusual chemical compound. It has the ability to retain large amounts of heat, and to reduce its density instead of increasing its density as it solidifies. Scientists at the Rockefeller University have been investigating the role of water in biology by measuring the interactions between molecules. In the liquid state, each water molecule interacts with its 4 nearest neighbours forming a tetrahedron. The tetrahedrons are not perfect however, and the degree of imperfection changes with changes in temperature and pressure. The more perfect the tetrahedrons are, the more ordered the system is. So scientists can now measure the amount of disorder, or entropy, of a system by measuring the degree of imperfection in the tetrahedrons. These studies could lead to a better understanding of why some substances, like drugs used in chemotherapy, are soluble in water and others are not. It could also lead to a better understanding of protein folding and degradation. Kumar et al. A tetrahedral entropy for water. Proceedings of the National Academy of Sciences, 2009; 106 (52): 22130 DOI: 10.1073/pnas.0911094106 |
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Self-mending Metals
- Posted at 11:03 AM on Feb. 25, 2010 by ausetute in Chemistry Update 'Cold-welding' has been observed at the macro scale when clean, flat pieces of similar metals are bonded together under high pressure or in a vacuum. Now, Rice University Scientists have discovered that gold and silver nano-wires between 3 and 10 billionths of a meter wide can join themselves together without applying heat or pressure. The self-mended wires form a single, strong wire, which, when broken, will not break in the same place as the join. Repeatedly breaking and mending the wires does not affect their electrical properties. Using heat to weld materials at the nano-scale in high density electronic devices can damage the materials' strength or conductivity. Cold-welding could be the solution. Yang Lu, Jian Yu Huang, Chao Wang, Shouheng Sun, Jun Lou. Cold welding of ultrathin gold nanowires. Nature Nanotechnology, 2010; DOI: 10.1038/nnano.2010.4 |
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Nonacene
- Posted at 6:34 AM on Feb. 22, 2010 by ausetute in Chemistry Update Nonacene is a compound with 9 benzene rings joined together in a line and belongs to a class of organic compounds called acenes which are known to be semiconductors and among the best in terms of electrical performance. Unfortunately, acenes are highly unstable, oxidizing rapidly in air. University of New Hampshire Chemists have just made the first stable nonacene derivative. This molecule has the 9 benzene ring backbone of nonacene, but has additional sulfur containing functional groups to provide stability and solubility. Nonacenes could be important to the future development of flexible organic electronic devices and in the production of less expensive solar cells. Kaur et al. Design, Synthesis, and Characterization of a Persistent Nonacene Derivative. Journal of the American Chemical Society, 2010; 132 (4): 1261 DOI: 10.1021/ja9095472 |
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A Biofuel Cell
- Posted at 12:19 PM on Feb. 19, 2010 by ausetute in Chemistry Update French scientists have succeeded in transforming the chemical energy of photosynthesis into electrical energy using a new biofuel cell. During photosynthesis, plants convert carbon dioxide (CO2) and water (H2O) into glucose (C6H12O6) and oxygen (O2), and transform solar energy into chemical energy. The new biofuel cell uses the products of photosynthesis, glucose and oxygen, and is made up of two enzyme-modified electrodes. When the biofuel cell was inserted into a cactus leaf, 9 W/cm2 power was generated. The yield of power is proportional to the intensity of the light, stronger illumination accelerates glucose and oxygen production so more fuel is available for the biofuel cell. |
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Metal Foam Bones
- Posted at 4:38 PM on Feb. 17, 2010 by ausetute in Chemistry Update North Carolina State University scientists have created a light-weight metal foam that has a similar elasticity to bone and could be used in the future for implants avoiding the problem of bone rejection that often results from more rigid implant materials like titanium. The metal foam can be made out of steel or a combination of steel and aluminium. The rough surface of the metal foam should foster bone growth onto the implant, improving the strength of the implant. Vendra et al. Evaluation of modulus of elasticity of composite metal foams by experimental and numerical techniques. Materials Science and Engineering A, 2010; 527 (7-8): 1784 DOI: 10.1016/j.msea.2009.11.004 |
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Catalysed Oxidation of Carbon Monoxide
- Posted at 7:35 AM on Feb. 15, 2010 by ausetute in Chemistry Update Toxic carbon monoxide, CO, is converted to carbon dioxide, CO2, in cars using a catalyst such as platinum. Swiss Chemists have been studying this reaction at the same high temperatures and pressures as exist in car exhaust to see how the electrons in platinum reorganize as the adsorption of CO takes place and to understand why catalysts are poisoned, ie, why catalytic activity is reduced. The strong bond between CO and the platinum blocks active sites and makes the metal less able to react with oxygen, lowering the activity of the catalyst. Glatzel et al. In Situ Characterization of the 5d Density of States of Pt Nanoparticles upon Adsorption of CO. Journal of the American Chemical Society, 2010; 100203075412003 DOI: 10.1021/ja907760p |
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Seebeck Thermoelectric Effect
- Posted at 4:23 PM on Feb. 11, 2010 by ausetute in Chemistry Update In 1821 Thomas Johann Seebeck observed that a temperature difference between two ends of a metal bar created an electric current, the voltage being directly proportional to the temperature difference. This is now known as the Seebeck thermoelectric effect and could be the key to converting waste heat into electricity. Good thermoelectric materials should have high thermopower, high electrical conductivity and low thermal conductivity. Unfortunately, increases in thermopower typically result in a reduction in electrical conductivity. Scientists have now modelled the use of a class of materials known as highly mismatched alloys (HMAs) to show that increasing thermopower is possible without the loss of electrical conductivity with these compounds. Joo-Hyoung Lee,Junqiao Wu,and Jeffrey C. Grossman. Enhancing the Thermoelectric Power Factor with Highly Mismatched Isoelectronic Doping. Physical Review Letters, PRL 104, 016602 (2010) DOI: 10.1103/PhysRevLett.104.016602 |
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Graphene in Lighting
- Posted at 11:25 AM on Feb. 9, 2010 by ausetute in Chemistry Update OLEDs, organic light diodes, used in mobile phones, cameras and very thin TVs, are composed of a light generating layer of plastic placed between 2 electrodes, one of which must be transparent. They are quite expensive to produce and the transparent electrode used is the metal alloy indium tin oxide. Indium is rare and and the electrode is difficult to recycle. Scientists have just discovered that graphene can be used as the transparent electrode creating an organic light-emitting electrochemical cell, LEC. Graphene, composed of a single layer of carbon atoms, has high electrical conductivity making it a suitable electrode, is virtually transparent, and can be produced in solution as graphene oxide, and it can be recycled. Since all the LEC components can be produced in solution, scientists think it should be possible to create illuminated displays that can be rolled up or applied as a wallpaper or on ceilings. The future is looking brighter :) Piotr Matyba, Hisato Yamaguchi, Goki Eda, Manish Chhowalla, Ludvig Edman, and Nathaniel D. Robinson. Graphene and Mobile Ions: The Key to All-Plastic, Solution-Processed Light-Emitting Devices. ACS Nano, 2010; 100204180201054 DOI: 10.1021/nn9018569 |
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Phthalates in PVC
- Posted at 10:45 AM on Feb. 5, 2010 by ausetute in Chemistry Update Polyvinyl chloride, PVC, is a polymer commonly used in the production of medical tubing, packaging and toys. Manufacturers add large amounts of plasticizers to PVC to make it flexible and durable. Phthalates, the most commonly used plasticizers, migrate to the surface of the plastic over time and escape into the environment causing the plastic to be less durable and flexible and posing health risks for people who come into contact with them. Chemists have now developed a way to make the phthalates bond permanently to the internal structure of PVC so that they will not migrate. This could lead to the production of safer, more durable PVC. Navarro et al. Phthalate Plasticizers Covalently Bound to PVC: Plasticization with Suppressed Migration. Macromolecules, 2010; 100121082610027 DOI: 10.1021/ma902740t |
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Water Tension and Adhesion
- Posted at 1:25 PM on Feb. 3, 2010 by ausetute in Chemistry Update Cornell scientists have invented a device that uses water surface tension to create an adhesive bond. A flat plate punched with micron-sized holes lies at the top of the device, with a liquid reservoir plate at the bottom, and a porous layer lies between these two plates. A 9-volt battery supplies an electric field to pump water through the device, causing droplets to squeeze through the top layer. The surface tension of the exposed droplets makes the device grip another surface. The adhesion is turned off by reversing the electric field, causing the water to pull back through the holes. A prototype device containing 1,000 300-micron-sized holes could hold 30 grams. More holes, and smaller holes, creates greater adhesion. The scientists estimate that a 1 square inch (6.5cm2) device with millions of 1-micron-sized holes could hold more than 15 pounds (6.8kg). This rapid adhesion mechanism could lead to shoes of gloves that stick and unstick to walls, enabling people to walk up walks just like Spiderman! Cornell University (2010, February 2). New adhesive device could let humans walk on walls. ScienceDaily. Retrieved February 3, 2010, from http://www.sciencedaily.com /releases/2010/02/100201184115.htm |
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Strength of Diamonds
- Posted at 10:59 AM on Jan. 29, 2010 by ausetute in Chemistry Update Diamonds are formed naturally out of carbon-containing minerals at high pressure and temperature and at depths of about 140-190km (87-120 miles) in the Earth's mantle, taking up to 3.3 billion years to grow. Diamonds are known to be very hard and very strong, easily cutting through glass and steel. Scientists have been measuring the behaviour of natural diamond crystals under shock-wave compression between 1 million and 10 million atmospheres pressure and have found that diamonds retain their strength right up to the point at which they melt (6million atmospheres pressure and 7800oC (14,000oF) R. S. McWilliams, J. H. Eggert, D. G. Hicks, D. K. Bradley, P. M. Celliers, D. K. Spaulding, T. R. Boehly, G. W. Collins, and R. Jeanloz. Strength effects in diamond under shock compression from 0.1 to 1 TPa. Physical Review B, 2010; 81 (1): 014111 DOI: 10.1103/PhysRevB.81.014111 |
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New Colligative Properties Resources
- Posted at 11:59 AM on Jan. 28, 2010 by ausetute in website update AUS-e-TUTE has just added new tutorials, tests, games, drills:
Contact us and tell us what you need. |
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Antarctic Ozone Hole Reduces Global Warming
- Posted at 7:15 AM on Jan. 27, 2010 by ausetute in Chemistry Update Recent research by scientists at the University of Leeds shows that the Antarctic ozone hole helps shield this region from carbon-induced global warming via the formation of bright summertime clouds which reflect more of the sun's rays. These clouds are the result of high-speed winds under the hole in the ozone layer which whip up large amounts of sea spray. The sea spray forms droplets and results in the formation of clouds. As the hole in the ozone layer is slowly closing, these clouds will disappear and global warming will increase. Aerosol climate feedback due to decadal increases in southern hemisphere wind speeds. Geophysical Research Letters, 2010; (in press) |
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Intermolecular Coulomb Decay
- Posted at 9:54 AM on Jan. 22, 2010 by ausetute in Chemistry Update Intermolecular Coulomb Decay is the process in which two adjacent molecules work together to achieve autoionisation. Autoionization results when radiation is absorbed by a molecule and some of this energy is used to ionize the molecule by releasing an electron. The rest of the energy remains stored in the ion which causes another electron to be released a few femtoseconds later, that is, the molecular ion ionizes itself. In the process of Intermolecular Coulomb Decay the molecular ion produced by the absorption of radiation transfers its excess energy to a second molecule which then releases an electron of its own. This transfer of energy does not result in the formation of a chemical bond. Intermolecular Coulomb Decay has been observed in frozen rare gases and has now been demonstrated as a possible process in water. Mucke et al. A hitherto unrecognized source of low-energy electrons in water. Nature Physics, 2010; DOI: 10.1038/nphys1500 |
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Boron Nitride Nanotubes
- Posted at 5:48 AM on Jan. 20, 2010 by ausetute in Chemistry Update Boron nitride nanotubes can withstand temperatures in excess of 1,100oC and they are perfect insulators that can be doped with other materials to form designer semiconductors. Transparent sheets of boron nitride nanotubes also display the lotus effect, they shed water like water off a duck's back, so they can be used to provide stain-resistant coatings. Until recently, boron nitride nanotubes have been difficult to grow. Scientists at the Michigan Technological University have now managed to grow boron nitride nanotubes on catalytic substrates such as magnesium oxide, iron and nickel. Michigan Technological University (2010, January 19). Harnessing the divas of the nanoworld. ScienceDaily. Retrieved January 20, 2010, from http://www.sciencedaily.com /releases/2010/01/100115112100.htm |
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