JPH03183662A - Production of ceramics composite material - Google Patents

Abstract

PURPOSE:To obtain the ceramics composite material having a low dielectric constant and high thermal conductivity in combination by impregnating a soln. mixture which contains an Al-alkoxide and C and is hydrolyzed in a porous hexagonal BN sintered body, then drying the soln. and subjecting the soln. to a heating treatment in an inert gaseous atmosphere contg. N2 or NH3. CONSTITUTION:The hydrolyzate of the soln. mixture contg. the Al-alkoxide, such as Al(OC2H5)3, and C, such as graphite, is impregnated into the porous hexagonal BN (hBN) sintered body of 5 to 50% porosity. After the porous hBN sintered body subjected to the impregnation treatment is dried, the sintered body is heated up to 1400 to 1600 deg.C at 1 to 20 deg.C/sec heating up rate in the inert gaseous atmosphere contg. the N2 or NH3 and thereafter, the sintered body is subjected to the heating treatment for 1 to 10 hours. As a result, the ceramics composite material having the structure in which the AlN exists on the surface of the BN particles in the porous hBN sintered body and/or the grain boundary of this sintered body is obtd. The composite material is usable particularly as the supporting material of a progressive wave tube for electronics.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention relates to a method for producing a ceramic composite material, and particularly relates to a method for producing a ceramic composite material used as a traveling wave tube support material for ELENE 1 to RONIX. be.

[Prior art] Conventional technologies include quartz, steatite,
Sapphire and herria have been considered in the new edition of Nippon Telegraph and Telephone Corporation Telecommunications Research published by Takumaruzen Co., Ltd., written by Tsugube Koyama.
Traveling Wave Tube” page 207>.

On the other hand, in recent years, in traveling wave tubes for communication satellites and broadcasting satellites, low dielectric constants have become important as supporting materials have better high frequency characteristics than conventional materials due to higher frequencies.

In order to prevent high frequency loss due to the inflow of electron beams and heating, the support is also required to have high thermal conductivity for heat dissipation. Conventional support materials such as quartz glass, quartz, steatite, sapphire, and beryllia each have a dielectric constant of 3.6 at room temperature. 4.3. 6.0. 9.6
．． 6.9, and their respective thermal conductivities are 2, 7, 3.
40°260W/mK, it was difficult to maintain high thermal conductivity while achieving a low dielectric constant. on the other hand,
Recently, hexagonal boron nitride (hBN) has been attracting attention as a material that has both low dielectric constant and high thermal conductivity.

[Problem to be solved by the invention] Hexagonal boron nitride (hBN> has a laminated structure of hexagonal network planes like graphite, the alN1 direction in the report is covalent bonding, and the C axis perpendicular to the laminated plane The dielectric constant and thermal conductivity of hBN exhibit remarkable anisotropy due to the crystal structure based on van der Waals bonding.That is, the dielectric constant and thermal conductivity of hBN in the a-axis direction are 5.1 and 62 W/m-, respectively. It is reported that the power consumption is 3.5 and 2 W/m- in the C-axis direction.

At present, Union, which is pyrolytic boron nitride (PBN) produced by vapor phase growth, is currently being used as a traveling wave tube support material.
Union Carbide's product name BOR^Ll-OY has been studied and some have been put into practical use. However, BOf? ALLOY has high orientation because it is formed on a substrate such as graphite by vapor phase growth, and as mentioned above, it is highly anisotropic, with dielectric constant and thermal conductivity significantly different between the in-plane direction and the thickness direction of the material. Therefore, it cannot exhibit low dielectric constant and high thermal conductivity at the same time. That is, low dielectric constant (
3, 5), when the C-axis direction is the direction in which the support is used, the thermal conductivity is approximately 2 W/m-, which is considerably lower than conventional quartz, steatite, sapphire, and heliaria. There was a problem with heat dissipation. In addition, if the support is used in the a-axis direction (62W/m-K), which has good thermal conductivity due to heat resistance, the dielectric constant is 5.1, which is the requirement for a low dielectric constant for high frequencies. It wasn't enough. Also B
Because ORALLOY has an oriented structure with anisotropy between the a-axes and the a-axes based on the layered structure, which is an essential property of hexagonal boron nitride, it often suffers from delamination and cracks between layers, resulting in poor reliability as a structure. There were also many problems. Furthermore, since pyrolytic boron nitride is manufactured using a vapor phase growth method, it is not possible to produce large, thick products in large quantities, and there are also industrial problems such as high costs.

In order to address these issues, the present inventor has carried out research into EiM, (+JI), and has found that a ceramic composite material composed of hexagonal boron nitride and aluminum nitride has both low dielectric constant and high thermal conductivity, and has a structurally superior They have discovered that it is optimal as a support for traveling wave tubes because of its excellent reliability, and have completed the present invention.

[Means for Solving the Problems] The present invention involves impregnating a porous hexagonal boron nitride sintered body with a mixed solution containing aluminum alkoxide, which is an aluminum nitride precursor, and carbon after hydrolysis, or by impregnating and adding water. After decomposing and then drying the sintered body,
This is a method for producing a ceramic composite material, which is characterized by heat treatment in an inert gas atmosphere containing nitrogen or ammonia.

The ceramic composite material obtained by the method of the present invention has a structure in which aluminum nitride is present on the surface of boron nitride particles of a porous hexagonal boron nitride sintered body and/or at the grain boundaries of the sintered body.

The present invention will be explained in more detail below.

The ceramic composite material produced by the method of the present invention is mainly composed of hexagonal boron nitride (hBN) and aluminum nitride (AfN). hB
A production process in which the inside of the N sintered body is hydrolyzed and then impregnated, or the N sintered body is impregnated and hydrolyzed, then dried and then heat-treated in an inert gas atmosphere containing nitrogen or ammonia to generate the N phase. It has process characteristics. As a result, the porous hBN sintered body has a composite structure in which an AIN phase is generated on the surfaces and grain boundaries of the h[3N particles. FIG. 1 is a cross-sectional view schematically showing the structure of the ceramic composite material 1 of the present invention, in which AI! , N3 exists.

Furthermore, in the ceramic composite material 1 of the present invention, hBN2
Ya Af! In addition to N3, it is also effective to contain pores 4 of up to 50% as shown in FIG. 1 in order to lower the dielectric constant. However, when the porosity exceeds 50%,
There is a problem in that mechanical strength is insufficient in structural applications such as traveling wave tube supports.

The content of boron nitride in the ceramic composite material of the present invention is not particularly limited, and if the amount of boron nitride is 50 to 99% by weight, there is an advantage that cutting can be performed using a cutting tool.

Next, a method for manufacturing Hiramix composite VJ-li of the present invention will be explained.

The porous hexagonal boron nitride (hBN') sintered body is
It is manufactured by pressureless sintering method or hot press method, and the purity is preferably 98% or more, or 95-98%.
It is also possible to use a medium-sized one. Porosity is AI! In order for the N precursor, aluminum alkoxide, a mixed solution containing 15 and carbon, or a hydrolyzed solution thereof, to uniformly penetrate into the hBN sintered body during the impregnation process, it is necessary to have a content of 5% or more. 5 to obtain sufficient mechanical strength
It is desirable that it is 0% or less.

Examples of aluminum alkoxide include aluminum edileate (Ai2 [OC2+15] 3 ), aluminum isopropylene-1 to CM [0C3H7] 3
), aluminum butyrate (M[0C4)+9 ]
3) Butoxyaluminum diisopropylene-1
-, ethyl acetoacetate aluminum diisopropylate, aluminum tris(ethyl acetate), alkyl acetoacetate aluminum diisopropylate, and many others are available.

On the other hand, as carbon, in addition to general carbon black and graphite powder, carbon source materials such as phenol resin, styrene resin, nylon resin, and acrylic resin, which generate carbon during heat treatment, are also effective.

These aluminum alkoxides and carbon are dissolved or fractionally mixed in a suitable solvent. The pH of the resulting mixed solution
Hydrolysis is performed while making adjustments, and then the porous hBN sintered body is placed in the hydrolyzed solution and impregnated, or the porous hBN sintered body is first impregnated with the mixed solution and then hydrolyzed. conduct. In either method, it is effective to inject under a reduced pressure atmosphere in order to improve the permeability of the mixed solution and to uniformly disperse and add the mixed solution during impregnation.

Thereafter, after drying this porous hBN sintered body, it was heated under an inert atmosphere containing nitrogen or ammonia for 1400 min.
After ttn heating to ~1600°C at a heating rate of 1 to 20'C/min, hn heat treatment is performed for 1 to 10 hours.

As a result of this, the surface of the boron nitride particles inside the BN sintered body becomes porous due to the reduction of the aluminum compound and the nitriding reaction.
, ; J, and/or aluminum nitride aluminum h at the grain boundaries of the sintered body.
Ceramic composite material with a unique structure111
It will be done.

The A2N phase containing T in the ceramic composite material of the present invention
It is possible to control the number of tails by repeating the impregnation d3 and heat treatment steps. Also, Af! was produced by 1J-3 in 1-11 heat treatment at 1400-1600'C! Since N is in the form of fine powder, the thermal conductivity does not significantly improve compared to the initial porous hBN sintered body. So this is 1600 ~
7 more times under an inert gas atmosphere such as nitrogen at 2000°C.
By IO heat treatment, Af! generated by thermal decomposition on the surface and grain boundaries of hBN particles. Because sintering of N powder occurs, thermal conductivity is significantly reduced and labor is saved.

EXAMPLES In order to explain the present invention more specifically, Examples will be given below, but the present invention is not limited to these Examples.

[Example] Example 1 Purity 99.5% (impurity oxygen 0.
4%), an average grain size of 5 μs, and a porosity of 20% hexagonal boron nitride sintered body was machined to 110X 11Ox5mm.
It was created in The electrical conductivity of this boron nitride sintered body at room temperature was 3.4, and the thermal conductivity was 55 W/m-.

Aluminum isopropylate (M[0-C3H7]3
) 1009 and carbon black (average particle size 2
0OA>9g was added into a beaker containing isobutyl alcohol 11 at 80°C and heated for 3 hours to form a homogeneous solution. Next, after cooling to room temperature, distilled water of 3009 was added dropwise, and further aqueous ammonia 803 with a concentration of 20% was added.
Holds time. Then, to complete the hydrolysis, 8
It was held at 0°C for 5 hours. The above-mentioned boron nitride sintered body was placed in this solution, and aluminum sol and carbon black were uniformly vacuum-impregnated into the boron nitride sintered body under a reduced pressure atmosphere.

Thereafter, this impregnated boron nitride sintered body was dried at 50'C, and then heated to 1500°C at 5°C/
It was heated at a temperature increase rate of min and held at 1500° C. for 5 hours. In order to sinter the powdered Ai'N produced in this process, the ceramic composite material consisting of hexagonal boron nitride and aluminum nitride was heated at 20°C/mi under a nitrogen atmosphere.
It was heated to 1900'C h0 at a heating rate of n and held for 2 hours. As a result, a Hiramix composite material composed of hexagonal boron nitride and aluminum nitride with a porosity of 15%, a dielectric constant of 3.6 at room temperature, and a thermal conductivity of 120 W/·K was obtained.

After cutting this ceramic composite material (FJ), 0.25
A traveling wave tube support in the shape of a long rectangular parallelepiped of X O, 5 x 100 mm was prepared and mounted on a traveling wave tube.

FIG. 2(a) is a sectional view thereof, and FIG. 2(b) is a sectional view taken along line AA in FIG. 2(a). The tungsten coil 6 is inserted into the stainless steel protection tube 9 from three directions using the three supports 5.
It is kept compressed by 7 is a cathode, and 8 is a collector. Although the support 5 was subjected to compressive and shear stress from three points: the tungsten coil 6 and the inner wall of the stainless steel protection tube 9, no peeling or cracking caused by pyrolytic boron nitride occurred.

Example 2 The boron nitride sintered body in Example 1 was impregnated with a solution containing aluminum sol and carbon black and dried three times.
The mixture was heated to C and kept in a nitrogen atmosphere for 5 hours. Thereafter, heat treatment was performed at 1900'C for 4 hours in a nitrogen atmosphere. As a result, a ceramic composite material composed of hexagonal boron nitride and aluminum nitride with a porosity of 10%, a dielectric constant of 3.7 at room temperature, and a thermal conductivity of 150 W/m was obtained.

[Effects of the Invention] As explained above, the ceramic composite material composed of hexagonal boron nitride and aluminum nitride produced by the method of the present invention can be used as a traveling wave tube support using conventional support materials such as quartz, It is a material that has a low dielectric constant and high thermal conductivity superior to steatite, sapphire, herria, and pyrolytic boron nitride, and has less anisotropy in properties than pyrolytic boron nitride, and does not cause peeling or cracking. No problem. It has many industrial advantages, including the ability to manufacture large, thick products in large quantities at low cost, which is difficult to do with pyrolytic boron nitride.

Furthermore, the ceramic composite material produced by the method of the present invention can also be used for electronic components, insulating substrates, high-temperature furnace jigs, etc. other than as supports for traveling wave tubes.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view schematically showing the structure of a ceramic composite material obtained by the method of the present invention, and Fig. 2 is a cross-sectional view of a traveling wave tube (a) and (a) a cross-sectional view taken along line A' (b).
It is. 1 Ceramic composite material 2 Hexagonal boron nitride 3 Aluminum nitride 4 Pore 5 Support 6 Tungsten coil 7 Cathode 8 Collector・・A- of stainless steel protection tube

Claims (1)

[Claims] (1) A porous hexagonal boron nitride sintered body is impregnated with a mixed solution containing aluminum alkoxide, which is an aluminum nitride precursor, and carbon, or hydrolyzed after impregnation, and then the sintered body is dried. 1. A method for producing a ceramic composite material, which comprises heating the composite material in an inert gas atmosphere containing nitrogen or ammonia.