Hostname: page-component-586b7cd67f-gb8f7 Total loading time: 0 Render date: 2024-11-25T16:45:55.956Z Has data issue: false hasContentIssue false
  • English
  • Français

Feasibility Of Directional Solidification Of Lanthanum Hexaboride In a Boron Matrix

Published online by Cambridge University Press:  15 February 2011

Kathryn V. Logan
Kathryn V. Logan*
Affiliation:
Materials Characterization Branch Engineering Experiment Station Georgia Institute of Technology Atlanta, Georgia 30332USA
Get access

Abstract

Attempts were made to directionally solidify lanthanum hexaboride as uniformly spaced rods, less than one micron in diameter, in a boron matrix. Lanthanum hexaboride and boron powders were combined in a near eutectic mixture, formed into right circular cylinders and melted by RF induction heating in a pure hydrogen atmosphere using a modified internal zone melting technique.

Ball milling, uniaxial cold pressing, isostatic pressing and hot pressing were investigated as possible means of increasing the sample density before melting in the RF induction furnace. RF coupling was achieved directly in the hot pressed pellet, and indirectly through the use of a molybdenum preheater in the uniaxially cold pressed pellets. Internal zone melting and conventional crucible melting in various materials were tried.

Directional growth was observed in the pellets that were uniaxially cold pressed and preheated with a molybdenum tube sleeve. Lanthanum hexaboride fibers with an ℓ/d ratio of about ten to one and other forms of aligned microstructures were observed in selected areas of the pellet.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 12: Symposium L – In Situ Composites IV , 1981 , 195
Copyright
Copyright © Materials Research Society 1982

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

1. Cochran, , et al. , “Low Voltage Field Emitter Arrays,” Interim Technical Report, Air Force Contract F33615–79–C–1832, Georgia Institute of Technology, School of Ceramic and Electrical Engineering, Sept. 1980.Google Scholar
2. Hill, D.N., “The Effect of Cathode Geometry on the Emission Characteristics of Low Voltage Field Emitters Fabricated From Uranium-Dioxide- Tungsten Composites,” a thesis for Doctor of Philosophy in Ceramic Engineering, Georgia Institute of Technology, August 1979.Google Scholar
3. Spear, K. E., “Rare Earth-Boron Phase Equilibria,” in Boron and Refractory Borides, Matkovitch, V. I. ed., Springer-Verlag, Berlin, Heidelberg, New York, 1977, pp. 439–456.CrossRefGoogle Scholar
4. Johnson, R. W., et al. , “The Lanthanum-Boride System,” J. Phys. Chem., 65 (1961), p. 909–915.CrossRefGoogle Scholar
5. Windsor, E. E., “Construction and Performance of Practical Field Emitters from Lanthanum Hexaboride,” Proc. IEEE, Vol. 116, No. 3, March 1969, p. 348–350.Google Scholar