ARCHIVED - Neutrons tell the inside story
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August 08, 2008— Ottawa, Ontario
"Behind every technological advance, there's an advance in materials science," says Dr. Ron Rogge, a senior scientist at the NRC Canadian Neutron Beam Centre in Chalk River, Ontario. Dr. Rogge manages the Applied Neutron Diffraction for Industry (ANDI) program — a unique resource that allows academic, industry and NRC researchers to undertake novel inquiries into materials.
"Scientists use several types of probes to help them characterize and improve materials, but neutron scattering is a tool like no other," says Dr. Rogge. "That's because of the special way that neutrons interact with matter."
|Dr. Ron Rogge (right) explains to Dr. Roxana Hutanu (now with Atomic Energy of Canada Ltd.) how neutron diffraction provided unique information about the stresses in the booster rocket casing of the Space Shuttle Challenger.|
NRC researchers at Chalk River are world leaders in the application of neutron diffraction to industrial research. They apply neutron scattering methods to characterize "structural materials" (metals, alloys, ceramics and composites), "functional materials" (nanostructures that store gases or help chemical reactions occur with less energy, and crystal structures for information storage or use in batteries) and "soft materials" (plastics, membranes, proteins, gels, milk and blood).
For example, the Chalk River team recently worked on a project with a steel company, a university researcher and CANMET — a government laboratory specializing in metallurgy. The partnership's objective was to determine how to enhance steels to achieve superior performance for key applications. NRC provided the neutron diffraction results that the university partner used in providing computer simulations of the material and the fabrication route. CANMET then simulated the fabrication process on a small scale. By combining the information gained from the neutron diffraction experiments and computer simulations, the company was able to enhance its product's performance.
Why is neutron diffraction such a powerful technique for materials research? "Matter is made of atoms that are arranged in various ways, depending on whether the matter is solid, liquid or gas," explains Dr. Rogge. "Neutrons are subatomic particles that interact with the nuclei of atoms and with atomic magnetic fields. We can shoot neutrons right through a material where they diffract in specific patterns that we can capture. From the measured patterns, we can determine the arrangement of the atoms in the material."
Neutron scattering techniques include diffraction, spectroscopy, reflectometry and small-angle scattering. Because of the high penetration depth and characteristic wavelength of neutrons, neutron diffraction techniques reveal structural information that simply cannot be gained through electron microscopy, ultrasonics and X-rays.
Neutron beams can penetrate most materials, providing information about full-scale engineering components, such as welds, pipes, and engine parts — without affecting the sample in any way. Neutrons can be used to map stresses in three dimensions, in metal components or in other polycrystalline materials. They can also be used to measure crystalline texture, or determine the volume fractions of various elements of composite materials. In addition, neutrons can be used to characterize how materials react to certain processes, over time.
"We can perform non-invasive thermometry and real-time tracking of oxidation," says Dr. Rogge. "We can also monitor electrochemical reactions and determine the homogeneity of material at its microstructural level. By characterizing the molecular and atomic-level structure and behaviour of materials, we're helping industry researchers make better decisions about manufacturing processes and improve the performance of their materials."
Dr. Rogge works mainly with clients from the aerospace, automotive, energy and environmental sectors. Clients supply a material or fully manufactured part to test, and NRC researchers use the Chalk River reactor to perform neutron scattering, analyze the diffraction and report the data. "Using neutrons, we can get a picture of that material's deep atomic structure before it is processed into a part," he says. "Then, we can test it again after it has been stressed and formed, and see how the process has affected the material properties." Such information helps to project the fatigue life of the part.
One of the greatest advantages of the ANDI program is that NRC can perform tests under realistic conditions including high temperature (up to 2000º C), high electric or magnetic fields, high tensile or compressive loads, and during operation in hostile environments. NRC can combine a variety of testing conditions, as required. "For example, we can apply a load to a sample while heating it to see how it performs in these conditions. Manufacturers need to know the tolerances of new materials before using them to manufacture products — particularly those related to public safety. And the new knowledge we can provide by neutron scattering techniques can also lead to innovative materials or fabrication methods that enhance competitiveness," notes Dr. Rogge.
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