JPS6396883A - Ceramic heater - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a ceramic heater, particularly a ceramic heater that is effectively applied to glow plugs of diesel engines, etc. [Prior Art] Glow plugs are used as starting parts at low temperatures), and glow plugs that heat quickly are required to improve engine starting performance. In order to meet this demand, the inventors created an electric cutting machine! It is made by sintering a mixed powder of molybdenum silicide (Mo5is), which is an electrically conductive 7'-oxidizing ceramic material, and silicon nitride (S1s Na), which is an insulating ceramic with a low coefficient of thermal expansion, on the outer periphery of the tip of a dielectric ceramic member. A glow plug was developed in which a heater was formed and placed so that the heater was exposed in the combustion atmosphere (Japanese Patent Application Laid-open No. 126484/1984). This glow plug has excellent heat-up properties because the ejector directly heats the inside of the combustion chamber. MOS'Ls is a component of the heater.
Sis Ha, which has a low coefficient of thermal expansion, also provides thermal shock resistance to the heater.

By the way, in this heater, the thermal shock resistance of the heater itself is excellent under extreme pressure, but the coefficient of thermal expansion of the insulating ceramic member supporting the heater and the joint part of the heater formed around it is low.

Differences in thermal properties such as thermal conductivity cause thermal stress, which reduces thermal shock resistance.

As a solution to this problem, the inventors constructed a heater with a central part and an outer peripheral part that surrounds the central part with a U-shaped cross section, and both the central part and the outer peripheral part were made of a mixture of molybdenum silicide (MO8i*) and silicon nitride (SiaNa). We have developed a ceramic heater in which the proportion of the same components is the same in both parts, and the specific resistance of both parts is adjusted by the particle size of the same component so that only the outer periphery is energized (Japanese Patent Application Laid-Open No. 1983-1999). No. 254586).

However, even in the ceramic heater, when the support member made of silicon nitride and alumina (A11On) and the heater are sintered together, the optimum firing conditions for both members are different, so the tangle characteristics of both members are affected. Not available at the same time.

Furthermore, the support member of a ceramic heater is housed and fixed in a metal housing, and the means for fixing it is generally to form a nickel plating layer on the surface of the support member, and to apply wax to the support member T-housing via this plating layer. Measures will be taken to attach it.

However, in the case of the 81m Ha-Ass On type sintered body, there is a problem in that the adhesion of the nickel μ plating is not good and sufficient bonding strength cannot be obtained.

[Problems to be solved by the present invention]

Therefore, the present invention provides a ceramic in which a heater made of a conductive ceramic sintered body is integrally sintered on the outer periphery of the tip of a supporting member made of an insulating ceramic sintered body. An object of the present invention is to provide a ceramic heater in which the bonding strength of the support member and the heater are not compromised, and in which the support member and the heater can exhibit their respective characteristics to the maximum extent, thereby solving the above-mentioned conventional problems.

Another object of the present invention is to provide a ceramic heater in which a support member and a housing are firmly connected.

[Means for solving problems]

In the ceramic heater of the present invention, both the supporting member and the heater are made of Mo81 heavy and 81s Na, and the mixing ratio of the same components is the same in both the supporting member and the heater,
The support member and the heater are integrally sintered. MO8j-
The blending weight ratio of * and Sis Na is 10-40:60 ~
The range should be around 90.

The supporting member consists of conductive M O81m particles and insulating Si.
s is surrounded by Na particles and divided, thereby M,
The structure is 9C insulation, and the heater is a conductive structure in which Sj-m N4 particles are wrapped by Movll particles and MO8j-particles are continuous.

As a means for realizing the above structure in the support member,
M OS 1m and poor wettability or K during sintering
First, a sintering aid that forms a glass layer with low viscosity is added and sintered. As a result, as shown in the model in FIG. 2, MOS:1. *The particles aggregate to form a sintered structure surrounded by Sis Na particles. As a sintering aid, for example, p, l* On% MgA mu o4, or K YI Ol together with these can be used.

The powders of MO8i,s and 51sN used for sintering the support member have the same average particle size and are almost the same, or are the powders of MO8i
+ Make the powder larger @5i4 in the heater
The Na powder used is MoSi, and the powder used also has a large average particle size.

By making the MO6i* powder sufficiently small and large, a sintered structure is created in which conductivity is achieved by continuous MO8j-snow particles surrounding one KMoSi particle and N4 particle, as shown in the model in Figure 3. Become. The specific resistance of the heater can be controlled by adjusting the relative particle diameters of MO8i* and S'Ls N4, it-. Sl,s
It is desirable that the average particle diameter of Na is about 2 tones or more than that of MO8i, t.

[Effect]

In this way, in the present invention, the support member and the heater have substantially the same components and composition, so when they are sintered together, the support member and the heater can be sintered under the same optimal conditions. Optimum characteristics can be obtained for both, and both can be strongly integrated. Furthermore, cracks do not occur at the joint due to the difference in thermal expansion coefficients between the two.

Furthermore, the presence of MO8i in the supporting member improves its adhesion to the nickel plating, resulting in a good bonding force with the metal housing.

[Example 1] The details of the present invention will be explained below using the following examples and experimental examples in which the present invention is applied to a glow plug.

(1) Rod-shaped support member 2 with a square cross section as shown in Fig. 1
The plate-like protrusion m21Vc formed at the tip of the heater 1 having a U-shaped cross section surrounds the plate-like protrusion m21Vc. The support member 2 includes tungsten conductive wires 3a and 31 whose tips are connected to the heater 1.
) is buried. A metal pipe 4 is attached to the outer periphery of the support member 2.
The pipe 41C is connected to one end of the cylindrical metal housing 5. The rear end of the energizing wire 3a extends to the base end of the support member 20 and is connected to the metal cap 6 fitted to the base end,
It is connected to a power source (not shown) via a cap 6 and a nickel wire +7. The rear end of the current-carrying wire 3b is connected to a metal sleeve.

The heater 1 and the support member 2 are both MO8i*3096 (
(the same applies hereinafter) and SLN.

Y*Os, ActOsf to 70% mixed powder
This is a sintered body of a mixture of eMO8L and S'ia Na added in an amount of 7% and 3%, respectively, based on the total amount, and the support member 2 and the heater 1 are integrally sintered.

The average particle size of the MoSi,g powder was 0.9 μm in both the support member 2 and the heater 1, and the average particle size of the S'raNa powder was 0.6 μm in the support member 2.

In heater 1, it is 13 μm.

The support member 2 and the pipe 4 are joined by applying nickel plating to the surface of the support member 2 and then attaching the pipe to the inside. Further, the pipe 4 and the housing 5 are connected by brazing.

In the glow plug of the present invention having the above structure, the support member 2
and heater 1 to 1560" C ~ near 60" 0.500A
Tests were conducted on the thermal shock resistance of the heater 1 and its joints, and the joint strength of the support member 2 and the pipe 4, which were integrally sintered by hot pressing under an argon pressure of 9/m and 1 atmosphere of argon.

In addition, as a comparison material, the support member 11 was made of 50% 81aNa-
50% MOS 03 with the other structure being the same as that of the present invention (Comparative Example U), and supporting member 2 with 50% MOS 1
m-50fli Alm Qs, and the cutter is composed of a central part corresponding to the protruding part 2 in FIG. A sintered body consisting of the above-mentioned Altos was made, and the central part of the p was made into a nearly insulating state by manipulating the particle size of the components, and this sinter was integrally sintered with the support member containing the above-mentioned Altos, and the rest had the same structure as the present invention. (Comparative Example 2, Meikai No. 60-254586)
A similar test was also conducted.

Thermal shock resistance is tested by a spalling test, that is, after applying a voltage to the glow plug and causing it to saturated heat to a predetermined temperature,
A particularly good evaluation was made by immersing the tip protruding from the pipe 4 in water of C and examining the presence or absence of cracks occurring on the surface of the pipe 4. Further, the bonding strength was evaluated by applying pressure to the tip of the heater 10 in the direction of the pipe number and determining the limit point at which the heater 1 sank into the pipe 4. The results are shown in Tables 1 and 2.

In Table 1, the x mark indicates the occurrence of cracks.As is known from Table 1, in the present invention, the heater and its supporting member are made of the same material, so the coefficient of thermal expansion between them is
Thermal stress caused by the difference in thermal conductivity can be significantly reduced, and therefore the energized impact resistance can be greatly improved. In addition, as shown in Table 2, since Mo5is is dispersed in the supporting member, the adhesion of nickel plating to the supporting member is improved, and therefore the bonding strength between the supporting member and the metal pipe surrounding it is significantly increased. improves.

(2) Used as a support member for 1 hour S1a Na −
The following experiment was conducted to investigate the insulation properties of the MO8i* sintered body.

Average particle size varies fk 7s Sin Na 7096
, A sintering aid was added to the MO8L30 mixed powder at varying amounts, and hot press firing was performed.9.

That is, after blending Sin Na and M O81m in the above ratio and mixing and stirring the mixed powder with a solvent such as ethanol, a plasticizer and a di-butyl phthalate were added to a binder and a poly-vinyl loop chiller/L/. (degree of polymerization 1000) and further kneading to obtain a viscosity of 3X10' to 10X
IO'poi8ecls? IJ-? After adjustment, a ceramic green sheet having a thickness of 0.74 after drying was prepared using a doctor blade method. After laminating multiple sheets of this sheet at approximately 120"C,
? A ceramic sintered body was obtained by holding the ceramic sintered body for 0.30 minutes and under the conditions of a pressure of 50,019 f/-.

The specific resistance of the obtained ceramic sintered body was measured.

The results are shown in Table 3.

As is well known, specific resistance can be controlled by controlling the particle size of Si, Na, and Mo81m, but particle size control is insufficient to achieve the disconnection required for the support member.

The supporting member must have a resistivity of 0, preferably 10Ω or more, and such insulating AII
It can be seen that it is possible to add os of 396 or more and MgA 04 of 2% or more.

Note that the sintering aid is not limited to those mentioned above, but also MoSi
, which have poor wettability with snow (and with good wettability with Si and sNa) can be used.

(3) Both the heater and supporting member are made of Sl, sNa.
=MOS 1 proverb MO8it-8'Ls Na in the ceramic and -ta of the present invention which are integrally sintered as a sintered body
[The body and the heater are MO8ix-S'i-s Na
Sintered body and support member? Sis Na-AA't On
The firing conditions and properties of the S'ia Na-A/OS sintered body (comparative material) in a conventional ceramic heater that is integrally sintered as a sintered body were tested. The results are shown in Table 4.

As is well known, 50 excellent Sis Na-n.

The strength of the %A l s Om sintered body rapidly decreases when fired at 1600°C or higher. This strength reduction is 581sl
b+ 2 AIl*Os-→2S'LaAl*0mNa
+ Sis Na and him by 510m naru reaction
It has been found that this is due to the progress of the solid solution reaction of Os, and the precipitation of 5101, which is a surplus component, in the grain boundary layer. Therefore, in order to obtain the necessary strength when using this sintered body as a support member, it should be fired at 1600°C or lower.

On the other hand, in the sts N-MoSi, m sintered body,
Due to its hardness to sinter, it can be heated up to 1640° even when hot-dressed.
Firing is required at a temperature of 1,680° C. or higher, preferably 1,680° C. or higher.

Therefore, in conventional ceramic heaters, Si, i N
a AJb Os support member and S'1. aN
It is extremely difficult to integrally sinter the a-MOS L tr and the -MOS L tr so that both exhibit superior characteristics at the same time.

On the other hand, both the support member and the heater are KSLs L
-Moult and having the same composition as the ceramic of the present invention, it is possible to maximize the excellent characteristics of both the support member and the heater by integral sintering.

As explained above, according to the present invention, the support member and the heater can be integrally sintered and each can exhibit excellent characteristics. In addition, since it is possible to match the macroscopic physical properties of the supporting member and the material, such as the coefficient of thermal expansion, excellent thermal shock resistance can be achieved without cracking due to thermal stress even after repeated heating and cooling. It will be done.

4. Explanation of the mouth surface O9 Figure 1 is a vertical cross-sectional view of a glow plug equipped with a ceramic heater of the present invention, fJI. FIG. 3 is a diagram schematically showing the structure of the heater portion in the ceramic heater.

1...--Heater 2---Supporting member 4--1 Metal vibrator 5...--Metal housing No.
1 Table 2 Table 1 Figure 20 Figure 3

Claims (4)

[Claims] (1) A support member made of an electrically insulating ceramic sintered body, a heater made of a conductive ceramic sintered body formed on the outer periphery of the tip of the support member, an energizing means for supplying electricity to the heater, and a support member that is housed and held. The support member and the heater are sintered bodies of mixed powders of molybdenum silicide and silicon nitride having the same blending ratio, and both are integrally sintered, and the support member is surrounded by molybdenum silicide particles. This ceramic heater has a structure separated from each other by silicon nitride particles, and the heater has a structure in which molybdenum silicide particles surrounding the silicon nitride particles are continuous. (2) The weight ratio of molybdenum silicide and silicon nitride in the support member and heater is 10 to 40:90 to 6.
0. The ceramic heater according to claim 1, wherein (3) The ceramic heater according to claim 1, wherein the average particle diameter of the silicon nitride in the heater is larger than that of the molybdenum silicide. (4) The ceramic heater according to claim 1, wherein the support member is brazed to the housing via nickel plating applied to the surface of the support member.