Reaction diffusion and phase equilibria in the V-N system
- Vienna Univ. of Technology (Austria). Inst. for Chemical Technology of Inorganic Material
- CNRS, Rennes (France). Lab. of Metallurgy and Physical Chemistry of Materials
- IFREMER Brest, Plouzane (France)
The formation of phase bands in in situ diffusion couples of the V-N system was studied by the reaction of vanadium sheet with pure nitrogen within the temperature range 1,100 C to 1,700 C and the nitrogen pressure range 2 to 24 bar. Under these conditions, phase bands of {beta}-V{sub 2}N and {delta}-VN{sub 1{minus}x} develop. The morphology of the {beta}-V{sub 2}N/{alpha}-V(N) interface depends on the saturation state of the {alpha}-V(N) core. If the nitrogen content in {alpha}-V(N) is high, the interface has a jagged appearance, whereas at low nitrogen contents of the {alpha}-V(N) phase, the interface is planar. Electron probe microanalysis (EPMA) was used to measure the diffusion profiles within the couples. The homogeneity regions of the nitride phases were established and the phase diagram accordingly corrected. From the growth rates of the phase bands, the mean composition-independent nitrogen diffusivities in {beta}-V{sub 2}N and {delta}-VN{sub 1{minus}x} were derived. These diffusivities follow an Arrhenius equation with activation energies of 2.92 ({beta}-V{sub 2}N) and 2.93 eV ({delta}-VN{sub 1{minus}x}). By using {delta}-VN{sub 1{minus}x} as a starting material and a low nitrogen pressure during annealing, it could be shown that the direction of nitrogen diffusion can be reversed, i.e., {beta}-V{sub 2}N is formed on the surface of the couple as a result of out-diffusion of nitrogen.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 484839
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 3A Vol. 28; ISSN 1073-5623; ISSN MMTAEB
- Country of Publication:
- United States
- Language:
- English
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