Statistics – Applications
Scientific paper
Jan 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aipc..387..371m&link_type=abstract
Space technology and applications international forum (STAIF - 97). AIP Conference Proceedings, Volume 387, pp. 371-376 (1997).
Statistics
Applications
Insulators, Composite Materials, Chemical Exchanges, Joining, Welding, Magnetohydrodynamic Generators And Thermionic Convertors, Plasma Diodes
Scientific paper
The compatibility of insulator material systems in a barium environment was investigated. This work is part of an ongoing program to identify weaknesses in insulator/braze/refractory metal materials systems which provide electrical insulation in alkali-metal enhanced thermionic devices and other alkali-metal thermal-to-electric converters. Test articles consisting of alumina or sapphire insulators brazed to molybdenum via a nominal Cu-30% Ni braze, were exposed to barium vapor to ascertain possible reactions and/or failure mechanisms. The test matrix consisted of eight samples; 5 with a sapphire insulator, 3 with an alumina insulator. Each sample was exposed to a different combination of insulator/braze region temperature (1000 K or 1100 K) and partial pressure of barium (10-3 or 10-2 torr) for approximately 750 hours. Initial analysis indicated that the ceramic portions were free from corrosion and that the braze material was the weak link in the material system. Evidence of formation of a Cu-Ba intermetallic at the braze region was visible. Further analysis indicated that in some cases Al2O3 was being reduced by the Barium. The results of this research imply that use of Al2O3 based ceramics in a barium environment may be suspect to failures in the long term and that Cu-Ni brazes are not suitable for the barium environment.
Merrill John M.
Schuller Michael
Zee Ralph
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