Radial furnace, with a long graphite vaporization tube, maintains a uniform thermal gradient, favoring the growth of straight boron carbide whiskers. This concept seems to offer potential for both the quality and yield of whiskers

Feingold, E.

English

NASA Technical Reports Server

April 1967
	 Brief 67-10070 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Radial Furnace Shows Promise for Growing Straight Boron Carbide Whiskers 
Vacuum 
II 
------------J L--------------
' 4 Substrate Tube 
Substrate Support Tube 
Vaporization Tube 4_____-i 
I.Radial Holes .. ..........:':.':'.... ,  
............................... 
Boron Carbide Whiskers 	 Boron Carbide Powder L_ - - _J= - - - - - I r- - - - - - - - - - __ - __ _ J 
L:z	 Inert Gas 
To Power Supplies 
A vapor deposition method of growing boron car-
bide whiskers is described in Tech Brief 65-10262. 
Although the chimney-type furnace used in that 
method produced whiskers of generally high strength 
and in sufficient yield for tensile testing and charac-
terization studies, the whiskers were short and had 
both a taper and a curvature. 
Further study has shown that by providing a more 
uniform thermal gradient than can be maintained in 
the chimney-type furnace, the growth of straight 
whiskers would be favored. Experiments were there-
fore conducted with a radial furnace in which the 
thermal gradients required for whisker growth are 
normal to the deposition (substrate) surface. The 
essential features of the furnace are a long graphite 
vaporization tube with a series of radial holes sym-
metrically spaced in the central portion of the tube 
and a concentric graphite tube of larger diameter 
which supports a graphite substrate tube.
The boron carbide powder contained in the central 
portion of the vaporization tube is heated to approxi-
mately 1900°C, and the resultant vapors diffuse 
through the radial holes. As the vapors come into 
contact with the cooler substrate tube they condense 
and grow into boron carbide whiskers. The proper 
operating temperatures of the inner and outer tubes 
are maintained through resistance heating with 
adjustable power supplies. With this arrangement, 
the temperature gradient in the annular region be-
tween the concentric tubes is radial (i.e., normal) with 
respect to the surfaces of the tubes. As a consequence, 
the whiskers tend to grow straight in a direction 
parallel to the temperature gradient. 
Although the whiskers grown in this furnace were

straight (not curved like those grown in the chimney

furnace) they were only 1 millimeter long and their

growth rate was still low. The number of whiskers

grown, however, was much greater than in the chim-

(continued overleul) 
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https://ntrs.nasa.gov/search.jsp?R=19670000070 2020-03-11T20:21:14+00:00Z
ney furnace, since the available surface area for 
nucleation and growth of the whiskers was much 
larger. The concept of the radial furnace appears to 
offer the greater potential in terms of both quality 
(high strength) and yield of whisker product. 
Note: 
Inquiries concerning the radial furnace may be di-
rected to:
Technology Utilization Officer 
Headquarters 
National Aeronautics and Space 
Administration 
Washington, D.C. 20546 
Reference: B67-10070
Patent status: 
No patent action is contemplated by NASA. 
Source: Earl Feingold 
of General Electric Company 
under contract to 
Headquarters, NASA 
(HQ-50)
S 
Brief 67-10070	 Category 03


Radial furnace shows promise for growing straight boron carbide whiskers

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