Nitrogen solubility in solid niobium
- PDF / 353,137 Bytes
- 4 Pages / 603.28 x 783.28 pts Page_size
- 11 Downloads / 241 Views
\
/
12o
where PN2 is in pascals. The terminal solubility of nitrogen in niobium with respect to Nb2N was found to be: [ 9270'~ wt pet N : 78.1 e x p ~ - - - ~ - ?
I.
INTRODUCTION
SINCE niobium and many of its alloys exhibit superconductivity, they are of great interest for power generation, propulsion devices, fusion research, and electronic devices.I~l Other potential areas of application are in many fields such as power transmission, generators and motors, ultrasensitive magnetic sensors, high field magnets for fusion energy, magnetically levitated vehicles, and high speed computers. Improving the purity of niobium provides a valuable safety margin for achieving superconductor performance close to theoretical promise, f21 Interstitially dissolved impurities such as carbon, nitrogen, and oxygen degrade the performance significantly. At low concentrations of impurities, the residual resistivity caused by homogeneous distribution of impurities is proportional to their concentration. 13] From the examination of the proportionality constants, it can be concluded that the harmful effect of nitrogen far exceeds the undesirable effects due to the presence of most other impurities in niobium. Therefore, elimination of nitrogen from niobium is of significant interest. The difficulty in the determination of a formal relation between the concentrations of nitrogen in the atmosphere and in the niobium originates, to a large extent, due to the highly reactive nature of niobium at elevated temperatures. Niobium melts at 2744 K and at temperatures close to the melting point, both the determination of nitrogen concentration in niobium and the prevention of sample contamination from the container become formidable tasks. In view of these difficulties it is not surprising that conflicting data have been reported about the solubility of nitrogen in niobium, I4-81 the heat of solution of nitrogen in niobium, t4-91 and the terminal solubility of nitrogen in niobium11~ with respect to Nb2N. The solubility of nitrogen in solid niobium was determined at temperatures close to the melting point by electromagnetic 9
M. ALAM, Postdoctoral Research Associate, and T. DEBROY, Associate Professor of Metallurgy, are with the Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802. Manuscript submitted November 11, 1987. METALLURGICAL TRANSACTIONS B
levitation technique where the problem of container contamination and sample purity are largely eliminated. Apart from providing important information about nitrogen solubility, it is hoped that the data will be useful in resolving some of the discrepancies in the data reported in the literature.
II.
PROCEDURES
A schematic diagram of the experimental set-up is shown in Figure 1. The set-up consisted of a levitation coil connected to a high frequency induction furnace, a vertical vycor levitation chamber, and a lower aluminum chamber with a rotating base plate that contained a quartz specimen holder. The specimen holder was used for the init
Data Loading...
