JP2507151B2 - Conductive ceramics sintered body and method for producing the same - Google Patents

Description

The present invention relates to a conductive ceramics sintered body and a method for manufacturing the same. In particular, it is used in heater materials that generate heat with electric energy.

(B) Conventional technology In heaters used for electric appliances such as heaters and cookers, metal-based heating elements such as nichrome wires or bands are usually the mainstream, and PTC ceramic heating elements are used in part. All of these heating elements are used for radiation or generation of warm air.

As a ceramic heating element, various proposals have been made on a conductive ceramic material for a heater, which is mainly composed of SiC ceramics (for example, USP866444, Japanese Patent Publication 57).
-41796, JP-B-61-38144, JP-A-58-209084, JP-A-SHO
60-27653, JP-A-60-51661, JP-A-61-146760).

(C) Problems to be Solved by the Invention As described above, in the metal-based heating element, the specific resistance (specific resistance) is too small (100 to 200 μΩ for Nichrome wire.
cm), the heat generation area cannot be made large and uniform with respect to the electric power required as a heater, and there is a problem in efficient heat generation. In addition, since the shape is a line or band, a three-dimensional heater (for example, We couldn't make a honeycomb heater. Also, since the coefficient of thermal expansion is large, there is a problem such as deformation during heat generation, and there is also a problem in durability (especially durability in a steam atmosphere or corrosive gas) due to high temperature oxidation and corrosion. It was The PTC ceramic heating element is expensive and cannot be used under conditions such as rapid heating and quenching because the heating element itself is inferior in thermal shock, and this heater has a Curie point (currently on the market). Since the heater in (1) has a Curie point of 250 ° C or less), there is a problem that it cannot generate high temperature heat.
Further, in the conventional conductive ceramics, which have been proposed in various forms, there are few industrially used ones due to the large variation in the electrical characteristics in the cost and manufacturing. SiC-based heaters are only used as industrial electric furnace heaters.
However, this was also expensive and was never used for general electric appliances.

The present invention solves all of these problems, uses inexpensive SiC raw material, and has relatively little variation in electrical characteristics in a relatively simple manufacturing process, and can be mass-produced. By having a specific resistance that is easy to use in products, it is a high-area heating element (for example, a honeycomb heater, a wide-area surface heater, etc.) and has excellent durability, and it can be used at a wide range of temperatures from low to high. An object of the present invention is to provide a conductive ceramics sintered body that can be used for a heater and a method for manufacturing the same.

(D) Means for Solving the Problems According to the present invention, the silicon carbide particles that have been highly purified by an acid containing hydrofluoric acid are bonded in a porous manner with silicon nitride produced by nitriding of metal silicon. Naru, 10 ^-1 ~ 10
Provided is a conductive ceramic sintered body having a specific resistance of ² Ω · cm.

The silicon carbide particles are for constituting a conductive ceramics sintered body, and preferably have a purity of usually 99% by weight or more and an average particle size of 1 to 10 μm. Among these, those having an average particle diameter of 2 to 7 μm are particularly preferable. If the average particle size exceeds 10 μm, the abrasion of the molding machine is significant and there is a problem in production, and at the same time, abrasion powder is mixed in the raw material, which adversely affects the physical properties and electrical characteristics of the sintered product.
On the other hand, if it is less than 1 μm, it is difficult to highly purify the silicon carbide powder, the moldability is deteriorated, and the variation in the electrical characteristics of the sintered body is increased. This silicon carbide particle is a silicon oxide (Si oxide) present on the particle surface as compared with a commercially available silicon carbide particle obtained by heating carbon powder and silica in an indirect resistance furnace at 1800 to 1900 ° C.
It is possible to use those containing very few impurities such as O ₂ ) and iron. The silicon carbide particles can be produced, for example, by treating commercially available silicon carbide having an average particle diameter of 1 to 10 μm with an acid aqueous solution containing hydrofluoric acid. As the acid containing hydrofluoric acid, only hydrofluoric acid may be used, or hydrofluoric acid and other acids may be mixed and used. Acids other than hydrofluoric acid include nitric acid, hydrochloric acid, sulfuric acid and the like, and hydrofluoric acid aqueous solution prepared by mixing these acids can also be used.

Even if the silicon nitride is used to bond the silicon carbide particles in a porous manner, the metal silicon powder having an average particle diameter of 1 to 10 μm is mixed with the silicon carbide particles to nitrid the metal silicon powder, and the silicon carbide It can be used by binding the particles.

The conductive ceramics sintered body in the present invention is for constituting a heater that generates heat by electric energy, and has a specific resistance of 10 ⁻¹ to 10 ² Ω · cm, preferably 0.5.
It is possible to use one having a value of -50 Ω · cm.

Next, a method for manufacturing the conductive ceramics sintered body of the present invention will be described.

According to the present invention, an acid containing hydrofluoric acid has a purity of 99%.
A raw material consisting of 60 to 90 parts by weight of silicon carbide powder having an average particle size of 1 to 10 μm and 10 to 40 parts by weight of a metal silicon powder having an average particle size of 1 to 10 μm, which has been highly purified to a weight percentage or more, and a forming aid. Water is added and mixed, and the mixture is molded into a predetermined shape and then sintered by heating in a nitrogen atmosphere to form the conductive ceramics sintered body according to claim 1, wherein the conductive ceramics sintered body is formed. A method of manufacturing a body is provided.

In the present invention, purity of 99% by weight with hydrofluoric acid
A raw material comprising 60 to 90 parts by weight of silicon carbide powder having an average particle size of 1 to 10 μm and 10 to 40 parts by weight of metallic silicon powder having an average particle size of 1 to 10 μm is used.

If the amount of the above-mentioned silicon carbide powder is less than 60 parts by weight, the specific resistance of the obtained conductive ceramics sintered body becomes large, which is not preferable, and if it exceeds 90 parts by weight, the toughness deteriorates, which is not preferable. Among these, 65 to 75 parts by weight is particularly preferable.

If the amount of the above-mentioned metallic silicon powder is less than 10 parts by weight, the toughness of the obtained conductive ceramics sintered body will be deteriorated, and if it exceeds 40 parts by weight, the specific resistance will be large, which is not preferable. Among these, 25 to 35 parts by weight is particularly preferable.

In the present invention, a molding aid and water are added to the above raw materials and mixed. Examples of the molding aid include organic resin binders and surfactants, and usually 5 to 20 parts by weight can be used per 100 parts by weight of the total amount of silicon carbide powder and metallic silicon powder. Water can usually be used in an amount of 15 to 30 parts by weight.

The organic resin binder is an organic resin binder in which 80 to 98% is vaporized by thermal decomposition by heating up to 1000 ° C. in a N ₂ atmosphere, and 2 to 20% remains as a carbon-based substance (for example, a polymer cellulose resin). Is preferably used, and these binders can also prevent the raw material SiC and metallic silicon from being oxidized by a small amount of oxygen contained in the nitrogen atmosphere during firing. In other words, when heated up to 1000 ° C in a nitrogen atmosphere, an organic resin binder that remains as carbon in 2 to 20% is used, so a small amount of oxygen and carbon contained in the nitrogen atmosphere during firing react preferentially and at the same time high temperature. At times, it also reacts with metallic silicon to partially generate silicon carbide. As a result, silicon carbide and metallic silicon in the raw material are prevented from being oxidized, so that the specific resistance of the fired product is reduced and the variation in the specific resistance is reduced. When the residual amount of the organic resin binder is 2% or less, the antioxidant effect is poor,
Further, if it is 20% or more, the sinterability is adversely affected and the strength is reduced. Further, as the surfactant, for example, a nonionic surfactant such as fatty acid sorbitan ester polyethylene glycol is preferable. It is preferable that the above mixing is usually carried out by mixing with a mixer and further kneading.

In the present invention, this mixture is formed into a predetermined shape, dried, and then heat-sintered in a nitrogen atmosphere so that silicon carbide particles are bonded in a porous form 10 ^-1 to 10 ² Ω.
-Form a conductive ceramics sintered body having a specific resistance of cm. This molding can be performed, for example, by using an extrusion molding machine or the like into a plate shape, a honeycomb shape, or the like.

The heating and sintering is performed on the dried mixture in a nitrogen atmosphere,
For example, heating at 400-600 ° C for 2-6 hours to remove gas-generating substances such as molding aids, and again for 1300-14 in a nitrogen atmosphere.
It can be performed by heating to 50 ° C. and reacting and sintering for 2 to 24 hours.

The obtained conductive ceramics sintered body can be appropriately processed into a predetermined size, and electrodes can be formed on the sintered body to form a heater such as a heater or a cooker.

(E) Action Acid containing hydrofluoric acid dissolves and removes silicon oxide (SiO ₂ ) and iron existing on the surface of the silicon carbide particles to highly purify the silicon carbide particles, so that the silicon carbide subjected to the high purification treatment is A conductive ceramic sintered body is formed to reduce the specific resistance. Further, in the sintering with silicon nitride, which is performed by heating metallic silicon together with silicon carbide particles in a nitrogen atmosphere, the silicon carbide particles are not oxidized and some nitrogen atoms are solid-solved in the silicon carbide particles. It becomes resistive and forms a porous, lightweight and tough conductive ceramics sintered body.

(F) Examples Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Preparation of Silicon Carbide Powder A lump of silicon carbide produced by igniting at 1800 to 1900 ° C. by passing a linear current through a mixture of carbon powder (coke) and silica powder was crushed, crushed and washed with water to obtain a particle size. Furthermore, the silicon carbide powder is treated with an aqueous solution of hydrofluoric acid to form SiO ₂ (silicon dioxide) or iron which is formed and adhered to the surface of the silicon carbide powder during the manufacturing process (when synthesizing or crushing silicon carbide). And other impurities are removed, the average particle size is 5.5 μm, and the purity is 9
9% or more of high purity silicon carbide powder is produced. The average particle size and the purity of the obtained silicon carbide powder and two kinds of commercially available silicon carbide powder for comparison are as shown in Table 1.

Preparation of conductive ceramics sintered body Silicon carbide powder (purity 99% or more, average particle size 5.5 μm) 70
Parts by weight, 30 parts by weight of metal silicon powder (average particle size 5.9 μm), 12 parts by weight of methyl cellulose organic resin binder and fatty acid sorbitan ester polyethylene glycol (nonionic surfactant) as a molding aid, and water.
Add 21 parts by weight and mix with a mixer for about 5 minutes. After thoroughly kneading this mixture with a continuous kneader, use a high-pressure vacuum extruder to form a sheet with a thickness of 1 mm and a width of 70 mm at a molding pressure of 30 k.
Extrude at g / cm ² to make a plate-shaped test piece. Further, a rectangular honeycomb having an outer dimension of 22.5 × 22.5 mm, a cell dimension of 1.5 mm and a rib thickness of 0.5 mm is extruded at a molding pressure of 60 kg / cm ² by the same method to obtain a honeycomb test piece. These dried greens were debindered in a nitrogen atmosphere at 500 ° C. for 3 hours and then reacted and sintered in a nitrogen atmosphere at 1400 ° C. for 6 hours to form plate-shaped and honeycomb-shaped ceramic sintered bodies.

Physical Properties and Electrical Properties of Conductive Ceramics Sintered Body Physical properties and specific resistance values of the plate-shaped and honeycomb-shaped conductive ceramics sintered bodies obtained as described above are as shown in Table 2.

The electrode for measuring the electrical characteristics used was an ohmic silver paste applied and then baked at 580 ° C. for 10 minutes. The plate-shaped ceramics sintered body was cut to a diameter of 20 mm to form an electrode similar to the above, and then the change in specific resistance with respect to temperature was measured. As a result, a specific resistance as shown in the graph of FIG. 1 was exhibited. . As a result, it was confirmed that the obtained conductive ceramics sintered body was lower than the Comparative Examples described later and the variation was remarkably improved.

Comparative Example 1 In Example 1, instead of using the silicon carbide powder produced as described above, the silicon carbide powder of the commercial product A shown in Table 1 was used, and otherwise the conductivity was the same as in Example 1. A ceramic sintered body was produced.

The specific resistance of this conductive ceramics sintered body was 150 Ω · cm at room temperature, which was high.

Comparative Example 2 In Example 1, instead of using the silicon carbide powder produced as described above, a commercially available product B silicon carbide powder shown in Table 1 was used, and otherwise the conductivity was the same as in Example 1. A ceramic sintered body was produced.

The specific resistance of this conductive ceramics sintered body was 1940 Ω · cm at room temperature, which was extremely high.

The conductive ceramics sintered body made in this way uses inexpensive SiC and metallic silicon, and can be mass-produced with a relatively simple manufacturing process, so it has a constant cost, very little variation in electrical characteristics, and low thermal expansion. The material is suitable as a heating heater with good durability.

Example 2 Instead of setting the compounding ratio of silicon carbide powder and metallic silicon powder to 70/30 in Example 1, 80/20, 75/25, 7
A conductive ceramics sintered body was produced in the same manner as in Example 1 except that 0/30 and 65/35 were changed. The physical properties and specific resistance values of the obtained plate-shaped and honeycomb-shaped ceramics sintered bodies are as shown in Table 3.

In this way, by changing the compounding ratio of silicon carbide and metallic silicon, it becomes possible to produce sintered bodies having different specific resistances as needed. In addition, the blending ratio of silicon carbide is 90
If it is more than 60%, the strength is remarkably reduced, and it is not suitable as a heater material. If it is 60% or less, the specific resistance is remarkably increased and it is not suitable as a heater material.

Example 3 A sheet having a thickness of 3 mm and a width of 150 mm was extruded at a forming pressure of 35 kg / cm ² using a large-sized extrusion molding machine by mixing the same raw materials as in Example 1. Similarly, the external dimensions are 140 x 40 and the cell dimensions are
Forming honeycomb with 2.2 x 2.2 and 0.5 mm rib thickness 50 kg / cm
Extrude with ² . After drying these molded products, they are cut to an appropriate size and fired under the same conditions as in Example 1. An electrode is formed on each of these fired samples by thermal spraying of aluminum to form a heating heater.

FIG. 2 shows an explanatory view of the obtained sheet-shaped (plate-shaped) heater. The surface heater 1 has a room temperature resistance of 40Ω and an external dimension of 220mm x 2
When a voltage of 150V is applied between the electrodes 2 through the lead plate 3 with 50mm × 3mm, electrode width 10mm, and electrode distance 200mm, the heater temperature is 300 ℃ on average and the power is 1200W. It is extremely suitable as a heat generating heater.

FIG. 3 is an explanatory diagram of the honeycomb heater. Honeycomb heater 4 has room temperature resistance of 13Ω and outer dimension 140 (width) x 4
An electrode 5 having a size of 0 (height) × 20 (depth) mm and facing in the height direction is formed, and a voltage is applied to the electrode 5 via a lead plate 6 to generate heat. Cell 7 has dimensions 2 x 2 mm and thickness
It is a hole surrounded by a 0.5 mm rib 8 and penetrates in the depth direction. FIG. 4 is an explanatory view of a warm air generator using the honeycomb heater 4 shown in FIG. Cold air is sent to the air passage 11 by the fan 10 connected to the motor 9, and the air rectified by the rectifying plate 12 passes through the heat-generated honeycomb heater 4 and exits as warm air. At this time, when an AC voltage of 100 V was applied to the electrode 5 formed on the honeycomb heater 4 and the air flow rate was 1 m ³ per minute, the average warm air temperature was about 120 ° C. (at room temperature 20 ° C.) The temperature is about 200
C, power is 1200W. This is a very suitable heating element, usually as an electric hot air fan heater. In the case of an actual product, the warm air generator shown in FIG. 4 is equipped with a thermostat, a thermistor or a current limiter as a circuit as a temperature control and safety device.

(G) Effect of the Invention According to the present invention, a sheet heating element that requires a surface of a large area has a suitable specific resistance as a honeycomb heating element, and at the same time has excellent durability and a small variation in the specific resistance, resulting in low cost. The present invention provides a conductive ceramics sintered body as a heat generating heater material and a method for manufacturing the same.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the temperature-resistivity characteristics of a plate-shaped conductive ceramics sintered body produced in an example of the present invention, and FIG. 2 is a graph showing the conductive ceramics sintered body of the present invention. FIG. 3 is an explanatory view of a planar heater used, FIG. 3 is an explanatory view of a honeycomb heater using the conductive ceramics sintered body of the present invention, and FIG. 4 is a hot air generation using the conductive ceramics sintered body of the present invention. It is an explanatory view of a machine. 1 ... Sheet heater, 2 ... Electrode, 3 ... Lead plate, 4 ... Honeycomb heater, 5 ... Electrode, 6 ... Lead plate, 7 ... Cell, 8 ... Lip, 9 ... Motor, 10 …… fan, 11 …… blower, 12 …… rectifier plate.

Claims (3)

(57) [Claims] 1. Silicon carbide particles highly purified by an acid containing hydrofluoric acid are porous bonded with silicon nitride produced by nitriding metallic silicon. 10 ⁻¹ to 10 ² Ω · cm
Conductive ceramics sintered body having specific resistance of. 2. 60 to 90 parts by weight of silicon carbide powder having an average particle size of 1 to 10 .mu.m and highly purified by an acid containing hydrofluoric acid to a purity of 99% by weight or more, and metallic silicon having an average particle size of 1 to 10 .mu.m. Powder
The conductive ceramics sinter according to claim 1, wherein a raw material consisting of 10 to 40 parts by weight is mixed with a molding aid and water, and the mixture is molded into a predetermined shape and then heat-sintered in a nitrogen atmosphere. A method for producing a conductive ceramics sintered body, which comprises forming a body. 3. The molding aid as claimed in claim 2, wherein 80 to 98% by weight is vaporized by heating up to 1000 ° C. in a nitrogen atmosphere and 2 to 20% by weight is an organic resin binder which remains as a carbonaceous substance. Production method.