Noble-metal braze applied to appropriately prepared zirconia parts produces a gas-tight, durable seal that can withstand temperature of 825 C for over 2000 hours without deterioration

Smart, W.

English

NASA Technical Reports Server

May 1972	 B72-10199 
NASA TECH BRIEF 
Ames Research Center 
NASA Tech Briefs announcenew 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. 
High-Temperature Ceramic-to-Ceramic Seals 
The problem: 
To produce gas-tight, durable seals between pieces 
of zirconia ceramics; the seals must withstand tem-
peratures as high as 825'C for years. 
The solution: 
A noble-metal braze applied to appropriately pre-
pared zirconia parts. 
How it's done: 
The areas that are not intended to be metallized 
are masked with stop-off lacquer or tape. Then, the 
areas to be joined are cleaned in a nonabrasive alka-
line cleaning solution. 
The unmasked surfaces are sensitized for electro-
plating by depositing on them a very thin film of 
platinum or palladium. (Solutions of these metals in 
contact with the clean zirconia surfaces are reduced 
by sodium borohydride or hydrazine.) 
The sensitized areas are then coated with 0.002 to 
0.030 mm of platinum electrodeposited from baths 
of the composition ordinarily employed for this 
purpose. 
Finally, the metallized surfaces are overlain with 
preforms of precious metals or their alloys, clamped 
securely, and the seal is formed by heating in a 
furnace at the melting point of the alloy. 
The metat film plated on the ceramic must have 
a coefficient of thermal expansion close to that of 
the ceramic parts to be joined. Thus, gold is to be 
used on magnesia, platinum on zirconia, and rhodium 
on alumina. The braze metal should melt at a tem-
perature lower than the metal plated on the ceramic. 
As a rule, gold or gold alloys can be used as a braze
for the ceramics listed above, but since gold braze 
on gold—magnesia would be difficult to process, a 
gold—palladium alloy (higher m.p.) should be plated 
on the magnesia. 
Zirconia-to-zirconia seals made as indicated above 
(platinum with gold braze) have withstood a tem-
perature of 850°C for over 2000 hours without 
deterioration. 
Reference: 
Weissbart, J
.
; Smart, W.; and Wydeven, T.: Oxygen 
Reclamation from Carbon Dioxide Using a Solid 
Oxide Electrolyte. Aerospace Medicine, vol. 40, No. 2, 
p. 136, 1969. 
Notes: 
1. 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-73464 (N70-32473), De-
velopment of a CO2-H20 Solid Electrolyte 
Electrolysis System. 
2. No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B72-10199 
Patent status: 
No patent action is contemplated by NASA. 
(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=19720000199 2020-03-17T03:32:30+00:00Z
Source: Wilson Smart of 
Applied Electrochemistry, Inc. 
under contract to
Ames Research Center 
(ARC-10319) 
B72-10199	 Category 04


High-temperature ceramic-to-ceramic seals

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