. | . |
Ultrastable materials investigated in depth by Staff Writers Braunschweig, Germany (SPX) Nov 26, 2015
Space holds numerous fascinating objects which we can only investigate by observing their radiation - even beyond the visible range. For space telescopes such as the European Space Agency's (ESA) infrared observatory Herschel, whose mission is to observe radiation in the far-infrared, cooling the instruments is of vital importance, since the instruments themselves must not emit disturbing infrared radiation. The mirrors of these telescopes, which are used at temperatures below 190C, are made of special, ultrastable ceramics such as silicon carbide. In order to plan the exact dimensions correctly, even at such low temperatures, the precise thermal expansion of the materials used must be known. Within the scope of a recently completed ESA project, the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig measured the thermal expansion of these ceramics as well as that of single-crystal silicon in the temperature range from 266C to 20C with high accuracy. In vast parts of the temperature range investigated, the accuracy attained corresponds to a relative change in length of approx. one billionth per degree Celsius. The investigations have also shown that the values used to date for the reference material of "single-crystal silicon" must be corrected. The latest issue of the renowned scientific journal "Physical Review B" contains a report dedicated to the latter of these two subjects. Space telescopes such as Herschel explore spectral ranges that are not accessible from the Earth; they can therefore only be used in space. How critical it is to know the exact thermal expansion of the materials used when setting up such telescopes was clearly demonstrated during one of the latest ESA missions, as it was revealed that the simulations performed previously were not in agreement with the manufactured mirrors. The discrepancies were fortunately not discovered in space, but still led to unnecessary delays. To prevent such unpleasant surprises from recurring in the future, in-depth investigations of the materials used were required. For their investigations within the scope of the ESA project, Rene Schodel's research group used PTB's ultra-precise interferometer to measure the length of the samples across the whole temperature range with nanometer accuracy. This interferometer is the only one of its kind in the world. To allow measurements to be taken with similar accuracy but with less effort, even at other institutes, reference materials whose exact thermal expansion is known are usually used for comparison. One such reference material is single-crystal silicon, which is characterized by a continuous lattice structure with very few defects; it was also investigated by the researchers. Similar to some of the ultrastable ceramic materials, silicon exhibits a peculiar behavior: at low temperatures, it starts re-expanding below a certain temperature. This dynamic characteristic - which is rather unexpected in everyday life - was also exactly measured by the scientists from PTB. Their measurements yielded an important result: across a vast temperature range, they discovered significant deviations from the reference values used to date for single-crystal silicon. This suggests that the reference values must be corrected. The results of the project are of importance for further space missions that have already been planned, such as the James Webb Space Telescope (JWST), for which temperatures of use below 220C are planned, or the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), for which even lower temperatures of use are envisaged. Thomas Middelmann, Alexander Walkov, Guido Bartl, Rene Schodel: Thermal expansion coefficient of single-crystal silicon from 7 K to 293 K. Phys. Rev. B 92, 174113 (2015)
Related Links Physikalisch-Technische Bundesanstalt (PTB Space Technology News - Applications and Research
|
|
The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us. |