JP4253565B2 - Hexagonal boron nitride molded body, production method and use thereof - Google Patents

Description

The present invention relates to a hexagonal boron nitride molded body, a method for producing the same, and an application thereof. More specifically, the present invention relates to a hexagonal boron nitride molded body for obtaining a hexagonal boron nitride sintered body in which cracks and cracks are unlikely to occur in a curved portion, and a manufacturing method thereof, and further, a hexagonal boron nitride having a curved portion. This relates to a sintered body.

Hexagonal boron nitride is thermally and chemically stable and is an electrically insulating material. It is known as a free-cutting ceramic that has a crystal structure similar to graphite and has a slidability and easy machining because it has a layered structure in which the bonding force of atoms in the C-axis direction is weak. Although it is a ceramic with such characteristics, it is a typical hard-to-sinter material, and it is dense by hot pressing or hot isostatic pressing at a high temperature of about 2000 ° C. with the addition of a sintering aid. As sintering aids, B ₂ O ₃ , Y ₂ O ₃ , Al ₂ O ₃ , CaF ₂ , MgO, Si, CaB ₆ , MgB _{x and the} like are known (Non-patent Document 1).
"Boron Nitrides-Properties, Synthesis and Applications and Applications", R. Haubner, M. Wilhelm, R. Weissenbacher, B. Lux, Structure and Bonding, Vol.102, pp.1-45 (2002)

The hexagonal boron nitride sintered body not only has severe firing conditions, but also prevents the material from spreading because the raw material powder is expensive and difficult to mold. That is, the hexagonal boron nitride particles take a so-called scale-like form that is undeveloped in the C-axis direction, so that it is oriented during molding and the strength in a specific direction is reduced. It is easy to cause. In particular, this tendency is significant in a sintered body having a curved portion, and it is difficult to reduce the raw material boron nitride powder and processing costs.

  As described above, hexagonal boron nitride is a material that is difficult to be densified, and the molded body often expands and the density decreases due to heat treatment. Therefore, it is desirable that the molded body before heat treatment is as dense as possible, and a technique of pressure molding at high pressure is often employed. However, at that time, the particles are oriented in the direction in which the C-axis coincides with the pressing direction, and a layered peeling phenomenon called lamination occurs. Or even if it does not reach lamination, the overlap of the scaly particles tends to be peeled off during the heat treatment, resulting in a defect. Such defects significantly reduce the reliability, and various other devices for eliminating the lamination have been studied.

  In view of the above, an object of the present invention is to provide a hexagonal boron nitride molded body for obtaining a hexagonal boron nitride sintered body in which cracks and cracks are unlikely to occur in a curved portion, a manufacturing method thereof, and a sintering method thereof. The hexagonal boron nitride sintered body thus obtained is provided.

That is, the present invention is a molded body having a curved portion containing hexagonal boron nitride powder, the orientation angle defined below is 33 to 37 °, and includes hexagonal boron nitride powder or the same. The mixed powder is filled into a rubber press mold by a method of applying vibration (tap vibration) to a density of 0.57 to 0.61 g / cm ³ , and then subjected to isostatic pressing to a density of 1.61. It is a manufacturing method of the hexagonal boron nitride molded object characterized by setting to -1.69 g / cm ³ .
The orientation angle is determined by measuring the diffraction line intensities I002 and I100 of the (002) plane and (100) plane of powder X-ray diffraction from the direction perpendicular to the bending direction of the curved portion, and the formula (orientation angle) = tan ⁻¹ {6.25 / (I002 / I100)}.
In this case, it is preferable that the hexagonal boron nitride powder contains 20 to 80% by mass of crystalline particles having a graphitization index of 2 or less.

In a further, the present invention, the hexagonal boron nitride membrane formed body under a non-oxidizing atmosphere, a method for producing a hexagonal boron nitride sintered body, characterized in that the heat treatment at 1,700-2100 ° C..

  According to the present invention, a hexagonal boron nitride molded body that is less prone to lamination and defects even when a relatively high density molded body is produced by applying a high pressure during molding can be obtained. As a result, when this is heat-treated to produce a hexagonal boron nitride sintered body having a curved portion, the yield during handling and firing of the hexagonal boron nitride molded body is improved, and the hexagonal is reliable. A crystalline boron nitride sintered body can be produced. The hexagonal boron nitride sintered body of the present invention can be widely applied to various conventionally used hexagonal boron nitride sintered bodies including various semiconductor jigs.

  The hexagonal boron nitride compact (hereinafter also referred to as “BN compact”) of the present invention is, for example, a hexagonal boron nitride sintered compact (hereinafter referred to as “BN quality sintered body”) having a curved portion by heat treatment. It is also used to produce a "conjunct". The BN compact according to the present invention is mainly composed of hexagonal boron nitride powder or hexagonal boron nitride powder and other inorganic powder, and contains an organic medium, an organic binder, a sintering aid, and the like as necessary. Is.

Hexagonal boron nitride powder is a hard-to-sinter material and uses amorphous or low-crystalline raw materials to facilitate sintering, but these contain a relatively large amount of oxygen and therefore volatilize when heated. Increases boric acid content. Since a dense BN compact is difficult to degas, the generated gas pressure tends to cause defects in the BN sintered compact. In severe cases, cracks and cracks may be damaged. On the other hand, in the hexagonal boron nitride powder that has been crystallized, the generation of gas is small and the outgassing is good, but the mechanical properties such as the bending strength of the sintered body are lowered. In order to satisfy such contradictory characteristics and obtain a BN molded body that can be used, it is preferable to use the following hexagonal boron nitride powder in the present invention. Of course, ordinary hexagonal boron nitride powder can also be used.

That is, preferred hexagonal boron nitride powder used in the present invention contains 20 to 80% by mass of crystalline particles having a graphitization index of 2 or less. The graphitization index (Graphite Index, often referred to as GI value) represents the degree of crystallization, and is a powder X-ray diffraction analysis of diffraction lines on each surface of (100), (101), (102). The strengths I ₁₀₀ , I ₁₀₁ , and I ₁₀₂ are measured, and then calculated by (graphitization index) = (I ₁₀₀ + I ₁₀₁ ) / (I ₁₀₂ ). The smaller this value is, the more graphitization, that is, the crystallization progresses. Theoretically, when it is completely crystallized, it becomes 1.6. May take.

A graphitization index of 2 or less indicates a state in which crystallization has progressed. Generally, a crystallinity index exceeding 4 to 5 is a low crystalline hexagonal boron nitride. In the present invention, it is preferable to use hexagonal boron nitride powder containing 20 to 80% by mass of the crystallized particles. If this ratio is 20% by mass or less, the mechanical properties are inferior, and if it exceeds 80% by mass, the BN sintered body tends to be damaged. A preferable content rate is 25 to 75% by mass, and more preferably 30 to 70% by mass.

The other inorganic powder is one or more selected from aluminum nitride powder, silicon nitride powder, silica powder, alumina powder, etc., and 0 to 500 parts by mass per 100 parts by mass of hexagonal boron nitride powder is used. Can do. When no other inorganic powder is used, the BN compact is a BN compact, and when it is used, it is a BN composite compact. The ratio of these main components is preferably 60% by volume or more, particularly 70% by volume or more in the BN molded article. The balance is one or more of water, an organic medium, an organic binder, a sintering aid, and the like, which are contained as necessary.

Examples of the organic medium include alcohols such as methanol, ethanol, butanol, and isopropyl alcohol, acetone, toluene, and the like, and the ratio thereof is 5% by volume or less (including 0) in the BN compact. . Examples of the organic binder include polyvinyl alcohol, butyral, acrylic resin, and the like, and the ratio thereof is 3% by volume or less (including 0) in the BN quality molded body. When manufacturing a BN sintered body by heat-treating a BN compact using an organic binder, the binder is removed before the heat treatment. Examples of the sintering aid include the aforementioned B ₂ O ₃ , Y ₂ O ₃ , Al ₂ O ₃ , CaF ₂ , MgO, Si, CaB ₆ , MgB _{x and the} like, and the ratio is BN 5% by volume or less (including 0) in the molded body.

  In the present invention, the molded body having a curved portion literally has a curved portion, and the shape thereof is not limited. In practice, the most clear shape is, for example, a cylindrical shape or a tube shape, but may have a corner R. The preferable size of R is 10 mm or more, particularly 15 mm or more.

  In the BN molded article of the present invention, the bending direction of the bending portion and the C-axis direction of the BN crystal are the same (parallel) for some or all hexagonal boron nitride particles present in the bending portion. . The C-axis direction of the BN crystal is the direction perpendicular to the scaly flat surface, that is, the particle thickness direction. In an ordinary BN compact, the hexagonal boron nitride particles are easily oriented with the C axis of the BN crystal aligned, so for those having a curved portion, the bending direction of the curved portion and the C axis direction of the BN crystal Is vertical. For this reason, since the bending and tensile strength of the BN quality molded body, particularly at the curved portion, is low, the reliability of the BN quality sintered body produced by heat-treating it is not sufficient.

Te present invention smell, the orientation angle of the hexagonal boron nitride particles in the curved portion is by powder X-ray diffraction, carried out by measuring the direction perpendicular to the bending direction of the bent portion. This is a widely used method. From the diffraction line intensities I002 and I100 of the (002) plane and the (100) plane, the formula (orientation angle) = tan-1 {6.25 / (I002 / I100)} .

When the orientation angle is 45 °, complete non-orientation occurs, and the C-axis direction of the BN crystal of hexagonal boron nitride particles existing in the curved portion and the bending direction of the curved portion are completely matched (parallel). On the other hand, when the orientation angle is 0 ° or 90 °, complete orientation is obtained, and both directions are completely perpendicular. An ordinary hexagonal boron nitride powder press-molded body has an orientation angle of 10 ° or less. In the BN molded article of the present invention, an orientation angle of 20 ° or more is necessary. If it is smaller than this, cracks and cracks are likely to occur in the curved portion, and a more reliable BN sintered body cannot be produced. A preferred orientation angle is 25 ° or more, and more preferably 30 ° or more. The manufacturing method of such a BN molded body will be described below.

In the method for producing a BN compact according to the present invention, if necessary, an organic medium, an organic binder, and a sintering aid are present in a mixed powder containing hexagonal boron nitride powder or other inorganic powder. , and filled into a rubber press mold, after the density 0.57~0.61 g / cm ^3, it is an density 1.61~1.69g / cm ³ and isostatic pressure molding. The rubber press mold is often used when the powder is subjected to isotropic pressure pressing, so-called CIP molding, and is made of a material that transmits pressure but does not pass a pressurizing medium. Usually, water, an ethylene glycol aqueous solution, glycerin or the like is selected as the pressure medium, and rubber is used as the mold material. In the present invention, this rubber press mold is used, and the orientation angle is controlled using the difference between the packing density and the CIP density.

When a rubber press mold is filled with powder, in order to increase the CIP density, it is usually filled as densely as possible. For example, a method in which powder is gradually added and tamped, or a pre-forming method using a uniaxial press if a simple shape is employed. In the present invention, the density when the powder is filled in the mold is set to 0.57 to 0.61 g / cm ³ . This is a loose filling that is contrary to conventional common sense as a filling state. When the packing density is less than 0.4 g / cm ³ , the molded body is greatly deformed during molding, and voids and defects tend to remain in the molded body. On the other hand, if it exceeds 0.8 g / cm ³ , the effect of orientation control becomes small. Subsequently, this filling powder is CIP-molded, and the CIP density of the molded body is set to 1.61 to 1.69 g / cm ³ . The CIP molding method is not particularly limited, but a hydrostatic pressure of 50 to 250 MPa is appropriate, and the cyclic CIP molding method in which pressure is repeatedly applied is more effective.

When mixing the raw material powder, attention should be paid to the contamination of impurities including the mixing medium. Mixing of heavy metals such as iron, alkali metals and halogens should be avoided as much as possible. Further, in the case of mixing in which pulverization is performed at the same time, pulverization for too long is not efficient, and there is a problem that oxidation proceeds. Examples of suitable mixing equipment include a ball mill, a vibration mill, an attritor mill, a Henschel mixer, a Banbury mixer, and a powerful mixer.

One application of the BN quality molded body of the present invention is to produce a BN quality sintered body having a curved portion by heat-treating it. This heat treatment is preferably performed at 1700 to 2100 ° C. in a non-oxidizing atmosphere. As the non-oxidizing atmosphere, for example, nitrogen, argon, ammonia or the like is used.

  Commercially available hexagonal boron nitride powder A (graphitization index 1.6) and hexagonal boron nitride powder B (graphitization index 5.2) were mixed in the predetermined proportions shown in Table 1. A commercially available silicon nitride powder (trade name “NP-600” manufactured by Denki Kagaku Kogyo Co., Ltd.) was used as the SN of the BN molded body 4.

Each raw material was subjected to 6 hrs ball mill mixing using alumina balls, and the obtained mixed raw material was filled into a rubber press mold to obtain a filling density. The rubber press mold was in the shape of a rubber pipe, and the powder filling portion used had an inner diameter of 100 mm, an outer diameter of 120 mm, a thickness of 10 mm, and a height of 200 mm. The packing density was calculated from the mass of the filled powder. The packing density was adjusted by (1) just filling the raw material powder, (2) applying vibration (tap vibration), (3) pressing lightly, (4) pressing strongly, and (5) tamping. The packing density increased in the order of (1) to (5) above. Next, after performing CIP molding at a predetermined molding pressure, the mold was removed and the dimensions were measured to calculate the CIP density. Each BN compact was produced in duplicate under the same conditions, and the packing density and molding density were average values of both. The results are shown in Table 1.

A sample was cut out from one of the BN compacts produced two by two, and the powder X-ray diffraction was measured from the thickness direction of the pipe shape to determine the orientation angle. Next, the remaining BN compact was heat-treated at 2100 ° C. for 12 hours in a nitrogen atmosphere to produce a BN sintered compact. After examining the appearance of each BN sintered body, the sample was cut out and the bending strength was measured according to JIS R1404. Samples were cut out in the longitudinal direction of the pipe, and each sample was produced five times, the strength was measured, and the average value was calculated. The results are shown in Table 2.

As is clear from the table, when the BN molded body of the present invention was used, a BN sintered body having a good appearance and a relatively high bending strength was obtained, whereas a BN quality molded body having a too low filling density was obtained. In No. 5, cracking occurred and broke during molding. In the comparative example using No. 8, cracking occurred during heating, resulting in a BN sintered body with low strength. On the other hand, in the comparative example using the BN compacts 6 and 7 having a too high packing density, the orientation angle was small and cracks were generated, and these also became low strength BN sintered bodies.

  The BN molded body of the present invention is used to produce a BN sintered body by heat-treating it. These molded bodies and sintered bodies are not only used as they are, but are also considered to be used as base materials for further various processing utilizing the free-cutting properties. In addition, the BN sintered body of the present invention can be widely applied to various uses of BN sintered bodies that have been conventionally known, including various semiconductor jigs.

Claims (3)

A molded body having a curved portion containing hexagonal boron nitride powder, the orientation angle defined below is 33 to 37 °, and vibration is applied to hexagonal boron nitride powder or a mixed powder containing the same. A rubber press mold is filled by a method of giving (tap vibration) to make the density 0.57 to 0.61 g / cm ³ , and then isotropically pressure-molded to make the density 1.61 to 1.69 g / cm ^3. A method for producing a hexagonal boron nitride shaped article characterized in that
(Definition of orientation angle)
From the direction perpendicular to the bending direction of the curved portion, the diffraction line intensities I002 and I100 of the (002) plane and (100) plane of powder X-ray diffraction are measured, and the formula: (orientation angle) = tan ⁻¹ {6 .25 / (I002 / I100)}. The method for producing a hexagonal boron nitride molded body according to claim 1, wherein the hexagonal boron nitride powder contains 20 to 80% by mass of crystalline particles having a graphitization index of 2 or less. A hexagonal boron nitride shaped article is produced by the method for producing a hexagonal boron nitride shaped article according to claim 1 or 2 , and further heat-treated at 1700 to 2100 ° C in a non-oxidizing atmosphere. A method for producing a crystalline boron nitride sintered body.