JPH10236879A - Burning method of ceramic, burning device and burning tool of ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a discharged matter such as assistant component subjected to a mass transfer to its outside by leaching and diffusion from allowing to react with a burning tool such as sleeve and a punch, etc., during the heating of an unburned matter at the time of heating and burning an unburned matter of a ceramic. SOLUTION: The device is provided with absorbent bodies 16 and 17 for absorbing the discharged matter discharged from the unburned matter during the heating of the unburned matters 18A, 18B and 18C. The absorbent body is composed of a material having a melting point more than a burning temp. of the ceramic and hardly reacting substantially with the ceramic preferably, and the absorbent body is a boron nitride powder, carbon powder, carbon fiber, carbon felt, carbon cloth, etc., concretely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for firing various ceramics.

[0002]

2. Description of the Related Art A pressure sintering method of ceramics by a hot press method has been used for sintering various ceramics such as silicon nitride, silicon carbide and aluminum nitride. Used to manufacture electronic materials such as conductive piezoelectric ceramics, translucent ceramics, and translucent piezoelectric ceramics, and base materials for semiconductor manufacturing equipment such as ceramic heaters, ceramic electrostatic chucks, ceramic high-frequency electrode devices, and ceramic susceptors. Have been.

[0003] A ceramic hot pressing device basically comprises a pressing mechanism and a heating mechanism.
Usually, a press die and a punch are included. The material of the pressing mechanism is a material having sufficient mechanical strength to withstand a predetermined pressure at a temperature of, for example, 1000 to 2500 ° C. under a heating condition of the ceramic powder or the molded body, and has a chemical reaction with the ceramic powder or the like. Is not required. As such a material, for example, graphite is used in a vacuum or in an inert gas such as N ₂ or Ar. Further, since high dimensional accuracy is required for the pressing die and the punch, the manufacturing cost is high and expensive.

However, in an actual hot press apparatus, at high temperature and high pressure, for example, a sleeve for holding a ceramic compact or powder adheres or reacts with such a ceramic raw material or a sintering aid, or the upper surface of the sleeve presses. The punch and the lower punch sometimes adhered or reacted with the ceramic raw material or the sintering aid. In such a case, ceramics and their chemical reaction products react strongly to the inner surface of the sleeve and the surfaces of the upper and lower punches. After hot pressing, a great deal of pressure is applied between the sleeve, upper punch, lower punch, etc. and the ceramic (fired product), so it is inherently difficult to remove the fired product. The removal of the fired product has become more difficult due to the presence of such strong reactants.

[0005] This phenomenon is schematically shown in FIG.
(B). For example, when the pedestal 31 and the mold 32 are combined, the discharged powder 33 discharged from the ceramic powder or the molded body thereof, or the reactant 33 generated by reacting with the material of the mold 32 becomes the mold 32. Reacts with the inner surface 32a of the Some of these discharges flow down along the inner surface of the mold 32 and reach the surface of the cradle 31 and the gap between the cradle 31 and the mold 32.

[0006] This discharge or reaction product 33 not only makes it difficult to remove the fired product, but also removes the discharge or reaction product 33 from the sleeve 32A or the pedestal 31A as indicated by 34. May occur.

As a result, the fired product is converted into a sleeve, an upper punch,
When detaching from the lower punch or the like, the sleeve or the like may be locally damaged. In addition, chipping may occur when removing reactants such as ceramics and their chemical reaction products that have strongly reacted with the sleeve or the like. In such a case, it is necessary to replace expensive firing jigs such as a sleeve, an upper punch, and a lower punch, which causes an increase in the manufacturing cost of a fired product.

In order to solve this problem, the present applicant has
In Japanese Patent Application Laid-Open No. 5-318427, it has been proposed that the inner surface of the sleeve and the surface that comes into contact with the molded body of the punch be covered with a heat-resistant foil piece such as graphite foil. This is an extremely effective method for preventing a product produced by a chemical reaction between the sleeve or the punch and the ceramic at a high temperature and a high pressure or a ceramic from firmly adhering to the sleeve or the punch.

[0009]

However, it has been found that even with this method, a problem still occurs under the kind of ceramics and specific conditions. For example, when an auxiliary agent such as Y ₂ O ₃ is contained in a ceramic raw material powder or a molded body thereof, the auxiliary agent or auxiliary component diffuses in a hot press sleeve and a punch. Mass transfer.

The assistant or assistant component which has been diffused and transferred in this way reacts with a part of the graphite foil, and further reacts with a firing jig such as a sleeve or a punch, which is embrittled and has a long life. Was sometimes shortened. If the reaction between the auxiliary component and the firing jig is remarkable, it is difficult to remove the fired product from the firing jig such as a sleeve (unmolding). In the worst case, the fired product may be damaged. Or the punch or sleeve was damaged.

In particular, when a sintering aid is contained in a raw material of a liquid phase sintering type ceramic such as an aluminum nitride ceramic, the above-described phenomenon is likely to occur.

An object of the present invention is to discharge an auxiliary component or the like which is leached and diffused to the outside during heating of an unsintered ceramic material during heating and firing the unsintered ceramic material. It is an object to effectively prevent an object from reacting with a firing jig such as a sleeve or a punch.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a method for heating and firing an unfired ceramic material, wherein the ceramic material is used for absorbing the discharge discharged from the unfired material while heating the unfired material. It is characterized by placing the body.

Further, the present invention is directed to a baking apparatus for heating and firing an unfired ceramic material, wherein the absorber absorbs a discharge discharged from the unfired material while heating the unfired material. It is characterized by having.

The present invention also relates to a firing jig used for a firing apparatus for firing an unfired ceramic material by pressing and heating, wherein the unfired material is held inside the firing jig. A pressing member is capable of entering along an inner surface of the firing jig, and a concave portion is provided on the inner surface at a lower portion of the firing jig where no unfired material is disposed. It is related to the tool.

[0016] The term "unfired material" described in the present specification includes all of powders, compacts and calcined bodies.

Hereinafter, the present invention will be further described with reference to the drawings as appropriate. FIG. 1 is a sectional view schematically showing one embodiment of the firing apparatus of the present invention. This baking apparatus is for hot pressing. In FIG. 1, substantially semi-cylindrical sleeves 4A and 4B are accommodated so as to be in contact with the inner side surface 3a of the mold 3. In the present embodiment, the fired product is easily taken out of the mold 3 after firing by dividing the sleeve into two. The sleeve can be divided into three or more.

The upper punch 1 can be moved along the inner side surface 4a of the sleeves 4A, 4B in one axial direction (vertical direction in FIG. 1). Under the sleeves 4A and 4B, a receiving table 2 is installed and fixed on a furnace body (not shown).
And the pressing surface 2a of the cradle 2 oppose each other to form a space for hot pressing. The upper punch 1 and the receiving base 2 are pressing members referred to in the present invention.

A spacer 5A is provided inside the pressing surface 1a of the upper punch 1, and a spacer 5B is provided inside the pressing surface 2a of the pedestal 2. The body 8 to be fired is accommodated between the spacers 5A and 5B. The body 8 to be fired is preferably a ceramic raw material powder or a pressed compact of powder, but may be a degreased body of this compact.

The pressing surface 8a of the object 8 and the spacer 5A
And between the pressing surface 8b and the spacer 5B,
Each is provided with a planar absorber 7. Further, the non-pressurized surface 8c of the fired body 8 and the inner side surfaces 4a of the sleeves 4A and 4B.
, An absorber 6 is provided.

Each of these absorbers 6 and 7 absorbs auxiliary components discharged from the unfired material 8 as the sintering of the unfired material 8 proceeds, and Avoid direct contact with the sleeves 4A and 4B and the spacers 5A and 5B. As a result, the respective fired products are firmly joined to the firing jigs such as the sleeves 4A and 4B, and the fired products cannot be taken out of the mold, or the fired products cannot be removed from the sleeve 4A.
It is possible to prevent the sleeve from being damaged when the sleeve is removed from A and 4B.

Such a sintering method and apparatus can be applied to ceramics in general, and particularly to ceramics containing a sintering aid. Examples of such ceramics include silicon nitride, aluminum nitride, alumina, a silicon nitride-based composite material, an aluminum nitride-based composite material, and an alumina-based composite material. Examples of the sintering aid include rare earth elements such as Y ₂ O ₃ and Yb ₂ O ₃ and IIA group elements such as Ca and Mg.

The present invention is particularly suitable for liquid phase sintering ceramics such as aluminum nitride ceramics. Aluminum nitride ceramics go through a sintering process called liquid phase sintering. That is, the aluminum nitride particles once react with the auxiliary component to be liquefied, and then undergo a process of solidifying in a cooling process.

Usually, a sintering aid such as yttria is added to the aluminum nitride powder in an amount of 5% by weight or less.
Heat. At this time, the aluminum oxide phase on the surface of the aluminum nitride raw material powder and a sintering aid such as Y ₂ O ₃ react to produce yttrium aluminate, and the liquid phase sintering proceeds. When carbon is used as a firing jig and fired in nitrogen for a long time, a reduction nitridation reaction with carbon gas
Mass transfer occurs relatively easily, so that the oxide moves from the center of the sintered body toward the surface and is discharged from the inside of the sintered body to the outside.

The discharge of such sintering aids is quite large,
For this reason, when only a non-reactive coating such as graphite foil is used, it is considered that a considerable amount of the sintering aid reacts toward the graphite foil and the foil is easily broken. The present invention relates to a sintering process such as hot pressing, in which a considerable amount of the sintering aid discharged from the unsintered material is placed in the vicinity of the unsintered material or by an absorber installed so as to contact the unsintered material. The feature is that it is actively absorbed at the same time as the disease progresses.

Hereinafter, more specific embodiments will be described. The absorber used in the present invention preferably has a melting point equal to or higher than the firing temperature of ceramics, and is preferably made of a material that does not substantially react with ceramics. As such a material, in addition to boron nitride and carbon, a high melting point metal that does not melt at the firing temperature, such as molybdenum, tungsten, tantalum, niobium, and hafnium, is preferable.

The form of the absorber may be a powder, a fiber or a molded body. When the absorber is a powder, a boron nitride powder or a carbon powder is particularly preferred.

The form of the absorber may be fiber, felt or cloth. Since the powder of the high melting point metal is troublesome to handle, a flat plate made of a sintered powder is preferable. In particular, an absorber made of a carbon material is preferable because it has low reactivity with aluminum nitride ceramics and hardly becomes an impurity, and carbon fibers, carbon felt or carbon cloth is more preferable.

As the absorber on the holding member side provided between the inner surface of the holding member such as a sleeve and the non-pressurized surface 8c of the green body 8, any of powder, fiber, felt and cloth can be used. On the other hand, as the absorber provided between the pressing surfaces 8a and 8b of the holding member 8 and the spacer, powder, felt, and cloth are preferable because powder is difficult to handle.

When a felt molded article is used, its bulk density is preferably 0.05 to 0.5 g / cm ³ . Further, it is preferable that the thickness be 0.5 to 20 mm.

However, it is preferable that the thickness of the felt is changed according to the place where the felt is used and the amount of the discharged material.

More specifically, when the amount of discharged material is small, first, a felt wound around the outer peripheral portion of the green body is used, and
It can be as thin as ~ 2 mm. At this time, particularly in the case of the furnace material configuration shown in FIGS. 1 to 3, it is preferable to reduce the thickness of the felt to 1 to 2 mm in that the generation of burrs can be reduced. This may be a cross.

If the amount of effluent is large and cannot be accommodated by this felt, the thickness of the felt can be increased. However, in this case, burrs may be generated.

When it is desired to prevent the generation of burrs, or when the thickness of the felt wound around the outer periphery of the green body is larger than 2 mm, it is not possible to cope with the discharge, the following (1) and ( It is preferred to carry out one or both of 2).

(1) The furnace material configuration shown in FIG. 4 is adopted. In the case of the furnace material configuration shown in FIG. 4, since the generation of burrs can be suppressed, the thickness of the felt may be increased to 5 to 10 mm. (2) Felts are placed above and below the unfired material.

When the felt is inserted between the spacer and the unfired material as in (2), and the unfired material is an embedded product such as an electrode (electrostatic chuck, susceptor with built-in plasma electrode). When the thickness of the felt used is large, the thickness of the film of the product after firing tends to vary, so the thickness of the felt is preferably set to 1 to 2 mm.

If none of the above can cope with the discharge, the recess of the sleeve can be filled with felt. The thickness of the felt used at this time is preferably from 10 to 20 mm from the viewpoint of workability. This is because it can be set more easily than when thin felts are set one upon another.

When a cloth is used, the basis weight is 150 g.
/ M ^{2 to} 300 g / m ² are good, and the thickness is 0.3 to
1 mm is preferred. The use may be handled in the same manner as the felt. For cross, although absorbency is lowered than the felt, does not powdering be loaded with 200 kg / cm ² about the surface pressure, as compared with felt that powdered with 30 g / cm ² of about surface pressure, after baking It is easier to take out the product.

FIG. 2 is a sectional view schematically showing a hot press apparatus according to another embodiment of the present invention. The sleeve 14A is brought into contact with the inner surface 13a of the mold 13 of this device.
And 14B are provided. The inner side surface 13a of the mold 13 is provided with a constant taper, and a sleeve 14A,
The inner side surface 14a of 14B extends straight from top to bottom in FIG.

The receiving base 12 is fixed below the mold 13 and the sleeves 14A and 14B. Sleeve 14A, 1
4B, four spacers 5 and three unfired materials 18A, 18B, 1
8C is accommodated. Pressing surface 11 of upper punch 11
a, the spacer 5 is in contact with the pressing surface 12a of the receiving table 12, respectively.

Each spacer 5 and each unfired product 18A, 1
A planar absorber 17 is interposed between each of the pressing surfaces 18a and 18b of 8B and 18C. The holding member-side absorber 16 is provided between the non-pressing surface of each spacer 5 and the non-pressing surface 18c of each unfired material and the sleeves 14A and 14B.

According to such a hot press apparatus, in addition to the above-described functions and effects of the present invention, a large number of fired products can be manufactured by a single hot press operation.

However, when the baking step was actually performed by this hot press apparatus, it was found that the following problems were further encountered. That is, when a plurality of sheets, in some cases 10 or more sheets, of unsintered products are laminated and hot-pressed at the same time, a large amount of discharge such as the sintering aid is generated inside the mold. Many of these effluents or volatiles are considerably absorbed by the absorbers 16 and 17, but under the condition that a large pressure is applied, the effluent that cannot be completely absorbed is converted into the sleeves 14A and 14B and the unburned material and In some cases, it flowed down between the spacers and reached the cradle 12. This is because a large number of unfired materials are stacked and processed collectively, so that the amount of discharged materials is large.

For this reason, the present inventor has found that, in a firing jig (sleeve or the like) into which at least one pressing member (upper punch or lower punch or the like) can enter, an unfired material is not disposed among the firing jigs. At the bottom, the inventor has conceived to provide a recess on the inner surface of the firing jig. And in this recess,
An absorber for absorbing the discharge discharged from the unfired material while heating the unfired material was installed.

FIGS. 3 and 4 are cross-sectional views schematically showing a hot press apparatus according to this embodiment of the present invention. However, the same members as those shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

In the apparatus of FIG. 3, the sleeve 24A,
A step portion or a concave portion 21 is formed in a lower portion of the inner side surface 24a of the 24B that does not contact the unfired material. Each recess 21 is close to the cradle 12. Each of the recesses 21 is filled with an absorber 22, and each of the absorbers 22 in the recess is provided with the holding member-side absorber 1.
6 is in contact.

The sleeve 24 is discharged from each unfired material.
The discharge that has flowed down the gaps between A, 24B and each unfired material and the spacer 5 and has not been absorbed by the holding member-side absorber 16 is absorbed by the absorber 22 in the concave portion. Therefore, it is possible to prevent the discharged material from directly contacting the cradle 12 and reacting.

In the apparatus shown in FIG. 4 as well, each spacer 5 and each unfired material 28A, 28B, 28C are alternately laminated, and the pressing surface of each spacer 5 is
A, 28B, and 28C are in contact with the pressing surfaces 28a, 28b. In the present embodiment, the size of each unfired material 28A, 28B, 28C is smaller than the size of each spacer 5, and the non-pressurized surface 28c of each unfired material 28A, 28B, 28C and the holding member-side absorber 16 A space was formed between them. Then, in this space, the non-pressing surface side absorber 29 was installed so as to surround each unfired material.

The operation and effect obtained by such a configuration will be described. In the apparatus as shown in FIG. 2 and FIG. 3, the dimensions of each spacer 5 and the dimensions of each unfired material substantially match. When each unfired product is fired under such conditions, so-called "burrs" may be generated at corners of the fired product.

For example, as schematically shown in FIG. 5, the size of the unfired material 18A (18B, 18C) substantially coincides with the imaginary line A indicating the size of the spacer (not shown). In this state, when pressure is applied in the vertical direction in FIGS. 2 and 3, the components constituting the unfired material are plastically deformed together with shrinkage when the temperature exceeds the liquid phase generation temperature in the firing process, and a part of the unfired material is deformed. It is pushed out toward the corner. As a result, FIG.
“Burrs” or small projections 30 a are formed at the corners of the fired product 30 shown in FIG.

On the other hand, as shown in FIG. 4, by providing the non-pressing surface side absorber 29 in the space between each unfired material 28A, 28B, 28C and the absorber 16, the above-described structure is obtained. We succeeded in effectively preventing the occurrence of "burrs". This is because, as schematically shown in FIG. 5B, the dimensions of the unfired products 28A, 28B, and 28C (represented by imaginary lines B)
Is smaller than the dimension of the spacer (indicated by the imaginary line A), and the absorber 29 is installed in the space created by this dimensional difference.

At the time of hot pressing, the unsintered material undergoes plastic deformation together with shrinkage when the temperature becomes equal to or higher than the liquid phase generation temperature during the sintering process, and spreads toward the sleeves 24A and 24B.
A baked product 30A is generated. That is, the size of the fired product 30A is larger than the size of the unfired product, and the virtual line A
Is approaching. However, the expansion of the dimension in the radial direction is stopped by the action of the absorber 29 in the gap, and the constituent material of the unfired material is transferred to the non-pressed surface of the spacer 5 and the sleeves 24A and 24B.
Does not enter the gap with the inner side surface 24a, thereby preventing the occurrence of "burrs".

[0053]

EXAMPLES Hereinafter, more specific experimental results will be described. (Experiment 1) A firing experiment was performed using the hot press apparatus shown in FIG. AlN10 as ceramic raw material
A disk-shaped compact 8 of aluminum nitride powder containing 5% by weight of yttria with respect to 0% by weight was used. The diameter of this molded body was 45 mm, and the thickness was 30 mm. The pressing surface 2a of the cradle 2 has a diameter of 50 mm, and a 0.25 mm-thick graphite foil is placed thereon via a spacer 5B. A 0.7 mm-thick carbon felt sheet is used as the absorber 7 on this. The disk-shaped molded body 8 was placed on the absorber 7 and placed.

A carbon felt sheet having a thickness of 2 mm is placed on the disk-shaped molded body 8 as an absorber 7, a graphite foil having a thickness of 0.25 mm is placed thereon, and a spacer 5 A is placed thereon. Punch 1 was placed.

An average particle diameter of 500 μm is provided between the non-pressing surface 8c of the disk-shaped molded body 8 and the inner surfaces 4a of the sleeves 4A and 4B.
High-purity carbon powder having an ash content of 20 m or less was filled to a thickness of about 2.5 mm to obtain a holding member-side absorber 6. In this embodiment, high-purity carbon is used. However, if there is no effect on the product, carbon containing about 0.1% ash may be used.

In this state, the compact was hot-pressed.
In this case, under a nitrogen atmosphere at a gauge pressure of 1.5 atm,
It was kept at a maximum temperature of 1850 ° C. for 4 hours while applying a pressure of 200 kg / cm ² .

As a result, no leaching of the yttria component into the sleeve or the like was observed, and the fired product could be easily removed from the mold 3. The carbon powder 6 filled around the molded body absorbed yttria and was baked, but did not reach the reaction of the yttria component to the sleeve side. The average strength of the fired body thus obtained is 420 M
Pa, the average bulk density is 3.36 g / cc,
Good results were obtained.

(Experiment 2) A baking experiment was performed using the hot press apparatus shown in FIG. The diameter of this compact is 240
mm and the thickness was 50 mm. Sleeve 24A, 2
The inner diameter of 4B was 244 mm. However, the inner diameter of the concave portion 21 of the sleeve was 257 mm. The diameter of the pressing surface 12a of the receiving table 12 and the diameter of the spacer 5 were set to 244 mm.

As each planar absorber 17, a felt having a thickness of 2 mm was used. As the absorber 22 in the recess 21,
A ring-shaped felt having an outer diameter of 57 mm, an inner diameter of 244 mm, and a thickness of 6.5 mm was used. Holding member-side absorber 16
Was changed as shown in Table 1.

Ten unfired products 18A and the like were laminated. The raw material of each unsintered product, the sintering aid, and the amount of the sintering aid added were changed as shown in FIG. The firing pressure is 200kg
/ Cm ^2, and the maximum temperature in the firing step and the holding time at the maximum temperature were changed as shown in Table 1.

[0061]

[Table 1]

After firing, the load when removing from the mold 13
Table 1 shows the state of the fired body taken out of the mold. Also, little or no reaction between the fired body and the spacers 24A and 24B was observed.

Next, a comparative experiment was performed according to the same procedure as described above. However, the absorbers 16 and 17 in FIG.
22 is not provided and the thickness of the absorber 16 is 0.25 mm.
Flexible graphite sheet (graphite foil) was installed. Further, the type of the raw material, the type of the sintering aid, the amount of the sintering aid added, the maximum temperature in the firing step, and the holding time at the maximum temperature were changed as shown in Table 2.

[0064]

[Table 2]

When the amount of the sintering aid added is 3% by weight or more, the load required for taking out the fired product from the mold 13 after firing must be 20 tons or more, and Dice damaged. Further, the sleeve and the baked product reacted violently, and the baked product removed from the mold was chipped or cracked.

When the addition amount of the sintering aid is 0.1% by weight, the load when removing the fired product from the mold 13 after firing is 10 tons or less, and the fired product lacks and cracks are observed. I couldn't. However, it was found that the service life of the sleeve was shortened because the fired product and the sleeve partially reacted.

[0067]

As described above, according to the present invention, when heating and firing an unsintered ceramic material, the unsintered ceramic material is leached to the outside during heating, and mass transfer due to a diffusion reaction. It is possible to effectively prevent the discharged waste such as the auxiliary component from reacting with a firing jig such as a sleeve, a punch, or the like.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a hot press apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a hot press apparatus for simultaneously processing a plurality of unfired materials according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view schematically showing a hot press apparatus for simultaneously processing a plurality of unfired materials according to still another embodiment of the present invention.

FIG. 4 is a cross-sectional view schematically showing a hot press apparatus for simultaneously processing a plurality of unfired materials according to still another embodiment of the present invention.

FIGS. 5A and 5B are schematic cross-sectional views for explaining the operation and effect of the hot press device of FIG. 4;

FIGS. 6 (a) and (b) are schematic views for explaining the state of attachment or breakage of a discharge, a reactant, etc. to a receiving stand or a sleeve.

[Explanation of symbols]

1, 11 Upper punch, 1a, 11a Upper punch pressing surface, 2, 12 pedestal, 2a, 12a Pressing surface of pedestal, 3, 13 type, 4A, 4B, 14A, 14
B, 24A, 24B Sleeve, 5, 5A, 5B Spacer, 6, 16 Holding member side absorber, 7, 17
Planar absorber, 8, 18A, 18B, 18C, 28
A, 28B, 28C Unfired, 8a, 8b, 18
a, 18b, 28a, 28b Pressing surface of unfired material, 8
c, 18c, 28c Non-pressurized surface of unfired material, 29 Non-pressurized surface side absorber

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tetsuhisa Abe 2-56 Suda-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Insulator Co., Ltd.

Claims (10)

[Claims] 1. An apparatus for heating and firing an unfired ceramic material, comprising installing an absorber for absorbing a discharge discharged from the unfired material while heating the unfired material. Characteristic method of firing ceramics. 2. The method of firing ceramics according to claim 1, wherein said absorber has a melting point higher than the firing temperature of said ceramics and is made of a material which does not substantially react with said ceramics. 3. The method for firing ceramics according to claim 2, wherein said absorber comprises at least one powder selected from the group consisting of boron nitride powder and carbon powder. 4. The method for firing ceramics according to claim 2, wherein said absorber is made of at least one material selected from the group consisting of carbon fiber, carbon felt and carbon cloth. 5. A firing apparatus for heating and firing an unfired ceramic material, comprising an absorber for absorbing a discharge discharged from the unfired material while heating the unfired material. An apparatus for firing ceramics, comprising: 6. A firing apparatus for firing the unsintered material by pressing and heating, wherein a pair of pressurizing members for pressing the unsintered material and the unsintered material are held. A holding member into which at least one of the pressurizing members can enter along an inner surface of the holding member. A holding member-side absorber is provided as the absorber between the pressure member and the pressure surface,
An apparatus for firing a ceramic according to claim 5. 7. A concave portion is provided on the inner surface at a lower portion of the holding member where the unsintered material is not arranged, and a concave-portion absorber is provided in the concave portion as the absorber. The ceramic firing apparatus according to claim 6, wherein: 8. A plurality of unfired materials are accommodated in the holding member, and a planar absorber is interposed between the unfired materials as the absorber. An apparatus for firing ceramics according to claim 6. 9. The holding member, wherein the unfired materials and the spacers are alternately laminated, and the planar absorber is interposed between each unfired material and each spacer. Each spacer is in contact with the holding member-side absorber, and a gap is provided between the non-pressurized surface of each of the unfired materials and the holding member-side absorber. The ceramic firing apparatus according to any one of claims 6 to 8, wherein a non-pressurized surface-side absorber is provided as a body. 10. A firing jig used for a firing apparatus for firing an unfired ceramic material by pressing and heating, wherein the unfired material is held inside the firing jig. A pressing member can enter along an inner surface of the firing jig, and a concave portion is provided on the inner surface at a lower portion of the firing jig where the unfired material is not arranged. jig.