Study reveals how oxygen is like kryptonite to titanium

UC Berkeley scientists have found the mechanism by which titanium, prized for its high strength-to-weight ratio and natural resistance to corrosion, becomes brittle with just a few extra atoms of oxygen.

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Shown is a cross section of grade 3 titanium (containing 0.3 percent oxygen) that has been put under stress and deformed. The defects in the crystal are evident. Oxygen impurities forced the defects to spread onto different planes of the material. (Image by Qian Yu)

The discovery, described in the Feb. 6 issue of the journal Science, has the potential to open the door to more practical, cost-effective uses of titanium in a broader range of applications. The popular silver-gray metal can already be found in high-end bicycles, laptops and human implants, among other products. But high-grade titanium with low levels of oxygen is hard to come by, and the expense of purifying the metal has prevented its wider use in applications for the construction, automotive and aerospace industries.

“If you could process titanium in a way that retained its optimal properties but at a cost comparable to aluminum, you would find uses in cars, trucks, aircraft and ships,” said study senior author Andrew Minor, an associate professor of materials science and engineering and faculty scientist at Lawrence Berkeley National Laboratory. “The high corrosion resistance and excellent specific properties of titanium are very attractive, and reducing the costs to the level of aluminum would make using the material a no-brainer.”

Minor led a research team from the department of materials science and engineering that focused on solving the long-standing mystery in metallurgy of how oxygen causes such a profound change in the characteristics of metals.

“Oxygen is like poison to titanium,” said Minor. “With more oxygen, the material gets harder and more susceptible to cracks, qualities that are not desirable for structural materials.”

A good structural material will have the right balance of ductility — the ability to bend in response to stress — and strength. Minor noted that glass is strong and hard, but not ductile, which is why that material is not used to build vehicles or bridges.

The light blue lines in this schematic illustrate a moving defect, or dislocation, in titanium. The interaction between the dislocation and an oxygen impurity (red atom) leads to the creation of additional dislocations, shown as dark blue lines. (Image by Liang Qi)

Minor added that while many metals have the potential to become brittle with oxygen, titanium is particularly sensitive to even tiny bits of the element. Grade 3 titanium is only 0.3 percent oxygen, yet it is one-third as tough as grade 1 titanium, which is 0.1 percent oxygen. Understanding how oxygen hardens titanium offers a target for research into control of the process, the study authors said.

The researchers subjected various grades of titanium samples to nanocompression tests and examined the resulting impact using advanced transmission electron microscopy techniques and quantum mechanical predictions of defect structures. They found that the interactions between oxygen and the crystalline defects, known as dislocations, that are characteristic of titanium were key to how the material hardened.

The researchers found that oxygen atoms acted like bumps in the road for the corkscrew-shaped dislocations found in titanium. “The mechanical shuffling that occurs as dislocations pop up and over those atomic bumps creates a domino effect of more dislocations,” said study co-author Daryl Chrzan, a professor of materials science and engineering who led the theoretical effort in the project. With increased oxygen, the titanium becomes more difficult to bend and therefore more susceptible to cracking, the researchers found.

A similar effect is seen by bending a paper clip until it breaks. The more the metal bends, the greater the number of dislocations. Dislocations interfere with the motion of other defects, making the paper clip more difficult to bend. Eventually, the number of dislocations is so high that the paper clip can no longer bend, and instead it breaks.

“Now that we know what it is about the oxygen found in inexpensive titanium that causes the material to harden, we can work on figuring out a way to process it to move oxygen atoms to a place where they don’t cause problems,” said study co-author Mark Asta, a professor of materials science and engineering.

Minor noted that this is already done in the semiconductor industry since oxygen and other impurities are also damaging to silicon-based microprocessors.

Other co-authors of the study included researchers from the Berkeley Lab, Japan’s Nuclear Science and Engineering Directorate and Rolls Royce.

The Office of Naval Research helped support this work. Experiments were performed at the National Center for Electron Microscopy in the Molecular Foundry at Berkeley Lab, which is supported by the U.S. Department of Energy.

Source: UC Berekely

Graphene Is Strongest Material in the World Even with Defects

Graphene remains the strongest material ever measured and, as Professor Hone once put it, so strong that "it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap.” —Illustration by Andrew Shea for Columbia Engineering

In a new study, published in Science May 31, 2013, Columbia Engineering researchers demonstrate that graphene, even if stitched together from many small crystalline grains, is almost as strong as graphene in its perfect crystalline form. This work resolves a contradiction between theoretical simulations, which predicted that grain boundaries can be strong, and earlier experiments, which indicated that they were much weaker than the perfect lattice.

Graphene consists of a single atomic layer of carbon, arranged in a honeycomb lattice. “Our first Science paper, in 2008, studied the strength graphene can achieve if it has no defects—its intrinsic strength,” says James Hone, professor of mechanical engineering, who led the study with Jeffrey Kysar, professor of mechanical engineering. “But defect-free, pristine graphene exists only in very small areas. Large-area sheets required for applications must contain many small grains connected at grain boundaries, and it was unclear how strong those grain boundaries were. This, our second Science paper, reports on the strength of large-area graphene films grown using chemical vapor deposition (CVD), and we’re excited to say that graphene is back and stronger than ever.”

The study verifies that commonly used methods for post-processing CVD-grown graphene weaken grain boundaries, resulting in the extremely low strength seen in previous studies. The Columbia Engineering team developed a new process that prevents any damage of graphene during transfer. “We substituted a different etchant and were able to create test samples without harming the graphene,” notes the paper’s lead author, Gwan-Hyoung Lee, a postdoctoral fellow in the Hone lab. “Our findings clearly correct the mistaken consensus that grain boundaries of graphene are weak. This is great news because graphene offers such a plethora of opportunities both for fundamental scientific research and industrial applications.”

                                              Profs. James Hone and Jeffrey Kysar
In its perfect crystalline form, graphene (a one-atom-thick carbon layer) is the strongest material ever measured, as the Columbia Engineering team reported in Science in 2008—so strong that, as Hone observed, “it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap.” For the first study, the team obtained small, structurally perfect flakes of graphene by mechanical exfoliation, or mechanical peeling, from a crystal of graphite. But exfoliation is a time-consuming process that will never be practical for any of the many potential applications of graphene that require industrial mass production.

Currently, scientists can grow sheets of graphene as large as a television screen by using chemical vapor deposition (CVD), in which single layers of graphene are grown on copper substrates in a high-temperature furnace. One of the first applications of graphene may be as a conducting layer in flexible displays.

“But CVD graphene is ‘stitched’ together from many small crystalline grains—like a quilt—at grain boundaries that contain defects in the atomic structure,” Kysar explains. “These grain boundaries can severely limit the strength of large-area graphene if they break much more easily than the perfect crystal lattice, and so there has been intense interest in understanding how strong they can be.”

The Columbia Engineering team wanted to discover what was making CVD graphene so weak. In studying the processing techniques used to create their samples for testing, they found that the chemical most commonly used to remove the copper substrate also causes damage to the graphene, severely degrading its strength.

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Click on the Video to watch Prof. James Hone take us on a tour of his synthesis lab in the Northwest Corner Building, where he grows graphene and nanotubes.

Their experiments demonstrated that CVD graphene with large grains is exactly as strong as exfoliated graphene, showing that its crystal lattice is just as perfect. And, more surprisingly, their experiments also showed that CVD graphene with small grains, even when tested right at a grain boundary, is about 90% as strong as the ideal crystal.

“This is an exciting result for the future of graphene, because it provides experimental evidence that the exceptional strength it possesses at the atomic scale can persist all the way up to samples inches or more in size,” says Hone. “This strength will be invaluable as scientists continue to develop new flexible electronics and ultrastrong composite materials.”

Strong, large-area graphene can be used for a wide variety of applications such as flexible electronics and strengthening components—potentially, a television screen that rolls up like a poster or ultrastrong composites that could replace carbon fiber. Or, the researchers speculate, a science fiction idea of a space elevator that could connect an orbiting satellite to Earth by a long cord that might consist of sheets of CVD graphene, since graphene (and its cousin material, carbon nanotubes) is the only material with the high strength-to-weight ratio required for this kind of hypothetical application.

The team is also excited about studying 2D materials like graphene. “Very little is known about the effects of grain boundaries in 2D materials,” Kysar adds. “Our work shows that grain boundaries in 2D materials can be much more sensitive to processing than in 3D materials. This is due to all the atoms in graphene being surface atoms, so surface damage that would normally not degrade the strength of 3D materials can completely destroy the strength of 2D materials. However with appropriate processing that avoids surface damage, grain boundaries in 2D materials, especially graphene, can be nearly as strong as the perfect, defect-free structure.”

The study was supported by grants from the Air Force Office of Scientific Research and the National Science Foundation.

—by Holly Evarts

Source: Columbia University

Simple textiles can be used with catalysts to enable complex chemical reactions

To attach the "chemical tools" to the nylon fibers the chemist simply irradiate the soaked textile with UV light.

In future, it will be much easier to produce some active pharmaceutical substances and chemical compounds than was the case to date. An international team working with chemists from the Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr have immobilised various catalysts on nylon in a very simple way. Catalysts mediate between the reagents in a chemical reaction and control the process leading to the desired end product. When textile material is used as a support for the chemical auxiliaries, the reaction can proceed on a large surface thereby increasing its efficiency.

One of the catalysts that the researchers used in this way plays an important role in the synthesis of a pharmaceutical agent which could only be used previously in dissolved form, making the production process very complicated and expensive. Immobilising this catalyst on fabric simplifies production considerably. This process may be expected to yield similar advantages for other chemical processes.

Functional textiles are usually understood as the textiles used to make windproof jackets, breathable footwear and particularly effective thermal underwear. However, the term could soon refer to something else -- textiles which are "functionalised" with the help of organic catalysts. Working in collaboration with scientists from the Deutsches 

Textilforschungszentrum in Krefeld and Sungkyunkwan University in Suwon, Korea, researchers at the Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr have developed a process for immobilising different organic catalysts on textiles with the help of ultraviolet light. The fabric thereby acts as a support for the substances on which a chemical reaction occurs.

Up to now, science has focused more on the macroscopic functionality of textiles, for example clothing, explains Dr. Ji-Woong Lee, who recently completed his doctorate at the Max-Planck-Institut für Kohlenforschung under the supervision of Professor Benjamin List, head of the Institute's Homogenous Catalysis Group. "As opposed to this, our method can give simple textiles microscopic functionalities," explains the Korean scientist. Together with his colleagues, Dr. Lee armed pieces of nylon with catalysts. The latter can be imagined as chemical tools which fulfil various tasks during chemical reactions.

Excellent yields, little wear and tear

For their tests, the Mühlheim-based researchers used three organic catalysts: a base (dimethylaminopyridine, DMAP), a sulfonic acid and a catalyst which functions as both an acid and a base. The latter is used in the pharmaceuticals industry to steer a reaction to one of two products, which are chemically completely identical. The two forms have mirror-image structures, like a left and right hand, but only one variant has the desired medical effect. Up to now, the catalyst that generates this variant could only be used in dissolved form and then had to be separated again. The complicated separation process could be avoided using a catalyst immobilised on fabric.

To attach the catalysts to the nylon fibres, the chemists irradiated the textile to which a catalyst was applied with UV light for five minutes -- but no longer, as this would impede the activity of the catalyst and its immobilisation on the nylon. A comparable process did not exist up to now.

The catalysts, which were practically interwoven with the fabric, displayed all of the characteristics that the chemists expect from such a system: the result of the chemical reactions which the scientists undertook with the catalyst-loaded nylon strips is impressive. 

All three catalysts converted around 90 percent of the source materials to the desired products. And the catalyst which is used in the pharmaceutical industry and only generates one out of two mirror-image molecules, achieved a success rate of over 95 percent without showing any major signs of wear and tear. Ji-Woong Lee carried out several hundred test-runs and observed that the catalysts relinquished little of their functionality.

A large surface makes chemical reactions more efficient

Compared with other ways of immobilising catalysts, "organotextile catalysis" has several advantages: in particular, it provides the reagents with a larger surface than other supports, for example plastic spheres or foils -- the larger the surface, the more efficiently a reaction proceeds. Moreover, nylon is flexible and very inexpensive. Dry textiles loaded with catalysts are easy to transport, which means that it is simpler to meet the requirements for some chemical processes where it is practically impossible to set up sophisticated chemical systems. For example, organotextile catalysis could help in the treatment of water in locations where people are cut off from the water supply.

"Our method enables the low-cost production of long-term functionalised textiles without causing any pollution," says Ji-Woong Lee. He is entirely convinced that the process can be applied in several scientific areas -- and industrial processes. "In addition to chemistry, these could include biology, the materials science and pharmaceutics."

Source: Max-Planck-Institut für Kohlenforschung

Glove shows its true colors: Identifies poisons on contact

The sensor glove turns blue in the presence of hazardous substances. Credit: © Fraunhofer EMFT

Security takes top priority in laboratories and in production. In the future, employees exposed to risks will only have to put on a glove in order to receive a toxic substance warning: This textile identifi es poisonous substances, and points them out immediately.

Employees in chemical production, the semiconductor industry or in laboratories are frequently exposed to harmful substances. The problem: Many of these aggressive substances are imperceptible to human senses, which makes handling them so risky. That's why there is a broad range of solutions that employers can use to protect their staff from hazardous substances -- from highly sensitive measuring equipment to heat imaging cameras. Soon, this spectrum will be enhanced by one more clever solution that is easy to handle, and that dispenses with a power supply. Researchers at the Fraunhofer Research Institution for Modular Solid State Technologies EMFT in Regensburg have engineered a glove that recognizes if toxic substances are present in the surrounding air.

The protective glove is equipped with custom-made sensor materials and indicates the presence of toxic substances by changing colors. In this regard, the scientists adapted the materials to the corresponding analytes, and thus, the application. The color change -- from colorless (no toxic substance) to blue (toxic substance detected), for example -- warns the employee immediately. "By synthesizing the adapted color sensor materials, we can detect gases like carbon monoxide, for example, or hydrogen sulfide. Still, this protective gear represents only one potential area of application. Sensor materials could also be deployed for the quick detection of leaks in gas lines," explains Dr. Sabine Trupp, head of the Fraunhofer EMFT Sensor Materials group. The researcher and her team will exhibit this occupational safety article of clothing at Fraunhofer's joint exhibition booth (Hall 12, Booth 537) at the Sensor + Test trade show in Nuremberg from May 14 to 16.

Tailor-made indicator dyes

The warning signal is triggered by an indicator dye integrated into the glove that reacts to the presence of analytes, in this case, the toxic substances. The experts at EMFT used a variety of techniques in order to furnish textiles with sensor-activated dyes. The sensor-activated dyes are applied to the clothing with the customary dye and print process, for example, by affixing them in an immersion bath. Previously, the researchers used targeted chemical modification to adapt the color molecules to the fiber properties of the respective textile. Alternatively, the textiles can also be coated with sensor particles that are furnished with sensor dyes. For this purpose, the scientists integrated the dye molecules either into commercial pigments or they built them up on an entirely synthetic basis. The pigments are then manufactured according to the customary textile finishing process, for instance, the sensor particles are also suitable for silkscreening. "Which version we opt for depends on the requirements of the planned application," says Trupp.

The challenge lies foremost in the tailored development of sensor dyes. "The dye molecule must detect a specific analyte in a targeted manner -- only then will a chemical reaction occur. Moreover, the dye must adhere securely; it cannot disappear due to washing. We aim for the customer's preferences in the color selection as well. All of these aspects must be kept in mind when developing the molecule and pigment properties," explains Trupp.

The expert already has new ideas about how the solution could be developed further. For example, a miniaturized sensor module, integrated into textiles, could record toxic substances, store the measurement data and even transmit them to a main unit. This way, you could document how frequently an individual within a hazardous environment was exposed to poisonous concentrations over a longer period of time.

The researchers also envision other potential applications in the foodstuffs industry: In the future, color indicator systems integrated into foils or bottle closures are intended to make the quality status of the packaged foods visible. Because the sell-by date does not represent a guarantee of any kind. Foodstuffs may often spoil prematurely -- unnoticed by the consumer -- due to a packaging error, or in the warehousing, or due to disruptions in the refrigeration chain. Oil-based and fat-containing products are specifically prone to this, as are meats, fish and ready meals.

Source: Fraunhofer-Gesellschaft

Ancient, hydrogen-rich waters deep underground around the world: Waters could support isolated life

Energy-rich waters discharge kilometers below the surface in a South African mine.
Credit: G. Borgonie, 2014

A team of scientists, led by the University of Toronto's Barbara Sherwood Lollar, has mapped the location of hydrogen-rich waters found trapped kilometres beneath Earth's surface in rock fractures in Canada, South Africa and Scandinavia.

Common in Precambrian Shield rocks -- the oldest rocks on Earth -- the ancient waters have a chemistry similar to that found near deep sea vents, suggesting these waters can support microbes living in isolation from the surface.

The study, to be published in Nature on December 18, includes data from 19 different mine sites that were explored by Sherwood Lollar, a geoscientist at U of T's Department of Earth Sciences, U of T senior research associate Georges Lacrampe-Couloume, and colleagues at Oxford and Princeton universities.

The scientists also explain how two chemical reactions combine to produce substantial quantities of hydrogen, doubling estimates of global production from these processes which had previously been based only on hydrogen coming out of the ocean floor.

"This represents a quantum change in our understanding of the total volume of Earth's crust that may be habitable," said Sherwood Lollar.

"Until now, none of the estimates of global hydrogen production sustaining deep microbial populations had included a contribution from the ancient continents. Since Precambrian rocks make up more than 70 per cent of the surface of Earth's crust, Sherwood Lollar likens these terrains to a "sleeping giant," a huge area that has now been discovered to be a source of possible energy for life," she said.

One process, known as radiolytic decomposition of water, involves water undergoing a breakdown into hydrogen when exposed to radiation. The other is a chemical reaction called serpentization, a mineral alteration reaction that is common in such ancient rocks.
This study has important implications for the search for deep microbial life. Quantifying the global hydrogen budget is key to understanding the amount of Earth's biomass that is in the subsurface, as many deep ecosystems contain chemolithotrophic -- so-called "rock-eating" -- organisms that consume hydrogen. In the deep gold mines of South Africa, and under the sea, at hydrothermal vents where breaks in the fissure of Earth's surface that release geothermally heated waters -- hydrogen-rich fluids host complex microbial communities that are nurtured by the chemicals dissolved in the fluids. This study identifies a global network of sites with hydrogen-rich waters that will be targeted for exploration for deep life over the coming years.

Further, because Mars -- like the Precambrian crust -- consists of billions-of-year-old rocks with hydrogen-producing potential, this finding has ramifications for astrobiology. "If the ancient rocks of Earth are producing this much hydrogen, it may be that similar processes are taking place on Mars," said Sherwood Lollar.

Other key members of the research team are Chris Ballentine of Oxford University, Tulis Onstott at Princeton University and Georges Lacrampe-Couloume of the University of Toronto. The research was funded by the Canada Research Chairs program, the Natural Sciences & Engineering Research Council, the Sloan Foundation Deep Carbon Observatory, the Canadian Space Agency and the National Science Foundation.

Source: University of Toronto