Bonding of an element comprising sapphire, ruby or blue sapphire to another element of such material with a eutectic mixture of aluminum oxide and zirconium oxide is discussed. The bonding mixture may be applied in the form of a distilled water slurry or by electron beam vapor deposition. In one embodiment the eutectic is formed in situ by applying a layer of zirconium oxide and then heating the assembly to a temperature above the eutectic temperature and below the melting point of the material from which the elements are formed. The formation of a sapphire rubidium maser cell utilizing eutectic bonding is shown

Deluca, J. J.

English

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REPLY TO
ATTN OF: GP
TO:
FROM:
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
JftW 2 9 1975
KSI/Scientific & Technical Information Division
Attn: Miss Winnie M. Morgan
GP/Office of Assistant General
Counsel for Patent Matters
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SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No. : J^
Government or :_
Corporate Employee
Supplementary Corporate :_
Source (if applicable)
NASA Patent case No. :
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NOTE - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
YES /—7 NO
Pursuant to Section 305(a) of the National Aeronautics and
Space- Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
inventor (author) appears at the heading of column No. 1 of
the Specification, following the words "...with respect to
an invention of ..."
Bonnie L. Woerner
Enclosure
https://ntrs.nasa.gov/search.jsp?R=19750007920 2020-03-19T20:54:02+00:00Z
United States Patent
DeLuca
[ i i ] 3,859,714
[45] Jan. 14, 1975
[54] BONDING OF SAPPHIRE TO SAPPHIRE BY
EUTECTIC MIXTURE OF ALUMINUM
OXIDE AND ZIRCONIUM OXIDE
[75] Inventor: John J. DeLuca, Silver Spring, Md.
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: Jan. 12, 1973
[21] Appl. No.: 322,997
[52] U.S. Cl 29/472.7, 65/43, 156/89,
156/99, 117/93.3, 117/106 A, 29/473.1
[51] Int. Cl B23k 31/02
[58] Field of Search 29/472.7, 25.13, 600, 601,
29/572, 473.1; 65/43; 330/4; 220/2.1;
156/89, 99
[56] References Cited
UNITED STATES PATENTS
3,088,194 5/1963 Donadio 29/472.7 X
3,267,204 8/1966 Peters 65/43 UX
3,281,309 10/1966 Ross 65/43 X
3,467,510 9/1969 Knochel et al 65/43 X
3,469,729 9/1969 Grekila et al : 65/43 UX
3,479,170 11/1969 Louden 65/43 X
3,540,957 11/1970
3,736,222 5/1973
3,747,173 7/1973
Bowa et al 156/89
Arendt 156/89 X
Lind 65/43 X
OTHER PUBLICATIONS
Cannon, Melvin C., "How to Bond Sapphire to Other
Materials," American Machinist, August 29, 1946, pp.
129, 131.
Primary Examiner—Francis S. Husar
Assistant Examiner—Ronald J. Shore
Attorney, Agent, or Firm—R. F. Kempf; J. R. Manning
[57] ABSTRACT
Bonding of an element comprising sapphire, ruby or
blue sapphire to another element of such material with
a eutectic mixture of aluminum oxide and zirconium
' oxide. The bonding mixture may be applied in the
form of a distilled water slurry or by electron beam
vapor deposition. In one embodiment the eutectic is
formed in situ' by applying a layer of zirconium oxide
and then heating the assembly to a temperature above
the eutectic temperature and below the melting point
of the material from which the elements are formed.
The formation of a sapphire rubidium maser cell uti-
lizing eutectic bonding is shown.
10 Claims, 3 Drawing Figures
1600
1100
DEGREES
C.
18OO
140O
OPTIMUM
BOHO\HG
"TEMPERMURE
0 10 40 60 80 100 ZrOa
\00 80 feO 40 70 O
MOL PERCENT
PATENTED ^ '41975 3,859,714
C.
1600
110O
D 10 4<
^
D 6
/
0 8
1
/
•0 10
OPT\MUM
80HD\HG
TEMPtRMV
D ZrOi
"
1400
Al-jO-j, \00 &0 GO 4O 10
MOL PERCENT
^^\\\\\\\\\\\\\\\\\\\\\V
14
•• • w 3,859,714
1 2
BONDING OF SAPPHIRE TO SAPPHIRE BY interface and wetting the surfaces to be bonded thereby
EUTECTIC MIXTURE OF ALUMINUM OXIDE AND resulting in a vacuum tight and mechanically strong
ZIRCONIUM OXIDE bond which will withstand temperature cycling at high
level.
noir-iM r>c TUK i\r\/i7\rrrr>M 5 According to a preferred feature of the invention, theORIGIN OF THE INVENTION
 bond js composed mostly of A,iOj SQ as to hav£ the
The invention described herein was made by an em- closest thermal expansion match to the sapphire from
ployee of the United States Government and may be which the elements being bonded are formed,
manufactured and used by and for the Government for Various techniques may be utilized to provide the eu-
governmental purposes without the payment of any 10 tectic mixture. For example, the eutectic can be
royalties thereon or therefor. formed in situ by depositing a layer of zirconium oxide
DA/-i^/-D/-»itxn-> /-.IT TMJC iKM/cviTi^vi on tne surfaces to be bonded and, after assembly, heat-BACKGROUND OF THE INVENTION
 jng the artide to a temperature above the eutect
J
ic tem.
This invention relates the bonding of an element perature and below the melting of sapphire whereby
comprising sapphire, ruby or blue sapphire to another 15 the eutectic will be formed between the zirconium
element of such material and relates particularly to the oxide and the aluminum oxide of the sapphire at the in-
use of a eutectic mixture of aluminum oxide and zirco- . terface. Alternatively, a homogeneous mixture of alu-
nium oxide to bond such elements to each other. Spe- minum oxide and zirconium oxide powders in a dis-
cifically, the instant inventive concepts relate to the tilled water slurry can be painted onto the surfaces to
formation of an article such as a sapphire rubidium 20 be bonded resulting in the eutectic mixture when the
maser cell with a eutectic bonding agent, although simi- temperature has been raised to the proper level. The
lar concepts can be used for the formation of various zirconium oxide or a mixture of aluminum oxide and
articles from such materials such as thermionic conver- zirconium oxide can also be applied to the surfaces by
tors, vacuum tubes, high temperature sapphire lamp electron beam vapor deposition and, it is within the
bulbs and the like. 25 concepts of this invention to first form zirconium alu-
Particular problems exist in bonding of sapphire to minate from a mixture of aluminum oxide and zirco-
sapphire to form a closed cell that can be outgassed at nium oxide, and then to grind this material into a pow-
a high temperature, evacuated and filled with rubidium der which is utilized for the formation of the eutectic
vapor as in the formation of a sapphire rubidium maser bonding agent.
cell. The cell must be vacuum tight after sealing and 30
 DD,CI: rMrc/-DiDTir>M /->r -rue r>D A«/IM/-
non-reactive to the rubidium vapor. Sapphire has such BRIEF DESCRIPTION OF THE DRAWING
a narrow temperature range between solid and liquid, The invention itself will be better understood and ad-
only 1° C, that it is impractical to bond sapphire to sap- ditional features and advantages thereof will become
phire directly. apparent to those skilled in the art from the following
Most bonding heretofore has been done at low tem- 35 detailed description of preferred embodiments, such
perature with cementitious materials or at elevated description making reference to the accompanying
temperatures with the use of metallizers and brazing drawing wherein:
techniques or by the use of graded glass sealing tech- FIG. 1 is a liquidus curve of aluminum oxide and zir-
niques. Most'metals and glass outgas at high tempera- conium oxide;
tures in a vacuum or otherwise react with the rubidium 40 FIG. 2 is a plan view of a sapphire rubidium maser
vapor thereby contaminating the cell. cell formed utilizing the instant inventive concepts; and
ci,\*\*\ov r>c TUC iM\/cMTir»M FIG- 3 is a transverse cross-section or view thereofSUMMARY OF THE INVENTION
 taken substantially a)ong the lines 3_3 of FIG 2.
The instant invention relates to an improved method Like reference numerals refer to like parts through-
of bonding sapphire (A12O3), ruby (Al2O3 + Cr) or blue out the several views of the drawing.
sapphire (AI2O3 + Fe + T,O2) wherein the bonding is nFTAII Fn nPSCRIPTION OF THF PRFFFRRFn
accomplished at high temperatures, and unlike sinter- DETAILED DESCRIPTION OF THE PREFERRED
ing, is formed by a eutectic mixture that becomes fluid bMBUUiMfctN IJ>
at the bonding temperature and wets the surfaces to be Referring now to the drawing, and more particularly
bonded. Thus, the basic object of the instant invention to FIG. 1, a liquidus curve for aluminum oxide and zir-
is the provision of a bonding technique for sapphire, conium oxide is shown. At any temperature above the
ruby or blue sapphire elements which results in a mech- liquidus line, a mixture of the two ingredients will form
nically strong bond between the elements that is vac- a eutectic. Since the melting point of sapphire is 2050°
uum tight and highly resistant to chemical attack. C. it is only necessary to operate within a temperature
More specifically, it is an important object of this in- range above the liquidus curve and below the melting
vention to provide for the production of a sapphire ru- point.
bidium maser cell wherein the bond between the sap- In FIGS. 2 and 3 a sapphire rubidium maser cell is
phire elements is such that the cell can be outgassed at designated generally by the reference numeral 10 and
a higher temperature prior to filling than any other
 Q will be seen to comprise a cylindrical body element 12,
known sealing technique. Moreover, according to the a lower end plate 14, an upper end plate 16 and an
instant inventive concepts, the resultant bond is specifi- evacuation tube 18. The lower and upper end plates 14,
cally highly resistant to attack by alkali vapors such as 16 are bonded to the body element 12 by the eutectic
rubidium and cesium. mixture as shown at 20, 22, respectively, and the evac-
In accordance with this invention, a eutectic mixture
 65 uation tube 18 is bonded to the upper plate 16 by the
of aluminum oxide and zirconium oxide is formed at an eutectic mixture as shown at 24. The thickness of the
interface between surfaces of the elements to be eutectic bonding layer is exaggerated in the drawing for
bonded, this mixture, while molten, spreading over the illustrative clarity since the smallest quantity of eutec-
3,859,714
3 4
tic mixture should be utilized consistent with providing in the formation of the eutectic mixture in situ from the
an adequate bond. Generally, a layer on the order of zirconium oxide and the aluminum oxide of the ele-
about 0.005 inches is adequate, depending on the ments themselves at the interface.
closeness of the fit of the parts. Although reference has been made in the detailed de-
As indicated previously, it is desirable to select a pro- 5 scription primarily to sapphire, it is to be understood
portion between the materials that has the lowest melt- that similar techniques are applicable to ruby and blue
ing point on the liquidus curve and also the highest per- sapphire.
centage of aluminum oxide so that the bond is com- Following the techniques of the instant inventive
posed primarily of aluminum oxide and, therefore, has concepts a vacuum tight, mechanically strong bond is
the closest thermal expansion match to the sapphire. 10 formed which is h.ghly resistant to chemical attack and
Thus, a preferred -mixture comprises 75 mol percent ^^V to attack by alkali vapors such as rub.d.um
aluminum oxide with 25 mol percent zirconium oxide, «"d cesmm A sapphire rubidium maser cell formed I ac-
i u u -. -ii u c T?,/-* i .u v. • cording to these techniques can be outgassed at a high
although ,t will be seen from FIG. 1 that the eutectic temperature, evacuated^and filled with rubidium vapor
mixture can comprise from about 85 to about 35 mol
 according to known techniques without deleteriously
percent aluminum oxide with from about 15 to about 15
 affecting the bond between the elernentSj resu|ting in 'a
65 mol percent zirconium oxide. The bonding tempera- vacuum tight seal which is non-reactive to the rubidium
ture, depending upon the particular mixture of ingredi-
 vapor Thus; it win be seen that the objectives set forth
ents being utilized can vary' from the liquidus point up
 at the outset of the specification are successfully
to the melting point of the material of the elements achieved by the use of the instant inventive concepts.
being bonded, a preferred temperature range being be- 20 i
 ciaim:
tween 1,900° and 2,000° C., with approximately 1975° 1. A method of bonding an element comprising a ma-
C. being optimum. terial selected from the group consisting of sapphire,
In order to insure homogeneity in the eutectic, it is ruby and blue sapphire to another element of such ma-
desirable to use powders of relatively fine particle size, terial comprising forming a eutectic mixture of alumi-
300 mesh or finer being generally acceptable, although 25 num oxide and zirconium oxide at an interface between
the optimum material has a particle size of about 325 surfaces of the elements to be bonded, and then cooling
mesh. the same to a temperature below the eutectic tempera-
According to one embodiment of the instant inven- ture-
live concept, a mixture of aluminum oxide and zirco- 2- A method according to claim 1 wherein said eutec-
nium oxide powders may be formed into a slurry with ™ tic mixtur,e comprises from about 85 to about 35 mol
distilled water painted onto the surface to be bonded, Pf"5"' al"m'»«m oxlde with from about 15 to about
and, after assembly, allowed to dry for approximately 65, mol percent zirconium oxide.
2 hours. The assembly is then placed in a high tempera- 3' A method according to claim 2 wherein the alurm-
,. j r j • • • „ • num oxide and zirconium oxide each have a particleture furnace and fired in air, inert gas or vacuum, rais-
 sjze Qf 30Q mesh Qr fjner
ing the temperature from ambient at a temperature
 4 A method accordi to daim 2 wherein said eutec.
above the hquidus or eutectic temperature and below
 tic mixture is formed in situ b applying a ,ayer of zirco.
the melting point of the material from which the ele-
 nium oxide to each of the surfaces of the elements to
ments being bonded are formed over a period of ap-
 be bonded, juxtaposing said surfaces, and then heating
proximately two hours. The eutectic temperature is
 sarne to a temperature above the eutectic temperature
maintained for approximately one-half hour and then 4U
 and below the melting point of said material.
the assembly is cooled to ambient over a period of 5. A method according to claim 4 wherein said tem-
about 4 hours. Of course, the times given are merely perature is between about 1900° and 2000° C.
illustrative and not critical to the instant inventive con- 6. A method according to claim 4 wherein said layer
cepts. After cooling, the bonded assembly will with- of zirconium oxide is applied by an electron beam
stand temperature cycling up to 1800°C. vapor deposition.
It is preferable to have the bonding surfaces ground 7. A method according to claim 2 wherein the eutec-
to fit, the orientation of the crystalline axis of the indi- tic mixture is formed by applying a layer of a homoge-
vidual parts being matched when assembled so as to re- neous mixture of aluminum oxide and zirconium oxide
duce stresses. ' to eacn °f the surfaces of the elements to be bonded,
It is also helpful to apply a small holding force on the 50 juxtaposing said surfaces, and then heating same to a
assembly and to pull a vacuum in the furnace chamber temperature above the eutectic temperature and below
while the bonds are molten so as to exclude entrapped th| melting point of said material.
8. A method according to claim 7 wherein said tern-
55 mix-
,s by electron beam vapor deposition of e.ther the pow-
 ture Qf aluminum oxide *nd zirconiurn oxide is applied
der mixture or solid crystals of the same composition
 jn the form of a s|urry jn djstj|,ed water
as the powder mixture. This method has the advantage ,0 A method according to c)aim 2 wherein a homo-
of avoiding the necessity for drying of the assembled
 geneous mixture of about 75 mol percent aluminum
parts and there is less air entrapment in the bond.
 6Q oxide of about 325 mesh and 25 mol percent zirconium
While the use of a mixture of aluminum oxide and
 oxjde of about 325 mesh in a distilled water slurry is ap-
zirconium oxide insures the desired proportion of these p)jed to each of the surfaces of the elements to be
ingredients in the eutectic mixture, it is possible to form bonded after grinding said surfaces to provide a close
the eutectic in situ by depositing a layer of zirconium fit and cleaning same, said surfaces are juxtaposed and
oxide onto the surfaces to be bonded by an electron
 65 maintained in contact under pressure, and then the as-
beam vacuum deposition, assembling the elements, sembly is heated to about 1975° C. under vacuum to
heating the same in a furnace and otherwise processing form said eutectic mixture.
t h e assembly a s indicated previously, thereby resulting * * * * *


Bonding of sapphire to sapphire by eutectic mixture of aluminum oxide and zirconium oxide

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