JPH10335050A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict the ceramic migration so as to prevent the generation of micro lack, and provide a ceramic heater, which has a long lifetime and which can be used at a high temperature, by interposing an electric force line shutting-off body, which is formed of a conductive material, in a block, in which the maximum electric potential difference of a heating resistor embedded in the ceramic body is generated. SOLUTION: A heating resistor 14 made of W and Mo-Mn is embedded in a ceramic body of SiN or the like, which is formed into a desirable shape such as a plate or a cylindrical shape, and an electric force line shutting-off body 15, which is formed of a conductive member, is interposed in a block, in which the maximum electric potential difference of the heating resistor 14 is generated, namely between a maximum electric potential part 18 and a minimum electric potential part 19. As the electric force line shutting-off body 15, a material, which is mainly composed of a high melting point metal such as W, Mo, Re, Ti and various compound thereof, is desirable, and thickness thereof is set at 0.2-0.6 mm, and it is desirably provided inside the heating resistor 14 with a distance at 0.2-0.3 mm and it is concentrically provided at a width at five times or more of a width 20 of the heating resistor 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic heater, and more particularly to a ceramic heater provided with a DC power supply.

[0002]

2. Description of the Related Art Conventionally, as a device using a ceramic heater which is used at a high temperature using a DC power supply,
Heaters for heating oxygen sensors used in exhaust gas detection system parts of automobiles, ceramic glow plugs used for ignition in diesel engines, and the like are known as typical examples.

[0003] Among them, the heater for the oxygen sensor is formed by screen-printing a heating resistor mainly composed of a high-melting-point metal on a ceramic green sheet and then molding the same, and then forming a conductive lead having a smaller resistance value than the heating resistor. The parts are also overlapped by printing. A green sheet with a heater manufactured in such a manner is formed into a round bar by winding it around a ceramic rod, and a sheet obtained by laminating sheets in a plate shape is integrally sintered. (JP-A-62-2130)
No. 84, JP-A-8-148260) Also, as a glow plug for ignition of a diesel engine, a powder ceramic such as silicon nitride is formed by a press molding method, and a high melting point metal is formed on the molded body by screen printing. Or a high melting point metal wire into a coil shape, and sinter the ceramic substrate obtained by such a method as embedding in powder at the time of press molding by hot pressing etc., and subject it to HIP treatment if necessary What you can get was known. (Japanese Unexamined Patent Publication No. 62-59858, Tokuheikai 4
(See -4717)

[0004]

When silicon nitride or the like is used for the ceramic heater as described above, for example,
When used for a long time in a high temperature state exceeding 700 ° C,
Micro cracks occur from the part where the bonding strength is relatively weak compared to other parts such as the laminated interface in ceramic porcelain,
The microcracks may grow until they reach the porcelain surface. As a result, oxygen passes through the cracks into the heating resistor portion and enters the inside, and the heating resistor is oxidized. The oxidized heating resistor becomes unstable, causing a local resistance change due to thermal expansion due to heat generation and a change in the contact state when the matrix component moves, and the resistance of the oxidized portion is locally caused by repeated use at high temperatures. There is a problem in that the wire is broken due to an increase in the number of the heating resistors and the heating resistor itself becomes brittle.

In examining the problem of such a conventional ceramic heater, it has been found that a phenomenon called so-called ceramic migration at a high temperature as described above is involved in the above problem.

[0006] The ceramic migration means that the matrix component is ionized and moved from the heating resistor and the peripheral porcelain portion. As the ceramic migration progresses, the matrix component of the portion of the heating resistor which has the highest potential when energized is energized. Moved to a porous state. When the heater is used at a high temperature for a long time, microcracks are generated in the vicinity of the highest potential portion from a portion where the bonding strength is relatively weak as compared with other portions such as a lamination interface, as described above. The tip will travel down the porous site and travel to the surface.

When porous alumina is used for a ceramic heater, cracks do not occur due to the porous nature of the ceramic heater. However, the movement of the matrix around the resistance of the heating element destabilizes this portion, and the heating resistor is disconnected. There was something to do.

As described above, it has been found that the heating resistor is disconnected due to ceramic migration. However, the present inventor has further studied and found that ceramic migration in the ceramic heater is caused by electric lines of force generated when electric current is applied. It came to the knowledge that it occurred along.

FIG. 6 shows an example of a ceramic heater in which a heating element is screen-printed on a ceramic green sheet as described above, and then a green sheet with a heater is wound around a ceramic rod to form a round bar. The results of the model analysis are shown schematically, as shown in the figure, between the sites where the potential difference is largest in the heating resistor,
That is, the lines of electric force indicated by arrows are directed from the entrance portion 30 '(anode side) of the heating resistor, which has the highest potential when energized, to the exit portion 31' (cathode side) of the heating resistor, which has the lowest potential. ing. Note that the direction of the arrow is the direction of the line of electric force, and the length thereof indicates its strength.

Accordingly, an object of the present invention is to suppress the flow of lines of electric force when power is supplied to a ceramic heater in order to solve the above problems.

[0011]

In order to solve such a problem, the present invention provides an electric field line breaker made of a conductive material between a highest potential portion and a lowest potential portion of the heating resistor. It is intended to provide an interposed ceramic heater.

[0012]

As described above, in the ceramic heater of the present invention, the electric line of force interrupter made of the conductive material has no charge even when energized, so that it functions as a neutral medium and absorbs electric lines of electric force. ,Cut off. Accordingly, the movement of the ionized matrix component is prevented, so that the disconnection of the heating resistor can be prevented.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a ceramic heater 10 according to the present embodiment.
The ceramic heater 10 has a round rod-shaped ceramic body 12 and is electrically connected to an external DC power supply 13.

The ceramic heater 10 can set a resistance value to a required calorific value on a ceramic green sheet made of a powder of alumina, beryllia or the like having excellent electrical insulation and thermal conductivity even at a high temperature. A resistor that becomes a heating resistor by a thick film method such as screen printing using a paste such as tungsten, molybdenum-manganese, etc. in a predetermined width, thickness, and length in an arbitrary shape such as a comb-like or spiral shape. The pattern is printed, and further, the raw sheet is superimposed on the ceramic raw sheet, and the paste of the conductive material is printed on the ceramic raw sheet by a thick film method such as screen printing, so that an electric wire interrupter to be described later is formed. After formation, these printed raw sheets are wound around a ceramic rod to form a round bar, which is sintered and integrated in a firing atmosphere. Is Kkuhita.

FIG. 2 is a sectional view taken along line XX of FIG.
A cross-sectional view of the rear end portion of the area A where the heating resistor 14 of the ceramic heater 10 is provided. As shown in the drawing, the ceramic heater 10 is formed of a conductive material inside the heating resistor 14 and is concentric. The electric field line breaker 15 formed in the shape of an arc is provided. In addition, the installation position of the electric flux line interrupter 15 is determined between the portions of the heating resistor 14 where the potential difference is the largest, that is, the portion 18 having the highest potential on the anode side entrance and the potential on the cathode side exit of the heating resistor 14. A portion that shields between the lowest portion 19 is used.

The electric field line breaker 15 is made of a conductive material and is electrically neutral because it is isolated from an external power supply, and a voltage is applied to the heating resistor 14 from the DC power supply 13 (see FIG. 1). Since the electric flux line interrupter 15 has no electric charge, it acts as a neutral medium and absorbs and blocks the electric flux lines. Accordingly, the movement of the ionized matrix component is suppressed, so that microcracks are less likely to occur, and therefore, a situation in which the heating resistor is disconnected can be prevented.

It is desirable that the electric line of force interrupter 15 be installed circumferentially (or cylindrically) without any break inside the heating resistor, but in the manufacturing process of the ceramic heater 10, the ceramic rod and the green sheet are used. For example, if the distance between the heating resistor 14 and the electric field line breaker 15 is set to 0.2 to 0.3 mm, at least the width 20 of the heating resistor 14 may be impaired. If it is installed at five times the width, it is possible to obtain an effect similar to the effect of suppressing the movement of the matrix component in the case where the installation is performed in a circumferentially continuous manner. The conductive material constituting the electric flux line interrupter 15 is W · M which can be integrally sintered by firing.
It is desirable to use as a main component at least one of a high melting point metal such as o, Re, and Ti or various compounds of the metal.

FIG. 3 shows an oxygen sensor as an example of the use of the ceramic heater 10. As shown in FIG. 3, the oxygen sensor 1 is fixed to the exhaust pipe 2 of the vehicle.
And a sensor unit 4 indicated by the fixing unit 3
It is mainly composed of The sensor unit 4 includes the zirconia oxygen sensor 9 and the ceramic heater 10 arranged so that the zirconia element in the sensor is heated when the engine is started so that the sensor 9 can detect the sensor satisfactorily. One end of a lead wire 11 for taking out the electromotive force generated in the above is connected, and DC power supply to the ceramic heater 10 is performed by the anode 6 wired from the rear of the sensor cover 7,
It is provided by a cathode 5 connected from the engine body.

Next, FIGS. 4 and 5 show another embodiment of the present invention in which a powder ceramic such as silicon nitride is formed by press molding to finally obtain a ceramic heater.

Ceramic molded body 2 obtained by press molding
As shown in FIG. 4A, the heating resistor 22 is formed in a U-shape as shown in FIG. 4A, and one end of the refractory metal wire 23 is overlapped with the end of the heating resistor 22 as a lead extraction portion, and the other end is formed. (B) as shown in FIG. 3 (b), which is screen-printed with a material containing a high melting point metal compound as a main component so as to overlap the electrode take-out portion 24. Combine. That is, between the heating resistors 22 of the screen-printed ceramic molded body 21, there is a groove 26 for mounting the electric flux barrier 25, so that the groove 26 protrudes from the other ceramic molded body 27. The buried electric field line breaker 25 is fitted in the groove 26.

In this way, the combined and integrally sintered body is obtained as the ceramic heater base 28 shown in FIG. The ceramic heater substrate 28 is subjected to outer diameter cutting with a cutting tool to finally obtain a round bar-shaped ceramic heater.

This ceramic heater can also be incorporated in the oxygen sensor 1 shown in FIG.

Further, the heating resistor 22 and the electric force line breaker 2
It is desirable that the insulation distance of No. 5 is at least 0.2 mm or more. This is because, in the case of a material such as silicon nitride, a conductive metal substance such as Mo3Si4 is contained as a component in the composition, and this lowers the insulation resistance at a high temperature.

The electric field line breaker 25 is preferably made of a high melting point metal such as W, Mo, Re, Ti, or at least one of various compounds of the above metals. Is preferably a tablet obtained by pressing a metal powder or a general metal plate obtained by rolling or the like. The tablet thickness or plate thickness at this time is 0. .
When it is set to about 0.6 mm, there is little problem in production. If the plate thickness is 0.2 mm or less, deformation tends to occur due to the pressure during press molding. If the plate thickness is 0.6 mm or more, the distance to the outer surface can be set as small as 0.5 mm, and cracks will occur. Because it is easy.

In the above embodiment, the round bar-shaped ceramic heater has been described. However, the heater may be a flat plate without cutting the outer diameter. In addition, in order to adjust the resistance value, a plurality of ceramic molded bodies equipped with a heater function are laminated,
The electrodes may be connected in parallel by a metalizing method or the like at the exposed surface of the electrode take-out section 24 or the like.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A ceramic heater 1 shown in FIGS.
0 was manufactured, and the change in the resistance value of the heating resistor 14 and the disconnection rate were examined. The specifications and test conditions are as follows.

Total length: 50 mm Diameter: 3.5 mm Heating resistor length: 12 mm Heating resistor width: 0.25 mm Electric flux blocking line width: 1.5 mm Material of heating resistor, electrical flux blocking material: Tungsten ceramic Material: Alumina Temperature coefficient of resistance (20 ° C to 800 ° C): 3000 PPM /
C. Power consumption (at 12 V): 10 W Further, as a comparative example, a ceramic heater identical to the above ceramic heater was produced except that the electric flux line breaker 25 was not formed.

Ten ceramic heaters were prepared and heated to 1200 ° C. for acceleration evaluation.
The applied voltage at this time was 24 to 25V. The resistance was measured after leaving it in a room maintained at 23 ° C. ± 1 ° C. for 30 minutes or more to stabilize the resistance. Table 1 shows the results (Example A / Comparative Example B).

[0029]

[Table 1]

The disconnection rate in the table is the percentage of the number of the heating element patterns having no resistance value when measuring the resistance value.

As is clear from Table 1, the ceramic heater 10 of this embodiment has a much smaller change in resistance than the comparative example, and is less likely to break.

Further, model analysis was performed on these ceramic heaters by the finite element method, and a schematic diagram of the form of the lines of electric force was prepared.

This uses an analysis program by a computer to prepare a cross-sectional model of a heating resistor portion of a ceramic heater and add a predetermined mesh to the cross-sectional model. The analysis conditions for each mesh are given, and the stress and the electric field are analyzed. As the analysis conditions, application conditions such as voltage and current and physical property conditions of the ceramic, for example, specific transmittance, specific gravity, heat transfer coefficient and the like were applied.

FIGS. 5 and 6 schematically show the results of model analysis of each of the above ceramic heaters by the finite element method. FIG. 5 shows the ceramic heater of this embodiment.
FIG. 6 shows a ceramic heater of a comparative example. The lines of electric force indicated by the arrows are directed between the portions of the heat generating resistor having the largest potential difference, that is, from the portions 30 and 30 'having the highest potential when energized to the portion 31' having the lowest potential. Note that the direction of the arrow is the direction of the line of electric force, and the length thereof indicates its strength.

As is clear from the comparison of these figures, in the ceramic heater of the embodiment, the electric flux line breaker 31 absorbs and cuts off the electric flux lines generated from the highest potential portion 30 when the DC power is applied. While the number of lines of electric force reaching the potential portion 32 is extremely small, the number of lines of electric force is significantly increased in the comparative example. As described above, since the ionized matrix component moves along the lines of electric force, it is understood that the ionized matrix component is less likely to move due to the electric line of force interrupter 31.

[0036]

As described above, according to the ceramic heater of the present invention, the electric line breaker made of a conductive material has no electric charge even when energized, so that it functions as a neutral medium. Absorbs and blocks lines. Along with this, the movement of the ionized matrix component is suppressed, so that the situation of disconnection of the heating resistor can be prevented, so that even if a DC power is applied, long-term reliability is improved and the life is extended. The practical effect is remarkable, as it can withstand use at a higher temperature than before.

[Brief description of the drawings]

FIG. 1 is a plan view showing the appearance of a ceramic heater according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line XX of the ceramic heater of FIG.

FIG. 3 is a vertical sectional view showing an oxygen sensor as an example of an apparatus using the ceramic heater.

FIG. 4 is a perspective explanatory view showing a state in the course of manufacturing a ceramic heater of another embodiment.

FIG. 5 is a model diagram showing the results of a model analysis of electric lines of force by the finite element method for the ceramic heater according to the embodiment of the present invention in a vertical cross section.

FIG. 6 is a model diagram showing the results of a model analysis of electric lines of force by a finite element method for a conventional ceramic heater (comparative example) in a vertical section.

[Explanation of symbols]

 Reference Signs List 10, 29 Ceramic heater 12 Ceramic body 13 DC power supply 14, 22, Heating resistor 15, 25 Electric field line breaker 18 Highest potential part 19 Lowest potential part 20 Width 1 Oxygen sensor 2 Exhaust pipe 3 Fixed part 4 Sensor part 5 Cathode 6 Anode 7 Sensor cover 9 (zirconia oxygen sensor) 21, 27 Ceramic molded body 23 High melting point metal wire 24 Electrode extraction part 28 Ceramic heater base

Claims (2)

[Claims] 1. A heating resistor is buried in a ceramic body having a desired shape such as a plate or a cylinder, and an electric line breaker made of a conductive material is interposed between portions of the heating resistor having a largest potential difference. Ceramic heater made. 2. The electric field line breaker is W.Mo.Re.T.
2. The ceramic heater according to claim 1, wherein the ceramic heater is made of a material having at least one selected from the group consisting of a high melting point metal such as i and various compounds of the high melting point metal.