LabNews 09/12/2008
—
PDF
(1 Mb)
By Nigel Hey
The very word diamond coaxes ideas of beauty and romance to the mind. Yet the gem is a carbon cousin to the relatively unlovely graphite we find in pencil leads, brake linings, and lubricants. Diamond is very hard and brittle, a good conductor of heat, and an electrical insulator; graphite is fairly soft, a poor conductor of heat, and electrical conductor. Put the two minerals under a microscope, and you’ll find they are made up of differently shaped crystals.
Diamonds are easily as mysterious as they are beautiful. Though it has colorless tetrahedral crystals, like stretched-out cubes, its carbon sister graphite has more complex, hexagonal crystals. Nature requires that crystals are formed when solid structures are formed from liquid. How then can carbon, which has never been reported in liquid form, become a diamond? Apparently the transformation occurs very quickly. This magic of mineralogy has now been replicated and witnessed in the laboratory — at Sandia, by research scientist Jianyu Huang.
Natural diamonds form deep below the Earth’s surface, when extremes of heat and temperature melt concentrations of carbon-bearing materials into a new material capable of being cut and polished into brilliant gemstone. Synthetic diamonds are made when huge presses provide the necessary heat and pressure to force carbon into a new form. Jianyu made his — momentarily — with a nanoscale heater. The big news is that, thanks to transmission electron microscopy (TEM), Jianyu was able to make a stop-motion record of “quasimolten” diamond as it took form and solidified again. Under normal atmospheric pressure and very high temperatures, diamond does not melt but instead turns into graphite.
Jianyu is quick to point out that he did not melt graphite with his experiments; nor did he produce liquid diamond. Nothing actually flowed — the process happened too quickly for this, before changing its state again. The material “flickers” between the two forms of carbon, melting then refreezing to its original state within a few seconds. This is called quasimelting, because no liquid flow occurs.
Jianyu’s discovery — made originally at Boston College, then analyzed and replicated at Sandia — offers a new method of studying the structures of carbon at extreme conditions in situ and at an atomic scale. On the geologic scale, such studies may increase understanding of the conditions that exist in Earth’s mantle, where natural diamonds form. The behavior of materials under extreme conditions of high pressure and temperature has long been of interest to researchers in physics, astronomy, and geology. Since diamond possesses the highest hardness, thermal conductivity, and melting temperature of all materials, it has been the focus of numerous studies at extreme conditions.
The Sandia experiments focused on heating tiny graphite spheres which, because they consist of many concentric layers of carbon, were dubbed “onions” by researchers Florian Banhart of the Institute for Physical Chemistry in Mainz, Germany, and Pulickel Ajayan of Rensselaer Polytechnic Institute, New York. In a research paper published in Nature in 1996, Banhart and Ajayan reported that they had changed diamond into graphite under conditions of high pressure and temperature. But they were unable to observe and record the process of transformation.
“They were able to convert ‘onion’ to diamond at about 700 degrees C under electron beam irradiation, using a TEM heating stage,” explains Jianyu. “We are heating only very locally, to a much higher temperature, using a carbon nanotube. That is why we observed the quasimelting behavior, whereas the 1996 experiment was unable to detect this process.”
Jianyu says this 1996 paper inspired him to apply nanotechnology to learn more about the quasimelting process. “While pursuing research in carbon nanotubes, I found that I could generate a temperature higher than 2,000 degrees C by passing a high current through the nanotube, similar to passing a current through a light bulb,” he says. “Then I thought, what will happen if I heat the carbon onion with my carbon nanotube? I thought it an interesting experiment because nobody had been able to generate such a high pressure and high temperature in situ before.”
In the Sandia experiments, the graphite-like onion, about 20 nanometers in diameter, is first bound to the nanotubes. By heating the carbon onions with the nanotube and simultaneously applying electron beam irradiation, temperatures inside the onion are raised to greater than 2,000 degrees C. The onion then self-compresses, generating very high internal pressure. “The pressure in the center of the onion is estimated to be over 400,000 atmospheres,” says Jianyu. “Isn’t that amazing!”
Sequential transmission electron microscope images made at the rate of two to three frames per second show in real time how diamond forms, then repeatedly melts and refreezes in crystal configurations that differ in terms of size, shape, internal structure, and crystal orientation. The structural changes in structure are determined by analyzing the changing image of the crystal lattice.
Jianyu now has Laboratory Directed Research and Development funding to investigate the thermal property of nanotubes, a remarkable material in its own right, with a host of special properties. But molten diamond will not be forgotten. “We’re still continuing the study,” he says. “We would like to know how the giant onion structure shrinks, how the shrink generates such high pressure, and how the graphite is initially converted to diamond. There is still a lot to explore.” -- Nigel Hey
Top of page
Return to Lab News home page
By Bill Murphy
Sandia National Laboratories' Center 2700 — the Responsive Neutron Generator Product Deployment Center — has a vision: to be the model of operational excellence for the entire nuclear weapons complex. Now that it’s won the prestigious and coveted Shingo Prize for 2008 — the first and only public sector organization so honored — it can validate that it is on track toward achieving that vision.
Shingo, more than any other business prize, promotes awareness of lean concepts and recognizes companies in the US, Canada, and Mexico that achieve world-class status in lean transformation.
BusinessWeek, as authoritative a voice as there is in matters related to US business activity, has called the Shingo Prize “the Nobel Prize for manufacturing” because it establishes a standard for excellence through focused improvements in core manufacturing and business processes.
The Shingo Prize was established in 1988 by the John M. Huntsman School of Business at Utah State University. The prize is named for Japanese industrial engineer Shigeo Shingo, who distinguished himself as one of the world’s leading experts in improving manufacturing processes. He helped create and write about many aspects of the revolutionary manufacturing practices that comprise the renowned Toyota Production System.
This year’s award isn’t Center 2700’s first encounter with the Shingo organization. In 2006, the center won a Shingo bronze medallion for its implementation of lean principles in its production activities. The 2008 award is broader in scope, recognizing the center for its implementation of lean principles across the entire neutron generator life cycle activities.
Great feedback from first visit
That 2006 prize, and the activities leading up to it, offered a real learning opportunity, says Center Director Kathleen McCaughey. “Part of the [prize competition] process,” she says, “is to get a feedback report from the Shingo organization. We got some great feedback, which motivated us to put an action plan in place.”
That action plan — which Kathleen and her team approached with the fervor of a campaign — included implementing lean principles throughout the entire neutron generator life cycle. The NG life cycle incorporates the science and technology foundations of neutron generators, design, development, production, materials management, component stewardship, and shared services.
The motivations for embarking on a lean journey were several and all were compelling. To begin with, production was unstable, and the center wasn’t meeting its internal production schedules. The center didn’t have the budget to add employees and it wasn’t the right answer anyway. The center’s leadership team acknowledged a glaring and undeniable truth: The problems were systemic and demanded a systemic solution. They all read a book called Lean Thinking, and decided to “go lean.”
Culture has changed
Through leadership commitment, engagement, and direction, the center’s culture has changed. Today, more than half of the employees are either green belt or black belt lean practitioners. Those credentials are earned through training and the application of lean principles in everyday work. (There are about 250 Sandians in the center, counting FTEs and LTEs, and because the center deals with the entire life cycle of the neutron generator products, its staff members come from every job ladder in the Labs.)
Keeping the team focused
To keep everyone focused, there are full-time assigned black belts (like Maria Galaviz and Anne Lacy), who help keep the center on the right track and moving forward.
Going lean, says Kathleen, was initially about being able to deliver products, but later turned into more globally meeting the customer — NNSA’s — requirements: becoming more responsive to changing demands in the complex and more cost-effective in meeting its needs.
And there was, of course, that Shingo Prize — an industry benchmark for operational excellence, which compares your systems and results against others. Having tasted bronze in 2006, five years into its lean journey, the leadership team makes no bones about the fact that the center was actively committed to achieving a higher award level than before, and for a larger scope.
They didn’t expect to win the Shingo Prize in 2008, Kathleen says. “It was gratifying to see lean principles begin to make a difference in the Center’s operations from the very beginning. With culture change, you can see improvements right away. You see growth, you see maturity. You see your team beginning to think lean. You can see it in the results.”
By 2008, the Shingo examiners certainly saw the change in Center 2700, and liked what they found. The center had evolved from tools-centric, to principle-based systems. One example was the center’s value creation process with a one-page policy deployment.
Shingo Lingo Jeopardy
To prepare for the examiners’ visit, the black belts invented “Shingo Lingo Jeopardy.” This activity helped communicate to all employees the center’s lean model (principles, enablers, systems), and achievements across all departments. When the visiting examiners started talking to Center 2700 employees, it became apparent that they were engaged in improving work processes.
Kathleen says the road her team has traveled is one that other organizations around Sandia can follow. Her simple message: “Lean works. Any organization that realizes products will benefit from lean, just as we have. You have to integrate lean into your everyday work.”
Center 2700 representatives will attend the 2008 Shingo conference and awards ceremony Oct. 9 in Washington, D.C., where they will be recognized for their achievement. — Bill Murphy
Top of page
Return to Lab News home page
By Patti Koning
While more than half of all cars sold in Europe run on diesel engines, the technology has yet to take hold in the American consumer car market. That could change as the twin pressures of skyrocketing gas prices and increased levels of carbon dioxide emissions are driving major shifts away from the status quo in the automotive industry. Mercedes-Benz, Volkswagen, BMW, and Honda are among car companies that plan to release diesel engine models in the US in the near future.
Diesel engines have several advantages over gas-powered engines: They burn less fuel, have better drivability, and last longer. Even with higher diesel fuel costs, drivers will still get more bang for the buck from a diesel engine. Diesels, unfortunately, have a reputation for being loud, smelly, and smoky, but a new generation of clean diesel engines aims to allay those concerns.
These engines often employ low-temperature combustion techniques to reduce nitrogen oxides (NOx) and soot emissions. These techniques, however, can lead to high carbon monoxide (CO) emissions — with concomitant efficiency loss — particularly at light loads. Understanding the detailed sources of CO emissions is critical to minimizing them, but, until now, in-cylinder visualization of these emissions had never been achieved.
Recently Paul Miles, Will Colban, and Isaac Ekoto (all 8362), along with Duksang Kim, a visiting researcher from Kookmin University, Korea, succeeded in visualizing the CO distribution in an operating diesel engine for the first time using a two-photon laser-induced fluorescence (LIF) technique. The work is funded by DOE’s Energy Efficiency and Renewable Energy (EERE) Office of Vehicle Technologies and General Motors.
“Knowing the sources of combustion inefficiency embodied in carbon monoxide can drive design decisions that will make engines more efficient,” says Paul.
Using LIF to visualize carbon monoxide emissions proved technically challenging. Single photon excitation doesn’t work with CO, since the molecular transitions aren’t accessible with visible wavelengths or near-UV. With single photon LIF, a wide laser beam that comes to a focus within the engine is typically used to avoid damage to the engine windows. The strong signal variation with beam intensity of two-photon LIF means the beam must be nearly the same width as it traverses the engine, which results in a more intense beam going through the windows.
“We used the highest grade of UV fused silica windows and we still only got about 2,000 shots before we damaged the window,” explains Paul. The researchers learned to shoot through only the top of the circular windows, and then rotate them to extend their life.
The testing is done on engines in the Combustion Research Facility that have the same geometry as production engines, down to the details of the piston bowl shape and valve cutouts. Paul says the team carefully characterized the spectral nature of the emissions to be sure they were not getting interference from unburned hydrocarbons.
A major finding was that the squish volume of the engine is a source of emissions. “The squish volume is a feature of the combustion system that is needed for good conventional diesel performance. Our results point to the possibility that different combustion chamber designs could be more appropriate for low temperature combustion systems,” explains Paul.
The results of the project have also enabled validation of numerical simulations on which engines are designed. Paul says that simulations successfully predict trends in emissions, but the details of what is happening in-cylinder, which could lead to optimized geometries, just aren’t well known or accurately predicted.
The Basic Energy Sciences work done on CO fluorescence proved invaluable to the success of this project. “Previous researchers had measured photo-ionization cross-sections, absorption cross-sections, and CO quenching cross-sections with all the major partners as a function of temperature,” says Paul. “It was a godsend to have the fundamental data. It enabled us to come up with semi-quantitative measurements.”
The measurements are expected to help improve the accuracy of the models used for engine design and optimization.
While Paul notes that quantifying what these results could mean, in terms of improved fuel efficiency, is difficult, he does think it could lead to a 4-5 percent increase. “These results will have a direct impact on engine design,” he says. “This research is more closely aligned to the needs of industry than anything else I’ve done at Sandia.” — Patti Koning
Top of page
Return to Lab News home page