JP2000133419A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high durability with small change of resistance by making an electrode taking-out part led-through to one end of a heating part, out of a mixture material of an inorganic insulating material and an inorganic conductive material, and determining its hardness to be more than a specific value. SOLUTION: A ceramic heater 1 is manufactured by burying a heating part 2 and an electrode taking-out part 4 in a ceramic body 3, and one end of the electrode taking-out part 4 is exposed. A metallic layer 5 made of a brazing filler metal or the like, is formed on this exposed part, and a joining stress relaxation material 6 bonded with a lead wire 7 (electrode metal fitting 8 together), is bonded thereto by the brazing filler metal or the like. The hardness of the electrode taking-out part 4 is determined to be above 11.5 GPa for preventing the change of resistance caused by the cracking by the difference of the thermal expansion properties between the ceramic body 3 and the metallic lead wire 7. The electrode taking-out part 4 is made of an inorganic conductive material and an inorganic insulating material, and the total hardness can be increased by increasing a ratio of the inorganic insulating material of high hardness, or by reducing its particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as an ignition heater for various combustion devices such as a petroleum fan heater, various sensors for various sensors such as an oxygen sensor, a heater for measuring devices, and a glow plug for an automobile. It relates to a ceramic heater.

[0002]

2. Description of the Related Art In addition to oxide-based ceramics conventionally used as insulating bases for various electronic components, in recent years,
Non-oxide ceramics, which have outstanding characteristics of high heat resistance, corrosion resistance, wear resistance, and electrical insulation, high strength and low specific gravity, are used in various industrial machinery such as chemical plants and machine tools. It has been widely used as an internal combustion engine component such as a diesel engine for an automobile.

For example, when starting or idling a diesel engine, a glow plug for an internal combustion engine used for rapidly preheating the sub-combustion chamber and an oxygen concentration in exhaust gas of the internal combustion engine are detected to control exhaust gas. Various auxiliary heating heaters such as heaters installed to promote the activation of the oxygen sensor element to perform the heat generation are inferior in the conventional rapid temperature rising characteristics and inferior durability such as wear resistance and corrosion resistance. Instead of a sheathed heater in which a resistance wire and a heat-resistant insulating powder are embedded in a heat-resistant metal cylinder, a high-melting-point metal and its compound, and those containing them as a main component, are used as an electrically insulating ceramic sintered body with good thermal conductivity. 2. Description of the Related Art Ceramic heaters integrally supporting a heat-generating resistor made of various inorganic conductive materials, and bonding or embedding the heat-generating resistor have been widely used.

However, in a joined body of a ceramic member and a metal member, the thermal expansion coefficients of the two members are greatly different from each other. In the various heaters,
It occurs at the joint between the electrode take-out part of the ceramic heating resistor and the electrode fitting, especially at the joint interface, and decreases the joining strength between the ceramic member and the metal member, and the shrinkage of the ceramic member or the metal member itself due to the contraction force of the metal member. Destruction,
There is a drawback that separation from the bonding interface is easily caused.

The structure of a conventional ceramic heater will be described with reference to FIG. On the upper surface of a ceramic green sheet (not shown), a heating section 2 and an electrode take-out section 4 are formed by printing, a tungsten lead is placed so as to connect them, and the same ceramic green sheet as described above is overlaid.
Hot press firing is performed to obtain a sintered body of the ceramic heater 1. Then, after polishing the end surface of the sintered body of the ceramic heater 1 so that the end surface of the electrode take-out portion 4 is exposed, a metal layer 5 which is a brazing material is formed by printing, and 800 to 13 in vacuum.
Bake at 00 ° C. By mounting and brazing the bonding stress relieving material 6 to which the lead wire 7 is bonded, the difference in thermal expansion between the ceramic body 3 and the lead wire 7 is eliminated, and the bonding strength is maintained up to a high temperature. Has been proposed.

[0006]

However, the ceramic body 3 and the metal lead wire 7 are joined via the joining stress relieving material 6, and a brazing material containing an active metal having a high joining strength is used as the metal layer 5. Even if it is joined by using, the occurrence of micro cracks cannot be prevented, and this micro crack is
There is a problem that the resistance reaches the electrode lead portion 4 to cause a resistance change.

Conventionally, in a heater of several tens of ohms such as general household electric appliances, the resistance change due to the microcracks is very small and does not affect the heat generation. In recent years, in a low-resistance heater used at a low voltage, the resistance change due to the microcracks occupies a large proportion of the overall resistance of the heater, and as a result, the electrode extraction portion 4 generates heat, and the durability is reduced. there were.

In addition to the above problem, there is another problem that the peel strength of the lead wire 7 and the bonding stress relieving material 6 varies.

[0009]

As a result of studying the above problems, the hardness of the lead-out portion of the electrode has an effect on the development of cracks, which affects the resistance change and durability. It has been found that the bonding length and position of the alloy have an influence on the peel strength.

Therefore, the hardness determined by the ratio and particle size of the inorganic insulating material and the inorganic conductive material constituting the electrode lead portion, the joining length between the lead wire and the joining stress relieving material, the distance from the joining portion to the outer periphery of the joining stress relieving material. As a result, it was found that the above problem could be solved, and it was revealed that excellent durability with little change in resistance could be obtained.

That is, in the ceramic heater according to the present invention, a heating section made of an inorganic conductive material which generates heat by energization is supported, joined, or buried in a non-oxide ceramic body to constitute the ceramic heater. Is formed of an inorganic insulating material and an inorganic conductive material, and has a hardness of 11.5 GPa or more.

A lead wire is joined to the electrode lead-out portion by joining a joining stress relieving material, the joining length of the lead wire is set to 25 to 75% of the length of the joining stress relieving material, and the joining portion is formed. The connection is made such that the distance from the electrode to the outer peripheral end of the joining stress relieving material is at least 25% of the length of the joining stress relieving material.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a ceramic heater according to the present invention will be described with reference to the drawings.

In FIG. 1, a ceramic heater 1 has a heat generating portion 2 and an electrode take-out portion 4 embedded in a ceramic body 1.
One end of the electrode take-out portion 4 is exposed, a metal layer 5 made of a brazing material or the like is provided on the exposed portion, and a joining stress relieving material 6 (together, an electrode fitting 8) to which a lead wire 7 is joined is joined by brazing or the like. It was done.

In the present invention, the electrode take-out portion 4 is provided.
By setting the hardness to 11.5 GPa or more, resistance change due to cracks due to a difference in thermal expansion between the ceramic body 3 and the metal lead wire 7 is prevented. The electrode take-out part 4 is made of an inorganic conductive material and an inorganic insulating material, and the overall hardness can be increased by increasing the proportion of the inorganic insulating material having a high hardness or by reducing the particle size, thereby increasing the distribution of the inorganic insulating material. By increasing the hardness, the development of cracks can be prevented.

The joining length and joining position between the lead wire 7 forming the electrode fitting 8 and the joining stress relieving material 6 affect the peel strength. Therefore, as shown in FIG. 2, the joining length C of the lead wire 7 is 25 to 75% of the length A of the joining stress relieving material 6.
The length B from the joint of the lead wire 7 to the outer periphery 6a on the electrode side of the joining stress relieving material 6 is set to 25% or more of the length A of the joining stress relieving material 6.

This is because when the length B from the joint of the lead wire 7 to the outer periphery 6a on the electrode side of the joining stress relaxing material 6 is less than 25% of the length A of the joining stress relaxing material 6, the joining stress relaxing This is because a residual stress is generated on the electrode-side outer periphery 6a of the material 6, and the stress is concentrated on the electrode-side outer periphery 6a of the bonding stress relieving material 6 when a load is applied to the lead wire 7, so that the peel strength is weakened.

If the joining length C is less than 25%, the joining force between the lead wire 7 and the joining stress relieving material 6 becomes weak, and the two are separated from each other. Therefore, the joining length C between the lead wire 7 and the joining stress relieving material 6 must be 25% or more, and since the length B is 25% or more, the joining length C is 75% or less.

In the present invention, the material applicable as the ceramic body 3 is a non-oxide ceramic, which is mainly composed of silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), sialon, aluminum nitride (AlN) or the like. And those each containing a predetermined sintering aid are used. These ceramics have a Vickers hardness of 10 GPa or more, and it is preferable to use a non-oxide ceramic having such a hardness.

Examples of the inorganic conductive material applicable to the heating section 2 and the electrode take-out section 4 include high melting point metals such as tungsten (W), molybdenum (Mo), and titanium (Ti), tungsten carbide (WC), and silicide. Molybdenum (Mo
A resistor mainly composed of carbide, silicide, nitride, or the like of a high melting point metal such as Si ₂ ) and titanium nitride (TiN) can be used. In view of the difference in thermal expansion from the non-oxide ceramic body 3 and the difficulty in reacting with them even at high temperatures, WC
Alternatively, a material containing W as a main component is preferable.

On the other hand, with respect to the main component of the inorganic conductive material,
Silicon nitride (Si ₃ N ₄ ) and boron nitride (B) are used to control the growth to prevent cracks due to the difference in thermal expansion from the ceramic body 3, and to prevent the electrode lead-out portion 4 from cracking due to metal members. BN), aluminum nitride (AlN) or silicon carbide (SiC).

The content of the inorganic conductive material is 10 to 2
0% by weight, the average particle size of the inorganic conductive material is 0.1 to 1.3 μm
m, preferably in the range of 0.2 to 1.0 μm,
The hardness may be 11.5 GPa or more within this range.

The metal layer 5 is composed mainly of at least one of gold (Au), nickel (Ni), copper (Cu), silver (Ag) and palladium (Pd).
A material that does not deteriorate due to oxidation even when used at a high temperature of 0 ° C or more is used. For example, considering the prevention of migration under use conditions involving the energization of a DC power supply, the metal layer 5 contains 50 to 99% by weight of gold (Au) and nickel (N
i) 1 to 50% by weight of gold (Au) and nickel (Ni)
Is most suitable.

In the metal layer 5, titanium (Ti), vanadium (V), manganese (Mn), cobalt (Co), nickel (Ni), copper (Ni), which is a group 4a element of the periodic table as an active metal, is formed. Cu), molybdenum (Mo), silicon (Si), zirconium (Zr), hafnium (H
It is preferable to contain at least one of f). In particular, from the viewpoint that the metal layer 5 has good wettability to the ceramic body 3 and does not deteriorate the strength of the ceramic body 3, it is preferable to include at least one of vanadium (V) or molybdenum (Mo) as an active metal. Optimally, such active metals may be included in the form of nitrides, carbides, hydroxides and the like.

The joining stress relieving material 6 to be joined to the ceramic body 3 is a metal having a value close to the coefficient of thermal expansion of the ceramic body 3, for example, a low thermal expansion metal such as molybdenum (Mo) or tungsten (W). And an Fe-Ni-based Invar alloy, an Fe-P-based Elinvar alloy, a WC-TiC-Co-based cemented carbide, and the like. From the viewpoints of oxidation resistance, workability, and cost, Fe is used. -N
An i-Co alloy or an Fe-Ni alloy is desirable.

[0026]

EXAMPLES The present invention was evaluated as described in detail below.

First, a ceramic raw material powder obtained by adding a sintering aid composed of an oxide of a rare earth element such as ytterbium (Yb) or yttrium (Y) to silicon nitride (Si ₃ N ₄ ) powder is subjected to a known press molding method or the like. The heating part 2 is formed in a U-shaped pattern by a screen printing method using a paste containing WC as a main component on the surface on one end side of the molded body by using From the other end to the side surface of the molded body, an electrode take-out part 4 made of a mixture of an inorganic conductive material and an inorganic insulating material having a ratio and a particle size shown in Tables 1 to 4
Was formed.

Next, a lead portion is placed so as to electrically connect the heating portion 2 and the electrode take-out portion 4, and another ceramic molded body is placed thereon.
The ceramic heater 1 was manufactured by firing and integrating at a temperature of 00 to 1900 ° C.

Thereafter, by grinding the ceramic heater 1, Au, N
The metal layer 5 was applied by a screen printing method using a paste containing i and V, and baked in a vacuum atmosphere at 800 to 1300 ° C. to form the metal layer 5 by adhesion.

Next, an electrode in which a Ni lead wire 7 was previously connected to the ceramic heater 1 by spot welding to a bonding stress relieving material 6 made of an Fe—Ni—Co alloy having a width of 2 mm × a length of 3 mm × a thickness of 0.2 mm. Metal fitting 8 at 800 to 1300 ° C
In a vacuum atmosphere.

The ceramic heater 1 thus obtained was cut and polished at the portion including the electrode take-out portion 4 and the Vickers hardness of the electrode take-out portion 4 was measured under a load of 20 kgf.

The temperature of the ceramic heater 1 is set to room temperature and 450
Each exposure to a temperature atmosphere of ° C. was repeated as one cycle, the resistance value of the ceramic heater 1 after 3000 cycles was measured, and the rate of resistance change with respect to the initial resistance value before the test was measured. In this test, in order to clarify the difference between the conditions, the end of the bonding stress relieving material 6 was bonded onto the electrode take-out portion 4 so that cracks were easily formed.

As shown in Tables 1 to 4, the hardness of the electrode take-out portion 4 is determined by the ratio of the insulating material to the conductive material and the particle size of the insulating material, and the Vickers hardness of the present invention is less than 11.5 GPa. Sample numbers 1 to 15 and 21 outside the claims
-30, 41-45, the resistance change rate was 10% or more.

On the other hand, in the embodiment of the present invention in which the Vickers hardness of the electrode take-out portion 4 is 11.5 GPa or more,
It can be seen that when the rate of change in resistance is less than 10%, the progress of cracks is effectively mitigated.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

Next, the joining position and length of the lead wire 7 to the joining stress relieving material 6 were changed as shown in Tables 5 and 6, and the joining strength was evaluated. The ceramic heater 1 for evaluation was fixed, and the lead wire 7 of the joined electrode fitting was pulled in a direction perpendicular to the ceramic heater 1, and the ceramic heater 1 was heated.
The peel strength (kgf) when the fracture between the bonding stress relieving material 6 and between the bonding stress relieving material 6 and the lead wire 7 was measured and evaluated together with the fracture mode.

The length a of the joining stress relieving material 6 is 3 mm.
The dimension D in Tables 5 and 6 is the distance from the midpoint of the joint to the outer peripheral end of the joint stress relieving member 6 on the heating element side as shown in FIG.

As is clear from Tables 5 and 6, the length B from the joining portion to the outer peripheral end 6a on the electrode side of the joining stress relieving material 6 and
If any of the bond lengths C is outside the scope of the present invention,
There was a substance having a large variation in the peeling strength and less than 10 kgf. That is, when the joining length C is less than 25% of the length A of the joining stress relieving material 6, the joining force between them is small. When the length B of the joining stress relieving material 6 to the electrode side outer peripheral end 6a is less than 25% or more than 75% of the length A of the joining stress relieving material 6, the stress is reduced to the electrode side outer peripheral end 6a. And the bonding strength is not stable.

On the other hand, in the embodiment of the present invention, the peel strength is stable at 15 kgf or more, the stress is effectively reduced,
Further, it can be seen that the joining force between the joining stress relieving material 6 and the lead wire 7 can be maintained.

In this embodiment, the lead wire 7 has a wire diameter φ.
Although a wire having a diameter of 1.0 mm was used, when the wire diameter was smaller than φ0.7 mm, the breaking mode would be that the lead wire 7 would break, and it would be determined by the tensile strength of the lead wire 7.

[0044]

[Table 5]

[0045]

[Table 6]

[0046]

According to the present invention, there is provided a ceramic heater in which a non-oxide ceramic is provided with a heat generating portion and an electrode take-out portion, and a lead wire is joined to one end of the electrode take-out portion by using a brazing material. Hardness 11.5 GP
By setting a or more, it is possible to suppress the development of cracks and obtain a ceramic heater having excellent resistance and little resistance change.

[Brief description of the drawings]

FIG. 1A is a perspective view showing a ceramic heater of the present invention, and FIG. 1B is a cross-sectional view of an electrode take-out portion.

FIG. 2 is a perspective view showing an electrode fitting used for the ceramic heater of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Ceramic heater 2 Heating part 3 Ceramic body 4 Electrode take-out part 5 Metal layer 6 Bonding stress relieving material 7 Lead wire 8 Electrode fitting A Length of bonding stress relieving material B Outer side of joining stress relieving material from the lead wire joint Length to end C Joining length of joining stress relieving material and lead wire

Claims (3)

[Claims] 1. A ceramic heater comprising a non-oxide ceramic body having a heat generating portion and an electrode take-out portion, and a lead wire joined to one end of the electrode take-out portion using a brazing material, wherein the electrode take-out portion is made of an inorganic conductive material. A ceramic heater comprising a mixture of inorganic insulating materials and having a hardness of 11.5 GPa or more. 2. The ceramic heater according to claim 1, wherein the inorganic conductive material contains at least one of nitride, silicide, and carbide such as W, Mo, and Ti as a main component. 3. A lead wire is joined to one end of the electrode take-out portion via a joining stress relieving material, and the joining length between the joining stress relieving material and the lead wire is 25 to 75 with respect to the length of the joining stress relieving material.
%, And the distance from the joining portion to the outer periphery of the outer peripheral end of the joining stress relieving material on the electrode side is 25% with respect to the length of the joining stress relieving material.
2. The ceramic heater according to claim 1, wherein: