Nav: Home

Carbon nanotubes improve metal's longevity under radiation

March 02, 2016

One of the main reasons for limiting the operating lifetimes of nuclear reactors is that metals exposed to the strong radiation environment near the reactor core become porous and brittle, which can lead to cracking and failure. Now, a team of researchers at MIT and elsewhere has found that, at least in some reactors, adding a tiny quantity of carbon nanotubes to the metal can dramatically slow this breakdown process.

For now, the method has only proved effective for aluminum, which limits its applications to the lower-temperature environments found in research reactors. But the team says the method may also be usable in the higher-temperature alloys used in commercial reactors.

The findings are described in the journal Nano Energy, in a paper by MIT Professor Ju Li, postdocs Kang Pyo So and Mingda Li, research scientist Akihiro Kushima, and 10 others at MIT, Texas A&M University, and universities in South Korea, Chile, and Argentina.

Aluminum is currently used in not only research reactor components but also nuclear batteries and spacecraft, and it has been proposed as material for storage containers for nuclear waste. So, improving its operating lifetime could have significant benefits, says Ju Li, who is the Battelle Energy Alliance Professor of Nuclear Science and Engineering and a professor of materials science and engineering.

Long-term stability

The metal with carbon nanotubes uniformly dispersed inside "is designed to mitigate radiation damage" for long periods without degrading, says Kang Pyo So.

Helium from radiation transmutation takes up residence inside metals and causes the material to become riddled with tiny bubbles along grain boundaries and progressively more brittle, the researchers explain. The nanotubes, despite only making up a small fraction of the volume -- less than 2 percent -- can form a percolating, one-dimensional transport network, to provide pathways for the helium to leak back out instead of being trapped within the metal, where it could continue to do damage.

Testing showed that after exposure to radiation, the carbon nanotubes within the metal can be chemically altered to carbides, but they still retain their slender shape, "almost like insects trapped in amber," Ju Li says. "It's quite amazing -- you don't see a blob; they retain their morphology. It's still one-dimensional." The huge total interfacial area of these 1-D nanostructures provides a way for radiation-induced point defects to recombine in the metal, alleviating a process that also leads to embrittlement. The researchers showed that the 1-D structure was able to survive up to 70 DPA of radiation damage. (DPA is a unit that refers to how many times, on average, every atom in the crystal lattice is knocked out of its site by radiation, so 70 DPA means a lot of radiation damage.)

After radiation exposure, Ju Li says, "we see pores in the control sample, but no pores" in the new material, "and mechanical data shows it has much less embrittlement." For a given amount of exposure to radiation, the tests have shown the amount of embrittlement is reduced about five to tenfold.

The new material needs only tiny quantities of carbon nanotubes (CNTs) -- about 1 percent by weight added to the metal -- and these are inexpensive to produce and process, the team says. The composite can be manufactured at low cost by common industrial methods and is already being produced by the ton by manufacturers in Korea, for the automotive industry.

Strength and resilience

Even before exposure to radiation, the addition of this small amount of nanotubes improves the strength of the material by 50 percent and also improves its tensile ductility -- its ability to deform without breaking -- the team says.

"This is a proof of principle," says Kang Pyo So. While the material used for testing was aluminum, the team plans to run similar tests with zirconium, a metal widely used for high-temperature reactor applications such as the cladding of nuclear fuel pellets. "We think this is a generic property of metal-CNT systems," he says.

"This is a development of considerable significance for nuclear materials science, where composites -- particularly oxide dispersion-strengthened steels -- have long been considered promising candidate materials for applications involving high temperature and high irradiation dose," says Sergei Dudarev, a professor of materials science at Oxford University in the U.K., who was not involved in this work.

Dudarev adds that this new composite material "proves remarkably stable under prolonged irradiation, indicating that the material is able to self-recover and partially retain its original properties after exposure to high irradiation dose at room temperature. The fact that the new material can be produced at relatively low cost is also an advantage."
-end-
The team also included researchers Sangtae Kim, Yang Yang, and Ziqiang Wang at MIT; Di Chen and Shao Lin at Texas A&M University; Jong Gil Park and Young Hee Lee at the Institute for Basic Science in South Korea; Rafael Gonzalez and Miguel Kiwi at the University of Chile; and Eduardo Bringa at the National University of Cuyo, in Argentina. The work was supported by the U.S. Department of Energy and the National Research Foundation of Korea.

Additional background

ARCHIVE: Profile: Ju Li explores new nanomaterials http://news.mit.edu/2012/faculty-profile-li-dmse-nse-1010

ARCHIVE: Harnessing the energy of small bending motions http://news.mit.edu/2016/harnessing-energy-bending-motions-0106

ARCHIVE: Unusual magnetic behavior observed at a material interface http://news.mit.edu/2015/unusual-magnetic-behavior-quantum-computers-0818

ARCHIVE: Solid nanoparticles can deform like a liquid http://news.mit.edu/2014/solid-nanoparticles-deform-like-liquid-1012

Massachusetts Institute of Technology

Related Carbon Nanotubes Articles:

Why modified carbon nanotubes can help the reproducibility problem
Scientists at Tokyo Institute of Technology (Tokyo Tech) conducted an in-depth study on how carbon nanotubes with oxygen-containing groups can be used to greatly enhance the performance of perovskite solar cells.
Tensile strength of carbon nanotubes depends on their chiral structures
Single-walled carbon nanotubes should theoretically be extremely strong, but it remains unclear why their experimental tensile strengths are lower and vary among nanotubes.
New study reveals carbon nanotubes measurement possible for the first time
Swansea University scientists report an entirely new approach to manipulation of carbon nanotubes that allows physical measurements to be made on carbon nanotubes that have previously only been possible by theoretical computation.
Neural networks will help manufacture carbon nanotubes
A team of scientists from Skoltech's Laboratory of Nanomaterials proposed a neural-network-based method for monitoring the growth of carbon nanotubes, preparing the ground for a new generation of sophisticated electronic devices.
Efficient, interconnected, stable: New carbon nanotubes to grow neurons
Carbon nanotubes able to take on the desired shapes thanks to a special chemical treatment, called crosslinking and, at the same time, able to function as substrata for the growth of nerve cells, finely tuning their growth and activity.
OU Researcher determines catalytic active sites using carbon nanotubes
Catalytic research led by University of Oklahoma researcher Steven Crossley has developed a new and more definitive way to determine the active site in a complex catalyst.
Carbon in color: First-ever colored thin films of nanotubes created
A method developed at Aalto University, Finland, can produce large quantities of pristine single-walled carbon nanotubes in select shades of the rainbow.
FEFU scientists reported on toxicity of carbon and silicon nanotubes and carbon nanofibers
Nanoparticles with a wide range of applying, including medicine, damage cells of microalgae Heterosigma akashivo badly.
Making carbon nanotubes as usable as common plastics
By using an inexpensive, already mass produced, simple solvent called cresol, Northwestern University's Jiaxing Huang has discovered a way to make disperse carbon nanotubes at unprecedentedly high concentrations without the need for additives or harsh chemical reactions to modify the nanotubes.
Carbon nanotubes devices may have a limit to how 'nano' they can be
Carbon nanotubes bound for electronics not only need to be as clean as possible to maximize their utility in next-generation nanoscale devices, but contact effects may limit how small a nano device can be, according to researchers at the Energy Safety Research Institute (ESRI) at Swansea University in collaboration with researchers at Rice University.
More Carbon Nanotubes News and Carbon Nanotubes Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.