JPH04357167A - Ceramics heater - Google Patents

Abstract

PURPOSE:To obtain a ceramics heater free from partial ununiformity of temperature by mutually bonding hydrofluoric acid-treated silicon carbide particles into a porous aggregate using silicon nitride generated by nitriding of metallic silicon and attaching electrode units to a sintered molding of the porous aggregate. CONSTITUTION:Silicon carbide particles are subjected to high-purification treatment of a metallic silicon powder with a hydrofluoric acid-containing acid and and then a molding assistant (e.g. high-molecular cellulose resin) and water are blended therewith. The resultant mixture is formed into a desired shape and dried. The dried material is then heated and sintered in an atmosphere of nitrogen gas so that the silicon carbide particles may be mutually bonded into a porous aggregate by silicon nitride generated by nitriding of metallic silicon. An electroconductive ceramics sintered molding having 0.1-100cm resistivity is produced thereby and a pair of electrode units are then attached to the resultant sintered molding, thus obtaining the objective ceramic heater. This ceramics heater is suitably used as a heater for a rice cooker, etc.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater, and more specifically to a ceramic heater that can be used as a heating element for use in electrical appliances, such as heating elements for rice cookers and hot plates.

0002

[Prior Art] A conventional heat generating heater is a structure in which a sheathed heater 22 and a hot plate 21 are integrated as shown in FIGS. 14 to 17, and the heat from the sheathed heater 22 is transferred to the hot plate 21 by thermal conduction and is radiated. There are known types of structures that generate a temperature difference between the area around the sheathed heater 22 and the area without the sheathed heater 22, which are used in cooking appliances, etc. (for example,
Special Publication No. 54-67070, Special Publication No. 55-43804
(Refer to Japanese Patent Publication No. 55-48460).

0003

[Problem to be solved by the invention] The above-mentioned heat plate using a conventional sheathed heater has a structure that utilizes heat conduction from the sheathed heater, so there is a temperature difference between the area around the sheathed heater and the area without the sheathed heater. There was a drawback that a large amount of This invention was developed in consideration of the above circumstances, and is a heating element (
The main purpose is to provide heaters.

0004

[Means and effects for solving the problems] According to the present invention, silicon carbide particles that have been highly purified with an acid including hydrofluoric acid are bonded in a porous manner with silicon nitride produced by nitriding metal silicon. A ceramic heater is provided that includes a conductive ceramic sintered body having a specific resistance of 0.1 to 100 Ω·cm and a pair of electrode parts attached to the sintered body.

The silicon carbide particles are used to constitute a conductive ceramic sintered body (or sintered body), and usually have a purity of 99% by weight or more and a purity of 1 to 10% by weight.
Those having an average particle size of μm are preferred. Among these, 2
Particularly preferred are those with an average particle size of ~7 μm. If the average particle size exceeds 10 μm, the molding machine will be significantly worn, which will cause problems in production, and at the same time, abrasion powder will be mixed into the raw material, adversely affecting the physical properties and electrical properties of the sintered product. Furthermore, if the diameter is less than 1 μm, it is difficult to obtain a high purity carbonized powder, and the moldability deteriorates, resulting in large variations in the electrical properties of the sintered body. These silicon carbide particles are produced by combining carbon powder and silica stone in an indirect resistance furnace.
Compared to commercially available silicon carbide particles obtained by heating to 800 to 1900° C., particles with significantly less impurities such as silicon oxide and iron present on the particle surface can be used. The silicon carbide particles can be manufactured using, for example, commercially available average particle diameters of 1 to 10 μm.
This can be carried out by treating silicon carbide (m) with an acid aqueous solution containing hydrofluoric acid. As the acid containing hydrofluoric acid, only hydrofluoric acid may be used, or a mixture of hydrofluoric acid and other acids may be used. Examples of acids other than hydrofluoric acid include nitric acid, hydrochloric acid, and sulfuric acid, and an aqueous hydrofluoric acid solution containing a mixture of these acids can also be used.

[0006] The silicon nitride is used to bond silicon carbide particles in a porous manner, and has an average particle diameter of 1 to 10 μm.
It can be used by mixing metal silicon powder with silicon carbide particles, nitriding the metal silicon powder, and binding it between the silicon carbide particles. The conductive ceramic sintered compact according to the present invention is used to configure a heater that generates heat using electrical energy, and has a specific resistance of 0.
1 to 100Ω・cm, preferably 0.5 to 50Ω・cm
can be used.

Next, a method for manufacturing a conductive ceramic sintered body according to the present invention will be described. That is, the purity is 99% by weight with an acid including hydrofluoric acid.
A molding aid and water are added to the raw material consisting of 60 to 90 parts by weight of silicon carbide powder with an average particle size of 1 to 10 μm and 10 to 40 parts by weight of silicon metal powder with an average particle size of 1 to 10 μm, which have been highly purified as described above. A conductive ceramic sintered body can be obtained by adding and mixing, molding this mixture into a predetermined shape, and heating and sintering it in a nitrogen atmosphere.

[0008] As a raw material, purity of 99% is obtained using hydrofluoric acid.
A raw material consisting of 60 to 90 parts by weight of silicon carbide powder with an average particle size of 1 to 10 μm and 10 to 40 parts by weight of silicon carbide powder with an average particle size of 1 to 10 μm, which is highly purified to a weight percent or higher, is used. If the amount of the silicon carbide powder is less than 60 parts by weight, the specific resistance of the resulting conductive ceramic sintered body will increase, which is not preferable, and if it exceeds 90 parts by weight, the toughness will decrease, which is not preferable. Among these, 65 to 75 parts by weight is particularly preferred.

[0009] If the amount of the metal silicon powder is less than 10 parts by weight, the toughness of the resulting conductive ceramic sintered body will decrease, which is not preferable, and if it exceeds 40 parts by weight, the resistivity will increase, which is not preferable. Among these, especially 25-3
5 parts by weight is preferred. A molding aid and water are added to the above raw materials and mixed. Examples of molding aids include organic resin binders, surfactants, and the like, and can be used in an amount of usually 5 to 20 parts by weight based on 100 parts by weight of the total amount of silicon carbide powder and metal silicon powder. Usually 15 to 30 parts by weight of water can be used.

[0010] The above-mentioned organic resin binder is heated to 1000°C in a nitrogen gas atmosphere, and 80 to 98% of the organic resin binder is thermally decomposed and vaporized, and 2 to 20% remains as a carbon-based material (for example, polymer cellulose). It is preferable to use binders such as resins, etc., and these binders are used to bind the raw material SiC due to the trace amount of oxygen contained in the nitrogen gas atmosphere during firing.
It is also possible to prevent metal silicon from being oxidized. In other words, since we use an organic resin binder that remains as 2-20% carbon when heated to 1000°C in a nitrogen atmosphere, the trace amount of oxygen contained in the nitrogen gas atmosphere during firing reacts preferentially with carbon. At high temperatures,
It also reacts with metal silicon to partially produce silicon carbide. These things prevent silicon carbide and metal silicon in the raw materials from being oxidized, lowering the specific resistance of the fired product and reducing variations in the specific resistance. If the residual amount of the organic resin binder is less than 2%, the antioxidant effect will be poor;
% or more, it will have an adverse effect on sinterability, etc., and the strength will decrease. Furthermore, as the surfactant, nonionic surfactants such as fatty acid sorbitan ester polyethylene glycol are preferred. The above mixing is preferably carried out by mixing usually with a mixer and then kneading with a kneader.

In the present invention, the mixture is formed into a predetermined shape, dried, and then heated and sintered in a nitrogen gas atmosphere to bond silicon carbide particles in a porous form with a diameter of 0.1 to 100 Ω·cm. A conductive ceramic sintered compact having a resistivity of . This molding can be performed using, for example, an extrusion molding machine, a casting molding machine, etc., into a shape such as a plate shape, a honeycomb shape, a dish shape, a container shape, or the like.

Heat sintering is performed by heating the dried mixture in a nitrogen gas atmosphere at, for example, 400 to 600°C for 2 to 6 hours to remove gas-generating substances such as forming aids, and then returning the mixture to a nitrogen gas atmosphere. Raise the temperature to 1300-1450℃ in a 2-
This can be carried out by reaction sintering for 24 hours. The obtained conductive ceramic sintered molded body can be appropriately processed to a predetermined size, and electrodes can be formed thereon to constitute a heater for a space heater, a cooking device, or the like.

[0013] An acid containing hydrofluoric acid dissolves and removes silicon oxide and iron present on the surface of silicon carbide particles to highly purify the silicon carbide particles, and the highly purified silicon carbide is used to form conductive ceramic sintered materials. Configure the shape to lower specific resistance. In addition, in sintering with silicon nitride, which is performed by heating metal silicon together with silicon carbide particles in a nitrogen gas atmosphere, the silicon carbide particles are not oxidized, and some nitrogen atoms are dissolved in the silicon carbide particles, resulting in a moderate amount of sintering. It has a specific resistance and forms a porous, lightweight, and strong conductive ceramic sintered body.

In the present invention, a pair of electrode portions are formed on the conductive ceramic sintered body. This electrode portion is preferably formed by first forming a conductive layer on the surface of the molded body, and then bonding an electrode plate to the conductive layer. The conductive layer is formed, for example, by thermal spraying aluminum onto the surface of the molded body. In this invention, an insulating film is formed on the surface of the conductive ceramic sintered body except for the above-mentioned electrode portion forming portion. This insulating film is formed by applying, for example, a lithium-based and cordierite-based glaze to a thickness of about 100 μm and firing in a nitrogen gas atmosphere.

[0015]

[Embodiments] The present invention will be described in detail below based on embodiments shown in the drawings. Note that this invention is not limited to this. First, in Fig. 1, the ceramic heater (4) consists of a plate-shaped ceramic sintered body (plane heater element) (4a) and an aluminum material sprayed along two opposite sides of the back side of the body to a width of 12 mm and a thickness of 12 mm. 100μ
The electrode layer (2) (2) formed by m and the molded body (4a)
An insulating part (film) (1) formed on the front and back surfaces other than the electrode layer (2) (2) forming part, and an aluminum film formed by ultrasonic welding on the electrode part (2) (2) surface. It consists of electrode plates (3) (3). The electrode layers (3) (3) and the electrode layers (2) (2) constitute an electrode section.

The preparation of the ceramic sintered body (4a) will be described in detail later, but the insulating part (1) molded on the surface of the body is coated with lithium and cordierite glazes.
It is applied to a thickness of 0 μm and fired in a nitrogen gas atmosphere. Preparation of silicon carbide powder A mixture of carbonized powder (coke) and silica powder is ignited to 1,800 to 1,900°C by passing a linear current through it, and the produced silicon carbide lumps are crushed, crushed, and washed with water to make the particle size uniform, and then This silicon carbide powder is treated with an aqueous hydrofluoric acid solution to remove impurities such as silicon dioxide and iron that are generated and adhered to the surface of the silicon carbide powder during the manufacturing process (during the synthesis or pulverization of silicon carbide), High purity silicon carbide powder with an average particle size of 5.5 μm and a purity of 99% or more is produced. The average particle diameter and purity of the obtained silicon carbide powder and two types of commercially available silicon carbide powder for comparison are as shown in Table 1.

[0017]

[Table 1]

Production of conductive ceramic sintered compact Silicon carbide powder (purity 99% or more, average particle size 5.5 μm) 70
Parts by weight, 30 parts by weight of metallic silicon powder (average grains 5.9 μm), 12 parts by weight in total of methylcellulose-based organic resin binder and fatty acid sorbitan ester polyethylene glycol (nonionic surfactant) as molding aids, and 21 parts by weight of water. Add and mix with a mixer for about 5 minutes. After thoroughly kneading this mixture using a continuous kneader, a sheet having a thickness of 1 mm and a width of 70 mm is extruded using a high-pressure vacuum extrusion molding machine at a molding pressure of 30 kg/cm 2 to form a plate-shaped test piece. These dried greens were debindered in a nitrogen gas atmosphere at 500°C for 3 hours, and then reacted and sintered in a nitrogen gas atmosphere at 1400°C for 6 hours to form a plate-shaped ceramic sintered body. Physical properties and electrical resistance of the conductive ceramic sintered body The physical properties and specific resistance values of the plate-shaped conductive ceramic sintered body obtained as described above are as shown in Table 2.

[0019]

[Table 2]

The plate-shaped sintered ceramic body was cut into 20 mm diameter pieces to form electrodes, and then the specific resistance with respect to temperature was measured. As a result, it was confirmed that the obtained conductive ceramic sintered compact had a lower resistivity and significantly improved variation in resistivity than the comparative example described below. Comparative Example 1 In Example 1, instead of using the silicon carbide powder prepared as described above, silicon carbide powder of commercial product A shown in Table 1 was used, and conductive ceramics were fired in the same manner as in Example 1. Created a formation.

The specific resistance of this conductive ceramic 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 prepared as described above, silicon carbide powder of commercial product B shown in Table 1 was used, and conductive ceramics were fired in the same manner as in Example 1. The specific resistance of the formed body is 1940Ω・at room temperature.
cm, which was extremely high.

The conductive ceramic sintered compact made in this way uses inexpensive SiC and metal silicon and can be mass-produced through a relatively simple manufacturing process, so it is low cost and has very little variation in electrical properties. It becomes a durable heat generating heater with low coefficient of thermal expansion. Example 2 In Example 1, instead of setting the blending ratio of silicon carbide powder and metal silicon powder to 70/30, it was changed to 80/20, 7
A conductive ceramic sintered body was produced in the same manner as in Example 1 except that the values were changed to 5/25, 70/30, and 65/35. The physical properties and specific resistance values of the obtained plate-shaped ceramic sintered body are as shown in Table 3.

[0023]

[Table 3]

[0024] Thus, by changing the blending ratio of silicon carbide and metal silicon, it is possible to produce sintered bodies having different specific resistances as required. Note that if the blending ratio of silicon carbide is 90% or more, the strength will drop significantly, making it unsuitable as a heater material, and if it is less than 60%, the specific resistance will become extremely high, making it unsuitable as a heater material. Example 3 A sheet having a thickness of 2.5 mm and a width of 280 mm is extruded using a large extrusion molding machine using the same blend of raw materials as in Example 1 at a molding pressure of 35 kg/cm2. After drying, these molded products were cut into appropriate sizes and fired under the same conditions as in Example 1.

Next, when two ceramic heaters (4) are used in the explanatory diagram created as described above, a wall-mounted panel heater (11) as shown in FIG. 2 is obtained. That is, this wall-mounted panel heater (11) includes two ceramic heaters (4) (4) and a heat insulating board (made of ceramic fibers) stacked on these ceramic panel heaters (
5) and this insulation board and ceramic heater (4) (4)
A frame body (6
) and becomes the main character.

The two ceramic heaters (4) (4) are connected to each other in the same plane as shown in FIG. 3(A).
) are arranged in contact so that they face each other, and the opposing electrode parts (
2) Bridge the electrode plate (3) to (2) and connect both heaters (
4) (4) are connected in series. The insulation board (5) is shown in Figure 3.
As shown in (B), there is a recessed part (7) into which the ceramic heater (4) (4) is fitted, and a through hole (8) for passing the electrode plate (3) through to the opposite side. Prepared to avoid contact. The external dimensions of the heat insulating board (5) are 5
The size is 95 x 295 x 20 mm.

The frame (6) has a channel shape with a substantially U-shaped cross section in FIG. 4, and is obtained by extrusion molding of aluminum or heat-resistant synthetic resin, and is divided into four parts (or two parts).
It is composed of In FIG. 4(B), a=25mm,
b=15mm, c=2mm. Production example 1 Ceramic panel heater obtained as above (1
1) is a heat insulating board (about 2 mm thick) with a suitable inorganic adhesive layer
5) is glued into the recessed step (7), and the frame (6) is attached to the outer periphery.
are fitted, integrated, and completed.

Note that when a voltage is applied to the ceramic panel heater (11), the adhesive layer is dried and integrated. Production Example 2 As another production example, as shown in Fig. 5, a ceramic panel heater (11) is placed in a mold with good mold releasability, a semi-kneaded inorganic adhesive layer (10) of about 2 mm is further provided, and a semi-kneaded inorganic adhesive layer (10) of about 2 mm is placed on top of the ceramic panel heater (11). After filling with kneaded ceramic fibers and a heat insulating material (5), the electrode plate (3) is inserted so as to pass through the through hole (8). Electrode plate (
3) When electricity is applied to (3), the adhesive layer (10) dries and the entire structure is integrated and completed. The obtained wall-mounted panel heater (11) had a surface temperature of 80° C. and a surface temperature of 50° C. or less through the heat insulating plate (5) (rated voltage 100 V, output 250 W). The state of use is shown in Figure 7 (A
). Art design for wall-mounted panel heaters: (1) Colorization by applying silicone heat-resistant paint, etc. (2) Design patterning by painting on pottery. (3) Designing by silkscreening and transfer using heat-resistant pigments. You can apply art designs such as

As shown in FIG. 6, a large number of wall-mounted panel heaters (11) can be combined in the same plane to form a large-sized panel heater. Figure 6 (A) shows external dimensions of 600
×283mm, (B) in Figure 6 has external dimensions 300×283
mm, and the long side dimension is 1800 m so that these panel heaters can be combined and installed under a standard window.
A large unit with the short side dimension of 849 m was created and embedded under the window of a room as an interior building material that has the heating function, insulation function, and soundproofing function of a panel heater. In this way, a large panel heater with a rated voltage of 100 V and an output of 1200 W was obtained, with a surface temperature of 60°C and a back temperature of 30°C through the insulation material.
It was ℃. This panel heater acts as a warm air curtain due to its draft effect, which prevents cold air from entering through the upper windows and has an effective heating effect. An example of use is shown in FIG. 7(B).

By using the unit as an interior building material for the ceiling as shown in FIG. 7C, a warm and comfortable heating effect can be obtained due to the effect of far infrared rays. Furthermore, as shown in FIG. 7(D), the unit can be used for flooring to perform floor heating. Note that the output of the panel in the above embodiment can be arbitrarily selected by changing the resistance value.

As is clear from the above explanation, panel heaters include panel heaters installed under desks, wall-mounted panel heaters, and embedded heating, insulation, and soundproofing functions on walls, ceilings, floors, etc. It can be used as an economical interior building material, and the dimensions can be set freely to provide heating according to each location. Furthermore, by applying various art designs, it is possible to provide products with a rich sense of art.

Unlike the above embodiments, the conductive ceramic sintered molded body is not shaped like a plate with a uniform thickness, but is shaped like a plate having a uniform thickness.
9, it is formed into a disk shape whose thickness decreases in the radial direction,
The metal spray electrode (2
4a) (24b) and the molded body (23)
An insulating film (26) may be formed on the entire surface except for the electrodes (24a) and (24b) on the surface. The molded body (23) was formed by a cast molding method (other molding methods, such as plastic molding methods, can also be employed).

[0033] Thus, by applying an AC voltage (25) of 100V to the electrodes (24a) (24b) of the molded body (23), the entire molded body (23) is uniformly heated and the output is 500W. In other words, in order to make the current density uniform in the part of the molded body (23) above the electrode (24b), the wall thickness is largely adjusted (maximum 21.5 to minimum 3 mm). Almost uniform temperature of 300℃
and the temperature difference in the flat part 175φmm is about 10℃
Good temperature distribution can be obtained.

[0034] As a conventional technique, as shown in Figs. 16 and 17, a heat plate 21 having a plate thickness of 4 mm and a diameter of 175 φ mm has a sheathed heater 22 built into an insulating pipe shape with a diameter of 140 φ mm, and the same output as the above conventional example is generated. In this example, heat is conducted from the sheathed heater 22 to the hot plate 21, and the temperature difference in the upper plane, that is, the temperature difference between the area surrounding the sheathed heater 21 and the area without the sheathed heater 21 is about 30° C., which is extremely large. Furthermore, the molded body 23 has a bulk density of 2.1 g/c.
m3, bending strength 10kg/mm2, thermal conductivity 0.03c
The thermal expansion coefficient is as high as al/cm・sec°C and is 4×10 6
Because of its low thermal shock resistance, it is excellent as a heating element.

[0035] Furthermore, in the above, the molded body 23 is
Although actual measurement results are shown using iC(70)-Si3N4(30) ceramic, similar effects can be obtained using high-purity SiC ceramics or recrystallized SiC ceramics. Furthermore, since an insulating film (26) is formed on the entire surface of the three-dimensional structure (container shape), there is no risk of electrical leakage and the structure can be used as a cooking device or the like. That is, it can have both the function of a uniform heating type heating element and the function of a container for cooking food. This is extremely suitable for use as a heating element for cooking appliances or for heating liquids.

As described above, according to the conductive ceramic sintered bodies shown in FIGS. 8 and 9, it is possible to make the current density of the heating element uniform by adjusting the wall thickness, and it is possible to Molded structure), it can be used as a heating element suitable for the product application, and by forming an insulating film on the entire heating element, it generates heat safely and efficiently without the risk of leakage even if it is touched with the hand while energized. You can donate your body.

In addition, the conductive ceramic sintered body can be formed into a dish shape as shown in FIGS. 10-11 or a container shape as shown in FIGS. 12-13. In the case of FIGS. 12 and 13, as in FIGS. 8 and 9, the wall thickness is adjusted to make the current density uniform.

[0038]

[Effects of the Invention] According to the present invention, since almost the entire structure is a heating element, there is almost no temperature difference, and it can be used as an excellent panel heater under a desk, on a wall, on a ceiling, on a floor, etc. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram illustrating an embodiment of a ceramic heater according to the present invention, in which (A) is a front side, (B) is a back side,
(C) shows a CC cross section.

FIG. 2 is a configuration explanatory diagram illustrating a ceramic panel heater as another example, in which (A) shows a front view and (B) shows a cross section.

3 is an explanatory diagram of the structure of the ceramic panel heater shown in FIG. 2, in which (A) is the front of the conductive ceramic sintered body, (B) is the front of the heat insulating plate, and (C) is the C of (B). −
C section is shown.

4 is an explanatory view of the configuration of the ceramic panel heater also shown in FIG. 2, in which (A) shows the front of the frame, and (B) shows the cross section.

FIG. 5 is an explanatory diagram of an apparatus configuration for explaining a method of manufacturing the ceramic panel heater shown in FIG. 2;

FIG. 6 is a front view illustrating a large panel heater as another example.

FIG. 7 is an explanatory diagram showing examples of how various ceramic panel heaters are used in a room.

FIG. 8 is a sectional view of a ceramic heater as another example.

9 is a bottom view of the ceramic heater of FIG. 8. FIG.

FIG. 10 is a diagram corresponding to FIG. 8 of another embodiment.

[
FIG. 11 is a diagram corresponding to FIG. 9;

FIG. 12 is a diagram corresponding to FIG. 8 of still another embodiment.

FIG. 13 is a diagram corresponding to FIG. 9;

FIG. 14 is a diagram corresponding to FIG. 8 showing a conventional example.

FIG. 15 is a diagram corresponding to FIG. 9;

FIG. 16 is a diagram corresponding to FIG. 8 showing another conventional example.

FIG. 17 is a diagram corresponding to FIG. 9;

[Explanation of symbols]

1 Insulating part (film) 2　Electrode layer 3　Electrode plate 4 Ceramic heater 5　Insulation board 6 Frame

Claims (3)

[Claims] 1. Silicon carbide particles highly purified with an acid containing hydrofluoric acid are bonded in a porous manner with silicon nitride produced by nitriding metal silicon, 0.1 to 10.
A ceramic heater consisting of a conductive ceramic sintered molded body having a specific resistance of 0 Ω·cm and a pair of electrode parts formed on this molded body. 2. The ceramic heater according to claim 1, wherein the conductive ceramic sintered molded body is plate-shaped, dish-shaped, or container-shaped, and an insulating film is formed on the surface of the molded body except for a portion where the electrode portion is formed. 3. The ceramic heater according to claim 1, wherein the conductive ceramic sintered molded body is plate-shaped, and an insulating film is formed on the surface of the molded body except for the electrode part forming part;
A ceramic panel heater consisting of a heat insulating plate made of ceramic fibers and a frame that overlaps the heat insulating plate and the ceramic heater and surrounds their periphery.