JPH0971468A - Conductive composite ceramics and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a conductive composite having high strength and excellent conductivity. SOLUTION: This conductive composite consists of 50-70wt.% of titanium boride, 10-45wt.% of boron nitride, 5-40wt.% of aluminum nitride and the rest of aluminum oxide and oxide of boron where the amount of B6 O is more than 3 times of B2 O3 in the atomic concentration ratio as oxides of boron in the rest. Titanium boride, boron nitride, aluminum nitride and aluminum metal and/or boron are blended, molded by cold uniaxial pressing or/and cold equilateral compression molding and calcined in a nitrogen atmosphere. This composite has widely controllable conductivity, high mechanical strength and high fire protecting character and the characteristics independent from the measuring direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive ceramics used for a resistance heating vapor deposition boat or crucibles used for vapor deposition of metals, and a manufacturing method for inexpensively providing the same.

The sintered body of the invention has a most important property, that is, electric conductivity and fire resistance (ratio of mechanical strength measured at room temperature and operating temperature), which can be controlled in a wide range, The field is not limited to the existing ones, but can be applied to new applications.

[0003]

_2. Description of the Related Art A ceramic boat for depositing metals such as aluminum is titanium diboride (TiB ₂ ) as a conductive component, and hexagonal boron nitride (HBN) for imparting workability (softening) to ceramics. ) And a component to which aluminum nitride (AlN) or the like is added in order to stabilize the electrical characteristics.

Since they are difficult to sinter, pressure sintering such as hot pressing or hot isostatic pressing (HIP) is generally used for manufacturing. Therefore, the degree of freedom in the selection of the shape of the product is lost and the manufacturing cost is increased.

In addition to the three main components mentioned above, these sinters also contain some oxides (mostly B ₂ O ₃ ) which have already formed in the starting powder and act as sintering aids.

The presence of these oxides reduces the performance as a vapor deposition boat. That is, the presence of the oxide not only promotes the grain growth of the sintered body, but the reaction between the oxide and the molten aluminum accelerates the melting and wear of the vapor deposition boat.

Further, there is a problem that the volatile oxide as a reaction product remarkably contaminates the chamber for vacuum deposition.

That is, most of the compounds used for producing materials used at high temperatures such as boats for vapor deposition have high melting points, and the presence of a molten phase cannot be expected when firing and producing these materials. .

Therefore, it is not possible to perform normal pressure firing like ordinary ceramics, and hot pressing or hot isostatic pressing (HI
Unless an expensive method such as P) is used, a material having satisfactory mechanical performance cannot be obtained.

In addition to this problem, titanium diboride, which is a major component of the vapor deposition boat, and particularly hexagonal boron nitride, is a substance having a remarkable anisotropy in crystal structure and physical properties.

The uniaxial action of the hot pressing pressure on these materials gives the material to be fired a preferential (selective) orientation which strongly depends on the pressure, and in particular the strength and the conductivity strongly depend on the pressing direction. This will create limited conditions for the use of materials such as changes.

[0012]

That is, the problems to be solved are, first, to develop a manufacturing method by atmospheric pressure firing that does not rely on expensive hot pressing, and to manufacture a member by eliminating the anisotropy of the material. The goal is to improve sex.

[0013]

According to the present invention, a conductive component (TiB ₂ or a compound similar thereto), boron nitride and aluminum nitride, and metallic BN and aluminum mixed with the raw material powder are formed by reaction. And Al
The present invention relates to a series of (composition) composite materials in which N is mixed.

Furthermore, the composite material according to the invention is electrically conductive and has a fire resistance which is particularly suitable for high temperature applications.

Specifically, titanium diboride (TiB ₂ ) 7
0 parts by weight, 5 to 30 parts by weight of boron nitride (BN), 5 to 30 parts by weight of aluminum nitride (AlN), and 3 to 15 parts by weight of metal aluminum (Al) or / and boron (B) are mixed and cold. At a pressure of 10 to 200 MPa (preferably 30 to 200 MPa) by uniaxial pressing or cold isostatic pressing, and then 1500 to 2300 ° C. in a nitrogen atmosphere.
It can be manufactured by baking at (desirably 1800 to 2100 ° C.).

The fired body of the present invention comprises titanium diboride (TiB).
₂ ) 50 to 70 wt% and boron nitride (BN) 10 to 4
5wt%, aluminum nitride (AlN) 5-40wt
%, With the balance being aluminum oxide (Al ₂ O ₃ ) and an oxide of boron, and B ₆ O serving as the remaining boron oxide being 3.0% of B ₂ O ₃ in terms of atomic concentration ratio. It is a conductive composite material that is more than double.

Further, for the production of such ceramics, methods such as spray drying, cast molding, extrusion molding or injection molding as usual processes can be applied.

According to the above-mentioned method, even in the case of a raw material powder having a poor sintering activity, the elemental substances (metal boron and aluminum) react with nitrogen during the firing of the powder compact, and BN and AlN. Sintering is promoted by a reaction such as the generation of slag and filling the pores of the molded body.

Undesirable boric acid (B ₂ O ₃ ) is B
It is converted to a refractory oxide with the chemical formula ₆ O.

Unlike hot pressing, no external pressure is applied during sintering, so that the final sintered body has more bulk properties, such as mechanical strength and electrical conductivity, than the hot pressed fired body. It has high isotropy.

The composition of the fired body is titanium diboride (Ti
If B ₂ ) is less than 50 wt%, the electric resistance is high, and 70 wt
%, It becomes hard and the workability deteriorates, and boron nitride (BN) is 1
If it is less than 0 wt%, the workability is poor, if it is more than 45 wt%, the strength is low, if the content of aluminum nitride (AlN) is less than 5 wt%, the sinterability is poor, and if it is more than 30 wt%, the workability is poor.

With respect to the manufacturing conditions, if the amount of metallic aluminum (Al) and / or boron (B) is less than 3 with respect to 70 parts by weight of titanium diboride (TiB ₂ ), the above-mentioned reaction effect will be sufficiently enjoyed. If it exceeds 15, it is not desirable from the economical aspect.

If the molding pressure is less than 10 MPa, sufficient molding cannot be performed, and if it exceeds 200 MPa, the equipment becomes expensive, and if the firing temperature is less than 1500 ° C., sufficient firing cannot be performed.
If it exceeds 300 ° C., the equipment becomes expensive, which is not desirable.

[0024]

The present invention will be described in detail below with reference to examples and comparative examples.

Using the raw material powders shown in Table 1, the trial production shown in Table 2 was conducted to prepare the materials shown in Examples 1 to 4, and Comparative Example 1
Performance comparison was performed with the commercially available materials indicated by 3 to 3.

First, the room temperature flexural strength of the material according to the present invention is higher than that of the commercially available materials (comparative examples 1 and 2) obtained by normal pressure firing, and the materials shown in Examples 3 and 4 are Despite the pressure firing, it shows a higher value than the commercially available hot pressed material. It has also been shown that the reduction in strength at high temperatures is relatively small.

Although the amount of TiB ₂ which is a conductive element is almost the same in the example and the comparative example, the specific resistance value is
It can be seen that the material according to the invention is low.

In particular, that of the material of Example 4 was
The specific resistance value was 1/6 of that of the commercially available material indicated by. The bending strength is measured according to JIS. R1601 and JIS. R160
4 is a 3-point bending test value, and the electrical resistivity value is a measurement value using a Kyowa RIKEN 4-pin type K-705RD measuring device.

Next, crucibles were made from the materials shown in Examples 1 to 4 and Comparative Examples 1 to 3, and powdered aluminum was filled in the crucibles and heated to 1000 ° C. in an Ar gas atmosphere. When the crucible contact surface of a small aluminum lump that was held for 10 hours and solidified after cooling was examined, the materials of Examples 1 to 4 according to the present invention had an appearance in which metallic luster was maintained, but Comparative Examples 1 to 3 The contact surface loses its metallic luster,
The color tone was cloudy as seen in aluminum oxide.

This means that the oxygen in the material of the present invention is stabilized so that it is not attacked by molten aluminum.

In order to achieve the above-mentioned properties, the principle of the new method for producing a conductive composite material is reaction-assisted sintering.

That is, a compound such as BN, A1N, TiB ₂ (or another conductive element) is mixed with an elemental substance such as metallic boron or aluminum.

The powders are first compacted to form a compact. Then, when it is fired in nitrogen, those elemental substances undergo a chemical reaction with nitrogen, each being converted into the corresponding nitride.

These secondary nitrides (particularly BN) have crystal grains much smaller than those of the compounds originally mixed as raw materials.

These elemental substances more effectively fill the pores in the molded body by forming secondary nitrides so as to strengthen the skeleton of the sintered body, and impart the sintering activity to the sintering. Contribute to the process.

Then, these elemental substances react with the oxide coating (for example, B ₂ O ₃ ) so as to passivate the surfaces of the compound crystal grains that originally exist, and the oxide is refractory. It has been transformed into a more stable phase such as B ₆ O or alumina, which has a high degree.

1 and 2 are SEM micrographs of the fracture surfaces of the materials shown in Example 4 and Comparative Example 3, respectively.

In FIG. 1, the reaction sintering effect of the elemental substances (boron and aluminum) is observed, and ultrafine crystal grains of secondary nitride smaller than the crystal grain size of the starting powder are generated.

Next, a similar material was analyzed by ESCA.
From the comparison of the oxygen-to-nitrogen ratio, comparing the material prepared by the reaction-accelerated atmospheric pressure firing (Example 4) and the commercially available hot-pressed material (Comparative Example 3), the oxygen content is low, reflecting the higher fire resistance. It has been found.

Further, this indicates that the oxide and the metal B or Al react with each other during sintering to generate a volatile oxide, which is released from the material.

This also means that the binding energy profile (sl B) of boron is measured and the amount of bound oxygen and B ₆
The ratio of O and B ₂ O ₃ is clear from the comparison between the example and the comparative example. That is, as shown in Table 3, the amount of boric acid in the material shown in Example 4 is lower than that in Comparative Example 3, and the ratio of the refractory oxide B ₆ O to the boric acid B ₂ O ₃ is also high.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

The composite material according to the invention has a wide range of controllable electrical conductivity, high mechanical strength, fire resistance and properties which are independent of the direction of measurement. They are,
It is as shown in Table 2 as an example.

[Brief description of drawings]

FIG. 1 is a structural photograph of a fired body of Example 4.

FIG. 2 is a structural photograph of a fired body of Comparative Example 3.

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[Procedure amendment]

[Submission date] December 13, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of drawings]

FIG. 1 is an SEM showing the structure of the ceramic material of Example 4.
Photo.

FIG. 2 is an SEM showing the structure of the ceramic material of Comparative Example 3.
Photo.

Claims (4)

[Claims] 1. Titanium diboride (TiB ₂ ) 50 to 70
wt%, boron nitride (BN) 10 to 45 wt%, aluminum nitride (AlN) 5 to 40 wt%, the balance being aluminum oxide (Al ₂ O ₃ ) and boron oxide, and the balance being B ₆ as the existing boron oxide
A conductive composite material, wherein O is 3.0 times or more of B ₂ O ₃ in atomic concentration ratio. _2. 70 parts by weight of titanium diboride (TiB ₂ ),
5 to 30 parts by weight of boron nitride (BN), 5 to 30 parts by weight of aluminum nitride (AlN), and aluminum aluminum (A)
1) or / and 3 to 15 parts by weight of boron (B) are mixed, cold uniaxial pressing or / and cold isostatic pressing is performed, and firing is performed in a nitrogen atmosphere. Method of manufacturing wood. 3. The pressure molding pressure according to claim 2,
~ 200 MPa, a method for producing a conductive composite material. 4. The method for producing a conductive composite material according to claim 2, wherein the firing temperature is 1500 to 2300 ° C.