JPH0455996B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a novel porous ceramic and a method for producing the same. A sintered body made of at least one metal carbide or nitride selected from the group consisting of aluminum, silicon, and boron;
A porous structure characterized in that continuous pores are formed in a part of crystal grains of carbide or nitride of at least one metal selected from the group consisting of aluminum, silicon, and boron, which are sintered and bonded. It is a sexual ceramic. The present invention also includes aluminum,
60-97% by weight of at least one metal carbide or nitride selected from the group consisting of silicon and boron
A method for producing porous ceramics, which comprises heating a sintered body consisting of carbon and 3 to 40% by weight of carbon at a temperature of 600 to 900°C in an atmosphere containing oxygen or carbon dioxide gas to remove the carbon contained therein. It also provides the following.

Conventionally, various ceramics or ceramic composites have been used in various industrial and consumer machines, equipment materials, electronic equipment materials, and the like. However, it is often difficult to industrially produce materials that meet the needs of specific applications.

The present inventors have worked diligently to develop various ceramic bodies having specific properties. In particular, as a result of continuing research on the industrial production of porous ceramics, we succeeded in developing a new porous ceramic, which we have proposed here.

That is, the alkali solution of the present invention is a sintered body made of carbide or nitride of at least one metal selected from the group consisting of aluminum, silicon, and boron, and is made of the aluminum, silicon, and boron bonded by sintering. This porous ceramic is characterized in that continuous pores are formed in a part of crystal grains of at least one metal carbide or nitride selected from the group. Further, the present invention provides a sintered body consisting of 60 to 97% by weight of at least one metal carbide or nitride selected from the group consisting of aluminum, silicon, and boron and 3 to 40% by weight of carbon, in the presence of oxygen or carbon dioxide gas. 600~900 under atmosphere containing
The present invention also provides a method for producing porous ceramics, characterized in that the carbon contained therein is removed by heating at a temperature of .degree.

The porous ceramic of the present invention is a sintered body whose component is at least one metal carbide or nitride (hereinafter simply referred to as sintered component compound) selected from the group consisting of aluminum, silicon, and boron. Some of the crystal grains of the sintered component compound have continuous pores. The shape, size, etc. of the pores are influenced by the manufacturing method and cannot be absolutely limited, but they can generally be selected from 0.1 to 100 μm. How these pores are structured can be determined by mechanically breaking the porous ceramic.
This can be confirmed by taking an electron micrograph of the fractured surface. For example, FIG. 1 of the accompanying drawings shows the porous ceramic obtained in Example 1 of the present invention mechanically fractured and the fractured surface taken with an electron microscope. As is clear from Figure 1, the crystals of the particles of the sintered component compound (aluminum nitride in Figure 1) are tightly packed with each other, and some of the grain boundaries of the particles are missing. However, this missing part forms a continuous hole. Therefore, the sintered component compounds have a part of their crystal grains that are sintered and linked together, so the strength is extremely high and the shape stability is also excellent. For example, the porous ceramic is 20%
Some even have a strength of 20 kg/mm ² or more with a porosity of .

Although there are no particular limitations on the manufacturing method of the porous ceramic of the present invention, typical examples thereof are as follows. First, a powder that will become the sintered component compound (hereinafter referred to as a first component compound) and carbon or a compound that can become carbon (hereinafter referred to as a second component compound) are mixed.
The first component compound is a known compound. As raw materials for obtaining the porous ceramic of the present invention, these known compounds may be used as they are and sintered. Generally, in order to improve sinterability, it is preferable that the particle size of the first component compound be as small as possible and have a uniform particle size distribution.
These particle sizes and particle size distributions vary depending on the type of the first component compound, sintering conditions, etc., and cannot be absolutely limited, but generally, for example, the average particle size is 5 μm or less, preferably 2 μm or less, and the particle size distribution is based on the average particle size. Diameter D
50% by weight of particles ranging from 0.4D to 1.6D
Those with a purity of 95% or more, preferably 98% or more are particularly preferably used. In particular, when aluminum nitride is used as the first component compound, it is preferable to use the following new aluminum nitride powder developed by the present inventors.

For example, it contains particles with an average particle diameter of 2 μm or less, 3 μm or less in a ratio of 70% by volume or more, and the oxygen content is 3.0% by weight or less, preferably 1.5% by weight.
Aluminum nitride powder with a purity of 95% or more and aluminum nitride.

The above aluminum nitride powder can be obtained by the following manufacturing method.

That is, (1) aluminum oxide fine particles with an average particle diameter of 2 μm or less and a purity of 99.0% or more, preferably 99.9% or more, and an ash content of 0.2% by weight or less, preferably 0.1% by weight.
The fine carbon powder having an average particle size of 1 μm or less is intimately mixed in a liquid dispersion medium, and the weight ratio of the fine aluminum oxide powder to the fine carbon powder is 1:0.36 to 1:1; (2) The intimate mixture obtained is suitably dried and calcined under an atmosphere of nitriding or ammonia at a temperature of 1400-1700°C; (3) The fine powder obtained is then heated under an oxygen-containing atmosphere at a temperature of 600-900°C. The unreacted carbon is removed by heating at a temperature of
3.0% by weight, preferably 1.5% by weight, and can be produced by producing aluminum nitride powder with an average particle size of 2 μm or less, in which the content of metal compounds as impurities is at most 0.3% by weight as metal. .

The second component compound of the porous ceramic of the present invention is carbon or a compound that can become carbon in the process of producing a sintered body. Therefore, it is not necessary to use carbon as a raw material for the second component compound. For example, compounds that can become carbon after sintering, such as polyethylene glycol, starch, etc., can also be used as raw materials. However, it is generally preferable to use carbon black, graphitized carbon, etc. as the raw material. The mixing ratio of the first component compound and the second component compound affects the porosity, pore diameter, etc. of the porous ceramic, as will be described later, so it may be adjusted as necessary. In general, it is preferable to select 60 to 97% by weight of the first component compound and 3 to 40% by weight of the second component compound, that is, carbon.

Next, by sintering the mixture of the first component compound and the second component compound, a composite ceramic of the first component compound and the second component compound can be obtained. The use of sintering aids, e.g. 0.1 to 5% by weight, is often a preferred embodiment. Since the sintering aid varies somewhat depending on the type of the first component compound, it may be selected from known sintering aids depending on the type of the first component compound. Generally preferred sintering aids are those listed in periodic table a.
metal oxides, metal carbonates, metal nitrates, etc. of group A, metal oxides, metal carbonates, metal nitrates, etc.

The raw material mixing ratio of the first component compound and the second component compound determines the porosity of the porous ceramic to be obtained. It is better to determine the mixing ratio of the component compounds in advance. Similarly, since the pore size of porous ceramics is in principle influenced by the particle size of the second component compound,
The particle size of the second component compound may be selected depending on the pore size required for the porous ceramic to be obtained. Although the above-mentioned mixing is not particularly limited, it is generally preferable to perform wet mixing in a known liquid dispersion such as water, hydrocarbons, alcohols, petroleum ether, or the like.

The above-mentioned mixture is dried as required and then subjected to sintering. The temperature for sintering varies depending on the type of the first component compound and cannot be absolutely limited, but it is generally suitable to select a temperature from 1,600 to 2,200°C.

The sintered body obtained by the above method is a composite ceramic consisting of the first component compound and carbon.
This composite ceramic is then heated at a temperature of 600 DEG to 900 DEG C. in an atmosphere containing oxygen or carbon dioxide. Through this heat treatment, carbon in the composite ceramic reacts with oxygen and is removed from the composite ceramic, resulting in the porous ceramic of the present invention.

The porous ceramic of the present invention has various properties as described above, but due to the appearance of porous ceramic with high strength, it is widely used industrially for various applications such as electronic equipment, electrical parts, and heat sinks.

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

Example 1 The purity is 99.99% (impurity analysis values are shown in Table 1), the average particle diameter is 0.52 μm, and the proportion of particles of 3 μm or less is
100 parts by weight of 95 vol% alumina and 50 parts by weight of carbon black having an ash content of 0.08 wt% and an average particle size of 0.45 μm were uniformly mixed in a ball mill using a nylon pot and a nylon-coated ball using ethanol as a dispersion medium. After drying the resulting mixture, it was placed in a flat plate made of high-purity graphite and heated at a temperature of 1600° C. for 6 hours while continuously supplying nitrogen gas at 3/min in an electric furnace. The resulting reaction mixture was heated in air at a temperature of 750° C. for 4 hours to oxidize and remove residual carbon. The white powder obtained is x
As a result of Xray diffraction analysis, it is single phase AlN, Al ₂ O ₃
There was no diffraction peak. The average particle diameter of the powder was measured using a particle size distribution analyzer (Horiba, Ltd. CAPA-500).
When measured using , it was 1.31 μm, and 90% by weight was 3 μm or less. When observed using a scanning electron microscope, this powder was found to be uniform particles with an average size of about 0.7 μm. Further, the measured value of the specific surface area was 4.0 m ² /g. The analytical values of this powder are shown in Table 2.

Table 1 Al ₂ O ₃ powder analysis values Al ₂ O ₃ content 99.99% Element content (PPM) Mg <5 Cr <10 Si 30 Zn <5 Fe 22 Cu <5 Ca <20 Ni 15 Ti <5 Table 2 AlN powder analysis value AlN content 97.8% Element Content Mg <5 (PPM) Cr 21 (〃) Si 125 (〃) Zn 9 (〃) Fe 20 (〃) Cu <5 (〃) Mn 5 ( 〃) Ni 27 (〃) Ti <5 (〃) Co <5 (〃) Al 64.8 (wt%) N 33.4 (〃) O 1.1 (〃) C 0.11 (〃) 80 parts by weight of the above aluminum nitride powder and the average 20 parts by weight of carbon black having a particle size of 0.4 μm were uniformly mixed in a ball mill using a nylon pot and a nylon-coated ball using ethanol as a dispersion medium. The obtained slurry was dried in a dryer at 60°C for 24 hours.

12 g of the above mixed powder was pressure sintered at 2000° C. for 3 hours in nitrogen at 1 atmosphere under a pressure of 200 kg/cm ² in a graphite mold with an inner diameter of 40 mm whose inner surface was coated with boron nitride powder. The obtained sintered body had a black luster.

Further, the density of this sintered body was 29.1 g/cm ³ .

Next, the composite sintered body was placed in an electric furnace and fired in air at 800°C for 12 hours to oxidize and remove carbon. The sintered body after the oxidation treatment was grayish white.
This sintered body was found to be an aluminum nitride porous body because only the diffraction line of aluminum nitride was detected by X-ray diffraction, and the porosity was 28% when measured.

A test piece approximately 3 mm square and approximately 40 mm long was cut out from the porous body, polished with No. 1500 sandpaper, and then its bending strength was measured. The measurement conditions are cross
Three-point bending was performed at a head speed of 1 mm/min and a span of 20 mm. The average bending strength calculated from the measured values was 6 kg/mm.

On the other hand, when the workability of the aluminum nitride porous body obtained in this example was investigated, it was found that it was easy to perform both drilling with a carbide drill and high-speed cutting with a carbide cutting tool, and was free-cutting.

Note that FIG. 1 is a scanning electron micrograph (3000x magnification) of a mechanically fractured surface of the aluminum nitride porous body obtained in this example.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph of a mechanically fractured surface of the aluminum nitride porous body used in Example 1.

Claims (1)

[Claims] 1. A sintered body made of a carbide or nitride of at least one metal selected from the group consisting of aluminum, silicon, and boron, and made of the aluminum, silicon, and boron bonded by sintering. A porous ceramic characterized in that continuous pores are formed in a part of crystal grains of at least one metal carbide or nitride selected from the group consisting of: 2. A sintered body consisting of 60 to 97% by weight of at least one metal carbide or nitride selected from the group consisting of aluminum, silicon, and boron and 3 to 40% by weight of carbon in an atmosphere containing oxygen or carbon dioxide gas. A method for producing porous ceramics, which comprises heating at a temperature of 600 to 900°C to remove carbon contained therein.