Dr. Mitsunori Kurahashi, a Principal Researcher of the NIMS Nano Characterization Unit, and Dr. Yasushi Yamauchi, a Group Leader in the same unit, presented decisive evidence clarifying the dynamical process of aluminum surface oxidation by using a molecular oxygen (O2) beam with a controlled molecular alignment, which was originally developed by the researchers, and thereby settled a 20-year dispute regarding the reaction mechanism.
Dr. Mitsunori Kurahashi, a Principal Researcher of the Nano Characterization Unit (Unit Director: Daisuke Fujita), National Institute for Materials Science (President: Sukekatsu Ushioda) and Dr. Yasushi Yamauchi, a Group Leader in the same unit, presented decisive evidence clarifying the dynamical process of aluminum surface oxidation by using an aligned O2 beam, which was originally developed by the researchers, and thereby settled a dispute which had continued for 20 years regarding the reaction mechanism.
Aluminum is widely used as a corrosion-resistant lightweight material despite its high reactivity for O2 because the dense oxide film that forms on the surface prevents corrosion by oxygen, etc. in the air. In the field of fundamental surface science, O2 adsorption on aluminum surfaces had been investigated for many years as the most representative system of surface oxidation.
However, previous experimental and/or theoretical studies on the atomic-scale process of O2 adsorption/dissociation contradict with each other.
As a result, the mechanism of this simple surface reaction still remained unclear, in spite of the research extending over more than 20 years.
Using an aligned O2 beam developed by the researchers, the team headed by Dr. Kurahashi clarified that the probability of O2 adsorption on an aluminum surface depends strongly on the alignment of the O2 molecular axis.
The NIMS researchers demonstrated that low velocity O2 molecules with kinetic energies of 0.1eV or less adsorb only when their axes are nearly parallel to the surface, whereas, O2 molecules in any molecular orientations can adsorb when the kinetic energy exceeds 0.2eV. Until now, O2 molecules with its axis perpendicular to the surface had been considered to adsorb under low energy conditions, and this had long confused the discussion on the reaction mechanism.
However, the present research has concluded that this reaction mechanism is not true.
This research also explains the previous experimental results, which had appeared contradictory, and thus elucidated the whole atomic-scale dynamical process of O2 adsorption on an aluminum surface, which had been unclear for many years. Moreover, this research indicates that the slight activation energy difference of 0.1 eV among different molecular orientations needs to be considered for the future study of O2 adsorption on surfaces. O2 adsorption is important not only in the oxidation of the material itself, but also in the catalytic processes happening on the surfaces of fuel cell electrodes, etc.
Expensive rare metals such as platinum are used as catalysts that efficiently dissociate O2 molecules. The aligned O2 beam used in this research would be useful not only in reaction analysis, but also in research on substitute catalysts.
FOR MORE INFORMATIONMitsunori Kurahashi
These research results were achieved as part of the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research/Basic Research (B) “Development of a Single Spin-Rotational State-Selected O2 Beam and its Application to Surface Reaction Analysis” (Research Representative: Mitsunori Kurahashi) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and the NIMS 3rd Mid-Term Program Project “Development and Application of Advanced Material Characterization Technologies” (Leader: Daisuke Fujita).
Mikiko Tanifuji | Research asia research news
New material for digital memories of the future
19.10.2017 | Linköping University
Electrode materials from the microwave oven
19.10.2017 | Technical University of Munich (TUM)
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
19.10.2017 | Materials Sciences
19.10.2017 | Materials Sciences
19.10.2017 | Physics and Astronomy