Eutectic mixture of aluminum oxide and zirconium oxide provides new bonding technique for sapphires and rubies. Technique effectively reduces possibility of contamination. Bonding material is aluminum oxide and zirconium oxide mixture that matches coefficient of thermal expansion of sapphire

Deluca, J. J.

English

NASA Technical Reports Server

August 1973	 .	 B73-10284 
• ,.
	 NASA TECH BRIEF 
Goddard Space Flight 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 TechBrief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Eutectic Bonding of Sapphire to Sapphire 
The problem: 
The bonding of sapphire to sapphire for production 
of sapphire rubidium maser cells involves certain diffi-
culties. First, because sapphire has a very narrow 
temperature range (one degree Kelvin) between its 
solid and liquid states, direct bonding is impractical. 
Second, bonding of sapphire at elevated temperatures by 
use of metalizers and brazing or by use of graded glass 
sealing increases the possibility of contamination because 
rubidium vapor reacts with metals and glass at high 
S temperatures. The solution: 
A eutectic mixture of aluminum oxide and zirconium 
oxide provides a new bonding technique for sapphires 
and rubies. The technique effectively reduces the ;pOSS1. 
bility of contamination. 
How it's done: 
The bonding material is an aluminum oxide and 
zirconium oxide mixture that matches the coefficient of 
thermal expansion of sapphire. In general, the pro-
portion of aluminum oxide in the mixture varies from 
about 85 to 35 mole percent and that of zirconium oxide 
from 15 to 65 mole percent, respectively. The optimum 
mixture of Al2 0 3 to Zr0 2 is 75 to 25 mole percent, 
respectively. The bonding temperature depends on the 
particular mixture and varies anywhere from 2173 to 
2273 K with approximately 2248 K being the optimum. 
To insure homogeneity in the eutectic mixture, 
these oxide powders must have a relatively fine powder 
size. A 300 mesh or finer grain is generally acceptable, 
with the optimum size being approximately 325 mesh. 
The bonding technique first requires mixing the 
Al 2 0 3 and Zr0 2 into a slurry with distilled water. This 
mixture is then painted on the sapphire surfaces to be 
bonded. The surfaces are then placed together, and the
entire assembly is put into a high-temperature furnace 
and fired in air, inert gas, or vacuum for about two hours. 
Temperature in the furnace during firing is above the 
eutectic temperature of sapphire, but below its melting 
point. After firing, the temperature in the furnace is 
dropped to the eutectic level for about half an hour. 
The assembly is then cooled to ambient temperature for 
about four hours. After cooling, the bonded assembly 
can withstand temperature cycling up to 2073 K. 
As an alternate, it is also possible to form the 
eutectic mixture in situ by depositing a layer of 
zirconium oxide on the sapphire surfaces by electron 
beam vacuum deposition. The sapphire surfaces are 
then assembled and bonded as described previously. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: TSP73- 10284 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial develop-
ment should be addressed to: 
Patent Counsel 
Goddard Space Flight Center 
Code 204 
Greenbelt, Maryland 20771 
Source: John J. DeLuca
Goddard Space Flight Center
(GSC. 1 1577) 
Category 04, 08 
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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Eutectic bonding of sapphire to sapphire

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