New process produces controlled purity, very high strength, single crystal fibers of materials with melting points to 4000 C. Process has been used to make single crystal fibers of highly refractory ceramics such as aluminum oxide, titanium carbide and yttrium oxide

Haggerty, J.

Menashi, W. P.

Wenckus, J. F.

Westfall, L. J.

English

NASA Technical Reports Server

August 1972	 B72-10491 
•	 NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Floating Zone Process for Drawing

Small Diameter Fibers of Refractory Materials 
Composites of different metals or of metals and 
ceramics permit the creation of materials that take ad-
vantage of the desirable properties of the constituents 
and minimize their undesirable properties. Superior 
properties can be achieved in fiber-reinforced composite 
products, and it is believed that these products can be 
produced economically by mass production techniques. 
One of the more promising groups of such materials 
under investigation today comprises metallic composites 
composed of a metal matrix reinforced with refractory 
fibers such as the ceramic aluminum oxide, Al203. 
Since the development of such composities is con-
tingent upon the development of high-temperature-
resistant refractory fibers, it is necessary to develop 
processes for the production of fibers which exhibit high 
strength and negligible creep at temperatures of 1093°C 
(2000°F) and above. Processes producing continuous 
fibers are highly desirable from the point of view of 
both manufacture and application. 
A process for drawing continuous fibers of ceramic 
materials has recently been developed and has potential 
for adaptation to mass production. The process produces 
controlled purity, very high strength, single crystal fibers 
of materials with melting points to 4000°C (72320F). 
It has been used to make single crystal fibers of highly 
refractory ceramics such as Al 2 03 , TiC and Y203. 
The fibers are produced directly from the melted 
ceramic without the use of  crucible, thus eliminating a 
principal source of contamination encountered in other 
processes. The heating source for this process is a 400 watt 
CO2
 laser, which is capable of producing temperatures 
of 4000°C (7232°F). 
To form a single crystal ceramic fiber, the laser is 
focused on the tip of a feed rod of the desired material 
(such as A 1 03 , plain or doped), and power is increased 
until the tip of the feed rod begins to melt. A single 
crystal seed of the same material is brought into contact 
with the molten tip of the feed rod in such a manner as
to initiate single crystal growth onto the seed from the 
molten drop. The seed crystal is then drawn away at a 
rate predetermined to achieve the desired dimensions 
(diameters between 0.025 cm (0.010 inch) and 0.065 cm 
(0.025 inch)) for the solidified single crystal filament. 
Since the feed rod is cylindrical and the surface tension 
forces tend to produce symmetrical low energy shapes, 
the solidified filament is also cylindrical with a glass-
smooth surface that has very few defects. 
A Cr2 03 -doped Al 2 03
 fiber which was produced by 
this process is a macroscopic oxide fiber with the highest 
strength at elevated temperature that has ever been 
produced. Room temperature strengths obtained to date 
are 3.93 x 10 N/rn2
 (570,000 psi) in tension and 
9.66 x 10 9
 N/m2
 (1,400,000 psi) in buckling. Average 
elevated temperature tensile values are 1.12240 x iü 
N/m 2
 (162,666 psi) at 1093°C (2000°F) and 0.75 x 109 
N/rn 2
 (109,000 psi) at 1316 0C (24000 F). Stress rupture 
results at 1093°C (2000°F) and 1316°C (2400°F) are 
1,524,000 cm (600,000 inches) for 100 hours and 
1,219,200 cm (480,000 inches) for 100 hours, re-
spectively. This doped Al 2 03
 fiber is twice as strong as 
any other macroscopic fiber for which data are available, 
on the basis of stress rupture-density at 1093°C (2000°F) 
and 13160C (24000F); it is thermodynamically more 
stable than high-temperature, high-strength, low-density 
fibers such as carbon. 
This process has also been used to produce single 
crystal fibers which can be made by no other known 
process. Small diameter fibers of Y 2 03
 and TiC, which 
melt at 2410°C (4370°F) and 3200°C (5702 0 F), re-
spectively, have been produced. 
Notes: 
1. This process is being used to produce ceramic fibers 
for both metal matrix and ceramic matrix fiber-
reinforced composites for applications at operating 
temperatures above 10930C (2000017). 
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000490 2020-03-17T03:40:14+00:00Z
1] 2. The small diameter fibers produced by this process can also be utilized for making high-temperature light 
pipes, and for making jewel bearings by slicing the 
fibers into disks. For these applications, this process 
should offer a reduction in cost over conventional 
processes by eliminating the need to machine bulk 
rods of Al 2 03 down to small diameter fiber size. 
3. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: NASA CR-728 11 (N7 1 . 19222), Pro. 
duction of Oxide Fibers by a Floating Zone 
Fiber Drawing Technique
4. Technical questions may be directed to 
Technology Utilization. Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B72-10491 
Patent status: 
Title to this invention has been waived under the pro-
visions of the National Aeronautics and Space Act /42 
U.S.C. 2457(f)!, to Arthur D. Little, Inc., Cambridge, 
Massachusetts 02140.
Source: L. J. Westfall
Lewis Research Center and
J. Haggerty, W. P. Menashi, and J. F. Wenckus of 
Arthur D. Little, Inc.
under contract to
Lewis Research Center 
(LEW-1 1380) 
B72-10491	 Category 04


Floating zone process for drawing small diameter fibers of refractory materials

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