JPH1143379A - Production of ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a strong ceramic high in air tightness and capable of realizing high insulation performance by nipping a paste comprising ceramic powder having specific physical properties, an organic binder and a solvent between a ceramic part preliminarily calcined at a temperature below a sintering temperature and another calcined ceramic part and subsequently sintering the combination. SOLUTION: This method for producing a ceramic comprises nipping a paste comprising an organic binder, a solvent and ceramic powder capable of being sintered at the same sintering temperature as that of a ceramic part, having the approximately same contraction coefficient as that of the ceramic part, and giving the approximately same thermal expansion rate as that of the ceramic part after sintered, between the ceramic part and another calcined ceramic part and subsequently sintering the combination. The ceramic part is obtained by mixing 0.5-3 μm ceramic raw material powder with a binder and a softening agent, spray-drying the mixture, molding the obtained molding raw material having particle diameters of 100-200 μm into a desired shape and subsequently calcining the molded product at a temperature below the sintering temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for joining ceramics formed of alumina, aluminum nitride, or the like.

[0002]

2. Description of the Related Art In order to make use of the characteristics and functions of SEMIX,
Demands for complicated shapes and large ceramic sintered bodies are increasing. As a method of manufacturing a ceramic sintered body having a complicated shape, first, a ceramic raw material containing water is used.
Molded by potter's wheel molding, extrusion molding, etc., divided into several parts to make a molded body, apply a slurry of the same ceramic raw material to the joining surface of the parts before drying, adhere the molded body, and dry, There is a method of sintering.

However, in a method of applying a ceramic raw material slurry or the like to a joining surface of a molded article containing a large amount of water or an organic binder, such as potter's wheel molding or extrusion molding, and joining, the ceramic material, molding method, molding density, etc. Cracks are likely to occur at the joints during drying due to unevenness of water, especially unevenness of moisture or uneven thickness. On the other hand, for example, when the above-described joining method is used for a molded body made of a raw material having a small amount of water or an organic binder, such as a molded body formed by dry die molding, cracks in the joined portion also occur frequently. This is because the water in the slurry applied to the joining portion penetrates into the molded body and lowers the bonding strength of the molded body.

As another manufacturing method for producing a ceramic sintered body having a complicated shape, there is a method in which a ceramic fired body is formed and the fired body is joined. Conventionally, as a method of joining ceramics, a ceramic sintered body is joined using cement, an inorganic adhesive, or an adhesive. A metal powder is applied to the ceramic surface to be joined, or high-temperature baking is performed after the application, and brazing is performed using a brazing material through the metal surface. A glass powder is applied to the joint surface and welded by heating. And so on.

[0005] Among these joining methods, joining with a metal is excellent in strength, airtightness, and heat resistance, and joining of a complicated shape is also possible. FIG. 3 is an external view of an insulating cylinder of a high-voltage switch made by the method described above. Two insulating cylinders 1 made of alumina having a flange 6 and an energizing electrode 2 at one end are welded to each other by metallized metal fittings 3 connected to the other end. Reference numeral 4 denotes a weld.

[0006]

However, each of the above-mentioned methods for joining ceramics has a problem. In the bonding using cement or an inorganic or organic adhesive, the strength of the bonding portion is lower than the strength of the ceramic itself to be bonded, the heat resistance is low, and the airtightness is often poor.

[0007] The joining using a metal is a method excellent in strength, airtightness, and heat resistance, and it is possible to join in a complicated shape. However, the insulation characteristic of ceramics is lost. For example, in the withstand voltage test between the upper and lower conducting electrodes of the switch using the insulating cylinder of FIG. 3, the withstand voltage test using the insulating cylinder having the same edge surface distance and having no metal part in the middle is 20 to 20.
The withstand voltage is 30% lower. This is because there is a conductive portion in the middle, and discharge occurs through this conductive portion. Therefore, in high-voltage equipment that requires high insulation performance, joining using a metal as an inclusion is not preferable.

In general, the ceramic surface does not show wettability with metal, and cannot be directly bonded. Therefore, a method of baking high melting point Mo at a high temperature or forming a Cr—Ni film by sputtering or the like. Requires complicated pre-processing such as metallization, and further requires joining such as brazing.
The method of applying and welding glass powder to the joint surface of (1) is inferior in thermal shock resistance because the glass material is brittle.

In view of the above problems, an object of the present invention is to provide a method for producing a ceramic which is strong, has high airtightness, and can realize high insulation performance.

[0010]

Means for Solving the Problems To solve the above-mentioned problems, a method of manufacturing a ceramic according to the present invention comprises the steps of: providing a ceramic component between a ceramic component preliminarily calcined at a temperature lower than a sintering temperature and another calcined ceramic component; It is assumed that the ceramic component is sintered at the same sintering temperature as the component, has the same contraction rate, and has a thermal expansion coefficient after sintering substantially equal to that of the ceramic component.

By doing so, the calcined ceramic part does not lose its shape, and the sintering and joining of the ceramic part are performed at the same time. To improve the bonding strength and airtightness at the time of bonding. Sintering temperature, shrinkage rate and thermal expansion coefficient after sintering can be prevented, especially when the main material of the ceramic powder is the same as the ceramic component. But almost exactly match.

If the paste containing the ceramic powder, the organic binder and the solvent is interposed and sintered, the solvent in the paste penetrates into the pores of the porous calcined body, and the ceramic powder in the paste And the paste becomes more dense and adheres closely to the ceramic parts. If the paste is applied to the end face of the joint, an appropriate amount can be uniformly arranged.

[0013]

FIG. 1 is a process flow chart of the present invention. After preparing and forming the ceramic material, it is calcined at a temperature lower than the firing temperature to form a calcined body, while a paste having similar characteristics to ceramics is prepared, and it is sandwiched between the calcined bodies and pressed. And firing.

Hereinafter, embodiments of the present invention will be described. [Example 1] An example using alumina will be described. Silicon oxide, magnesium oxide, and calcium oxide are added to alumina, pulverized and mixed by a wet method to a particle size of about 0.5 to 3 μm, and 2% of polyvinyl alcohol (PVA) is used as a binder, and wax emulsion 1 is used as a softener. %, And the slurry was dried by a spray dryer to prepare an alumina forming raw material having a particle size of 100 to 200 μm. The component ratio is, for example, alumina 90 to 100.
%, Silicon oxide 0-8%, magnesium oxide 0-2%,
Calcium oxide is 0 to 2%.

The raw material was formed into a cylindrical shape using an isostatic press, and then machined to a size that allows for shrinkage during sintering to obtain a formed body having an outer diameter of 240 / inner diameter of 210 and a height of 250 mm. This molded body is placed in an air atmosphere at a temperature lower than the sintering temperature of the ceramic by 10 to 30%, ie, 1200 to 200
It was fired at 1300 ° C. for 2 hours to obtain a porous calcined body. Shrinkage during calcination was about 1%.

On the other hand, silicon oxide, magnesium oxide, and calcium oxide are added to alumina, and a particle size of 0.5 is obtained by a wet method.
To a powder obtained by heating and drying a slurry pulverized and mixed to about 3 μm, a Cerasolve solution in which 5% of ethyl cellulose was dissolved was added and mixed to prepare a bonding paste. This paste was printed on the end face of the calcined body by a screen printer to a coating thickness of 30 to 50 μm. Immediately after printing, the end face of another calcined cylinder was pressed against the coated surface. Although the printing is performed on the end face of one calcined body, the printing may be performed on the end faces of both calcined bodies.

The cylinder in which the calcined body was pressed was set to 1550-1
Baking at 650 ° C. for 2 to 3 hours, sintering of alumina and joining of the calcined body are performed simultaneously, and the outer diameter is 197 / the inner diameter is 172.
X An alumina cylinder having a height of 405 mm was obtained. The upper and lower sides of the alumina cylinder were sealed, the interior of the cylinder was evacuated, and the air density at the joint was measured with a helium leak device.
In Pa, the leakage amount was 1 mPa · mL / sec or less.

Since the ceramic parts are calcined,
The solvent in the applied slurry does not penetrate into the molded body and does not lower the bonding strength of the molded body. When the paste is applied to the porous calcined body, the solvent in the paste penetrates into the holes, the concentration of the ceramic powder in the applied paste increases, and the applied paste becomes denser. In addition, a part of the paste enters the pores on the surface of the calcined body, so that the bonding strength and airtightness at the time of bonding are further improved.

Further, the alumina cylinder is placed at -40 ° C. to + 350 ° C.
A temperature cycle of 10 ° C. was performed 10 times, but there was no abnormality in appearance such as cracking or peeling, and no decrease in airtightness was observed. A joint part of the alumina cylinder produced under the same conditions as above and a part other than the joint part were cut into a size of 3 × 4 × 50 mm and subjected to a four-point bending strength test.

As a result, the strength was in the range of 300 to 350 MPa in all the test pieces, and there was no breakage at the joint especially in the test piece having the joint. After glazing the above-mentioned alumina cylinder, both ends were subjected to Mo metallization and further Ni plating to obtain an insulating cylinder at the opening / closing portion of the vacuum circuit breaker. FIG. 2 is an external view of the arc-extinguishing chamber of the high-voltage switch made by this method. At one end, two insulating cylinders 1 made of alumina having a flange 6 and a current-carrying electrode 2 are joined. Reference numeral 5 denotes a joint.

As compared with the conventional example in which two insulating cylinders are joined by welding metal parts as in the conventional example of FIG.
~ 30% higher. Therefore, if the switching unit has the same withstand voltage, the insulation distance can be shortened, and the size of the switch can be reduced. Further, in the switch using the joined insulating cylinder, no reduction in vacuum was observed, and it was also confirmed that the airtight performance was excellent.

For comparison, a calcined body was placed on top and bottom without applying a bonding agent to the cylindrical end surface of the calcined body, fired in the same manner as above, and subjected to an airtightness test and a strength test. ,
Notably, there were leaks from the joints and breakage of the joints at a strength of 250 MPa or less. The binder for granulating ceramics is not limited to PVA, but may be an organic binder such as methylcellulose. The molding method is not limited to the isostatic pressing, but may be a uniaxial press molding, an extrusion molding, or the like.

As the organic binder for forming the paste, methylcellulose, polyvinyl butyral and the like can be used, and as the solvent, water, alcohol and the like can be used. Embodiment 2 Next, an embodiment using aluminum nitride will be described.

3-7% of yttrium oxide is added to aluminum nitride powder, and the particle size is 0.3-2 μm in alcohol.
After mixing and pulverizing to about m, polyvinyl butyral (2%) was added and mixed as a binder, and this slurry was dried by a spray dryer to prepare an aluminum nitride forming raw material having a particle size of 100 to 200 μm. This raw material is formed into a cylindrical shape using a uniaxial pressurizing press and has an outer diameter of 75 /
A molded body having an inner diameter of 61 and a height of 35 mm was obtained.

The molded body is placed in a nitrogen atmosphere at 1500 to 1
It was fired at 700 ° C. for 2 hours to obtain a porous calcined body. On the other hand, yttrium oxide is added to aluminum nitride powder in a range of 3 to 7%.
%, And a slurry obtained by heating and drying a slurry obtained by pulverizing and mixing the particles in an alcohol to a particle size of about 0.3 to 2 μm is mixed with a Cerasolve solution in which 5% of ethyl cellulose is dissolved.
A joining paste was prepared.

This paste was printed on a cylindrical end surface of the calcined body by a screen printing machine to a coating thickness of 30 to 50 μm. Immediately after printing, the end face of another calcined cylinder was pressed against the coated surface. This calcined body was pressed against a cylinder in a nitrogen atmosphere,
Baking at 50-1850 ° C for 2-3 hours, sintering of aluminum nitride and joining of two calcined bodies,
2 / An aluminum nitride cylinder having an inner diameter of 50.5 and a height of 59 mm was obtained.

An airtightness test was performed in the same manner as in Example 1.
A temperature cycle test and a strength test were performed. As a result, there was no air leak at the joint, and no abnormality was observed in the temperature cycle. In addition, strength is 280-350MPa
And a strength comparable to that of an aluminum nitride sintered body, and there was no breakage particularly at the joint.

As described above, it was found that ceramics can be produced by using the method of the present invention also with aluminum nitride. As described above, by using the same material for the ceramic and paste to be joined, the shrinkage rate and the coefficient of thermal expansion during firing match, preventing cracks at the joint and eliminating damage due to distortion. Revealed. It should be noted that if the sintering temperature, the firing shrinkage rate, and the thermal expansion coefficient are almost the same, the materials need not necessarily be the same,
Application of this method is possible.

As a method of disposing the ceramic powder between the ceramic parts, it is possible to spray a liquid in which the ceramic powder is suspended or to simply sprinkle the powder with a sieve, although the uniformity is somewhat poor.

[0030]

As described above, according to the present invention,
In between a ceramic part calcined at a low temperature in advance and another calcined ceramic part, a powder or a paste containing the powder having characteristics similar to the ceramic part is sandwiched,
By sintering, a ceramic which is strong, has high airtightness, and can realize high insulation performance can be manufactured.

Since the present invention is suitable for a method for producing large-sized or complicated-shaped ceramics of various ceramic materials, its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a process flow chart of the present invention.

FIG. 2 is an external view of an insulating cylinder of a switch to which the present invention is applied.

FIG. 3 is an external view of an insulating cylinder of a conventional switch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulation cylinder 2 Current-carrying electrode 3 Welding bracket 4 Welded part 5 Joint part 6 Flange

Claims (4)

[Claims] A ceramic component which has been calcined at a temperature not higher than the sintering temperature and another calcined ceramic component.
It sinters at the same sintering temperature as ceramic parts, has almost the same shrinkage rate, and the coefficient of thermal expansion after sintering is almost equal to that of ceramic parts, sandwiching ceramic powder,
A method for producing ceramics, comprising sintering. 2. The method according to claim 1, wherein the main raw material of the ceramic powder is the same as the ceramic component. 3. The method for producing ceramics according to claim 1, wherein a paste containing ceramic powder, an organic binder and a solvent is sandwiched and sintered. 4. The method according to claim 3, wherein the paste is applied to the joint.