Archive for January 2012
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You are browsing the archives of 2012 January.
When Japanese officials acted out of desperation and used seawater to cool the cores at the Fukushima-Daiichi reactors last year, it looks like they made the right call. But, others that might be tempted to use seawater to cool fuel rods in the future might not be so lucky.
ACerS emeritus member and University of California, Davis professor, Alexandra Navrotsky, Notre Dame researcher Peter Burns and several of their colleagues have offered some cautionary food for thought. They say in a new paper in the Proceedings of the National Academy of Sciences that there does seem to be a mechanism for how nuclear fuel rods could be corroded by contact with sea water.
It should immediately be pointed out that the authors aren’t in any way suggesting that this type of corrosion happened during the Fukushima-Daiichi incident, and they say there is no evidence of uranium dispersion during that episode due to the seawater.
However, they say it appears there is a way for the fuel rod–seawater combination to form “uranium compounds that could potentially travel long distances, either in solution or as very small particles,” according to a UC Davis news release.
The release quotes Navrotsky, a distinguished professor of ceramic, earth and environmental materials chemistry, as saying, ”This is a phenomenon that has not been considered before. We don’t know how much this will increase the rate of corrosion, but it is something that will have to be considered in future.”
The uranium compounds in the fuel rods are thought to be generally insoluble in ordinary water. Nevertheless, she says it was previously known that if some of the water is converted to peroxide (radiation has the ability to do this conversion), the peroxide can then oxidize the uranium in the rods to uranium-VI, forming spherical uranium peroxide clusters that can dissolve in water.
The new wrinkle in this is that Navrotsky et al. discovered that if alkali metal ions are present — such as the sodium that is plentiful in seawater — the uranium peroxide clusters ”are stable enough to persist in solution or as small particles even when the oxidizing agent is removed.”
So, the worrisome scenario is one where seawater comes in contact with the rods and forms these clusters. The clusters dissolved in the seawater are then carried away. Because, according to Navrotsky, little is known about quickly these uranium peroxide clusters break down in the seawater, the clusters may hang around for months or years before being converted back into a common form of uranium that will precipitate out to the bottom of the ocean.
Late last year we told you about the reality-TV-inspired event ARPA-E is conducting — “America’s Next Top Energy Innovator” — to accelerate tech transfer out of national labs and into start-up companies to promote “innovative and promising solution[s] to the nation’s energy challenge.”
Readers — it is time to vote!
Fourteen of the 36 companies that signed option agreements are competing in the ANTEI challenge. The ARPA-E challenge website has nice summaries of each company that tells about the technology being presented, the national lab it came out of and a brief video profile. The website is also keeps a running tally of the votes.
Voting is easy: just click the “Like” button. The winner will be determined by combining the results of the voting with the evaluations of an expert panel from DOE. The agency also says the top startup companies will be invited to be featured at the premier annual gathering of clean energy investors and innovators around the country, the ARPA-E Energy Innovation Summit at the end of February.
The polls are open until Monday, Feb. 6 at 8:59 am.
While the first ANTEI is coming to a conclusion, DOE Secretary Steven Chu announced today that the agency is adding a second “season” to the program, and is launching the 2012-13 version of ANTEI Feb. 1.
To learn more about working with DOE labs and their technologies, check out the Energy Innovation Portal on the EERE website.
Do you recall where you were the weekend before the Super Bowl in 1987? Me neither. No matter, let’s play some Jeopardy, shall we?
Me: “Alex, I’ll take Super Bowl Weekends for $100.”
Alex: “The answer is YBCO.”
Me: “What is the abbreviated formula for the first high-temperature superconductor?”
Alex: “That is correct. The next answer is January 29, 1987.”
Me: “When were high-temperature superconductors discovered?”
Alex: “That’s right! Next answer: Jim Ashburn.”
Me: “Who was the graduate student that discovered high-temperature superconductors?”
Alex: “Right again! Next answer: M.K. Wu, University of Alabama in Hunstville.”
Me: “Who was Ashburn’s supervising professor and at what university did he work?”
Alex: “Right again! Next answer: Phil Simms.”
Me: “Ummmmm - Who was Wu’s postdoc?”
Alex: “No, so sorry. Phil Simms was the winning quarterback of Super Bowl XXI, leading the NY Giants to a 39-20 win over the Denver Broncos.”
If you were part of the ceramic science or physics world in 1987, you will recall it was a heady time. This new material rocked the world of solid state physics, and it was thought that an oxide material would be a disruptive technology for electricity transmission and other applications. In the 25 years since its discovery, we’ve seen that high Tc superconductor applications are not so easy to deploy, but progress is underway.
To mark the 25th anniversary of the historic discovery, the UAHuntsville unveiled a plaque in a recent ceremony.
A story on the university’s website recounts the events and thinking that led to Ashburn’s discovery. A physics graduate student at the time, Ashburn knew he was onto something that could be really big. With a good understanding of fundamental principles, especially the Periodic Table of the Elements, some coaching from a friend studying ceramic engineering, two textbooks and some fortunate bad luck, he formulated the first YBCO and demonstrated superconductivity at 93 K. (The story refers to one of the textbooks as “The Ceramic Bible,” which, presumably, is Introduction to Ceramics, by Kingery, Bowen and Uhlmann.)
The breakthrough that led Ashburn to the right formulation was the idea of “volume matching,” where atoms are substituted into a crystal lattice with compensations for their size. He says in the story, “I was learning that you have to put in things that were the right size with the right charge. It was basic crystal chemistry.” Knowing he wanted to try yttrium in the crystal, Ashburn turned to barium to get the required volume matching.
A little bit of fortunate bad luck followed. The usual furnace was unavailable for firing the compound, so Ashburn had to use the lab’s other furnace, which had a maximum temperature of 1,000°C, whereas the preferred furnace had a maximum firing temperature of 1,500°C. Later research would show that YBCO has a narrow processing sweet spot and melts at higher temperatures and solidifies into two separate compounds.
Ashburn has become an unofficial, self-appointed curator of the history of the discovery of high-temperature superconductors, however, he did not pursue a career in the field. He says, “My main interest is designing algorithms. I like to model things with math. That’s what I did then. It’s my job and it’s my happy place.”
This sounds like the type of breakthrough aerogel fans have yearning for.
A newly published paper in Angewandte Chemie reports on an Asian group’s success at using cellulose fibers as a scaffold/template for a resultant silica aerogel that delivers a product that has great mechanical strength and flexibility, while retaining a large surface area and semitransparency.
Aerogel has been something of a tease for many years. It has incredible insulating abilities, but the one enormous problem for silica aerogel is that it is frustratingly brittle and difficult to work into practical applications. Some developers have found limited success via hybridization techniques with support materials such as polyurethane, polystyrene or even nanofibrillar bacterial cellulose and microfibrillated cellulose gel.
However, with support from the Japan Society for the Promotion of Science’s Foreign Researcher Fund of Japan and the National Basic Research Program of China, researchers at Wuhan University, China, and University of Tokyo, took a different cellulose-based route. They already knew that they could exploit “cellulose II” crystallinity (dissolution and then regeneration/reassembly of fibrils) to form aerogels with good mechanical strength, light transmittance and high porosity — characteristics that they suspected would make it an effective substrate for silica aerogel.
In brief, the group, led by Lina Zhang, impregnated a sample of nanoporous cellulose gel (with its interconnected nanofibrillar network) with a silica precursor, tetraethyl orthosilicate. According to the paper, “The resulting composite gels were dried with supercritical CO2 to give cellulose–silica aerogels with low density, moderate light transmittance, a large surface area, high mechanical integrity and excellent heat insulation.”
They then went one step farther and used calcination to remove the cellulose matrix, leaving a silica-only aerogel. The key point here is that this silica aerogel’s structure is much different than pure silica aerogel. In the latter, primary silica nanoparticles form and then randomly coagulate resulting in an isotropic 3D network. “In contrast,” again quoting from the paper, the authors say, “the formation of silica nanoparticles in the cellulose gel seems to cause their deposition onto the cellulose fibrils. As a result, removal of cellulose by calcination results in the nanofibrillar silica network.”
The group compared a variety of aerogels, including silica-only and cellulose-only aerogels; cellulose-silica composites, with varying levels of silica; and cellulose-templated silica aerogel.
What they found at the macroscopic level is that the composite aerogels didn’t inherit the fragility of the silica, but instead seem to inherit the flexibility and strength of the cellulose network (see knotted sample of one of the composites, above).
While the tensile modulus and strength of the cellulose–silica aerogel were less than pure cellulose aerogel, “the compression modulus of the composite (7.9MPa) is more than two orders of magnitude higher than that of silica aerogel, and about 50 times higher than that of the aerogel prepared from bacterial cellulose.”
Because of the cellulose content, the composite aerogels break down when used above 300°C. However, below that temperature, the cellulose-silica aerogel retained strong heat insulating properties. Thermal conductivity of the prepared samples ranged from 0.025 W m-1 K-1 to 0.045 W m-1 K-1.
These numbers compare favorably with polystyrene foam (0.030 W m-1 K-1), however, the researchers note that the ability of the cellulose–silica aerogels to perform up to 300°C give it a leg up on insulation materials made of polymer that soften and breakdown at similar temperatures.
“Thus,” according to the authors,”the cellulose–silica composite is potentially useful as heat insulating material with high mechanical stability, together with processability to form sheets, fibers, or beads. … [They] retained the mechanical strength and flexibility, large surface area, semitransparency, and low thermal conductivity of the cellulose aerogels. The ease of preparation and wide tuneability of composition/properties with this method are expected to form the basis for the development of various advanced nano-porous materials.”
The paper, ”Cellulose-silica nanocomposite aerogels by in situ formation of silica in cellulose gel,” (doi:10.1002/ange.201105730) is written by Jie Cai, Shilin Liu, Jiao Feng, Satoshi Kimura, Masahisa Wada, Shigenori Kuga, and Lina Zhang.
Check ‘em out:
Researchers studied the bumps and grooves on the scorpions’ backs, scanning the creatures with a 3D laser device and developing a computer program that modeled the flow of sand-laden air over the scorpions. The team used the model in computer simulations to develop actual patterned surfaces to test which patterns perform best. At the same time, the erosion tests were conducted in the simple erosion wind tunnel for groove surface bionic samples at various impact conditions. Their results showed that a series of small grooves at a 30-degree angle to the flowing gas or liquid give steel surfaces the best protection from erosion.
At a hearing Jan. 26 before the U.S.-China Economic and Security Review Commission, Jeff Green testified that the US has lost critical supply chain capabilities and significant technological capital to China and that the lack of a deliberately thought-out U.S. policy for strategic and critical materials has resulted in economic and national security vulnerabilities. The hearing on “China’s Global Quest for Resources and Implications for the United States” examined Chinese efforts to acquire and manage various natural resources. Green president of the J.A. Green & Co., assists industrial clients in government relations, business development and strategic planning matters and is the former staff director to the House Armed Services Subcommittee on Readiness.
In semiconductor nanocrystals, the physical effects of deliberately included impurities, called dopants, may depend on the dopant position with the crystal. To date, there has not been an effective technique to determine the location of individual dopant atoms in nanocrystals. IRG-4 researchers demonstrated that a combination of scanning transmission electron microscopy and electron energy loss spectroscopy can be used to reveal the position of such “invisible” dopants.he physical effects of deliberately included impurities, called dopants, may depend on the dopant position with the crystal. To date, there has not been an effective technique to determine the location of individual dopant atoms in nanocrystals. IRG-4 researchers demonstrated that a combination of scanning transmission electron microscopy and electron energy loss spectroscopy can be used to reveal the position of such “invisible” dopants.
A discovery by a research team at North Dakota State University, Fargo, and the National Institute of Standards and Technology, shows that the flexibility and durability of carbon nanotube films and coatings are intimately linked to their electronic properties. The research could one day impact flexible electronic devices such as solar cells and wearable sensors.
University of California, Davis, researchers have proposed a radical new way of thinking about the chemical reactions between water and metal oxides, the most common minerals on Earth. Using computer simulations and comparing the resulting animations with lab experiments they found that the behavior of an atom on the surface of the cluster can be affected by an atom some distance away. Instead of moving through a sequence of transitional forms, as had been assumed, metal oxides interacting with water fall into a variety of “metastable states” - short-lived intermediates, the researchers found.
Researchers in London have developed a cheaper way of producing high-quality carbon nanotubes in larger quantities than existing methods. A team from the London Center for Nanotechnology has licensed the process, which separates nanotubes into usable quantities without damaging them, to German-based industrial gases company the Linde Group. LCN’s solution was to charge the nanotubes with electrons so that they naturally repel each other, by reacting them with an alkali metal such as sodium in a solution of ammonia. This solution of separated nanotubes can then be used for manufacturing things such as composites, or the nanotubes can be precipitated out of the solution.
“We found that collective exploration improved average success over independent exploration because good solutions could diffuse through the network. In contrast to prior work, however, we found that efficient networks outperformed inefficient networks, even in a problem space with qualitative properties thought to favor inefficient networks. We explain this result in terms of individual-level explore-exploit decisions, which we find were influenced by the network structure as well as by strategic considerations and the relative payoff between maxima. We conclude by discussing implications for real-world problem solving and possible extensions.”