Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Microscopy Reveals how Atom-High Steps Impede Oxidation of Metal Surfaces

30.12.2014

Rust never sleeps. Whether a reference to the 1979 Neil Young album or a product designed to protect metal surfaces, the phrase invokes the idea that corrosion from oxidation—the more general chemical name for rust and other reactions of metal with oxygen—is an inevitable, persistent process. But a new study performed at the Center for Functional Nanomaterials (CFN) at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory reveals that certain features of metal surfaces can stop the process of oxidation in its tracks.

The findings, published in the Proceedings of the National Academy of Sciences, could be relevant to understanding and perhaps controlling oxidation in a wide range of materials—from catalysts to the superalloys used in jet engine turbines and the oxides in microelectronics.


Brookhaven National Laboratory

Low-energy electron microscopy images of the nickel-aluminum surface before and after oxidation. The faint lines before oxidation indicate the atom-high steps that separate flat terrace sections of the crystal surface. As oxidation begins at a point on one terrace, the oxide spreads in elongated stripes along that terrace, pushing steps out of the way and bunching them closer and closer together. Eventually the bunching of steps stops the growth of the oxide stripe and another begins to form, often at right angles, to produce a grid-like pattern.


Brookhaven National Laboratory

(see above)

The experiments were performed by a team led by Guangwen Zhou of Binghamton University, in collaboration with Peter Sutter of the CFN, a DOE Office of Science User Facility. The team used a low-energy electron microscope (LEEM) to capture changes in the surface structure of a nickel-aluminum alloy as "stripes" of metal oxide formed and grew under a range of elevated temperatures.

"These microscopes are not that frequently found in ordinary research labs; there are only a handful around the U.S.," Sutter said. "We have a pretty lively 'user community' of scientists who come to the CFN just to use this type of instrument."

The metal Zhou wanted to study, nickel-aluminum, has a characteristic common to all crystal surfaces: a stepped structure composed of a series of flat terraces at different heights. The steps between terraces are only one atom high, but they can have a significant effect on material properties. Being able to see the steps and how they change is essential to understanding how the surface will behave in different environments, in this case in response to oxygen, Sutter said.

Said Zhou, "The acquisition of this kind of knowledge is essential for gaining control over the response of a metal surface to the environment."

Scientists have known for a while that the atoms at the edges of atomic steps are especially reactive. "They are not as completely surrounded as the atoms that are part of the flat terraces, so they are more free to interact with the environment," Sutter said. "That plays a role in the material's surface chemistry."

The new study showed that the aluminum atoms involved in forming aluminum oxide stripes came exclusively from the steps, not the terraces. But the LEEM images revealed even more: The growing oxide stripes could not "climb" up or down the steps, but were confined to the flat terraces. To continue to grow, they had to push the steps away as oxygen continued to grab aluminum atoms from the edges. This forced the steps to bunch closer and closer together, eventually slowing the rate of oxide stripe growth, and then completely stopping it.

"For the first time we show that atomic steps can slow surface oxidation at the earliest stages," Zhou said.

However, as one stripe stops growing, another begins to form. "As the oxide stripes grow along the two possible directions on the crystal, which are at right angles to one another, one ends up with these patterns of blocks and lines that are reminiscent of the grid-based paintings by Mondrian," Sutter said. "They are quite beautiful…" and persistent after all.

In fact, scientists who've studied a different "cut," or facet, of the crystalline nickel-aluminum alloy have observed that steps on that surface had no effect on oxide growth. In addition, on that surface, aluminum atoms throughout the bulk of the crystal could participate in the formation of aluminum oxide, and the oxide stripes could overrun the steps, Zhou said.

Still the details and differences of the two types of surfaces could offer new ways scientists might attempt to control oxidation depending on their purpose.

"Oxides are not all bad," Sutter said. "They form as a protective layer against corrosion attack. They play important roles in chemistry, for example in catalysis. Silicon oxide is the insulating material on microelectronic circuits, where it plays a central role in directing the flow of current."

Knowing which kind of surface a material has and its effects on oxidation—or how to engineer surfaces with desired properties—might improve the design of these and other materials.

This work was supported by the DOE Office of Science.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.

To see an electronic version of this news release with related graphics, go to:
http://www.bnl.gov/newsroom/news.php?a=11686

Media contact: Justin Eure, (631) 344-2347, jeure@bnl.gov

Karen Walsh | newswise

Further reports about: Brookhaven Department Oxidation aluminum oxide structure surfaces

More articles from Materials Sciences:

nachricht Multitasking monolayers
25.07.2017 | Vanderbilt University

nachricht Flexible proximity sensor creates smart surfaces
25.07.2017 | Fraunhofer-Institut für Produktionstechnik und Automatisierung IPA

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Carbon Nanotubes Turn Electrical Current into Light-emitting Quasi-particles

Strong light-matter coupling in these semiconducting tubes may hold the key to electrically pumped lasers

Light-matter quasi-particles can be generated electrically in semiconducting carbon nanotubes. Material scientists and physicists from Heidelberg University...

Im Focus: Flexible proximity sensor creates smart surfaces

Fraunhofer IPA has developed a proximity sensor made from silicone and carbon nanotubes (CNT) which detects objects and determines their position. The materials and printing process used mean that the sensor is extremely flexible, economical and can be used for large surfaces. Industry and research partners can use and further develop this innovation straight away.

At first glance, the proximity sensor appears to be nothing special: a thin, elastic layer of silicone onto which black square surfaces are printed, but these...

Im Focus: 3-D scanning with water

3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects

A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA mission surfs through waves in space to understand space weather

25.07.2017 | Physics and Astronomy

Strength of tectonic plates may explain shape of the Tibetan Plateau, study finds

25.07.2017 | Earth Sciences

The dense vessel network regulates formation of thrombocytes in the bone marrow

25.07.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>