Finding that nitrogen can combine with oxygen in zirconia to form NO may lead to safer materials for nuclear reactors

Aug 15, 2012
© istockphoto.com/MichaelUtech

The understanding of oxidation and corrosion processes is essential for a wide range of applications, particularly those related to the nuclear industry. Zhi Gen Yu at the A*STAR Institute of High Performance Computing and co-workers have now performed calculations to study how nitrogen degrades zirconium — a material widely used for cladding fuel rods in nuclear reactors — and found that nitrogen atoms entering zirconia (the oxidized form of zirconium) do not simply replace oxygen atoms. Instead, the researchers showed that nitrogen atoms combine with oxygen atoms to form nitrosyl (NO) radicals, which bind the zirconium lattice. They believe that this mechanism promotes the corrosion of zirconia in nuclear reactors.

The nuclear disaster in Fukushima last year is a recent and drastic example that illustrates the importance of studying corrosion processes in zirconium, with the goal of developing methods to prevent deteriorating processes. “Following the accident in Fukushima there were reports that due to the high temperatures and the presence of steam, oxidation of the zirconium cladding — designed to protect the nuclear-fuel rods — produced hydrogen, which only exacerbated the heat problem,” explains Yu.

An important property of zirconium is that, when exposed to air, it naturally forms a thin layer of zirconia, which acts as a barrier against further and corrosion. The stability of zirconia is normally very high. At elevated temperatures (as present when a reactor core overheats), however, the stability decreases substantially and the zirconia layer loses its protective function — just when it is most needed.

Scientists have yet to grasp the mechanism underlying the corrosion of zirconium. However, they know that one of the factors that influence the corrosion process is nitrogen impurities. To better understand the role of nitrogen in corrosion when it enters zirconia, Yu and co-workers have calculated the probability of every chemical processes that may happen in zirconia as nitrogen molecules intrude. They found that among all possible basic structures associated with nitrogen, the most likely species to form is NO molecules, which then occupy the sites where single oxygen atoms originally resided.

“We expect that for every two introduced, three oxygen atoms in the lattice are removed,” says Yu. “Our results suggest that two of the removed oxygen atoms combine with to form NO defects, whereas the remaining escape, leaving behind vacancies. Such vacancies could provide paths for oxygen diffusion, which promotes the rate of corrosion.”

Explore further: Recycling industrial waste water: Scientists discover a new method of producing hydrogen

More information: Yu, Z. G., Zhang, J., Singh, D. J. & Wu, P. First-principles investigation of nitrosyl formation in zirconia. Physical Review B 85, 144106 (2012). dx.doi.org/10.1103/PhysRevB.85.144106

add to favorites email to friend print save as pdf

Related Stories

Ceramic, heal thyself

Apr 17, 2008

A new computer simulation has revealed a self-healing behavior in a common ceramic that may lead to development of radiation-resistant materials for nuclear power plants and waste storage.

Carbon Nanotubes Make Fuel Cells Cheaper

Feb 09, 2009

(PhysOrg.com) -- As fuel cells are becoming more popular due to their potential use in applications such as hydrogen-powered vehicles, auxiliary power systems, and electronic devices, the need for the precious ...

Converting Nitrogen to a More Useful Form

Jan 09, 2007

Nitrogen-containing organic compounds are important products as well as intermediates for many pharmaceuticals, agrochemicals, and chemicals used in electronics. Air contains plenty of nitrogen, but it is in a form that cannot ...

Graphene is thinnest known anti-corrosion coating

Feb 22, 2012

New research has established the "miracle material" called graphene as the world's thinnest known coating for protecting metals against corrosion. Their study on this potential new use of graphene appears ...

Helping materials handle extreme stress

Oct 11, 2011

Important pressurized water nuclear reactor components are being made from a nickel-base alloy that contains twice the amount of chromium as the material previously used. The new alloy, called alloy 690, performs ...

Recommended for you

A greener source of polyester—cork trees

2 hours ago

On the scale of earth-friendly materials, you'd be hard pressed to find two that are farther apart than polyester (not at all) and cork (very). In an unexpected twist, however, scientists are figuring out ...

A beautiful, peculiar molecule

5 hours ago

"Carbon is peculiar," said Nobel laureate Sir Harold Kroto. "More peculiar than you think." He was speaking to a standing-room-only audience that filled the Raytheon Amphitheater on Monday afternoon for the ...

Metals go from strength to strength

Apr 15, 2014

To the human hand, metal feels hard, but at the nanoscale it is surprisingly malleable. Push a lump of metal with brute force through a right-angle mould or die, and while it might look much the same to the ...

User comments : 0

More news stories

Breakthrough points to new drugs from nature

Researchers at Griffith University's Eskitis Institute have developed a new technique for discovering natural compounds which could form the basis of novel therapeutic drugs.

A greener source of polyester—cork trees

On the scale of earth-friendly materials, you'd be hard pressed to find two that are farther apart than polyester (not at all) and cork (very). In an unexpected twist, however, scientists are figuring out ...

Progress in the fight against quantum dissipation

(Phys.org) —Scientists at Yale have confirmed a 50-year-old, previously untested theoretical prediction in physics and improved the energy storage time of a quantum switch by several orders of magnitude. ...