NIOBIUM PHASE DIAGRAMS. Report No. 5: Columbium-Hydrogen System. Report No. 6: Columbium-Nitrogen System. Report No. 7: Columbium-Oxygen-Nitrogen System. Report No. 8: Final Technical Report Covering the Period April 15, 1957 to April 15, 1960
ABS>The Nb- O equilibrium system was determined by metallographic examination of arc-cast alloys. Tbe oxides NbO and NbO/sub 2/ melted without decompcsition at 1945 and 1915 deg C, respectively. Eutectic reactions between Nb and NbO at 1915 deg C and between NbO and NbO/sub 2/ at 1810 deg C were found to exist. A peritectic reaction between NbO/sub 2/ and Nb/sub 2/O/sub 5/at 1510 deg C was supported by experimental evidence. The maximum solid solubility of O in Nb was determined to be 0.72 wt.%. Two carbides were found to exist in the C- Nb system; hexagonal Nb/sub 2/C with a limited range of homogeneity and cubic NbC with a solubility range of 8.25 to 10.25 wt.% C. The solubility of C in Nb was determined to be 0.80 wt.% at the eutectic temperature, but this value decreased rapidly with temperature. A peritectic reaction between melt, Nb/sub 2/C, ard NbC was indicated; alloys richer in C than NbC froze by eutectic reaction. H-Nb equilibrium was studied at 300 to 1500 deg C and O to 760 mm Hg equilibrium H/sub 2/ pressure by the Sieverts technique. A continuous solid solution was formed in the range, exhibiting bcc structure with lattice parameter increasing with increasing H content. The formation of the solid solution was exothermic. Below 300 deg C, the existence of a non-classical phase transformation was observed. The N - Nb equilibrium diagram was investigated in the composition range up to stoichiometric NbN and temperatures up to 2500 deg C. The boundary of the Nb-N solid solution was established by direct chemical analysis. Solubility was found to be 0.25 wt.% N at 1200 deg C and 2.5 wt.% at 2400 deg C. X-ray-diffraction studies revealed the existence of close-packed hexagonal Nb/sub 2/N, tetragonal NbN (Nb/sub 4/N/sub 3/), face-centered cubic NbN, and hexagonal NbN. A N-Nb phase diagram is presented which incorporates the observed equilibrium phenomena. X-raydiffraction studies and metallographic examinations of the Nb-Nb-O system revealed equilibrium between Nb/sub 2/N and NbO and between Nb/sub 2/ and NbO/sub 2/. (See also ARF-2120-3 and ARF-2120-4.) (C.J.G.)
- Research Organization:
- Illinois Inst. of Tech., Chicago. Armour Research Foundation
- NSA Number:
- NSA-14-022003
- OSTI ID:
- 4160796
- Report Number(s):
- ARF-2120(5thru8)
- Country of Publication:
- United States
- Language:
- English
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