JPH09278526A - Setter for ceramic firing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-cost setter for ceramic firing that does not develop cracks and cutouts by constructing the setter of a boron nitride which has average pore size in a predetermined range and a specific or higher value of higher bending strength. SOLUTION: This setter for ceramic firing is obtained by preparing hexagonal boron nitride powder that contains preferably 50wt.% or more of hexagonal boron nitride having 10μm or larger average particle size, and 0.5-1.5wt.% oxygen other than in the form of boron oxide, forming the hexagonal boron nitride powder by such a means as metal die press or extrusion while adjusting the forming pressure so that a sinter having average pore size of 0.1-0.4μm can be obtained by subsequent sintering, and then sintering the formed in-process product at room temperature in an inert atmosphere. Thus obtained setter for ceramic firing, which is composed of a boron nitride sinter having average pore size of 0.1-0.4μm and bending strength of 15MPa or more, can be repeatedly used without giving adverse effects to ceramics to be sintered and also without deforming the sinters, and needs no reprocessing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramics firing setter made of a boron nitride sintered body.

[0002]

2. Description of the Related Art A setter for firing ceramics (hereinafter,
It is called "setter". ), Heat resistance, thermal conductivity,
A hexagonal boron nitride (hereinafter, referred to as “hBN”) sintered body having excellent lubricity, releasability, reaction resistance, etc. is used.

The setter is used as a mounting table or a weighting material when firing the preform of the ceramic powder raw material, and as an interposing plate of each layer when the preform is a laminated body. The characteristics required for a setter are (1) no adverse effect on the ceramics to be fired, (2) long life without cracks or chips even after repeated use,
(3) It is not deformed by repeated use and does not require rework, (4) it is inexpensive, and (5) it is compatible with many types of ceramics.

Conventionally, as a setter, hBN powder containing 3% by weight or less of boron oxide or calcium oxide is hot-press-sintered or hydrostatically-pressed and then pressure-sintered, and if necessary, subjected to a purification treatment. The applied hBN sintered body (Japanese Patent Laid-Open No. 4-2
No. 24173), a mixed powder containing a hBN powder having a boron oxide content of 0.1% by weight or less, an aluminum nitride powder, and a sintering aid that is the same as the sintering additive added when firing the aluminum nitride powder. HBN sintered body produced by pressureless sintering, hot press sintering or HIP sintering
No. 310476) is known.

However, among the above methods, in the hot press sintering method or the HIP sintering method, most of the boron oxide and the sintering aid remain in the sintered body, so the average pore diameter of the hBN sintered body is Is less than 0.1 μm. Such h
When a BN sintered body is used as a setter, the residual components seep out during firing and are deposited at the interface with the fired ceramics to reduce the releasability of the setter, to modify the ceramics surface or to cause defects. It causes it. Further, since the average pore diameter is small, there are problems that unevenness on the surface of the setter increases or deformation occurs, and reprocessing must be frequently performed.

In order to solve this problem, there is a proposal to increase the purity of the hBN sintered body. As the method, there are a method of performing a purification treatment after sintering and a method of reducing the amount of boron oxide or a sintering aid used. For the former, acid solution treatment,
High-temperature heat treatment in a vacuum or in an inert gas atmosphere (JP-A-4-65366, JP-A-5-19403).
No. 9), the average pore diameter of the hBN sintered body is 0.
Since it is less than 1 μm, there is the above problem. Further, in the latter method of reducing the amount of boron oxide or sintering aid used, the strength of the hBN sintered body becomes extremely low, and when used as a setter, unevenness on the surface of the setter increases or the setter surface increases with a small number of uses. Cracks and chips occur in the product, resulting in a short life.

On the other hand, in the atmospheric pressure sintering method among the methods for manufacturing the above hBN sintered body, boron oxide and a low melting point sintering aid can be volatilized during sintering to achieve a high density. However, since the melting point of boron oxide is about 450 ° C, a considerable amount of boron oxide is volatilized at a temperature of 1400 ° C or higher at which sintering of hBN is considered to be active, and strength development that can withstand practical use is exhibited. Will be difficult. Therefore, by adding calcium oxide as a sintering aid, the compound (mCaO.nB ₂
The strength of the hBN sintered body can be strengthened by forming O ₃ ) and increasing the melting point, but in this case, the auxiliary component reduces the average pore size, and the above compound is not sufficiently volatilized to burn the hBN. It remains in the body. Such h
When the BN sintered body is used as, for example, a setter for firing aluminum nitride whose firing temperature is generally 1800 ° C. or higher, 3CaO.B ₂ O ₃ having the highest melting point among the sintering aid components remaining in the setter. However, since its melting point is about 1450 ° C., it melts and evaporates during aluminum nitride firing and adheres to the surface of the aluminum nitride fired product, which adversely affects the releasability and deterioration of the surface of the fired product.

On the other hand, in the method of using the same sintering aid as the sintering aid added to the ceramics to be fired in the production of the hBN sintered body, the above-mentioned adverse effects of the aid components are eliminated. There is a problem that the setter must be manufactured by changing the sintering aid for each type of ceramics to be fired.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to provide a setter for firing ceramics which has the above-mentioned required characteristics and is excellent in releasability and deformation resistance. is there.

[0010]

That is, the present invention is a setter for firing ceramics, characterized by comprising an hBN sintered body having an average pore diameter of 0.1 to 0.4 μm and a bending strength of 15 MPa or more.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The setter of the present invention comprises hBN having an average pore diameter measured by a mercury porosimeter of 0.1 to 0.4 μm.
It is made of a sintered body. In the hBN sintered body having an average pore diameter exceeding 0.4 μm, the setter strength is lowered. Further, if it is less than 0.1 μm, long-term sintering is required to volatilize the boron oxide that has acted as a sintering aid and raise the setter purity, and the releasability from the ceramic to be fired deteriorates or the setter surface The unevenness of the may become large. Although the reason is not clear, this phenomenon is particularly remarkable when a sintering aid having a low melting point is used in the ceramic to be fired.

The setter of the present invention has a porosity of 25.
It is preferably about 40%. If it exceeds 40%, the setter purity will decrease, and if it is less than 25%, the number of pores will be small, so long-term sintering will be required to increase the setter purity.

Further, the setter of the present invention is made of a hBN sintered body having a three-point bending strength of 15 MPa or more at room temperature. If it is less than 15 MPa, the setter surface will have irregularities, cracks, or chips after a small number of uses, resulting in a short life.

The purity of the setter of the present invention is hBN.
It is preferably 99% by weight or more. If it is less than 99% by weight, the impurity component exudes during firing and deposits at the interface with the ceramic to be fired, which adversely affects the release property of the setter and modifies the ceramic surface.

The setter of the present invention is preferably manufactured by pressureless sintering of hBN powder. By hot press sintering or HIP sintering, it is difficult to produce an hBN sintered body having an average pore diameter of 0.1 to 0.4 μm and a bending strength of 15 MPa or more.

The hBN powder used in the present invention includes:
It is preferable to contain 50% by weight or more of hBN powder having an average particle size of 10 μm or more. Average particle size 10 μm
Less than hBN powder only, or average particle size 10μ
When the proportion of hBN powder of m or more is less than 50% by weight, it is difficult to make the average pore diameter of the hBN sintered body 0.1 μm or more even by pressureless sintering.

The hBN powder used in the present invention is
The amount of oxygen other than boron oxide is preferably 0.6 to 1.5% by weight. As described above, the boron oxide in the hBN powder is h-bonded in the hot press sintering method or the HIP sintering method.
It is an effective component for the sintering of BN, but it is hB in the normal pressure sintering method.
Most of it volatilizes by the time it reaches the high temperature region where the sintering of N is active, so it is an unnecessary component in the present invention. Therefore, the boron oxide may be removed in advance with a nitric acid aqueous solution, methanol, or the like, but is preferably removed for high purification.

On the other hand, it is considered that oxygen other than boron oxide in the hBN powder remains in the hBN crystal and forms liquid-phase boron oxide at high temperature during sintering. In addition to acting as a co-agent, it volatilizes at high temperatures to enhance the purity of the hBN sintered body. When the amount of oxygen other than boron oxide is less than 0.6% by weight, the strength of the hBN sintered body decreases, and when it exceeds 1.5% by weight, the sintering time for increasing the purity of the hBN sintered body becomes long.

The hBN powder used in the present invention can be directly produced as such powder, and the hBN powder having an oxygen content of less than 0.6% by weight and an average particle size of 10 μm or more can be used.
It can also be produced by appropriately mixing powder and hBN powder such as hBN powder having an oxygen content of more than 1.5% by weight and an average particle size of less than 10 μm. The mixing method at that time is
A general method such as a ribbon blender or a ball mill may be used, but it should be noted that it is not preferable that the hBN powder is oxidized and boron oxide is generated by the mixing.

The hBN powder may be molded by any of a die press, a cold isostatic press, an extrusion molding and the like, but the molding pressure is adjusted so that the hBN sintered body has an average pore diameter of 0.1 to 0. Adjust so as to be 0.4 μm.

The pressureless sintering is carried out in an inert atmosphere such as N ₂ or Ar at a temperature of 1800 to 2300 ° C., particularly 1900 to 22.
It is preferably carried out at 00 ° C. If the sintering temperature is lower than 1800 ° C, it is necessary to lengthen the sintering time to improve the purity of the hBN sintered body, and if it exceeds 2300 ° C, the hB
The strength of the N sintered body is rather lowered.

[0023]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 to 6 Comparative Examples 1 to 4 hBN powders A, B and C and boron oxide powder D shown in Table 1 were mixed in a blending ratio shown in Table 2 with a ribbon blender. The hBN sintered body (about 120 mm square × 30 mm thickness) was manufactured by molding it under the preforming pressure shown in Table 2 and then sintering it under normal pressure.

From the obtained hBN sintered body, 3 × 3 × 3 mm
A sample of the shape was cut out, and the average pore diameter and porosity were measured by a mercury porosimeter (manufactured by Shimadzu Corporation).
Further, a sample of 3 × 4 × 40 mm shape was processed from the hBN sintered body, and the three-point bending strength at room temperature was measured.

Further, a setter having a thickness of 100 mm square and a thickness of 5 mm is processed from the hBN sintered body, and using this setter, firing of aluminum nitride powder using yttrium oxide as a sintering aid (firing temperature 1900 ° C.) is performed. Do 5 times, each time
The releasability and deformation resistance were evaluated according to the following. Table 2 shows the results.

The releasability is determined by the adhesion between the aluminum nitride fired product and the setter, and the h on the surface of the aluminum nitride fired product.
The one in which the BN powder was firmly adhered and the one in which the glassy deposit was observed were marked with "x", and the others were marked with "○".

Deformation resistance is "X" when unevenness and adhesion of glassy substances are visually recognized on the surface of the setter, and when the setter is placed on a flat glass plate, warpage is visually recognized. , Other than that was marked as "○".

Comparative Examples 5-6 The raw materials shown in Table 2 were hot-press sintered (HP) at a hot press pressure of 15 MPa (Comparative Example 5) and a hot press pressure of 10 MPa (Comparative Example 6) to produce an hBN sintered body. , A setter was produced. Table 2 shows the results.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

According to the present invention, (1) it does not adversely affect the ceramics to be fired, (2) it has a long service life without cracks or chips even after repeated use, and (3) it deforms even after repeated use. It is possible to provide a setter having excellent characteristics such as that there is no need for reprocessing, (4) it is inexpensive, (5) it can be applied to various types of ceramics, and the like.

Claims (1)

[Claims] 1. A setter for firing ceramics comprising a boron nitride sintered body having an average pore diameter of 0.1 to 0.4 μm and a bending strength of 15 MPa or more.