JPH04370690A - Ceramic heater - Google Patents

Abstract

PURPOSE:To provide a ceramic, heater which has less restriction on the design and in which the electrode takeout part of a heater element can be certainly joined with an electrode to be electrically connected therewith. CONSTITUTION:A W wire 3 as heat emitting body is embedded in a ceramic heater element 4 consisting of Si3N4 as major component, and a pair of ceramic electrodes 7, 8 contacting the ends 3a, 3b of the W wire 3 and consisting of 40 TiN and the rest of Si3N4 are joined with the two sides of the end part of the heater element 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heating element used at high temperatures, and for example to a ceramic heating element used in engine glow plugs, engine intake and exhaust heaters, and the like.

0002

2. Description of the Related Art Hitherto, ceramic heating elements with high heat resistance have been known as heaters used in high-temperature environments. These ceramic heating elements include those equipped with a heating element that generates heat by the ceramic itself, such as SiC (silicon carbide), and ceramic materials whose main component is Si3N4 (silicon nitride), with a heating resistor such as W There are some that are equipped with a heating element in which (tungsten) wire is embedded.

[0003] The ceramic heating element described above is used, for example, in a ceramic glow plug P1 for an engine, as shown in FIG.
It has a structure in which a cylindrical metal electrode P4 is fitted onto a cylindrical heating element P3 having a built-in cylindrical heating element P3.

In the glow plug P1, the W wire P2 of the heating element P3 and the metal electrode P4 are joined to each other through the cylindrical space P between the heating element P3 and the metal electrode P4.
5, this is done by shrink fitting brazing in which silver solder P6 is poured. Moreover, as the material of the metal electrode P4,
Conventionally, heat-resistant and corrosion-resistant metals such as pure Ni or Inconel 600 (7 weight % Fe, 15.5 weight % Cr, balance Ni) have been used. This is because when the heat generating element P3 itself becomes high temperature, the metal electrode P4 also becomes considerably high temperature, so that the electrode itself is required to have heat resistance.

[0005]

[Problems to be Solved by the Invention] However, as shown in Table 1 below, the thermal expansion coefficient of the metal electrode P4 is considerably larger than that of the ceramic heating element P3. There were problems like ■.

[0006]

[Table 1]

■Since the thermal expansion coefficients of the materials of the metal electrode P4 and the heating element P3 are significantly different, the metal electrode P4 and the electrode extraction part of the heating element P3 (the extraction part of the W wire P2) are chemically separated. It is difficult to join them directly, so they have to be joined using a conventional shrink fit brazing design, which is a design constraint.

[0008] Furthermore, in such a physical joining method such as shrink fit brazing, repeated heating and cooling of the heating element P3 causes contact failure between the metal electrode P4 and the take-out portion of the W wire P2. This caused problems with durability. The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a ceramic heating element that can reliably bond the electrode extraction portion of the heating element element and the electrode connected thereto, and has fewer design restrictions. do.

[0009]

[Means for Solving the Problem] The invention of claim 1 to achieve this object provides a heating element comprising a ceramic heating element and an electrode attached to the heating element, wherein the electrode is made of a ceramic material. The gist is a ceramic heating element characterized by being formed from a material as a main component.

[0010] The invention according to claim 2 also provides the ceramic heating element according to claim 1, wherein the coefficient of thermal expansion of the ceramic material forming the electrode is equal to or higher than the coefficient of thermal expansion of the ceramic heating element element. shall be.

[0011] As the ceramic heating element, for example, the ceramic itself becomes the heating resistor (S
iC), and one in which a heating resistor is embedded in ceramics (W wire embedded in Si3N4). Examples of the electrode material include low thermal expansion materials mainly composed of ceramics, such as Si3N4 -TiN, Si3N
4 -Ni, Si3N4 -ZrN, Al2TiO5-
A conductive ceramic composite material such as Ni, TiB2-Ni, or WC-Co, or a ceramic-metal composite material, or a ceramic material such as TiB2 or TiN that is conductive alone can be used.

[0012] The thermal expansion coefficients of the above electrode material and the ceramic heating element are preferably the same, but in some cases (the thermal expansion coefficient of the ceramic heating element material + 2 x 10-6)
[1/°C], and furthermore, a range up to (coefficient of thermal expansion of ceramic heating element material + 4 x 10-6) [1/°C] is also suitable.

Further, the material constituting the electrode material is preferably a material with excellent oxidation resistance, and the electrical resistance of the electrode material is 1.
It is preferably Ωcm or less. The above electrode and the ceramic heating element are bonded using Ti/Ag/Cu, Ti/Cu, Ti.
/Ag/Cu/Ni, Ti/Ag/Cu/In, T
A method in which a conductive layer is interposed, such as a joining method using an active metal alloy such as i/Ni/Cu, or a method using a metal or alloy such as Fe/Ni/Cr, Ni, Ni/Cr, etc. Anything is fine.

Furthermore, in joining the electrode and the ceramic heating element, a soft metal such as Ni or Ag may be interposed between the two members as necessary. Further, the above-mentioned joining may be performed by a hot pressing method, and in that case, the joining may be performed directly without intervening a metal layer as described above.

[0015]

[Operation] In the ceramic heating element of the present invention, the electrodes are formed of a material whose main component is a ceramic material.
The electrode and the ceramic heating element are attached by a bonding method using, for example, diffusion bonding, brazing, hot pressing, or other well-known chemical reactions.

[0016] Therefore, since the coefficient of thermal expansion of the ceramic heating element and the electrode are close, even when the ceramic heating element is repeatedly heated and cooled, the solid bonded state of the connection portion of the electrode is maintained. become. In particular, if the coefficient of thermal expansion of the ceramic material forming the electrode is equal to or higher than the coefficient of thermal expansion of the ceramic heating element, the temperature of the heating element during use is higher than that of the electrode. Its durability will be further improved.

[0017]

[Embodiments] A ceramic heater and a method for manufacturing the same, which are embodiments of the present invention, will be described below. Figure 1 shows the overall configuration of the ceramic heater of the first embodiment, and Figures 2 and 3
indicates the configuration of each part.

As shown in FIG. 1, the ceramic heater 1 of this embodiment includes a ceramic heating element 4 in which a W wire 3 is embedded in the ceramic body 2, and a ceramic heating element 4 on both sides of the rear end side of the ceramic heating element 4. It is composed of a pair of bonded ceramic electrodes 7 and 8.

As shown in FIG. 2, the ceramic body 2 is a columnar member measuring 10 mm in length, 50 mm in width, and 5 mm in height, and is mainly composed of Si3N4 and has heat resistance and insulation properties. . Further, the W wire 3 is a substantially U-shaped heating resistor that generates heat when a current is passed through it, and one end portion 3a thereof is bent upward as shown in FIG. The other end 3b is bent downward in the same figure and is exposed to the lower surface 2b of the ceramic body 2.
exposed to.

Furthermore, the pair of ceramic electrodes 7, 8
As shown in Figures 1 and 3, the length is 10 mm and the width is 20 mm.
, is a plate-shaped member with a height of 2 mm, and is mainly composed of TiN and Si3N4. The ceramic electrodes 7 and 8 are joined to face each other so as to sandwich the rear end side of the ceramic heating element 4.
, 8 are electrically connected to the ends 3a, 3b of the W wire 3 at the inner surfaces thereof. In addition, ceramic electrodes 7 and 8
A connecting hole 10 with a diameter of 3 mm for attaching a lead wire is provided near the end of the connector.

Next, a method of manufacturing the ceramic heater 1 having the above structure will be explained based on the exploded perspective view of FIG. ■First, as the material of the main body 2 of the ceramic heating element 4, Si3N490% by weight, the balance Al2O3, Y2
Using powders of O3, place W in the center of the mixture of powders.
Wire 3 was embedded and mold pressing was performed.

[0022] After that, the pressed molded product was applied with a pressure of 2
The ceramic heating element 4 was manufactured by heating with a high frequency hot press device at 1720° C. for 30 minutes under 00 kg/m 2 . ■Next, the ends 3a, 3 of the W wire 3
The electrode extraction portion (b) was ground using a diamond grinder.

[0023] On the other hand, as materials for the ceramic electrodes 7 and 8, for example, Si powder and TiN powder were mixed in predetermined amounts as shown in Table 2 below, and the mixture was molded using a mold press. (2) Thereafter, the pressed molded product was heated at 1700° C. for 3 hours in a nitrogen gas atmosphere to form ceramic electrodes 7 and 8.

■A commercially available brazing material is placed between the ceramic heating element 4 and the ceramic electrodes 7 and 8.
Ceramic heater 1 was obtained by heating at 850° C. in vacuum with g/Cu/Ti foils 12 and 13 interposed, and joining ceramic heating element 4 and ceramic electrodes 7 and 8 by brazing. .

Next, Experimental Examples 1 and 2 conducted to confirm the effects of this embodiment will be explained in detail. (Experimental Example 1) In this experiment, the materials shown in Table 2 below were used as ceramic electrode materials, and five ceramic heater samples were manufactured using the manufacturing method described above. Then, the bonding status of the ceramic electrodes in each sample,
The thermal expansion coefficient and electrical resistance at 30 to 800°C were investigated. The results are also shown in Table 2 below, of which No.
Samples Nos. 1 to 4 are of this example, and Nos. 5 and 6 are samples of comparative examples.

[0026]

[Table 2]

As a result of this experiment, no abnormality was observed in the bonding state in samples No. 1 to No. 4 of the example, but no abnormality was observed in the bonding state of the sample No. 5 of the comparative example, and in the sample No. 6. In 4 out of 5 ceramic heating element elements, cracks occurred. Furthermore, as is clear from Table 2 above, samples Nos. 1 to 4 of Examples have a small coefficient of thermal expansion, and a coefficient of thermal expansion of a ceramic heating element (Si3N4: 2.8).
×10-6[1/℃], SiC:4.5×10-6[1
/°C]), and the electrical resistance was not so large, which was suitable. On the other hand, samples Nos. 5 and 6 of the comparative example are made of metal, and therefore have a small electrical resistance but a very large coefficient of thermal expansion, making them unsuitable as electrodes to be bonded to a ceramic heating element.

(Experimental Example 2) Furthermore, among the samples used in Experimental Example 1, a heating/cooling cycle test was conducted using a sample with a good bonding state (or with no deterioration). This heating/cooling cycle test consists of -40°C cooling and 350°C cooling.
C. heating and heating cycles were repeated alternately, and this cycle was repeated 200 times for each sample.

As a result, although some oxidation was observed in the brazing materials of samples Nos. 1 to 4 of Examples, no abnormality was observed in conductivity. On the other hand, in samples Nos. 5 and 6 of the comparative example, the electrode and the ceramic heating element were separated, and an abnormality in conduction was observed. As described above, the ceramic heater 1 of the present embodiment is remarkable in that even if heating and cooling cycles are repeated frequently, abnormality does not easily occur in the bonding between the electrode and the ceramic heating element, and it is extremely durable. be effective.

Next, a second embodiment of the ceramic heater and its manufacturing method will be explained based on FIG. 5. As shown in FIG. 5, the ceramic heater 20 of this embodiment is
The method of joining the ceramic electrodes 22, 23 and the ceramic heating element 25 is significantly different from the ceramic heater 1 of the first embodiment.

That is, in this embodiment, between the pair of ceramic electrodes 22, 23 and the ceramic heating element 25, Ti foils 26, 27 with a thickness of 5 μm and Ti foils 27 with a thickness of 10 μm are placed from the ceramic heating element 25 side. Cu foil 28, 29,
Ni plates 30, 31 with a thickness of 0.2 mm, Ti plates with a thickness of 5 μm
Foils 32 and 33 are interposed. The laminated state of each of these members is then heated in a vacuum at 1200°C for 30 minutes to bond the ceramic electrodes 22, 23 and the ceramic heating element 25, and then subjected to a diffusion treatment at 1000°C. A ceramic heater 20 was obtained.

Next, Experimental Examples 3 and 4 conducted to confirm the effects of the second embodiment will be explained. (Experimental Example 3) In this experimental example, the materials in Table 2 above were used,
Five ceramic heater samples were each manufactured using the method of the second example. Then, the bonded state was observed in the same manner as in Experimental Example 1 above. As a result, no abnormality was observed in all of the samples Nos. 1 to 3, which are examples, which were bonded. Also No.4
Regarding the sample, only one out of five samples had a crack in the ceramic heating element. On the other hand, in samples Nos. 5 and 6 of the comparative example, cracks occurred in all ceramic heating element elements.

(Experimental Example 4) Among the samples used in Experimental Example 3 above, samples Nos. 1 to 4 of Examples were used to conduct a heating/cooling cycle test. In this heating/cooling cycle test, stainless steel nuts and bolts are connected to ceramic electrodes, and AC 100V is applied. At the same time, the AC current value and air flow rate are adjusted to
The temperature was varied up to ℃. Then, this heating and cooling cycle is
000 cycles were performed.

As a result, no abnormality was observed in the conductivity of the five samples No. 2 and No. 3, and there was no discoloration of the electrodes. In addition, in samples Nos. 1 and 4, the electrode surface layer was oxidized, but there was no abnormality in conduction. Note that the degree of oxidation was lower in No. 1. In this way, the ceramic heater 20 of this embodiment can be used even if the temperature change in the heating/cooling cycle is large and the number of cycles is large.
It has the remarkable effect that abnormalities are unlikely to occur in the bonding between the ceramic heating element 25 and the ceramic heating element 25, and the durability is extremely excellent.

Next, a ceramic heater according to a third embodiment and a method for manufacturing the same will be explained based on FIG. 6. As shown in FIG. 6, the ceramic heater 40 of this embodiment is
Unlike the type in which a metal wire generates heat as in the first and second embodiments, this embodiment includes a ceramic heating element 41 made of SiC in which the ceramic itself generates heat.

That is, in this embodiment, as a heating element, a ceramic heating element 41 made of SiC is used, which has a width of 3 mm at the center, a thickness of 3 mm, a length of 40 mm, and a width of 15 mm at both ends. ing. Ceramic electrodes 42 made of the same material as those in Embodiments 1 and 2 are provided on the upper and lower surfaces of both ends of the ceramic heating element 41.
are joined.

The ceramic electrode 42 is joined by brazing using a paste containing 95% by weight of Ag and 5% by weight of Ti and heated to 1000° C. in a vacuum. is manufactured. Next, Experimental Example 5, which was conducted to confirm the effects of this third embodiment, will be explained.

(Experimental Example 5) In this experimental example, N in Table 2 above
Five ceramic heater samples were each manufactured using the materials No. 4 and No. 5 by the method of the third example. Then, in the same manner as in Experimental Example 1 above, the bonding status and conduction status were observed.

As a result, sample No. 4, which is an example, had the following properties:
No abnormality was observed in all the connections, and there was no abnormality in conduction. On the other hand, in the comparative sample No. 5, the ceramic heating element was broken during brazing. Like this,
The ceramic heater 40 of this embodiment is of a type in which the ceramic itself generates heat, but its bondability is high, similar to a type of heater in which a metal wire generates heat, and it is fully usable for practical use.

[0040]

As described above, the ceramic heater of the present invention is characterized in that the electrodes are formed of a material whose main component is a ceramic material, so that the bonding between the ceramic heating element and the electrodes is high. Further, since the electrode mounting portion does not deteriorate even when exposed to high temperatures, it is possible to raise the temperature of the heater, such as by increasing the heating temperature or operating temperature of the heater. Furthermore, it has the effect of extremely high durability against repeated heating and cooling. Furthermore, there are fewer restrictions on the members and shapes used for the heater, unlike in the past, so there is an advantage that the heater can be designed more freely.

Particularly, when the thermal expansion coefficient of the electrode is equal to or higher than that of the ceramic heating element, the bondability and durability are further improved.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a ceramic heater according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a plane and a front view of the ceramic heating element element of the first embodiment.

FIG. 3 is an explanatory view showing a plane and a front view of the ceramic electrode of the first example.

FIG. 4 is an exploded perspective view of the ceramic heater of the first embodiment.

FIG. 5 is an exploded front view of the ceramic heater of the second embodiment.

FIG. 6 is an explanatory diagram showing a ceramic heating element and a ceramic heater of a third embodiment.

FIG. 7 is an explanatory diagram showing a conventional ceramic heater with a portion cut away.

[Explanation of symbols]

1, 20, 40...ceramic heater 3...W line

Claims (2)

[Claims] 1. A heating element comprising a ceramic heating element and an electrode attached to the heating element, wherein the electrode is formed of a material whose main component is a ceramic material. . 2. The ceramic heating element according to claim 1, wherein the thermal expansion coefficient of the ceramic material forming the electrode is equal to or greater than the thermal expansion coefficient of the ceramic heating element element.