Significance of oxygen on interstitial ordering in tantalum (The Ta/sub 64/C artifact)
Although the absence of equilibrium carbide precipitates on Ta/sub 64/C is explained by the particular polishing technique used, the observed diffraction and contrast effects are due to a different artifact. The alloys were prepared by evaporating thin layers of carbon onto pure tantalum sheet followed by a diffusion anneal at temperatures between 1000 and 2000/sup 0/C in a vacuum of 10/sup -4/ Pa. Annealing times were between 2 and 48h. According to published data, 0.1 mm sheets of tantalum can absorb 1 atm(unit) from an oxygen atmosphere at 10/sup -4/Pa in 3 h at 1700/sup 0/C by reaction. In water vapor, the same amount of oxygen is absorbed in 9h. The evaporated carbon film will initially react with residual gases at the vacuum/carbon interface and dissolve in the tantalum at the Ta/C interface. After the carbon layer has been removed, the oxygen that is adsorbed on the surface will then either go into solution, or react with the dissolved carbon to form carbon monoxide. Since the latter reaction is controlled by the slow diffusion of carbon to the tantalum surface, the solution of oxygen will be faster. These effects are found to be kinetically, thermodynamically, and structurally consistent with the ordered Ta/sub 12/O phase formed by oxygen contamination during the preparation of the alloys. 2 figures.
- Research Organization:
- Univ. of California, Berkeley
- OSTI ID:
- 5659414
- Journal Information:
- Scr. Metall.; (United States), Journal Name: Scr. Metall.; (United States) Vol. 13; ISSN SCRMB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ANNEALING
CARBIDES
CARBON
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTION YIELD
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DISSOLUTION
ELECTROLYSIS
ELECTROPOLISHING
ELEMENTS
FLUIDS
GASES
HEAT TREATMENTS
IMPURITIES
INTERSTITIALS
LOW PRESSURE
LYSIS
METALS
NONMETALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
POINT DEFECTS
POLISHING
PRESSURE DEPENDENCE
SURFACE FINISHING
SYNTHESIS
TANTALUM
TANTALUM CARBIDES
TANTALUM COMPOUNDS
TANTALUM OXIDES
TEMPERATURE DEPENDENCE
TIME DEPENDENCE
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
VERY HIGH TEMPERATURE
YIELDS