Adhesive for mutual union of oxide type ceramic articles and method for manufacture thereof

An adhesive agent having, as its active components, copper sulfide and at least one member selected from the group consisting of alumina, silica, and kaoline enables the opposed surfaces of two oxide-type ceramic articles to be joined to each other with high adhesive strength, this fast union being accomplished by interposing the adhesive agent between the opposed surfaces of the ceramic articles and heating the adhesive agent to a temperature of not less than 1000.degree. C.

BACKGROUND OF THE INVENTION: 
This invention relates to an adhesive agent for mutual union of two oxide 
type ceramic articles and to a method for the manufacture of this adhesive 
agent. 
Heretofore, mutual adhesion of two oxide type ceramic articles has been 
accomplished by adopting a method which comprises interposing a metal 
between the opposed surfaces of these ceramic articles and filling up the 
intervening gap with silver solder (Japanese Patent Publication Sho 
47(1972)-21569) or a solder glass method, for example. The former method 
entails time-consuming and complicated work because it requires 
interposition of a metal. Besides, this method is not workable when the 
ceramic articles to be joined have complicated shapes. Since the latter 
method uses a solder which is preponderantly formed of glass, it has the 
disadvantage that the solder sustains breakage under thermal strain, 
offers insufficient thermal resistance, and suffers heavy degradation of 
its ability to resist chemicals because of the occurrence of an alkali 
upon vitrification. 
For the union of ceramic articles in general including articles of oxide 
type ceramics, some of the present inventors participated in perfecting 
earlier inventions. One of these is the invention of U.S. Pat. No. 
4,293,356 which concerns an adhesive agent formed of a mixture of CuS, 
LaCrO.sub.3, SiO.sub.2, and Cu. Two others are the inventions of U.S. Pat. 
No. 4,486,257, granted Dec. 4, 1984 and U.S. Pat. No. 4,447,283, granted 
May 8, 1984 which concern adhesive agents respectively formed 
preponderantly of calcium fluoride or a mixture of calcium fluoride with 
kaoline and of an alkali fluoride or a mixture of an alkali fluoride with 
kaoline. All these adhesive agents exhibit contact strengths of not more 
than about 100 kg/cm.sup.2. As the use found for ceramics is now 
expanding, ceramic articles are now required to be available in a wide 
variety of shapes. In the circumstance, the adhesive agents used for 
mutual adhesion of these ceramic articles are naturally expected to offer 
ample adhesive strength. 
One object of this invention is to provide an adhesive agent capable of 
joining two oxide type ceramic articles with high adhesive strength. 
Another object of this invention is to provide a method for joining two 
oxide type ceramic articles to each other with high adhesive strength. 
SUMMARY OF THE INVENTION 
To attain the objects mentioned above, the inventors made a diligent study. 
They have consequently found that in the aforementioned invention of U.S. 
Pat. No. 4,293,356, the adhesive agent exhibits more than three times as 
high adhesive strength when incorporation of lanthanum chromite and 
powdered copper is omitted, that silica can be replaced by alumina or 
kaoline or can be used together with alumina and/or kaoline, and that the 
adhesive agent is not always required to be prepared in the form of paste 
and the heating is not required to be carried out under an oxidizing 
atmosphere when the substitution is made. This invention has been 
perfected on the basis of this knowledge. 
Specifically, this invention relates to an adhesive agent for mutual 
adhesion of two oxide type ceramic articles which has as principal 
components thereof copper sulfide and at least one member selected from 
the group consisting of alumina, silica, and kaoline and to a method for 
the mutual adhesion of two oxide type ceramic articles which is 
characterized by interposing the adhesive agent mentioned above between 
the opposed surfaces of the two oxide type ceramic articles and heating 
the adhesive agent to a temperature of not less than 1000.degree. C. 
DESCRIPTION OF THE PREFERRED EMBODIMENT: 
The adhesive agent of the aforementioned invention of U.S. Pat. No. 
4,293,356 is greatly increased in its adhesive strength by omitting 
incorporation of lanthanum chromite and powdered copper. Although this 
improvement in the adhesive strength can possibly be explained as stated 
later, the true reason therefor remains yet to be elucidated. As 
demonstrated in the working examples cited afterward, the adhesive agent 
of the present invention unmistakably shows more than three times as high 
adhesive strength as the adhesive agent of the U.S. patent mentioned 
above. 
The adhesive agent of this invention is supposed to fulfill its function 
through the following mechanism. Since it is heated to a temperature 
exceeding 1000.degree. C., the copper sulfide is decomposed into sulfur 
and copper and this copper combines with alumina and/or silica to give 
rise to a two-component or three-component adhesive phase and, at the same 
time, the sulfur permeates oxide type ceramic articles and the 
aforementioned adhesive phase is caused simultaneously to pass and spread 
into the ceramic articles. Since this adhesive phase has a relatively low 
melting point, it is in a molten state when the adhesive agent is heated 
to the aforementioned temperature. Thus, the molten adhesive phase, with 
cooperation from the sulfur, is allowed to permeate the ceramic articles 
smoothly. In this manner, the adhesive agent of this invention enjoys 
improved adhesive strength. 
According to the inventors' own experiment, the adhesive agent suffers from 
heavy loss of adhesive strength when the copper sulfide is replaced by 
some other copper compound such as, for example, copper carbonate, copper 
oxide, or copper chloride or when alumina, silica, or kaoline is replaced 
by zirconia or magnesia. This decline of the adhesive strength may 
possibly result from the absence of the aforementioned low-melting 
adhesive phase and the unavailability of the cooperation of sulfur. 
In the preparation of the adhesive agent of this invention, copper sulfide 
and alumina, silica, and/or kaoline are used in their powdered form, 
desirably in a particle size of not more than 3 .mu.m. Although these raw 
materials are desired to have as high purity as permissible, use of such 
raw materials as are normally commercially available suffices for the 
purpose of this invention. 
By "kaoline" is meant a clay (for pottery) having an average chemical 
composition of Al.sub.2 O.sub.3.2SiO.sub.2.2H.sub.2 O. Kaoline, when 
heated to about 600.degree. C., is decomposed with liberation of water of 
crystallization. Typical commercial products available in Japan are 
Kampaku Kaoline and Chosen Kaoline (of high purity). 
Generally, copper sulfide and at least one member selected from the group 
consisting of alumina, silica, and kaoline are desired to be used in 
proportions such that the former will account for 30 to 98% by weight and 
the latter for 70 to 2% by weight respectively based on the total amount 
of their mixture. Preferably, the proportions are 90% by weight of the 
former and 10% by weight of the latter. 
In working the present invention, copper sulfide and at least one member 
selected from the group consisting of alumina, and kaoline are thoroughly 
mixed at a ratio within the range described above. The resultant mixed 
powder may be used immediately in its unaltered form. Otherwise, it may be 
transformed into paste by addition thereto of a suitable binder and a 
solvent therefor such as, for example, screen oil or printing ink, and 
balsam before it is put to use. 
The adhesive agent obtained in the form of powder or paste as described 
above is interposed generally in an amount of 0.5 to 3 g/cm.sup.2, 
preferably 1 to 2 g/cm.sup.2, as principal components between the opposed 
surfaces of two oxide type ceramic articles and then heated to and 
maintained at a temperature in the range of about 1000.degree. to 
1300.degree. C., preferably 1050.degree. to 1200.degree. C., for a period 
of about 10 to 60 minutes. Consequently, the ceramic articles are joined 
with great strength. If the temperature is lower, the decomposition of 
copper sulfide is not enough to ensure fast mutual adhesion. If it is 
higher, there is the possibility of the adhesive phase flowing out of the 
adhesive agent. This application of heat may be advantageously carried out 
in the atmosphere. It is not required to be performed under the blanket of 
an oxidizing gas. The heating treatment does not call for use of any 
pressure means. Slight application of pressure may be desirable for the 
purpose of ensuring airtight contact between the opposed surfaces of the 
ceramic articles under treatment. 
The kinds of oxide type ceramics for which this invention provides 
effective mutual adhesion are not specifically limited. Fast mutual 
adhesion is offered to ceramics of alumina, mullite ceramics, and ceramics 
of magnesia, zirconia, cordielite, and beryllia. 
In accordance with this invention, two oxide type ceramic articles are 
joined fast by a simple operation of just one heating. The adhesive 
strength is generally not less than 1500 kg/cm.sup.2, a level more than 
three times as high as the level obtainable by any conventional adhesive 
agent. The adhesive agent of this invention is capable of readily joining 
ceramic articles of complicated shape and the adhesive layer formed in the 
joined ceramic articles excels in resistance to chemicals and in 
resistance to thermal shocks. 
Now, the present invention will be described more specifically below with 
reference to working examples.

EXAMPLE 1 
A pasty adhesive agent was obtained by mixing 90% by weight of powdered 
copper sulfide (having a particle size of not more than 3 .mu.m; the same 
applies hereinafter) with 10% by weight of powdered kaoline (having a 
particle size of not more than 3 .mu.m) and then mixing 100 parts by 
weight of the resultant mixed powder with 15 parts by weight of screen 
oil. This adhesive agent was interposed at a rate of 1 g/cm.sup.2 as 
principal components between two zirconia plates and maintained at 
1100.degree. C. for 30 minutes in the air to join the plates. 
A test piece of the joined plates thus obtained was tested for adhesive 
strength by the three-point load bending method under the conditions of 20 
mm of span and 0.5 mm/min. of load application speed. Thus, the adhesive 
strength was found to be 1880 kg/cm.sup.2. 
Another test piece was immersed in an aqueous 48% potassium hydroxide 
solution at 70.degree. C. for 50 hours to test for resistance to 
chemicals. At the end of the immersion, the test piece was found to have 
sustained no change of any sort in the portion of adhesion. 
This test piece was heated again to 1100.degree. C. and suddenly cooled in 
cold water to test for resistance to thermal shock. This harsh treatment 
produced no change of any sort in the portion of adhesion. 
EXAMPLE 2 
Mutual adhesion was tried by following the procedure of Example 1, except 
that alumina plates were used in the place of zirconia plates. 
A test piece of the resultant joined plates was found by test to possess 
adhesive strength of 2010 kg/cm.sup.2. Under the same test conditions as 
used in Example 1, this test piece showed high resistance to chemicals and 
to thermal shock. 
EXAMPLE 3 
An adhesive agent was obtained by mixing 90% by weight of powdered copper 
sulfide with 10% by weight of powdered kaoline (having a particle size of 
not more than 3 .mu.m). This adhesive agent was interposed at a rate of 1 
g/cm.sup.2 between the opposed surfaces of two zirconia plates and 
maintained at 1100.degree. C. for 30 minutes in the air, to join the two 
plates. 
A test piece of the joined plates was found by test to possess adhesive 
strength of 1860 kg/cm.sup.2. Under the same test conditions as used in 
Example 1, this test piece showed high resistance to chemicals and to 
thermal shock. 
EXAMPLE 4 
An adhesive agent was obtained by mixing 90% by weight of powdered copper 
sulfide with 10% by weight of powdered alumina (having a particle size of 
not more than 3 .mu.m). This adhesive agent was interposed at a rate of 1 
g/cm.sup.2 between the opposed surfaces of two zirconia plates and heated 
at 1100.degree. C. for 30 minutes in the air to join the two plates. 
A test piece of the joined plates was found by test to possess adhesive 
strength of 1890 kg/cm.sup.2. Under the same test conditions as used in 
Example 1, it showed high resistance to chemicals and to thermal shock. 
EXAMPLE 5 
An adhesive agent was obtained by mixing 90% by weight of powdered copper 
sulfide with 5% by weight of powdered alumina (having a particle size of 
not more than 3 .mu.m) and 5% by weight of powdered silica (having a 
particle size of not more than 3 .mu.m). This adhesive agent was 
interposed at a rate of 1 g/cm.sup.2 between the opposed surfaces of two 
zirconia plates and maintained at 1100.degree. C. for 30 minutes in the 
air, to join the two plates. 
A test piece of the joined plates was found by test to possess adhesive 
strength of 1790 kg/cm.sup.2. Under the same test conditions as used in 
Example 1, this test piece showed high resistance to chemicals and to 
thermal shock. 
EXAMPLE 6 
An adhesive agent was obtained by mixing 90% by weight of powdered copper 
sulfide with 10% by weight of powdered silica (having a particle size of 
not more than 3 .mu.m). This adhesive agent was interposed at a rate of 1 
g/cm.sup.2 between the opposed surfaces of two zirconia plates and 
maintained at 1100.degree. C. for 30 minutes, to join the two plates. 
A test piece of the joined plates was found by test to possess adhesive 
strength of 2050 kg/cm.sup.2. Under the same test conditions as used in 
Example 1, this test piece showed high resistance to chemicals and to 
thermal shock. 
EXAMPLE 7 
Adhesive agents were prepared by following the procedure of Example 1, 
except that the proportions of powdered copper sulfide and powdered 
kaoline were varied as indicated in Table 1. The adhesive agents were 
tested for adhesive strength. The results were as shown in Table 1. 
TABLE 1 
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Powdered copper sulfide (% by weight) 
95 70 40 
Powdered kaoline (% by weight) 
5 30 60 
Adhesive strength (kg/cm.sup.2) 
1780 1650 1800 
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Under the same test conditions as used in Example 1, the test pieces of the 
joined plates showed high resistance to chemicals and to thermal shocks. 
EXAMPLE 8 
Adhesive agents were prepared by following the procedure of Example 4, 
except that the proportions of powdered copper sulfide and powdered 
alumina were varied as indicated in Table 2. The results were as shown in 
the same table. 
TABLE 2 
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Powdered copper sulfide (% by weight) 
97 65 35 
Powdered alumina (% by weight) 
3 35 65 
Adhesive strength (kg/cm.sup.2) 
1540 1945 1480 
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Under the same test conditions as used in Example 1, the test pieces showed 
high resistance to chemicals and to thermal shocks. 
COMATIVE EXPERIMENT 1 
Adhesive agents were prepared by following the procedure of Example 1, 
except that the proportions of the powdered raw materials were varied as 
indicated in Table 3. The results were as shown in the same table. 
TABLE 3 
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Powdered copper sulfide (% by weight) 
99 20 
Powdered kaoline (% by weight) 
1 80 
Adhesive strength (kg/cm.sup.2) 
405 140 
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COMATIVE EXPERIMENT 2 
Adhesive agents were prepared by following the procedure of Example 4, 
except that the proportions of the powdered raw materials were varied as 
indicated in Table 4. The results were as shown in the same table. 
TABLE 4 
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Powdered copper sulfide (% by weight) 
98.5 15 
Powdered alumina (% by weight) 
1.5 85 
Adhesive strength (kg/cm.sup.2) 
515 90 
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