Composite of fine niobium wires in copper is used to study the size and proximity effects of a superconductor in a normal matrix. The niobium rod was drawn to a 100 angstrom diameter wire on a copper tubing

Cline, H. E.

Rose, R. M.

Wulff, J.

English

NASA Technical Reports Server

August 1968	 Brief 68-10279 
NASA TECH BRIEF	
_1a 
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. 
100 A Niobium Wire 
The size and proximity effects of a superconductor 
in a normal matrix has been investigated. A composite 
of fine niobium wires in copper was chosen for its 
desirable mechanical and chemical properties and a 
fabrication technique was developed from the method 
of Levi. 
The starting materials were 1/8-inch diameter 
electron-beam melted Nb rod, and OHFC copper tub-
ing with 0.375-inch od and 0.032-inch wall thickness. 
The tubing was swaged onto the rod and the ensemble 
then drawn to 0.0345-inch diameter wire which was 
cut into 56 pieces. These pieces were fitted into an-
other piece of copper tube, and the ensemble drawn 
down again to 0.0345-inch diameter. This procedure 
was repeated four times, and on the final sequence, 
the wire was drawn down to 0.006-inch diameter, 
which, on the assumption of uniform straining of the 
Nb and Cu, corresponds to a Nb diameter of about 
100 Angstroms. Before assembling each composite 
prior to a drawing 9equence, the surfaces of the wires 
and tube were carefully cleaned, degreased with a 
solvent (trichioroethylene) and abraded with No. 600 
metallographic paper and recleaned. Drawing was 
done at the uniform rate of one inch per minute by 
mounting dies and wire in an Instrom tensile testing 
machine. Commercial wire-drawing equipment was 
found to be insufficient even in its drawing rate, and 
all attempts to make composites using commercial 
equipment in the laboratory failed. The low draw-
ing rate was also necessary. The lubricant used was 
of the MoS2 type. 
At various stages in the fabrication, specimens were 
secured for optical electron micrography and diffrac-
tion. For the second and third sequences, optical 
metallography with routine diamond-dust polishing 
and no etching sufficed to delineate the structure. 
For subsequent operations, electron micrography was 
necessary. The Cu matrix was removed by etching 
with 50% HNO3, the resulting niobium "wool" 
was washed, broken up by ultrasonic cavitation, and 
removed from the water with a standard grid used 
for transmission electron micrography. 
Note: 
Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B68-10279 
Patent status: 
No patent action is contemplated by NASA. 
Source: H. E. Cline, R. M. Rose, 
and J. Wulff 
of Massachusetts Institute of Technology 
under contract to 
Lewis Research Center 
(LEW- 10128) 
Category 03 
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.
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One hundred angstrom niobium wire

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