Electrically conductive layer of zirconium on a zirconium-oxide film residing on a zirconium substrate is formed by reducing the oxide in a sodium-calcium solution. The reduced metal remains on the oxide surface as an adherent layer and seems to form a barrier that inhibits further reaction

Youngdahl, C. A.

English

NASA Technical Reports Server

June 1967
	 Brief 67-10187 
V Cot,
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the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Oxide Film on Metal Substrate Reduced to Form Metal-Oxide—Meta' Layer Structure 
The problem: 
To form an electrically conductive layer of zir-
conium on a zirconium-oxide film residing on a zir-
conium substrate. 
The solution: 
Reduce the oxide in a sodium—calcium solution at 
an elevated temperature so the reduced metal remains 
on the oxide surface as an adherent layer. 
How it's done: 
A zirconium alloy sample containing 1 % copper 
by weight and 1% iron by weight is preoxidized to 
form a surface oxide layer. The surface of the oxide 
is reduced by exposure to liquid sodium saturated 
with calcium (94% sodium by weight and 6% cal-
cium by weight) at a temperature near 600°C. A 
20-hour exposure period is typical for a sample having 
an oxide thickness of about 10 microns. The reduc-
tion takes place in an argon-filled 100-ml autoclave. 
The oxidized zirconium sample is suspended by a 
stainless steel wire from the top plug of the autoclave. 
The autoclave is then sealed, inverted, and heated to 
the process temperature. At the end of exposure, the 
vessel is turned upright and allowed to cool. The 
sample is then withdrawn and cleaned in water. 
The reduction process produces an adherent layer 
of zirconium on the outer surface of the oxide. This 
resultant adherent metallic layer is typically several 
microns thick and displays substantial electrical con-
ductivity between test probes contacting the surface. 
The reduced layer is characteristically very hard, im-
plying a high residual oxygen content. The layer is 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
readily etched away on brief exposure to nitric—hydro-
fluoric acid solution, producing loss of conductivity 
between surface probes. 
Notes: 
1. The reduced metal layer appears to form a barrier 
that inhibits further reaction at the initially rapid 
rate. 
2. The outer layer was found to be electrically shorted 
to the substrate metal, due probably to isolated 
cracks present in the oxide prior to reduction. If 
undesirable, such cracked areas might be sectioned 
out after reduction. Alternatively, use of thinner 
oxide films would minimize the occurrence of 
cracks. However, electrical leakage through the 
bulk oxide should be reduced by a thick insulating 
layer. Limitation of time and/or temperature dur-
ing reduction, oxygen enrichment of the underlying 
metal surface, or substrate alloying to inhibit 
oxygen diffusion should also improve the insulating 
character of the oxide in the final layer structure. 
3. The process does not depend on the particular 
alloy described. Surface reduction of unalloyed 
zirconium samples bearing corrosion films has 
also been accomplished by the technique described. 
Further, substrate materials other than zirconium 
might be susceptible to the technique, since the 
reduction of zirconium oxide is relatively difficult. 
4. This method of metal-oxide—metal layer forma-
tion or the oxidation-back reduction approach may 
find application in the manufacture of integrated 
circuitry and similar thin-layer devices and struc-
tures.
(continued overleaf) 
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000187 2020-03-11T20:50:56+00:00Z
5. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B67-10187 
Source: C. Arthur Youngdahl
Metallurgy Division 
(ARG-48)
Patent status: 
Inquiries about obtaining rights for commercial use 
of this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 67-10187	 Category 03


Oxide film on metal substrate reduced to form metal-oxide-metal layer structure

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