JPH10291858A - Whisker reinforced electrically conductive composite ceramics and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively produce electrically conductive ceramics forming an evaporation boat for direct resistance heating used for the vapor deposition of a metal, an electrode used in a molten metal, etc. SOLUTION: A mixture of 40-60 wt.% TiB2 powder with 40-45 wt.% AlN powder and 1-2 wt.% metal Al is compacted by cold uniaxial pressing under 10-200 MPa pressure and cold isostatic pressing under 100-200 MPa pressure and the resultant compact is fired at 1,500-2,300 deg.C in an atmosphere of nitrogen. During this firing, AlN whiskers account for 10-15% of the total AlN content after the firing. When 0-15 wt.% TiC and 0-2 wt.% Al2 O3 are added to the mixture, >=480 MPa bending strength at room temp. is ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive ceramic for forming an electrode or the like which is used by immersing it in a vapor deposition boat for direct current resistance heating or a molten metal used for metal vapor deposition, and to provide the same at low cost. It is about the method. In other words, the sintered body according to the present invention is significantly superior to ceramics conventionally used in this field in its most important properties, that is, mechanical strength at room temperature, electrical conductivity and thermal conductivity. , Their main areas of use are not limited to those that currently exist,
It can be used for new applications.

[0002]

_2. Description of the Related Art Ceramic boats for depositing aluminum and other metals include titanium diboride (TiB ₂ ) as a conductive component, and hexagonal boron nitride for imparting workability (softness) to ceramics. (H-BN),
In order to stabilize the electrical characteristics, it is constituted by a component to which aluminum nitride (AlN) or the like is added. Due to their difficulty in sintering, pressure sintering such as hot pressing or hot isostatic pressing (HIP) is generally used for production. Therefore, the degree of freedom in selecting the shape of the product is lost, which leads to an increase in manufacturing costs, and a product having sufficient strength has not been obtained.

[0003] The presence of oxides in the raw material powder used in the production of these boats not only promotes the growth of crystal grains during sintering, but also causes the oxides to react with molten aluminum when used as boats. Accelerates melting and wear of the evaporation boat. In addition, there is a problem that volatile oxides as reaction products significantly contaminate a chamber for vacuum evaporation.

[0004]

Most of the compounds used in the production of materials used at high temperatures, such as vapor deposition boats, have a high melting point. Can not expect. Therefore, normal pressure firing such as ordinary ceramics cannot be performed, and unless expensive methods such as hot pressing and hot isostatic pressing (HIP) are used, a material having satisfactory mechanical performance can be obtained. Can not. In addition to this problem, titanium diboride, particularly a hexagonal boron nitride, which is a main component of the deposition boat, 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 that is strongly dependent on the pressure, especially where the strength and conductivity change strongly depending on the pressing direction. This results in a limited condition for the use of the material.

[0005] Therefore, the problem to be solved by the present invention is to develop a manufacturing method by normal pressure sintering without using an expensive hot press and to aim at improvement of strength. Another object of the present invention is to obtain a whisker-reinforced conductive composite ceramic having desired properties.

[0006]

Means for Solving the Problems The present inventors, when sintering aluminum nitride (AlN), add metallic aluminum (Al) to the aluminum nitride under certain appropriate conditions.
The present inventors have found that whiskers of N are generated and that the strength of the sintered body is improved, leading to the present invention. That is, 40 to 6 by weight.
0% titanium diboride (TiB _2), 35-40 percent aluminum nitride, 0-11% of titanium carbide (TiC), 0
To 2% aluminum oxide (Al ₂ O ₃₎ of and 1-2% after mixing the aluminum (Al) in the elemental state, the pressure 10~200MPa cold (preferably, 30～200MP
In a), consolidation is performed by uniaxial pressing and cold isostatic pressing, and 1500 to 2300 ° C. (preferably 1800 to
2100 ° C.) to obtain titanium diboride (T
40% to 60% by weight of iB ₂ ) and 0% of titanium carbide (TiC).
~ 15wt%, aluminum nitride (AlN) 40 ~ 45
It is possible to produce conductive composites in which wt% and 10-15% of the aluminum nitride are present in the form of whiskers.

If the TiB ₂ content is less than 40%, sufficient conductivity cannot be obtained, and if it exceeds 60%, it becomes difficult to process the sintered body. Limited. If TiC is added in excess of 15%, the workability of the sintered body is similarly reduced. Further, AlN amount is determined by a balance between TiB _2, it is less than 40% there is a problem with the melting loss resistance to molten Al, since too much to lower the conductivity of the sintered body, the range 40 45 wt%. Al added to raw material powder
_The amount of ₂ O ₃ is determined by the balance with the amount of metal Al added at the same time. However, if it exceeds 2%, Al ₂ O ₃ remains as it is and may cause deterioration of the characteristics of the sintered body. And The amount of metal Al is also determined by the balance with the amount of AlN, and 1
２2%. Next, when the cold forming pressure as a manufacturing condition is less than 10 MPa, the effect is not exhibited,
Pressures over MPa cannot be implemented due to equipment limitations, so 10 to 200MPa
Limited to the range of a. If the sintering temperature is less than 1500 ° C, sufficient sintering and densification hardly occur, and the sintering temperature is 2300 ° C.
If it is more than one, abnormal grain growth of crystal grains occurs, which is not preferable in terms of the performance of the sintered body.

For the production of such ceramics, a method such as spray drying, casting, extrusion molding or injection molding as a usual process is also applicable.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conductive component (TiB ₂
Or the same compound as above), and boron and aluminum nitride mixed as a raw material powder to form B
A series of (composition) composites where N and AlN are mixed. Furthermore, the composite according to the invention is
It is electrically conductive and has a fire rating particularly suitable for high temperature applications.

According to the above-mentioned method, even if the raw material powder has a poor sintering activity, the elemental substances (metal boron and aluminum) react with nitrogen during firing of the pressed compact of the powder, and BN and AlN Sintering is promoted by such a reaction as to form pores of the compact. Also, the undesired boric acid is converted into a highly refractory oxide having the formula B ₆ O. Unlike hot press,
Since no external pressure is applied during sintering, the final sintered body is
Compared to a hot-press fired body, it has high bulk properties such as mechanical strength and electrical conductivity and isotropic.

[0011]

【Example】

Example 1 100 g of titanium diboride, 70 g of aluminum nitride and 2 g of metallic aluminum were mixed in a ball mill, cold-pressed in a steel mold at a pressure of 50 MPa, and cold isostatic pressure at a pressure of 200 MPa. Pressurized. Thereafter, the obtained substrate had a size of 120 × 20 × 10 mm and was fired in a nitrogen atmosphere at 2050 ° C. The fired body is cut and processed to obtain a 3 × 4 × 40 mm specimen, and the density and the room temperature bending strength (JIS R1) are determined by Archimedes' method.
601), the thermal conductivity was measured by a laser flash method, and the electrical resistance was measured by a four probe method. The whisker amount was calculated by measuring the area ratio in a scanning electron micrograph as shown in FIG.

Example 2 90 g of titanium diboride, 70 g
g of aluminum nitride, 20 g of titanium carbide and 2 g
Of metal aluminum is mixed in a ball mill and the pressure is 100
Cold press in steel mold at MPa and pressure 200MPa
And cold isostatic pressing. After that, the obtained base is 12
It had a size of 0 × 20 × 10 mm and was fired at 2050 ° C. in a nitrogen atmosphere. Cut the fired body 3 × 4 × 40mm
Processed to obtain a sample, density by Archimedes method,
The room temperature bending strength (JIS R1601), the thermal conductivity by the laser flash method and the electric resistance by the four probe method were measured. The whisker amount was calculated by measuring the area ratio in a scanning electron micrograph as shown in FIG.

Example 3 90 g of titanium diboride, 70
g of aluminum nitride, 20 g of titanium carbide, 1.5 g
Of metal Al and 2 g of alumina were mixed in a ball mill, cold-pressed in a steel mold at a pressure of 100 MPa, and
Cold isostatic pressing was performed at a pressure of 200 MPa. Thereafter, the obtained substrate had a size of 120 × 20 × 10 mm and was 205
It was fired in a nitrogen atmosphere at 0 ° C. The fired body is cut and 3
The sample was processed to obtain a 4 × 40 mm specimen, and the density, the room temperature bending strength (JIS R1601), the thermal conductivity by the laser flash method, and the electric resistance by the four probe method were measured by Archimedes method. In calculating the amount of whiskers,
The measurement was performed through measurement of the area ratio in a scanning electron micrograph as shown in FIG.

COMPARATIVE EXAMPLE 1 100 g of titanium diboride and 70 g of aluminum nitride were mixed in a ball mill, cold-pressed in a steel mold at a pressure of 100 MPa, and pressed at a pressure of 2 MPa.
Cold isostatic pressing was performed at 00 MPa. Thereafter, the obtained base material had a size of 120 × 20 × 10 mm and was at 2050 ° C.
Firing in a nitrogen atmosphere. Cut the fired body, 3 × 4
The sample was processed to obtain a × 40 mm specimen, and the density, the room temperature bending strength (JIS R1601), the thermal conductivity by the laser flash method, and the electric resistance by the four probe method were measured by the Archimedes method.

Comparative Example 2 100 g of titanium diboride, 7
0 g of aluminum nitride and 10 g of boron nitride were mixed in a ball mill, cold pressed in a steel mold at a pressure of 100 MPa, and cold isostatically pressed at a pressure of 200 MPa. Thereafter, the obtained substrate had a size of 120 × 20 × 10 mm and was fired in a nitrogen atmosphere at 2050 ° C. The fired body is cut and processed to obtain a 3 × 4 × 40 mm specimen,
Density, room temperature bending strength (JIS R) by Archimedes method
1601), the thermal conductivity was measured by the laser flash method, and the electric resistance was measured by the four probe method.

Comparative Example 3 100 g of titanium diboride, 2
9 g of aluminum nitride, 15 g of boron nitride, 7 g of metallic aluminum and 7 g of metallic boron were mixed in a ball mill, cold pressed in a steel mold at a pressure of 100 MPa, and cold isostatically pressed at a pressure of 200 MPa. Thereafter, the obtained substrate was 120 × 20 × 10 mm in size and 20
It was fired in a nitrogen atmosphere at 00 ° C. The fired body is cut,
Processed to obtain a 3 × 4 × 40 mm test piece, density, room temperature bending strength (JIS R1601) by Archimedes method,
The thermal conductivity was measured by the laser flash method and the electrical resistance was measured by the four probe method.

Comparative Example 4 100 g of titanium diboride, 1
5 g of aluminum nitride, 29 g of boron nitride, 7 g of metallic aluminum and 7 g of metallic boron were mixed in a ball mill, cold pressed in a steel mold at a pressure of 100 MPa, and cold isostatically pressed at a pressure of 200 MPa. Thereafter, the obtained substrate was 120 × 20 × 10 mm in size and 20
It was fired in a nitrogen atmosphere at 00 ° C. The fired body is cut,
Processed to obtain a 3 × 4 × 40 mm test piece, density, room temperature bending strength (JIS R1601) by Archimedes method,
The thermal conductivity was measured by the laser flash method and the electrical resistance was measured by the four probe method.

Table 1 below shows the manufacturing conditions of Examples 1 to 3 and Comparative Examples 1 to 4 and various measured properties of the sintered body. Table 1 shows that the composite material obtained according to the present invention has a wide range of controllable electrical conductivity, high mechanical strength, fire resistance and various properties independent of the direction of measurement.

[0019]

[Table 1]

[0020]

According to the present invention, a composite ceramic having excellent characteristics can be obtained. In order to achieve these properties, the principle of a new method for manufacturing conductive composites is:
There is sintering promoted by the reaction. That is, BN, AlN,
Compounds such as TiB ₂ (or other conductive elements) are mixed with elemental substances such as metallic aluminum. The powders are first compacted to form a compact, and then, during firing in nitrogen, the elemental materials undergo a chemical reaction with the nitrogen, each being converted to a corresponding nitride. . These secondary nitrides (particularly AlN whiskers) are formed during firing as shown in FIG. 1 and contribute to increasing the strength of the sintered body. (See SEM photograph in Fig. 1)

[Brief description of the drawings]

FIG. 1: Scanning electron microscope (SE) of AlN whiskers
M) A diagram based on a photograph.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuichi Sato 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division

Claims (2)

[Claims] 1. A titanium diboride the (TiB ₂₎ 40 to 60
wt%, titanium carbide (TiC) 0-15 wt% (including 0), and aluminum nitride (AlN) 40-45 wt%
%, And 10 to 15% of aluminum nitride is in the form of whiskers. 2. Titanium diboride (TiB ₂ ) 40 to 60 wt.
%, Aluminum nitride (AlN) 35-40 wt%, 0
~ 11wt% (including 0) titanium carbide (TiC), 0 ~
2 wt% (including 0) aluminum oxide (Al
₂ O ₃ ) and 1-2% by weight of metallic aluminum (A
l), and cold uniaxial pressing and cold isostatic pressing (1
0-200MPa) and press molding in a nitrogen atmosphere for 150
A method for producing a conductive composite material, comprising firing at 0 to 2300 ° C.