Sunday, March 25, 2012

Spallation Neutron Source puts the squeeze on methane hydrate cages

Our robot would find this energy source in shale deposits, notably here on the east coast of the United States. However, the most abundant deposits of natural gas are under water on the continental shelves and in the permafrost in the . At both poles, methane mixes with water and freezes, remaining trapped as an ice-like compound, for millions of years.

Much further afield, methane, along with water and ammonia, are major constituents of Saturn's icy . Some scientists speculate that on Titan there is a methanological cycle similar to the hydrological cycle here on earth. Surface methane evaporates into the atmosphere, where it condenses, and rains down to the surface again. NASA's Cassini-Huygens Titan probe has been there and sampled it.

Methane holds promise as an abundant energy source for tomorrow, but it is Janus-faced: While often referred to as the cleanest fossil fuel producing far less greenhouse gas than either coal or oil, historically it has been seen as a major source of . That's because burning it produces carbon dioxide, a very .

Scientists are looking at how to sequester that CO2 byproduct, in an ice-like state. Such a strategy would create a carbon 'energy cycle' in which the methane resource is recovered, used, and then the greenhouse gas sequestered in a form very closely related to the naturally occuring initial materials.

"What we do know right now is that when methane is taken up and released into the environment, water plays a critical role", said Chris Tulk, lead instrument scientist on the Spallation Neutrons and Pressure Diffractometer (SNAP) at ORNL. "Whether it is in the oceans where hydrates form on continental shelves, in the icy permafrost conditions, or even as these materials decompose and release the methane into the atmosphere to contribute to the greenhouse effect, water is certainly involved in the process. This research should lead to better models of how hydrocarbons are taken up and released in the environment."

To develop such models, they need to understand at the molecular level the relationship between methane and water. Researchers have discovered that water forms cages, called clathrates, that contain "guest" molecules of methane and of many of the Noble gases.

At SNAP, a combination of a state-of-the-art instrument, clever experimental technique, and excellent samples have for the first time yielded detailed data on the structure of these methane hydrate clathrates.

Under pressure of more than 600,000 pounds per square inch, they found that the correct occupancy for the largest cages in this beautiful structure is three methane molecules. This finding can now be used to benchmark methane and water interactions at various energy and pressure, and researchers can better characterize the hydrophobic interaction.

"We've done a lot of work on these clathrate compounds," said Tulk, "but this is the first work in which all the work could be done on SNAP.

"When we compress the methane clathrate hydrate, it goes through a phase change at the molecular level to a new high pressure form known as structure H, for the hexagonal (six-sided) arrangement of water," Tulk explained.

"As the pressure is increased and the sample becomes smaller, the overall density increases, as expected. But the water molecules re-arrange themselves to form larger cages. These larger cages can now accommodate more than one methane molecule. The key question in this research was, how many methane molecules are in these larger cages, and how are they arranged?"

The SNAP instrument is perfectly suited to provide these types of structural details. "The repulsive interaction between methane and water, called the hydrophobic interaction, is poorly understood," Tulk explained. "And the interaction between methane and methane, particularly when the molecules are nearly in contact and strongly repelling, is not well understood at all."

Understanding how many methanes are able to fit in each cage and how the methane molecules are arranged within these cages, provides insight into these interactions.

The research also assists computational simulation. There are currently no good models to predict clathrate structure. "Determining how many methane molecules are in a cage will give the computational chemistry folks something to shoot for with their hydrate models," Tulk said.

Given these experimental results to come up with a new "potential" -- i.e., a new calculation of the interaction force that exists between methane molecules, and between methane and water - computational chemists can calculate the way interacts with water in the larger environment.

The ball is now in the hands of the theorists, who must come up with a model that correctly predicts this experimental observation. Then they can extend the model to better predict how and hydrocarbons interact in the larger environment.

"That is the driving motivation for my research, to get a fundamental physics-chemistry perspective on these things that have such a large impact on the earth."

Provided by Oak Ridge National Laboratory (news : web)

Researchers devise simple, inexpensive approach to making soft magnetic films for microwave applications

Developers tend to use of soft magnetic materials, as opposed to their bulk form, in , such as cell phones and laptops, as well as , such as stealth aircrafts. However, the conventional approach to making soft magnetic films requires a high vacuum environment, which is expensive and time-consuming. Moreover, the usual fabrication system is not suitable for the preparation of large sheet films, thereby limiting its application in manufacturing the soft magnetic materials for absorption.

Bao-Yu Zong at the A*STAR Data Storage Institute and co-workers have now demonstrated the of fabricating soft magnetic thin films through electrodeposition, a plating technique that is scalable and can be performed at . The approach is not only simpler and cheaper to operate, but also versatile enough for making a wide range of soft magnetic materials for microwave applications.

The researchers chose to work with iron–cobalt–nickel alloy, a soft magnetic material with low permeability, high coercivity and other less-than-ideal properties. They added small amounts of organic compounds, including dimethylamine borane and sodium dodecyl sulfate, to the plating solution prior to deposition. The resulting thin films had much higher permeability and lower coercivity, which make them more desirable for microwave applications. The researchers suggest that the additives might have prevented iron from oxidizing during electrodeposition, thereby improving the quality of thin films obtained.

Zong and his team also explored the effect of adding inorganic compounds, such as aluminum potassium sulfate, to the plating solution. They detected an increased resistivity in the thin films — a result that is likely to be a consequence of the change in morphology of the material; that is, the shape of the nanoparticles changed from common granular to columnar (see image), as revealed by atomic force microscopy. The iron–cobalt–nickel thin films also exhibit strong microwave absorption in comparison to ordinary magnetic films. These unique properties are perfect for high-frequency microwave applications, including magnetic data storage, portable wireless and biotechnology devices.

The researchers have high hopes that their approach is applicable to the fabrication of a wide range of soft . "Our technique is cost-effective and scalable. We can create soft magnetic thin films on different size and type of substrates," says Zong. "In a subsequent step, we hope to transfer this methodology to related industrial companies."

More information: Research article in Journal of Materials Chemistry

Provided by Agency for Science, Technology and Research (A*STAR)

Atomtronics: Exotic new matter expected in ultracold atoms

 Just as NASA engineers test new rocket designs in computer studies before committing themselves to full prototypes, so physicists will often model matter under various circumstances to see whether something new appears. This is especially true of atomtronics, a relatively new science devoted to creating artificial tailored materials consisting of neutral atoms held in an array with laser beams, or atoms moving along a desired track under electric or magnetic influence. A new study shows how a simple "joystick" consisting of an adjustable magnetic field can create several new phases of atomtronic matter, several of them never seen before.

The results appear in an article in the journal Physical Review Letters.

One of the attractions of atomtronics is that the properties of electrons moving through solid state materials can often be mimicked using atoms operating under highly controlled circumstances. Why not just study electrons directly? Because in atomtronics the forces among the atoms can be controlled; you can't do that as well with electrons in solids. That is, atoms can be induced to interact via a force that can be dialed up or down, exploiting the large magnetic dipole moment of some atoms, such as dysprosium-161.

Charles Clark, co-director of the Joint Quantum Institute, and his co-authors at George Mason University, the University of Hamburg, Germany and the University of California, Riverside have studied what happens when ultracold highly magnetic atoms are held in an optical lattice and subjected to an external magnetic field, which can be steered in various directions. This field tugs on the atom-sized magnets and, along with the direction of the field itself, leave the atoms standing upright or pulled over on their sides at various inclinations described in the figure by the angles phi and theta. In this way, the researcher can tune the interaction-force on demand.

The atoms don't just stay put as they are being jerked around. They disport themselves into patterns. Each pattern can be considered a different phase of atomtronic matter. And just as water molecules can exist in phases -- ice, water, steam -- depending on how a joystick that controls temperature and pressure is deployed, so the magnetic atoms sort themselves into numerous phases depending on the magnetic joystick controlling the strength and orientation of the applied magnetic field.

The atom patterns can be mapped on a phase diagram where the x and y axis describe various values of the joystick orientation. One phase is labeled cb-CDW (the turquoise part), meaning that the atoms in the optical lattice come into a checkerboard pattern (cb) as electrons do in a solid orient themselves via a so-called "charge density wave" (CDW), in analogy with a collective state of electrons in metals that is being explored as an alternative vehicle for data encoding . In the small drawing to the left the red dots represent a greater chance that an atom will be in that spot while blue dots represent a lesser chance that an atom will be there.

Another phase (the orange part) consists of atoms preferentially patterned in stripes (st). A third phase is labeled BCS. Here, analogous to the pairs of electrons in superconductors (as described by the Bardeen-Cooper-Schrieffer theory), atoms weakly pair up via long-range forces across several atomic spacings.

Two other phases seen in the study were totally unexpected. These consist of pairs -- an atom yoked with a neighboring vacancy -- distributing themselves in a checkerboard or striped pattern. In other words, if such a pair finds itself at one place in the lattice, another pair might be more or less likely to be in a neighboring double slot. The authors call this new phase a "bond-order solid" (BOS) since in a sense the bonds between the atom-vacancy couplets seem to be forming the patterns rather than the atoms themselves. Bond-order phases have been conjectured previously in idealized one-dimensional models, but this is the first report of their presence in a realizable physical system.

These phases are associated with the presence of strong long-range dipole interactions between ultracold atoms, a feature that does not exist for electrons in solids or in the first generation of ultracold atomic and molecular systems. Recent experimental developments show prospects for implementing ultracold dipole fermion systems in the laboratory.

Satyan Bhongale (George Mason University), the lead author of this work, says, "As physicists we like to classify states of matter. Low-temperature electronic systems are very complicated and hard to control or observe in detail. Atomtronic systems are subject to exquisite control and characterization, providing direct access and a clear insight into novel phases of matter.

"Just by luck," said co-author and JQI co-director Charles Clark, "the first report of experimental production of ultracold magnetic fermion atoms was issued by a group at Stanford University this week, so we are getting close to practical realization of these systems."

Story Source:

The above story is reprinted from materials provided by Joint Quantum Institute.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

S. G. Bhongale, L. Mathey, Shan-Wen Tsai, Charles W. Clark, Erhai Zhao. Bond order solid of two-dimensional dipolar fermions. Physical Review Letters, 2012; (in press) [link]

New catalyst for safe, reversible hydrogen storage

Hydrogen is seen as an attractive fuel because it can efficiently be converted to energy without producing or . However, the storage and transportation of remain more problematic than for liquid fuels. The new work builds on earlier efforts to combine hydrogen with carbon dioxide to produce a liquid solution that can be transported using the same kind of infrastructure used to transport and oil.

“This is not the first capable of carrying out this reaction, but it is the first to work at room temperature, in an aqueous (water) solution, under atmospheric pressure — and that is capable of running the reaction in forward or reverse directions depending on the acidity of the solution,” said Brookhaven chemist Etsuko Fujita, who oversaw Brookhaven’s contributions to this research.

“When the release of hydrogen is desired for use in fuel cells or other applications, one can simply flip the ‘pH switch’ on the catalyst to run the reaction in reverse,” said Brookhaven chemist James Muckerman, a co-author on the study. He noted that the liquid formic acid might also be used directly in a formic-acid fuel cell.

Collaborator Yuichiro Himeda of the National Institute of Advanced Industrial Science and Technology (AIST) of Japan had been making substantial progress toward the goal of developing this type of catalyst for a number of years. He used iridium metal complexes containing aromatic diimine ligands (groups of atoms bound to the metal) with pendent, peripheral hydroxyl (OH) groups that can serve as acidic sites that release protons to become pendent bases.

Himeda recently entered into collaboration — via the U.S.-Japan Collaboration on Clean Energy Technology program — with Fujita, Muckerman, and Jonathan Hull (a Goldhaber Fellow working on Fujita’s team). The Brookhaven group carried out coordinated experimental and theoretical studies to understand the sequence of chemical steps by which these catalysts converted H2 and CO2 into formic acid. Their goal was to design new catalysts with improved performance.

The Brookhaven team’s key idea came from Nature: “We were inspired by the way hydrogen bonds and bases relay protons in the active sites of some enzymes,” Hull said.

“Good catalysts efficiently move protons and electrons around, taking them from some molecules and placing them onto others to produce the desired product,” he explained. “Nature has many ways of doing this. Under the right conditions, the hydroxyl groups on the diimine ligand of the catalyst help hydrogen react with carbon dioxide, which is difficult to do. We thought we could improve the reactivity by placing the pendent bases near the metal centers, rather than in peripheral positions.”

Once the Brookhaven team understood how Himeda’s catalysts worked, Hull realized that a novel ligand that had been synthesized by collaborators Brian Hashiguchi and Roy Periana of The Scripps Research Institute for an entirely different purpose would possibly be ideal for accomplishing this goal. The Brookhaven group designed a new iridium metal catalyst incorporating this new ligand.

Collaborator David Szalda of Baruch College (City University of New York) determined the atomic level crystal structure of the new catalyst to “see” how the arrangement of its atoms might explain its function.

Tests of the new catalyst revealed superior catalytic performance for storing and releasing H2 under very mild reaction conditions. For the reaction combining CO2 with H2, the scientists observed high turnovers at room temperature and ambient pressure; for the catalytic decomposition of formic acid to release hydrogen, the catalytic rate was faster than any previous report.

“We were able to convert a 1:1 mixture of H2 and CO2 to formate (the deprotonated form of formic acid) at room temperature, successfully regenerate H2, and then repeat the cycle. It’s a design principle we are very fortunate to have found,” said Hull.

The regenerated high-pressure gas mixture (hydrogen and ) is quite pure; importantly, no carbon monoxide (CO) — an impurity that can ‘poison’ fuel cells and thus reduce their lifetime — was detected. Therefore, this method of storing and regenerating hydrogen might have a use in hydrogen fuel cells.

Further efforts to optimize the hydrogen process are ongoing using several catalysts with the same design principle.

“This is a wonderful example of how fundamental research can lead to the understanding and control of factors that contribute to the solution of technologically important problems,” Muckerman concluded.

More information: “Reversible hydrogen storage using CO2 and a proton-switchable iridium catalyst in aqueous media under mild temperatures and pressures”, … 8/NCHEM.1295

Provided by Brookhaven National Laboratory (news : web)

New study of pine nuts leaves mystery of 'pine mouth' unsolved

Ali Reza Fardin-Kia, Sara M. Handy and Jeanne I. Rader note that more than 20,000 tons of pine nuts are produced each year worldwide. "Pine mouth," first reported in Belgium in 2000, is a bitter metallic taste that develops within one to two days of eating pine nuts and can last from one to two weeks. In 2009, the French Food Safety Administration reported a possible link between "pine mouth" and consumption of nuts of Pinus armandii, a pine species whose nuts are not traditionally eaten by humans. Researchers have identified certain fatty acids whose levels vary among pine species, making them a potentially useful tool for telling different species apart. To determine the source of pine nuts sold in the U.S., the first such effort, they measured the ratio of these compounds to the overall amount of in the nuts.

Using fatty acid composition and a fatty acid diagnostic index (DI) along with DNA analysis, they found that most pine nuts sold in the U.S. are mixtures of nuts from different pine species, including Pinus armandii. They report that combining the fatty acid DI and DNA analysis is a useful way to determine which samples of pine nuts are mixtures of nuts from several species, but that this information itself may not definitively predict which pine nuts may cause "pine mouth." Its cause remains a mystery.

More information: Characterization of Pine Nuts in the U.S. Market, Including Those Associated with “Pine Mouth”, by GC-FID, J. Agric. Food Chem., 2012, 60 (10), pp 2701–2711. DOI: 10.1021/jf205188m

Taste disturbances following consumption of pine nuts, referred to as “pine mouth”, have been reported by consumers in the United States and Europe. Nuts of Pinus armandii have been associated with pine mouth, and a diagnostic index (DI) measuring the content of ?5-unsaturated fatty acids relative to that of their fatty acid precursors has been proposed for identifying nuts from this species. A 100 m SLB-IL 111 GC column was used to improve fatty acid separations, and 45 pine nut samples were analyzed, including pine mouth-associated samples. This study examined the use of a DI for the identification of mixtures of pine nut species and showed the limitation of morphological characteristics for species identification. DI values for many commercial samples did not match those of known reference species, indicating that the majority of pine nuts collected in the U.S. market, including those associated with pine mouth, are mixtures of nuts from different Pinus species.

Provided by American Chemical Society (news : web)