Mentors and Inventors
Four outstanding researchers enjoy an unusual mentor-student relationship.
Some people may be surprised that Steve Zinkle, son of a Wisconsin farmer and elementary schoolteacher, grew up to be a successful scientist. "Science was my worst subject as a kid, possibly because I had to memorize a bunch of facts," he says. "I hated arithmetic, especially adding large numbers." But Zinkle won the eighth-grade science award and his aptitude scores led his high school guidance counselor to tell him, "You should go into engineering."
Between 1980 and 1985, Zinkle received his B.S. and Ph.D. degrees in nuclear engineering and his M.S. degree in materials science at the University of Wisconsin at Madison. For his thesis, he studied the effects of ion irradiation on the microstructure and properties of several copper alloys.
As a graduate student, Zinkle spent two summers doing research at Lawrence Livermore National Laboratory. "I would have taken a position at Livermore," he says. "if I hadn't been offered a Wigner Fellowship that resulted from an on-campus interview with an Oak Ridge recruiter who knew one of my Wisconsin professors."
Most of Zinkle's career has been spent in ORNL's Metals and Ceramics Division, interacting with the Laboratory's strong research staff in radiation effects in materials and using world-class tools such as the High Flux Isotope Reactor (HFIR) and analytical electron microscopes. Zinkle also worked in Germany, Denmark, and Russia. He has managed several large research programs while conducting his own research, which has had a major impact on materials science.
For example, published results in the literature concerning ceramic samples exposed to neutrons in different fission reactors provided conflicting information. "I was able to sort out what was going on," he says. "I explained how ionizing radiation affects the ways a material's defects migrate and recombine." For this work, Zinkle received a Best Paper award from the American Ceramic Society.
Zinkle is now leader of the fast-growing Nuclear Materials Science and Technology Group. He is involved in materials R&D for the fusion plasma containment structures of the planned International Thermonuclear Experimental Reactor (ITER). "My main research interests," he says, "are understanding how the microstructures of materials control their bulk properties, both at high temperatures and under neutron irradiation conditions."
Chad Duty is the first Wigner Fellow that Zinkle has mentored. "We have thrown him into a new area and he adapted very well, just as you'd expect of someone with his capabilities," Zinkle says. "Our group has a rapidly growing program on materials for reactors being developed for NASA's spacecraft probes that will explore planets, such as Jupiter, and their moons.
"Chad is one of the key members of the team that will help determine which refractory materials will be at the heart of the space reactor system. The selected materials must last 15 years, with very high reliability, at a temperature near 1000°C. NASA needs more data to determine which of the candidate alloys is least likely to soften over 15 years."
Duty is a native of Virginia who earned a Ph.D. in mechanical engineering from Georgia Tech, where he co-invented a rapid prototyping method using laser chemical vapor deposition. He is currently leading an effort to measure high-temperature thermal creep in samples of refractory materials exposed to liquid metal. NASA is trying to decide whether liquid metal or helium should be used as the reactor coolant. Tests must be conducted to see if liquid metal triggers any showstoppers in the candidate materials.
Besides Zinkle, Duty credits his other mentors—Jack Lackey, Craig Blue, and Ron Ott—for his early career successes.
Jang, who grew up in Seoul, Korea, obtained his B.S. and
M.S. degrees at Seoul National University.
Jang interviewed at ORNL on the recommendation of his thesis advisor, Yet Ming Chiang, who knew ORNL's Nancy Dudney from their days as MIT graduate students. After leaving Boston, the two continued to interact at battery conferences. Dudney, a native of Pittsburgh, Pennsylvania, and a graduate of William and Mary College in Virginia, came to ORNL's Solid State Division in 1979 as a Wigner fellow. A daughter of a Ph.D. solid-state chemist at Westinghouse Electric Corporation, Dudney is now leader of the Thin-Film Ceramic Group in ORNL's Condensed Matter Sciences Division.
In the late 1980s Dudney teamed with John Bates on a winning seed money proposal to construct a thin-film lithium battery. A prototype of the battery built at ORNL received considerable media attention. "It was a fun project," Dudney says. Bates left ORNL to start a company to commercialize the tiny battery. Other companies since have called Dudney asking her advice about marketing the technology.
"When Young-Il came here for an interview, it quickly became apparent that he had the right qualities to compete for a Wigner Fellowship," Dudney says. "The fellowship was an obvious thing to pursue."
Starting as a Wigner fellow in 2000, Jang worked with Dudney on the fundamental materials problems related to developing batteries for hybrid gasoline-electric cars. A Department of Energy goal is a battery that can store considerable electrical energy in a small, light package. Lithium is a choice material for at least one of the battery's electrodes because of the lightweight material's high specific energy.
One important issue relative to lithium ion batteries is the diffusion of lithium ions in electrode and electrolyte materials. While a Wigner fellow, Jang studied diffusion phenomena in lithium cobalt oxide, which is the most widely used commercial cathode material, as well as the exemplar of layered intercalation oxides.
"I recognized the thin-film battery provided the ideal geometry to study diffusion," says Jang. "Geometrical uncertainties plagued previous studies, and the literature values for lithium diffusivity varied by six orders of magnitude."
"The work will stand as the authoritative reference on transport properties in this compound," notes MIT's Chiang.Dudney and Jang have started research on lithium-sulfur batteries for hybrid vehicles. Their work is funded by DOE's Office of FreedomCAR and Vehicle Technologies in the Office of Energy Efficiency and Renewable Energy.
"DOE wants us to look at what's next in new materials for hybrid cars," Dudney says. "Like lithium, sulfur is lightweight, and both have a very high energy density. Each would be an electrode, and the electrolyte would likely be organic liquids. One problem that must be addressed is that these electrode materials may eventually lose their integrity."
Most of today's hybrid cars have nickel–metal hydride batteries. Nickel costs 200 times as much as sulfur. "In theory, a lithium-sulfur battery could provide the same runtime with only one-tenth the weight of today's hybrid car batteries," says Jang.
Jang considers Dudney a "great" mentor. "She makes herself available whenever I need her advice and encourages me to explore my own research interests."
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