JPS6018081B2 - Improved conductive composite ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conductive composite ceramic having improved mechanical strength, heat resistance, and chemical resistance.

Hitherto, metal resistors, conductive ceramics, conductive ceramic composites, conductive resin composites, and the like have been known as conductive materials.

However, the selection range of specific resistance of metal resistors is narrow,
They have the disadvantage of poor heat resistance and corrosion resistance, and conductive ceramics exhibit non-linear conductivity with respect to temperature, which limits the usable temperature range, and they also have low thermal shock resistance and mechanical strength. There is a drawback. If it is made into a conductive ceramic composite, the thermal shock properties can be improved to some extent, but it exhibits non-linear conductivity with respect to temperature and has low mechanical strength, as compared to conductive ceramics. The disadvantage is that the selection range of resistance is narrower than with conductive ceramics. Furthermore, conductive resin composites have the advantage that the temperature characteristics of resistivity, thermal shock resistance, mechanical strength, etc. can be adjusted appropriately by selecting the material, but the disadvantage is that the range of use is severely limited due to low heat resistance. has.

The present inventors have conducted extensive research in order to overcome the drawbacks of conventional conductive materials, exhibit excellent practical properties, and develop conductive materials that can be used in a wide range of fields. They discovered that a composite ceramic consisting of an agglomerated low thermal expansion ceramic phase and a conductive material phase can impart very excellent properties, and have accomplished the present invention.

That is, the present invention provides an adjacent ceramic comprising a ceramic phase selected from an insulating ceramic phase, a semiconducting ceramic phase, and a mixed phase thereof, and a conductive monolayer phase that is at least partially continuous, in which the ceramic phase is at least 30% The present invention provides conductive composite ceramics characterized by being composed of aggregates having Buddha's grains.

The composite ceramic of the present invention has a structure in which insulating ceramic particles, semiconductor ceramic particles, or a mixture thereof are aggregated into aggregates with a particle size of at least 30 mm, and these aggregates are bonded with a continuous phase of a conductive substance. are doing. The ratio of the ceramic phase to the dew-conducting substance phase depends on the properties of the desired composite ceramics and the types and properties of each component used as raw materials, and is not necessarily constant, but it is usually 50 to 50% by spot weight of the ceramic, The conductive material is selected in a range of 2 to 5% by weight.

Although it was necessary for conventional conductive ceramitas to contain a conductive substance in an amount of 3% by weight or more, in the present invention, sufficient conductivity can be achieved even when the amount of the conductive substance is 1% by weight or less. What was shown was completely unexpected. The ceramic aggregates used in the present invention need to have a particle size of at least 30 mm. If it is smaller than this, the effect of agglomerating it will not be sufficiently exhibited. There is no particular limit to the upper limit of this particle size, but in consideration of manufacturing conditions and workability, it is usually preferable to set the particle size to 1/4 or less of the thickness of the target composite ceramic. A small amount (approximately 0.0
．． It can be prepared by adding 5 to 2% by weight of a binder such as polyvinyl alcohol, grinding, granulating according to a conventional method, and drying. These aggregates may be prepared and then mixed with the conductive substance as is, or after being formed into aggregates as described above,
It may be preliminarily molded at high temperature or microencapsulated and then mixed with the atomizing material.

As the conductive substance phase in the present invention, a conductive substance may be used alone, or a mixture of ceramic particles in an amount of about 20 to 4% by weight may be used.

Methods for forming this conductive material phase include, for example, mixing ceramic aggregates into a conductive material solution or a mixture of ceramic particles therein and then solidifying the mixture, or first forming a molded body of ceramic aggregates or its aged There is a method in which a porous body is formed and a required conductive material phase is deposited on the surface of the aggregate in the gas phase. As the conductive material in the present invention, metals, carbon, cermets, metal nitrides, borides, carbides, or silicides, metal oxides, or mixtures thereof are used.

Examples of metals include silver, titanium, nichrome, etc. Examples of cermets include titanium, carbide chromium, etc. Examples of metal nitrides include titanium nitride, aluminum nitride, etc. Examples of metal borides Examples of the metal carbide include silicon carbide and zirconium carbide, and examples of the metal silicide include molybdenum silicide. Examples of metal oxides include Re0
3. Single oxides such as Ru02, LaTi03, Ca
MnQ, French Mn03, CaC(]3, Sd0r03, L
aCh]3, LaCo03, Fe03, NiFe04,
In addition to metal oxygen salts and composite oxides such as Buddha2Ni04 and La2Cu04, Cu20, Ti○, V○, Mh○,
Coo, Ni○, Zn○, Cd○, Ti203, V20
3, Fe203, Cr203, La203, Ti02,
Oxides such as Sn02, V2Q, Mm03, W03, Re03 or CaTi03, SrTi03, BaT
i03, LaTi03, Layama03, CaMn03, L
aMn03CaC(]3, SrCr03, BaCr03
, LaCr03, Fe304, NiFe204
, LaNi04, Buddha2Cu04, Life508
, MgW04, etc., which are based on metal oxyacid salts or composite oxides, and have conductivity imparted by adjusting the ratio of the metal to oxygen to a non-stoichiometric ratio. On the other hand, the ceramic particles used in agglomerated form in the present invention include insulating metal oxides and silica particles mainly composed of alumina, silica, magnesia, titania, zirconia, sillimanite, spinel, steatite, forsterite, etc. Based on the stone-feldspar-clay raw material system
Insulating general porcelain, P-cryptite, 3-spodumene, aluminum tinate, cordierite, tin oxide, zircon, feldspathic porcelain and other insulating porcelain with low thermal expansion and negative thermal expansion, as well as C-0, Ti○ ,V○,Mh○,C
oo, Ni○, Zn0, Cd0, Ti203, V203
, Fe2○3, Cra○3, La2○3, Ti○2, Sn
〇2, V2Q, Moo3, W03, oxides like Re03 or CaTi03, SrTi03, BaTi0
3, LaTi03, Layama03, CaMn03, L
aMn03, CaCr03, Srnko3, L
aCr03, LaCo03, Fe304,
NiFe204, L et al. Ni04, Ba2Cu04, Li
An example is a material based on a metal oxyacid salt or a composite oxide such as fe508 or MgW04, which is given a semiconductor by changing the ratio of the metal to oxygen to a non-stoichiometric ratio.

The conductive composite ceramic of the present invention can be produced by preparing insulating or semiconducting ceramic particles or a mixture thereof as aggregates of a predetermined size in advance, and mixing them with conductive substance powder, or by firing them to make them conductive. Mix a solution of salts that can be converted into natural substances, such as viscous, feldspar or carpoxymethyl cellulose, if necessary.
It can be manufactured by adding polyvinyl alcohol or the like, molding it into an appropriate shape, and firing it at a temperature appropriately selected depending on the type of material (for example, 900 to 1700 qo).

While conventional conductive ceramics exhibit non-linear conductivity with respect to temperature and exhibit large negative conductivity temperature characteristics in a temperature range of up to several hundred degrees, the composite ceramics of the present invention By selecting the types and proportions of both materials, it is possible to achieve not only non-linearity but also linearity, as well as the desired positive and negative temperature characteristics, and in addition, it is easy to obtain the desired electrical conductivity, so the operating temperature It is very convenient that the enclosure can be set over a wide range, the heating element can be easily controlled without any danger, and the shape and size can be made into desired shapes.

Next, the composite ceramic of the present invention can have any desired coefficient of thermal expansion by selecting the types of the two materials to be composited, their ratio, etc., so it has a low thermal expansion with a high thermal shock resistance for rapid heating and cooling applications. It is extremely convenient to use because it can be used in combination with other materials to obtain any desired coefficient of thermal expansion.

In addition, the composite ceramic of the present invention can be fired into a dense structure as required, so it has improved mechanical strength, which has been compromised due to the porous nature of conventional conductive ceramics.
It has great characteristics such as high resistance to streaks, corrosion resistance in high-temperature atmospheres, and excellent thermal conductivity.

As mentioned above, the composite ceramic of the present invention has various good characteristics in addition to conductivity, so it is suitable for use in '11 Heater - Chemical Riding Electrode, For example, Electrode for Electrolytic Oxidation Synthesis of Organic Materials'.
31 Static charge removal equipment, such as thread, tape, etc. Sardine guides, rotating sliding parts 4 Heat resistant, thermal shock resistant equipment '51 Thermistors - Useful especially for high temperatures, high temperature chemicals, or corrosion resistant in high temperature atmospheres. are doing.

Furthermore, when used as a heating element, it emits far-infrared heat rays, so it can dehydrate and dry, evaporate organic solvents, harden resins with lumps, etc.
Suitable for dry processing of resins, fibers, metals, and pharmaceuticals.

In this case, since the resistor and its holder can be integrated into a ceramic heater, there is an advantage that the structure can be simpler than that of a heater using nichrome, molybdenum silica, or the like. Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Polyvinyl alcohol was added to finely ground alumina powder to which 2% by weight of titanium oxide was added to form aggregates.

The aggregates were made in several sizes. Silver powder as a conductive substance and 1% by weight of clay were added to these aggregates and mixed well, and 1% by weight of polypynyl alcohol was added as a molding binder, molded and fired at 950 to 100 pi.
The properties of the fired ceramics were as follows. The results are shown in graphs in FIGS. 1 and 2. That is,
Figure 1 is a graph showing the change in thermal expansion coefficient when the mixing amount (wt%) of silver powder is changed, and Figure 2 is a graph showing the change in the coefficient of thermal expansion when the mixing amount (wt%) of silver powder is changed.
~0.5 ribs (average 0.3 skin), particle size 0.1~0
．． Aggregate grains with 2 ribs (average 0.15 ribs) [b}, grain size 0.04
Aggregates 'c' with ~0.1 ribs (average 0.07 ribs) and aggregates 'd with grain size 0.015-0.07 sides (average 0.03 ribs)
1 is a graph showing the relationship between the amount of silver powder mixed and specific resistance when 1 is used. The broken line in FIG. 2 is data for the conventional dispersion mixing method using ceramic particles (0.003 grain or less) that do not aggregate. In addition, 0.2 to 0.5
The temperature characteristic of resistivity of the composite ceramic containing 1% by weight of skin aggregates was 4.2×10-4/deg.

At this time, alumina to which 2% by weight of titanium oxide had been added was aggregated, sintered in advance at 950 qo, and silver powder was added to this, and the composite ceramics prepared in the same machine as above had the same properties. .

Example 2 In Example 1, when other conductive substances were used instead of silver, the properties of the obtained ceramics were as follows.
It was as shown in the table.

However, the particle size of the aggregates used was 0.2 to 0.5. Table 1 Example 3 A ceramic aggregate of 0.2 to 0.5 in Example 1 was prepared, and separately from this ceramic powder 3, weight % of the turtle-conducting substance MoSi27 was added. A well-mixed mixture was prepared.

70% conductive material phase 'B mixed with the former aggregate ■
} and 1% by weight of clay were added and mixed well, 1% by weight of polyvinyl alcohol was added as a molding binder, molded, and fired in vacuum at 1550-160°C. The properties of the fired ceramics were as shown in Table 2. Table 2 Example 4 Various finely ground ceramic materials were prepared as aggregates with a size of 0.2 to 0.5, and 1% by weight of silver powder as a conductive substance was added to these aggregates. 2% by weight of clay was added and mixed well, polyvinyl alcohol was added as a molding binder, molded and baked at 950-1000°C.

The properties of the fired ceramics were as shown in Table 3. Table 3

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the amount of silver powder mixed and the coefficient of thermal expansion in an example of the present invention, and FIG. 2 is a graph showing the relationship between the amount of silver powder mixed and the specific resistance. Figure 1 Figure 2

Claims (1)

[Claims] 1 a ceramic phase selected from an insulating ceramic phase, a semiconductor ceramic phase, and a mixed phase thereof;
A sintered ceramic comprising an at least partially continuous conductive material phase, characterized in that the ceramic phase is composed of aggregates having a grain size of at least 30 microns.