JPS6051661A - Electroconductive ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to conductive ceramics having good electrical conductivity.

[Background of the invention]

Conventionally known conductive ceramics include silicon carbide (STC) and lanthanum chrome (
Known materials include LaCrOs (LaCrOs) and zirconia (ZrO2). However, the electrical resistance of the above-mentioned conductive ceramics is relatively high, 10-2Ω at a high temperature of 1OOOC.
The lower limit is about the size of the mouth. Furthermore, the conductive ceramics have negative resistance-temperature characteristics, that is, the electrical resistance decreases as the temperature rises, so thermal runaway is likely to occur due to a sudden increase in current, making temperature control difficult when used as a heater.

Furthermore, the above-mentioned conductive ceramics usually have drawbacks such as being porous and having low mechanical strength.

[Purpose of the invention]

The present invention was made in order to eliminate the above-mentioned drawbacks of conventional conductive ceramics, and an object of the present invention is to provide a new conductive ceramic having high mechanical strength, low electrical resistance, and positive resistance-temperature characteristics. With the goal.

[Summary of the invention]

The present invention has discovered a material that can achieve the object of the present invention by combining aluminum oxide (KT203) or silicon carbide (SIC) with a conductive substance to form a composite.

That is, the present invention provides a conductive material obtained by dispersing and mixing a non-oxide conductive material having properties similar to metal in a base material phase mainly composed of A L 203 or SiC, and sintering it densely. ceramics. In the present invention, the non-oxide conductive material includes ll of the periodic table.
Among Group A elements, scandium (SC), yttrium (
Y) and compounds such as carbides, nitrides and borides of lanthanum (La), such as 5cI of scandium compounds
32゜SCC, 8CN, YB2゜YI14 of yttrium compound, YBs, YO2, YN and LaB of lanthanum compound 41 L aB a t L aCz
#LaN etc. are used. These materials have high electrical conductivity and positive resistance-temperature characteristics, and also have high melting points and oxidation resistance (9), so they are suitable as a single material.

On the other hand, the base material is At203.3 i C or 5jsN4
It is preferable to add one of the following, a sintering aid suitable for each component, and a component that suppresses grain growth. The reason for choosing the above-mentioned material as the base material component is that it has a high heat resistance, excellent thermal and chemical stability, high mechanical strength, and can overcome the trap of thermal shock resistance.

These features mean that, for example, when the present invention is used as a high-temperature heater material, it has excellent heat resistance and oxidation resistance, is durable against thermal shocks that are applied when it is instantaneously heated by electricity, and is highly conductive. It is suitable in combination with other materials.

The conductive ceramic of the present invention is prepared by mixing 1. the powder of the base material component and the above-mentioned 4-electronic powder in a volume range of 80 to 20 volumes and 20 to 80 volumes, respectively, and adding a molding binder such as polyvinyl alcohol (PVA) to this mixture. ) By adding and mixing an aqueous solution and molding it into a predetermined shape and sintering it at a temperature of 1500 to 2200 C in a vacuum or non-oxidizing atmosphere, it is possible to achieve a density of 90 cm or more in terms of theoretical density ratio and at room temperature. It is possible to produce a sintered body having a resistivity of 1 Ωm or less.

In the present invention, the reason why the base material component and the conductive R17 material are limited to the above ratio is that if the conductive material is less than 20% by volume, the resistivity of the sintered body is greater than 1Ωα, and the resistivity relative to the amount of the conductive material added is This is because the change becomes steep, making it difficult to control the resistivity, and furthermore, when the base material is SiC, the resistance temperature characteristic becomes negative. Also, if it exceeds 80 volume (HH%),
This is undesirable because the properties such as mechanical strength, oxidation resistance, and thermal shock resistance of the obtained sintered body deteriorate.

[Embodiments of the invention]

Next, the present invention will be explained in detail with reference to Examples.

Example 1 The base material contains At1Os and Si with an average particle size of about 3 μm.
C and Si3N4 powders were used, and YBa powder with an average particle size of about 2 μm was used as the conductive material. The sintering aid is
For SiC, 2% A L 20s powder, 5fsN4
and A t20 s with 5% MgO powder and 1
% (both Ichikawa%) was added. The above base material and Y B 6
Mix the powder in various proportions and add 3 to the total amount.
% PVA solution was added and mixed using a stirrer.

Next, the mixed raw material powder is molded into 1000 kg/
A pressure of cA was applied to form a molded product. This molded body was placed in a graphite die and hot-press sintered under reduced pressure with a degree of vacuum of 10-3 to 10-5 Torr (pressure was constant at 300 Kg/c4). The sintering temperature is 1600C, 81s for At203 series.
The Ni type is 1700C and the 8iC type is 2000G. All of the obtained sintered bodies were densified to a relative density of 95- or more. Further, the relationship between the resistivity of the sintered body at room temperature and the amount of YB6 mixed is as shown in the figure. In the same figure, curve A is based on SiC, curves B and C are based on 5jsN4 group and A
It is a t20s-based sintered body. From the results shown in the figure, the mixing amount of YB6, which is a conductive material, is 20 volumes 8! By appropriately selecting i% or more, a resistivity of any value within the range of approximately 1 to 5×10 −5 Ωm can be obtained.

Table 1 shows the relative density, temperature coefficient of resistance (20 to 800 C), and bending strength at room temperature of the above sintered body. Y
A sintered body with a B6 mixing amount of 20 to 80 volume t+7% has a relative density of 97% or more, a bending strength at room temperature of 20 Kg/ff1 or more, and has high density and high strength properties. When the amount of YB6 mixed exceeds 80 volumes, the relative density and bending strength decrease. On the other hand, the temperature coefficient of resistance, s i 3 N4 group and A
The 120 s matrix composite has a positive value of Y B s2020 volume. The SiC-based composite material has a negative temperature coefficient at YB620 volume, but a positive temperature coefficient of resistance at about 30 volume percent or more.

Example 2 The k120s powder was the same as in Example 1, and as the conductive material, various commercially available SC, Y, and La compounds with a purity of 99% or more and a particle size of 5 μm or less were used. A composition consisting of 60 volumes of Al t Os powder and 40 volumes of conductive material powder was mixed, molded into a disc shape at a pressure of 1000 Kg/cr/l, and then vacuum hot pressed using a vacuum hot press device. Press sintered. The issue of hot press sintering is pressure 30
0 to 9/i, temperature 1700C, 1 hour 1 b.

The properties of the obtained composite sintered body are shown in Table 2.

The relative densities of the prototype composite sintered bodies are all 97 inches or higher, which is high density. Although the resistivity varies slightly depending on the type of conductive material, it is highly conductive and has a bending strength of 351 (resistance) or higher than 2.Also, for all the sintered bodies in Table 1, the resistance at room temperature and when heated at 800C As a result of multiplying the values by 11!4, the value of resistance change varies depending on the type of conductive material, but in all cases, the resistance increases as the temperature rises, and they have positive humidity characteristics.

Example 3 Using the same Si, N, and powder as in Example 1, LaB4
Alternatively, LaB6 powder (average particle size in each case is 2 μm) was added in varying amounts, and molded and hot press sintered under the same conditions as in Example 1 to form 5i3N4-4. af34 series and S
j A 3N4-LaBe-based composite sintered body was produced. The relationship between the resistivity of both systems and the amount of conductive material mixed is shown by curve B in Figure 1.
It is almost equivalent to C. Also, the bending strength is almost the same as the values shown in Table 1, and the resistance temperature characteristics are positive between room temperature and 800C.

〔Effect of the invention〕

As described above in detail in the examples, the conductive ceramic of the present invention can have any resistivity in the range of 1 to 5 x 10-5 Ωm by adjusting the amount of conductive material powder mixed. . In addition, since it has positive resistance-temperature characteristics, it will not melt due to current runaway even in red-hot conditions, and because it is dense and has high mechanical strength, it is also highly resistant to oxidation and thermal shock.

Therefore, the conductive ceramics of the present invention having such features can be used, for example, in various heaters, glow plugs for automobiles, electric igniters for igniting liquid and gaseous fuels, and conductors for high-temperature applications. suitable for

[Brief explanation of drawings]

The figure is a continuation of the first page of conductive ceramics according to an example of the present invention ■Int, CI,' Identification code Internal serial number // H
01C71026918-5EC Inventor Satoshi Kosugi
Husband 3-chome Saiwaimachi, Hitachi City

Claims (1)

[Claims] 1. Carbides, nitrides and borides of group A elements in the periodic table as electrically conductive materials containing an appropriate amount of one of aluminum oxide, silicon carbide or silicon nitride and a sintering aid thereof. Conductive ceramics obtained by sintering a composition obtained by mixing 20 to 80 volumes of at least one of the following. 2. The conductive ceramic according to claim 1, which has an electrical resistivity of 1 Ωα or less at room temperature and a positive resistance-temperature characteristic. 3. The conductive ceramic according to claim 1, wherein the 111a group element is scandium, yttrium, or lanthanum.