JPH04329290A - Ceramic heater and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a ceramic heater which has a long life even under high temperature circumstances without the need for another means such as a detecting means and its manufacture. CONSTITUTION:A ceramics heater 1 consists of the first ceramic layer 3 which is formed on the surface of a ceramic base material 2, the second ceramic layer 4 which is laminated on the surface of the first ceramic layer 3 and a heating pattern 7 which has a heating section 8, an anode terminal 9a and a cathode terminal 9b arranged on a boundary 5 between the first and second ceramic layer 3, 4. An anode deterioration preventive pattern 11a which holds terminal voltage is connected to the anode terminal 9a and a cathode deterioration preventive pattern 11b which holds terminal voltage is connected to the cathode terminal 9b, with both deterioration preventive patterns 11 arranged adjacent to the outside of the heating section 8.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a ceramic heater attached to a sensor, etc., and a method for manufacturing the same, and more specifically, for example, a ceramic heater for heating an oxygen sensor that detects the oxygen concentration in exhaust gas of an internal combustion engine, and a method for manufacturing the same. Regarding.

0002

[Prior Art] Conventionally, oxygen sensors, for example, have been installed in the exhaust pipe of internal combustion engines and used to detect the oxygen concentration in exhaust gas. A ceramic heater is used to heat the element part of the device.

[0003] As the ceramic heater, for example, a plate-shaped or cylindrical heater is used depending on the shape of the sensor. Among these, cylindrical ceramic heaters are
For example, it is formed by laminating a green sheet on which a heat generating pattern is formed on the surface of a cylindrical ceramic base material made of alumina (Al2O3) and firing the same.

0004

However, when such a ceramic heater as described above is used to heat an oxygen sensor that is exposed to high temperatures for a long period of time, the following problems may occur.

[0005] In other words, if an oxygen sensor is exposed to high temperatures for a long period of time, the heating pattern may deteriorate and its resistance may increase during use, which may cause the heating pattern to break or the protection to be Cracks could occur in the layer. Furthermore, in the worst case, the protective layer may collapse, resulting in a shortened heater life. In this case, the area around the heating pattern near the cathode appears to be darkened, resulting in a so-called blackening phenomenon.

[0006] For this reason, the durable life of the heater is maintained by detecting the operating conditions of the heater and energizing it only when necessary. There is the problem that a separate device is required, which complicates the device.Furthermore, failure of the detection means, etc. may cause a new cause of reduced lifespan, so this problem cannot be a fundamental solution. there were.

The present invention has been made to solve the above-mentioned problems, and provides a ceramic heater that does not require additional means such as a detection means and has a long heater life even in a high-temperature environment, and a method for manufacturing the same. With the goal.

[0008]

[Means for Solving the Problems] The invention of claim 1 to achieve this object includes: a first ceramic layer; a second ceramic layer laminated on the surface of the first ceramic layer; A ceramic heater comprising: a heat generating part disposed on a boundary surface of a second ceramic layer; a heat generating pattern having an anode side terminal and a cathode side terminal; an anode side connected to the anode side terminal and holding a terminal voltage; The present invention provides a ceramic heater characterized in that a deterioration prevention pattern and a cathode deterioration prevention pattern connected to the cathode terminal and holding a terminal voltage are arranged adjacent to each other outside the heat generating part.

[0009] Furthermore, the invention according to claim 2 is preferable, when forming a heating element pattern having a heating part on the surface of a green sheet, a terminal voltage is connected to an anode side terminal on the outside of the anode side pattern of the heating part. At the same time, a cathode side deterioration prevention pattern is formed on the outside of the cathode side pattern of the heat generating part to hold the terminal voltage by being connected to the cathode side terminal, and then a surface of the heat generating pattern is formed. The gist of the present invention is a method for manufacturing a ceramic heater, which is characterized in that a laminate is formed with a heating pattern sandwiched therein by covering the green sheet with another green sheet, and the laminate is laminated on a ceramic base material and integrally fired.

[0010] The ceramic heater of the present invention may be provided with a sensor element, an insulating layer, etc. as a structure other than the above. Al2O3 is suitable as the material for forming the first and second ceramic layers, but in order to make it a high-temperature strength material with particularly excellent thermal conductivity,
2O3 has an average grain size of 10 μm or less and a relative theoretical density of 94
% or more.

[0011] Furthermore, as the first ceramic layer,
Ceramic base materials formed into various shapes such as cylindrical, rod-like, plate-like, etc. depending on the shape of the sensor to be heated, or those formed by firing a green sheet to cover the surface of the ceramic base material. Can be adopted. Moreover, as the second ceramic layer, one formed by firing a green sheet can be employed.

[0012] In addition to Al2O3, the ceramic base material may be a high-temperature, high-strength ceramic such as an alumina-like ceramic such as mullite or spinel. In addition, the ceramic layer formed from the green sheet protects the heating pattern in a high-temperature environment and improves the bonding property between the ceramic base material and the heating pattern. good.

[0013] As the material for the heating pattern, tungsten (W) and molybdenum (Mo) are mainly used, and high melting point metal components such as platinum (Pt) and rhodium (Rh) are mixed with these components. Good. Furthermore, Pt or Rh may be used alone in order to improve resistance characteristics. Incidentally, a small amount of oxide or the like made of the same material as the ceramic layer may be present as long as it does not have an adverse effect.

[0014] The heat generating pattern includes a heat generating part having high resistance, an anode side terminal and a cathode side terminal to which a voltage from a power supply is applied, and further includes a heat generating part with the anode side terminal, the cathode side terminal and the heat generating part. A lead portion is formed to connect the two.

[0015] The anode side and cathode side deterioration prevention patterns placed outside this heat generating part have a low wire resistance value (for example, 0.01 Ω/m at 20°C) in order to maintain the terminal voltage.
m), and therefore, for example, the width is about twice as wide as that of the heat generating part.

The outline of the method for manufacturing the ceramic heater is as follows. As a raw material, for example, the main component Al2
A powder made of O3 is prepared by wet mixing. In order to obtain dense high-temperature and high-strength properties, it is preferable that the raw material powder used be a high-purity powder with a purity of 90% or more, and its particle size should be 2 μm or less.

[0017] However, SiO2 and Mg, which are calcination accelerating components,
O, CaO, and B2O3 may be blended in the form of oxides, which can form a predetermined network structure during the firing process, such as hydroxides and salts (eg, carbonates).

[0018] The blended powder can be molded by various methods such as pressure molding (eg, isostatic pressing or doctor blade molding) or extrusion molding. Incidentally, during this molding, it is of course necessary to appropriately mix a prescribed solvent, binder, etc.

The heating pattern can be formed by various methods such as plating and vapor deposition (eg, sputtering, vapor deposition, etc.). In particular, when forming a heat generating pattern using a metal paste, a predetermined pattern is formed on a molded green sheet by, for example, screen printing, the pattern printed side is covered with a green sheet, and a predetermined pattern is formed on it. After that, it may be further covered with a green sheet and used for bonding with the ceramic base material. This is because if the metal pattern is directly bonded to the base material, the mutual adhesion will be insufficient, and there is a risk that oxidation of the heat-generating pattern components (cause of disconnection) due to the generation of pores may occur.

[0020] In order to improve the mutual adhesion between the ceramic base material and each ceramic layer, it is preferable to perform simultaneous firing. The firing method is mold pressurization (HP, HI
P) Various methods such as sintering, atmosphere pressure sintering, and reaction sintering can be employed, and the sintering temperature is preferably selected from the range of 1450 to 1600°C. The atmosphere is an inert gas (e.g. Ar
, N2), an oxidizing atmosphere (for example, in the atmosphere), or a reducing atmosphere (for example, H2 gas).

[0021] The ceramic heater thus obtained is
The terminals of the heating pattern are metallized, and the leads from the power source are connected by brazing. The ceramic heater of the present invention is particularly suitable as a heater for heating an oxygen sensor for air-fuel ratio control of an internal combustion engine that is used for a long time at high temperatures. In this case, the ceramic heater is
It may be inserted into the test tube type solid electrolyte oxygen sensor element, or may be attached to the oxygen sensor element.

[0022]

[Operation] The present inventors have analyzed the factors that cause sensor deterioration when used under high temperatures, and have completed the present invention based on this analysis. The analysis and consideration will be explained in detail below.

The mechanism of the heater disconnection phenomenon, as already disclosed in Japanese Patent Application No. 63-48721, is as follows. Figure 5 (
A) and its BB cross-sectional view is shown in FIG. 5(B). The results revealed the following facts (a) and (b). (b) Heat generating part P on the cathode side of the heat generating pattern P1
The area around No. 2 has locally changed from white (the normal color of Al2O3) to black. (b) Of the heating pattern P1, the heating part P on the anode side
Local cracks have occurred around No. 2.

[0024] Furthermore, the heater was placed in an air atmosphere at 1000°C and energized by continuous application of 17 V DC, and the change in resistance value of the heat generating part P2 was investigated. From the results, the following fact (
c) was found. (c) As shown in FIG. 6, the resistance of the first pattern portion P3 (FIG. 5(A)), which is the heat generating portion P2 closest to the anode side, is significantly increased compared to other pattern portions, etc. To be there. Note that FIG. 6 shows changes over time in the total resistance of the heat generating pattern P1, the resistance of the first pattern portion P3, and the resistance of other pattern portions.

Theoretical considerations made to elucidate the above facts are as follows. Consideration of (a) Since the alumina base material constituting the alumina heater is sintered with Al2O3 as the main component and various metal oxides as sintering accelerator components, the sintered body contains A
These metal oxides exist as a glass phase at the l2O3 grain boundaries.

When such an alumina heater is subjected to direct current at high temperature, magnesium (Mg
) and calcium (Ca) atoms become cations and move toward the cathode. On the other hand, oxygen (O) present near the component
In order to maintain electrical neutrality, the atoms become oxygen ions and move toward the anode. Therefore, Mg and Ca components are deposited in the vicinity of the cathode terminal as a single substance or as an oxide, resulting in blackening of the area. That is, by applying a direct current, Al
The flux component in the glass phase at the 2O3 grain boundary undergoes electrolysis.

Consideration of (b) Furthermore, the material of the heating pattern P1, such as tungsten (W), is oxidized by the oxygen ions that have moved to the anode side.
Increases the resistance value of that area.

Consideration of (c) Due to the oxidation reaction described in (b) above, the heating pattern P1 expands in volume, causing disconnection in the heating pattern P1, and stress is applied to the protective layer P4, causing cracks. Note that a part of the oxidized heat generating pattern P1 material moves to the protective layer P4 and further to the outside world due to diffusion, and in this sense also increases the resistance value.

Therefore, if such an alumina heater continues to be exposed to high temperatures, the material of the heating pattern P1 will be explosively oxidized by the outside air oxygen that has entered through the cracks in the protective layer P4, causing further volume expansion, and the protective layer P4 will Peeling of
considered to lead to collapse.

That is, the root cause of the disconnection mechanism of the heating pattern P1 is thought to be migration of Mg2+ and Ca2+ to the lower potential side and migration of O2- to the higher potential side.

Therefore, in order to prevent the heater from being disconnected due to the above mechanism, the present inventors formed an anode side deterioration prevention pattern that is connected to the anode side terminal and maintains the terminal voltage on the outside of the heat generating part of the heat generating pattern. At the same time, a cathode-side deterioration prevention pattern that is connected to the cathode-side terminal and holds the terminal voltage was formed, and both deterioration prevention patterns were arranged adjacent to each other.

For example, an anode side deterioration prevention pattern formed along and outside the anode side pattern of the heat generating section and a cathode side deterioration prevention pattern formed along the outside of the cathode side pattern of the heat generating section are as follows. By winding the laminate sandwiching the heat generating pattern around the ceramic base material, the anode side pattern and the cathode side pattern of the heat generating section are arranged close to each other.

As a result, in the conventional heater, the above-mentioned deterioration that had progressed in the anode side and cathode side patterns (first pattern portion), ie, the migration of Mg2+ and Ca2+ to the lower potential side and the increase in O2- In the product of the present invention, deterioration due to the movement toward the potential side progresses on the deterioration prevention pattern, so no deterioration occurs on the heat generating pattern.

Furthermore, since the deterioration prevention pattern is a non-heat generating pattern that holds the terminal voltage but does not allow current to flow, and its temperature is low, the aforementioned deterioration progresses on the deterioration prevention pattern as a result. It ends up being minor. Further, even if the deterioration prevention pattern were to be disconnected due to the progress of the deterioration described above, since the deterioration prevention pattern is a non-heat generating pattern, it would not have any adverse effect on the heating performance.

[0035]

[Embodiments] Hereinafter, embodiments of the ceramic heater of the present invention and its manufacturing method will be described.

As shown in FIG. 1, the ceramic heater 1 of this embodiment has two layers on the surface of a cylindrical ceramic base material 2.
Ceramic layers 3 and 4 are formed, and a heat generating pattern 7 is formed at the interface 5 between the first ceramic layer 3 and the second ceramic layer 4.

This heating pattern 7 is shown in FIG. 2 in an exploded perspective view.
As shown in the figure, there is a narrow heating section 8 that meanderes many times on the tip side of the ceramic heater 1, and an anode side terminal 9a and a cathode side terminal 9b arranged on the rear side of the ceramic heater 1 and connected to the power source. (generally referred to as the terminal section 9), and lead sections 10a and 10b that connect the heat generating section 8 and the terminal section 9.

Furthermore, in addition to the heating pattern 7, the boundary surface 5 has an anode deterioration prevention pattern 11a connected to the anode terminal 9a and a cathode deterioration prevention pattern 11b connected to the cathode terminal 9b. is formed.

The anode-side deterioration prevention pattern 11a extends from the anode-side terminal 9a along the lead portion 10a, and is connected to the anode-side pattern (anode-side first pattern portion 8a) of the heat generating portion 8.
On the other hand, the cathode-side deterioration prevention pattern 11b extends from the cathode-side terminal 9b along the lead portion 10b, and is formed parallel to the cathode-side pattern (cathode-side first pattern portion 8b) of the heat generating section 8. is formed.

Therefore, both deterioration prevention patterns 11a,
11b (generally referred to as 11) are arranged adjacent to each other on the boundary surface 5 of the ceramic heater 1, as shown in FIG. 3 (A-A sectional view in FIG. 1). In addition, both deterioration prevention pattern 1
1 is formed to be about twice as wide as the width of the heat generating part 8, and the wire resistance value is about 0.01Ω/cm so that the terminal voltage can be maintained.
It is set to mm.

Next, a method for manufacturing the ceramic heater 1 having the above structure will be explained based on FIG. 2. (a) Mixture of raw material powder: Al2O3 powder with an average particle size of 1.5 μm and a purity of 99.9%, and S as a sintering accelerator with an average particle size of 2 μm and a purity of 98%.
iO2 powder, MgO powder with an average particle size of 2 μm and a purity of 90%, and CaO powder with an average particle size of 2 μm and a purity of 93%,
They are mixed in a ratio of 97.2:2.5:0.1:0.1, wet mixed in a ball mill for 20 to 60 hours, and then dehydrated and dried. (b) Creation of base material Add 1 methyl cellulose to the blended powder produced in (a) above.
%, Maxelon (trade name) 15%, water 10% were added,
Knead. Next, it is formed into a cylindrical shape by extrusion molding, cut to a predetermined size, and then calcined at 1200° C. to obtain the base material 2. (c) Creation of first and second green sheets, heat generation pattern and deterioration prevention pattern The blended powder produced in (a) above contains 8% polyvinyl butyral, 4% DBP, methyl ethyl ketone, and 7% toluene.
Add 0% and mix in a ball mill to form a slurry. After degassing under reduced pressure, a second green sheet 4a having a thickness of 0.2 to 0.4 mm, which will become the second ceramic layer 4, is created by a doctor blade method.

Next, a pre-adjusted W paste is applied onto the surface of the second green sheet 4a by a thick film printing method.
Printed patterns 7a and 11 are screen printed to a thickness of 0 to 30 μm to become the heat generating pattern 7 and the deterioration prevention pattern 11.
form aa, 11bb.

Furthermore, on this printed surface, a first green sheet 3a having a thickness of 0.05 to 0.10 mm and forming the first ceramic layer 3, which is formed in the same manner as the second green sheet 4a, is pressed. Form a laminated sheet. (d) Integration of base material, first to second green sheets, heat generation pattern and deterioration prevention pattern 25% polyvinyl butyral, 8% DBP, and 30% butyl carbidol were added to the blended powder produced in (a) above. to produce a paste-like product, and this paste-like product,
It is applied to the surface of the first green sheet 3a of the laminated sheet obtained in (c) above.

Next, the laminated sheet is wrapped around the base material 2 so that this coated surface is used for bonding with the base material 2, and the laminated sheet is pressed into close contact with the base material 2. Next, after removing the resin at 250°C, it is fired at 1500 to 1600°C in a hydrogen furnace atmosphere to form the integrated ceramic heater 1. Thereafter, the tip of the terminal portion 9 of the ceramic heater 1 is plated with Ni, and is joined to a lead wire extraction terminal (not shown) using a brazing material.

Next, an example of an experiment conducted to confirm the effect of the ceramic heater 1 manufactured in this manner will be described. (Experimental Example 1) A high temperature durability test was conducted using the ceramic heater 1 of this example.

[0046] In the experiment, in a heated atmosphere of 1000° C., a DC 17 V current was applied to the heat generating pattern 7 which was equipped with the deterioration prevention pattern 11 and had a resistance value of 4.5 Ω, and the change in the resistance value over time was measured. . Further, as a comparative example, a high temperature durability test was similarly conducted on a heater formed with a conventional heat generation pattern without a deterioration prevention pattern. The results are shown in FIG. 4, where the vertical axis shows the resistance change rate (%) and the horizontal axis shows the durability time (Hr). In addition, in the experiment, experiments were conducted on five samples each as a present example and a comparative example.

As is clear from FIG. 4, the ceramic heater 1 of this example exhibits significantly less change in resistance value over time and has excellent high-temperature durability performance than that of the comparative example. On the other hand, the comparative example has 50 hours to 100 hours.
Since the resistance value increases rapidly over time,
It is inappropriate.

As described above, the ceramic heater 1 of this embodiment has the deterioration prevention patterns 11 on the anode side and the cathode side close to the outside of the heat generating part 8, so that Mg2+, Ca
The movement of 2+ to the low potential side and the movement of O2- to the high potential side proceed on the deterioration prevention pattern 11. As a result, the heating pattern 7 does not deteriorate at all.

Furthermore, the deterioration prevention pattern 11 is a non-heat generating pattern that holds the terminal voltage but does not allow current to flow, and its temperature is low, so that the deterioration described above is slight. Moreover, even if this deterioration prevention pattern 11 deteriorates and breaks, this is not a pattern that generates heat, so it will not have any adverse effect on heating performance.

As a result, the resistance value is less likely to increase due to deterioration of the heating pattern 7, so that the life of the ceramic heater 1 can be extended. Therefore, when this ceramic heater 1 is applied, for example, to an oxygen sensor for air-fuel ratio control that is exposed to high temperatures for a long period of time, the heat generation pattern 7 is unlikely to deteriorate and an increase in resistance can be prevented. It is possible to prevent the wire 7 from being disconnected or cracking the protective layer. As a result, even when the oxygen sensor is used at high temperatures, the ceramic heater 1 can be suitably used for a long period of time, which is a remarkable effect.

[0051]

[Effects of the Invention] As described above, since the ceramic heater of the present invention is provided with deterioration prevention patterns on the anode side and the cathode side, it is possible to prevent the heat generation pattern from deteriorating due to the movement of Mg2+, Ca2+, and O2-. be. In particular, the material of the present invention shows little change in resistance value even under conditions of exposure to high temperatures, can maintain stable heating characteristics for a long period of time, and has excellent durability. Moreover, the structure is simple and manufacturing is easy, since there is no need for detecting means or the like. Therefore, it can be suitably applied as a heater for various types of sensors, and is extremely useful.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of a ceramic heater according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of the ceramic heater of the example.

[Figure 3] A in Figure 1 of the ceramic heater of the example
-A sectional view.

FIG. 4 is a graph showing the results of durability tests of ceramic heaters of Examples and Comparative Examples.

FIG. 5 is an explanatory diagram showing problems with conventional ceramic heaters.

FIG. 6 is a graph showing a change in resistance value of a conventional ceramic heater.

[Explanation of symbols]

1... Ceramic heater 2...
Ceramic base materials 3, 4... Ceramic layer 5...
Boundary surface 7...Heat generation pattern
8...Heating part 9a...Anode side terminal
9b...Cathode side terminal 11a...Anode side deterioration prevention pattern 11b...Cathode side deterioration prevention pattern 11...Deterioration prevention pattern

Claims (2)

[Claims] 1. A first ceramic layer, a second ceramic layer laminated on the surface of the first ceramic layer, a heat generating part disposed at the interface between the first and second ceramic layers, an anode side terminal, and a second ceramic layer laminated on the surface of the first ceramic layer. a heat generating pattern having a cathode side terminal; an anode deterioration prevention pattern connected to the anode side terminal to hold the terminal voltage; and an anode side deterioration prevention pattern connected to the cathode side terminal to hold the terminal voltage. A ceramic heater characterized in that a cathode-side deterioration prevention pattern is disposed adjacently to the outside of the heat generating section. 2. When forming a heating element pattern with a heat generating part on the surface of a green sheet, an anode side deterioration prevention device that is connected to an anode side terminal on the outside of the anode side pattern of the heat generating part to maintain terminal voltage. At the same time as forming a pattern, a cathode-side deterioration prevention pattern that is connected to a cathode-side terminal and holds a terminal voltage is formed on the outside of the cathode-side pattern of the heat-generating part, and then the surface of the heat-generating pattern is covered with another green sheet. A method for manufacturing a ceramic heater, comprising: forming a laminate with a heating pattern sandwiched therebetween, laminating the laminate on a ceramic base material, and firing the laminate together.