Archive for May 2011
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You are browsing the archives of 2011 May.
Materials scientists have long recognized that grain boundaries and interfaces can limit a material’s bulk properties, especially at high temperatures. Significant research effort has gone into understanding their nature with an eye to engineering them to minimize deleterious affects, and with the advent of tools capable of characterizing materials in the nanoscale range, direct observation of interface phenomena has become possible.
Technion-Israel Institute of Technology researchers, Mor Baram and ACerS members Dominique Chatain (CNRS, France) and Wayne Kaplan, shed some new light on interfaces with a study of nanoscale intergranular films published last month in Science (doi 10.1126/science.1201596). Kaplan is dean of the Department of Materials Engineering at the Technion.
Intergranular films about 1 nm thick are found at grain boundaries, phase boundaries, and on free surfaces, however, it has not been known whether the IGFs are an equilibrium interface effect, a wetting film (a bulk phase), or a transient effect related to impurities, mass transport, etc. If the IGFs (also called complexions) are in a state of equilibrium, then it should be possible to map them onto bulk phase diagrams as tie-lines describing the 2-D state of grain boundaries and interfaces, opening the door to engineering their properties.
In the study, basal plane sapphire substrates were partially coated with anorthite glass droplets and then coated with gold films. Anorthite (CaO-2SiO2-Al2O3) was used because its constituent elements are often found in alumina grain boundary IGFs. On annealing, the gold films broke into particles dispersed across the substrate. By looking at the interfaces in an aberration-corrected, high resolution TEM, the authors were able to show that the IGF was not a bulk wetting film. Analyzing the dihedral and contact angles showed that the interface energy at the gold-sapphire interface was reduced when an IGF was present.
Another ACerS member, Martin Harmer, offered some perspectives on the Technion group’s work (”The Phase Behavior of Interfaces,” doi 10.1126/science.1204204). Harmer, director of Lehigh University’s Center for Advanced Materials and Nanotechnology, notes that IGFs are thermodynamically stabilized by the interface between grains, although they are not bulk phases. From the perspective of engineering the grain boundary, it is interesting that IGFs with different structures can coexist in equilibrium within the same material because, as Harmer observes, if the properties of the different IGF structures vary much, the effect on material behavior could be significant.
As Harmer explains, a better understanding of what’s happening at interfaces could explain phenomena like abnormal grain growth or embrittlement brought on by diffusion of impurities into the grain boundaries. Even better would be to add constituents to engineer the composition of grain boundaries and IGFs for improved high temperature properties, thus extending component service life.
It seems to me that an improved understanding of what is happening at interfaces will grow in importance as devices and systems shrink in size. I’m thinking about things like micro-electrical-mechanical systems or even nano-electrical-mechanical systems, ever-smaller electronic devices, implanted medical devices, etc., where any loss of integrity to the grain boundaries or material interfaces can become catastrophic quickly. On a larger scale (component-wise, that is), engineering the interfaces could yield better coatings, welds, composites, etc.
Aside from the interesting technical implications of Baram, et al’s work, this paper represents a good example of the practical importance of well-executed basic science research. But, that would be preaching to the choir, wouldn’t it?
The next few days should be fun for materials scientists and engineers. Tomorrow (May 25) begins the start of a three-day meeting where participants in the DOE’s 46 Energy Frontier Research Centers will begin the initial reporting-out (at least to the public) about what kind progress they have been able to make. There is a PDF brochure about all of the projects here.
These shouldn’t be expected to be anything close to final reports; most of the EFRCs are five-year projects begun in 2009, so they are only about one-third of the way through their work. It’s probably better to think about what will be reported as a combination of status report and dog-and-pony-show. I don’t intend this latter description to be taken as a negative. Political realities being what they are, the DOE and the Obama administration (not to mention the research teams, themselves) need to show how the monies for these projects are being spent, and what some of the eventual payoffs might be.
Unlike ARPA-E, the EFRCs are less applications- and deployment-oriented, and more aimed at basic science and discovery. The idea was to form “dream teams” of researchers who focus on fundamental breakthroughs needed for a new generation of “production, conversion, storage, transmission and waste mitigation.”
Put another way, without advances in basic science, applied technology and engineering would soon be tapped out. At the beginning, five major challenges were described:
One thing EFRCs have in common with ARPA-E projects is that there is considerable risk involved, at least in the sense that not every project is going to hit the jackpot. The EFRCs involve some highly theoretical and esoteric fields of study, so some educated guesswork had to be employed by DOE after it received over $1 billion in proposals (but only had the funding for about one-third). In this case, it’s better to think of the DOE as a venture capitalist who put together a large portfolio of promising investments knowing that there will be an enormous payoff even if only a few elements of the portfolio pan out.
I am sure we will be hearing much more in the next few days, but the DOE is teasing us with developments in four intriguing (and, coincidentally, materials-intensive) areas:
Microscopic Battery Charging — Lead institution: University of Maryland
“This research team has built the world’s smallest lithium battery inside an advanced microscope, and for the first time has been able to watch how its structure changes while it’s being charged. Understanding these changes may enable new design and production of batteries that perform better and last longer.”
Safer Materials for Nuclear Reactors — Lead institution: Los Alamos National Laboratory
“Using a combination of modeling tools, the research team is looking at improving the safety of our nuclear reactors and has discovered possible ’self-healing’ mechanisms for nuclear reactor materials.”
Controlling How Light Interacts with Materials — Lead institution: California Institute of Technology
“Using computer simulation, the research team found that small glass spheres could affect the absorption of sunlight by solar cells by helping to collect and retain light. The small glass spheres could enable efficient coupling of sunlight to ultrathin semiconductor layers, significantly increasing solar cell efficiency and cost-effectiveness.”
Improved LED’s for Homes and Businesses — Lead institution: University of California, Santa Barbara
“A new understanding of the mysterious drop-off in efficiency when LEDs are subjected to strong electric current could eventually help remove barriers to widespread use of low-energy solid-state lighting for homes and industry, greatly reducing power usage.”
In a 2009 interview I did with John Hemminger, who chairs the DOE’s Basic Energy Sciences Advisory Committee, he spoke optimistically about the prospect for EFRC success. ”We’ve developed capabilities to do certain materials engineering at an atomistic, nanometer-scale level combined with revolutionary computational abilities to predict materials properties in advanced of making them. We are at the dawn of a new age called control science, where we can say, ‘these are the properties we need,’ we can predict what the materials need to be like, and we have a way to make them,” he said. “Fundamental understanding of complex materials is essential to crating new energy strategies,” he said.
I also think the EFRCs have a far less discussed benefit: They also represent, to a large extent, investments in promising early-career scientists, and I give credit to DOE Secretary Steven Chu for noting in a news release that, ”In just two years, these research centers have inspired a new generation of talented young Americans to dedicate their careers to meeting our nation’s energy challenges.”
As announced in an earlier post, John Marra, chief research officer at Savannah River National Lab spoke at the conference dinner at the annual meeting of the Glass and Optical Materials Division on May 17. The title of the talk was “Beyond Fukushima: Advanced materials to enable enhanced nuclear power systems.”
Marra set the stage by providing some context for the strategic role of nuclear power in the energy portfolio of the United States and worldwide. At present, about 40% of the energy consumed in the U.S. is in the form of electricity, and, nationally, about 20% of U.S. electricity is produced by nuclear power plants. Globally, there are 436 operational nuclear energy plants, with about 100 located in the U.S.
The worldwide demand for electric power is expected to double by 2050, with much of the increase coming from transitional economies like India and China and emerging economies like sub-Saharan Africa and parts of the Middle East.
In the U.S., one the Obama administration’s energy goals is to reduce CO2 emissions by 80% by 2050. To reach that goal, Marra says nuclear power will have to continue be part of the nation’s energy portfolio because it is the only CO2-free power generation technology available that can also meet the demand. However, he noted traditional barriers to nuclear energy will have to be overcome, including the average $5 billion (or more) cost to build a standard size plant, more attention to siting considerations, other safety issues (real and perceived), proliferation risk and sustainable fuel cycles.
These barriers were addressed in a DOE report to Congress, “Nuclear Energy Research and Development Roadmap (PDF),” which identifies four key R&D objectives for the nuclear industry as it looks to expand the use of nuclear power in the nation’s energy portfolio. There are opportunities for the materials community to contribute to each of the Roadmap’s objectives (paraphrasing)
Look for more about ways the materials community can respond to Roadmap objectives in the August issue of the Bulletin, which will include more extensive comments from John Marra about the role specific materials will play
In the second part of his talk, Marra summarized the sequence of events that occurred on March 11 in Japan. When the magnitude 9 earthquake struck, all safety systems in the plant operated as designed and shut down the three reactors, rendering them safe and stable.
But, of course, about 80 minutes after the earthquake, the 14-meter (imagine a 40-foot wall) tsunami, more than twice the size the plant had been designed to withstand, slammed into the shore-side plant, knocking out the grid feed, the diesel generators that were running cooling water pumps, and significantly damaged the building. Even so, a back-up cooling system operated with waste heat and batteries pumped cooling water, but eventually until the batteries drained and crippled the back-up system.
With the loss of cooling, reactor cores were exposed and temperatures rose, eventually exceeding 900 oC, above which the Zircalloy fuel cladding begins to lose structural integrity. With failure of the cladding alloy, fission products were released. When the cladding temperature reached 1200 °C, the Zircalloy reacted with steam in the reactor, producing hydrogen gas and leading to the dramatic explosion (broadcast instantly around the world), and releasing the accumulated fission products into the atmosphere. Ultimately, the reactor cores were drowned with seawater, and cooling water was restored to the reactor cores (within seven hours for two of the reactors and in 27 hours for the third).
Marra observed that in the face of a catastrophic, natural event that exceeded all design contingencies (and perhaps even imagination) and caused multiple system failures, the Fukushima plant personnel very quickly returned the plant to a safe and stable condition.
According to Marra, the impact of the Fukushima incident will be “significant and worldwide,” for existing plants and new builds. He expects ceramic materials to adopted to “buy time” in emergency situations. For example, claddings of silicon carbide are able to withstand reactor temperatures well beyond what Zircalloy can tolerate. New glass-to-metal seal materials would need to be developed to seal endcaps to SiC claddings. There are alternative fuel configurations in development that would use silicon carbide to self-encapsulate spent fuel, thus preventing the accidental release of fission products. Materials like pyrolytic carbon or cabon-carbon composites may find applications in the so-called “small modular reactors” (more about those in a future post). Waste containment continues to be a pressing materials problem, and nuclear fuel is expected to be oxide-based for the foreseeable future.
Marra cautioned, however, that it can take the Nuclear Regulatory Commission up to 15 years qualify new materials for reactor components, thus the first new materials likely to be adopted are those about which much is already known like silicon carbide, silicon nitride, carbon-carbon composites, etc.
In light of timelines like these, and the added scrutiny and political pressure that the Fukushima incident will inevitably create, the Obama administration’s goal of 80% CO2 reduction by 2050 makes the 39-year interval until then look very, very tight.
On behalf of The American Ceramic Society, I am very pleased to officially announce that Eileen De Guire is now writing for this blog, and I expect her stories will be a welcomed alternative for readers to my meandering attempts to provide scientific and technical insights on ceramics, glass and other materials-related stories.
De Guire is an honest-to-goodness ceramic engineer (educated at University of Illinois at Urbana-Champaign) with lots of experiences and colleagues in the materials field. She is also an experienced editor! A perfect combination, as far as I am concerned.
She also will be working with me to plan, write and edit ACerS’ Bulletin magazine, as well as on video production and other special projects.
One final note: I know that recently things have been a little quieter than usual around this blog, but we will soon be back to the normal posting pace, In fact, De Guire and I are in Savannah, Ga., and have been attending the Glass & Optical Material Division’s annual meeting and symposia. We’ve mined a lot stories and taped some great presentations. She and I over the next few weeks will be bringing you many of the news, videos and trends being discussed at the GOMD confab.
Although it seems that the decision actually was made several weeks ago, news is just now starting to bubble up about how officials managing the development and construction of the new 1 World Trade Center building in New York City have axed plans to sheath the first section of the new structure in large and special prismatic glass panels.
This part of the construction project had been in the works for many months, and a story in the the New York Times reports that production was underway and that $10 million had already been spent on the panels before the plug was pulled.
The NYT story provides many of the details, but allow me to summarize: The 13′4″ x 4″ (I haven’t been able to determine the thickness) panels were designed by the architects and engineers to be made of ultraclear (low-iron) tempered glass that, once formed, would have unique wedges cut into them to provide prism-like optical effects. After heat strengthening, several panels would be laminated together and, according to the architect’s (SOM) website, attached to an aluminum screen framework. Two thousand of the resultant five-foot thick units would have been required.
The region of the building where the panels were to be attached has been plagued with problems. The panels were an aesthetic afterthought added when critics complained that the architectural concept for the base appeared to be a large, concrete or stone bunker. The glass panels were meant to provide a colorful and more inviting entry level. But, a furor ensued when planners announce that the panels and structural assemblies would be made in China. Eventually, WTC officials backtracked (the NYT reports the decision was based on production inabilities, not politics) and gave PPG a contract to make the glass using its Starphire composition (with Chinese companies and others doing the post-glassmaking work).
As far as I know, Glass Magazine, on May 4, was the first media outlet to catch wind of the problems with making the panels.
It appears that the problem with the panels is linked to glass-strenthening issues, a topic covered by many speakers at the Glass & Optical Materials Division meeting that just finished in Savannah, Ga. Several of those in attendance at the GOMD event also turned out to be aware of the 1 WTC project, but not surprised by reports that “the glass panels tended to bow after they were cut and tempered, which interfered with the lamination process. The ridges cut into the glass also proved to be too brittle and broke into large pieces, rather than tiny pellets.”
The experts I spoke with said that it makes sense that that tempering proved to be problematic. Quality tempering on even small pieces can be difficult, and tempering large structural glass pieces requires rare skills. These experts said that when the cutting to create the prism wedges is added as a prior step, consistent tempering would be even more difficult and fraught with quality control problems.
From a technical viewpoint, the tempering difficulties arise because the wedges create distinct differences in panel thickness. When heated to begin tempering, it would be difficult to maintain consistent temperature depth profiles on all of the surfaces. Then, when the quenching temperature is reached and sudden cooling is required — an extremely critical step to attain the strength-adding surface compressive stress — the same temperature management problems are going to be present.
So, at this point, it appears that at least one Chinese manufacturer and PPG failed to figure out a cost-effective way to make the panels without excessive production failures.
Nevertheless, SOM says on its website, “The prismatic glass was developed over the course of four years in conjunction with some of the world’s top glass manufacturers, who worked with the architects to achieve the desired visual qualities and to produce the innovative prismatic glass.” Neither PPG nor SOM, to my knowledge, have issued a response to the latest developments.
Tempering isn’t the only way to strengthen glass. Ion exchange (chemical treatment) would have been another option and it is impossible to imagine that planners didn’t considered it at some point. But ion-exchange techniques tend to have higher costs associated with them, and there aren’t a lot of experts or facilities to treat 13-foot panels. Thus, my guess is that several overly optimistic participants thought they were making the correct business decision to take the tempering route and not the ion-exchange path.
After burning through $10 million and incurring another PR black eye, I am sure that’s a decision they now regret. Pennywise-and-pound-foolish, and all that …