JPH01157084A - Ceramic heating element and its manufacture - Google Patents

Abstract

PURPOSE:To improve durability against thermal history of a ceramic by forming an intermediate layer made of a non-oxide ceramic such as the same metal element as the main metal element of a heating resistance wire or the nitride, carbide, silicide, carbide silicide thereof or the like, at the boundary face with the heating resistor wire. CONSTITUTION:A heating resistance wire 3 connect a heating coil 33 made of such an alloy as molybdenum, rhenium or the like to tungsten electrode takeout wires 31, 32, and is buried in silicon nitride sintered body 2. At the boundary face between the sintered body 2 and the wires 31, 32 near the exposed faces 31a, 32a of the wires 31, 32, an intermediate layer 4 made of a non-oxide ceramic such as nitride, carbide, silicate, silicone carbide or the like being the main component metal of the wires 31, 32 are formed. It is thus possible to improve continuous durability against the thermal history of ceramic because tight connection between the wire 3 and the sintered body 2 is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a ceramic heating element in which an electric resistance wire is embedded in an insulating ceramic, and the resistance wire is energized to generate heat.

[Prior Art] Ceramic heating elements are made by embedding a heating resistance wire of tungsten, tungsten-rhenium alloy, etc. in a silicon nitride sintered body, and a reaction occurs at the interface between the heating resistance wire and the ceramic during firing. When a reactant is generated and subjected to thermal history due to use, the difference in thermal expansion between the two causes peeling or small racks to occur at the interface. Especially for removing the electrodes.
If a metal outer cylinder that also serves as an electrical terminal is brazed to the exposed part of the heating resistance wire on the outer periphery of the ceramic, the electrode section will be pulled by the outer cylinder when subjected to thermal history, causing the heating resistance wire to break. easy.

In order to prevent the occurrence of peeling and minute racks at the interface, JP-A-61-179084 discloses that titanium nitride (TiN) is added to the interface between the heating resistance wire and the ceramic.
Titanium nitride carbide (TiCN), aluminum nitride (Af
JN), boron nitride (BN), silicon carbide (SiC>,
Cubic boron nitride (CBN), titanium boride (TiB)
Ceramic heaters with a non-oxide ceramic coating such as 2) have been proposed.

[Problems to be Solved by the Invention] However, in the above ceramic heater, sufficient consideration has not been given to the bonding strength between the heating resistance wire and the non-oxide ceramic coating. It is not strong enough and does not have the durability to withstand long-term thermal history. Further, in the above ceramic heater, no consideration was given to the integration of the non-oxide ceramic coating and the silicon nitride sintered body, and the bonding strength of this bonding surface was also insufficient.

The inventor discovered that the bonding strength of the interface between the heat generating resistance wire and the ceramic sintered body can be improved by adding an intermediate layer containing a predetermined proportion of the same metal element as the main constituent element of the heat generating resistance wire to this interface. Based on the knowledge that the above-mentioned bonding strength can be increased significantly by intervening the ceramic material in the intermediate layer, and further increasing the bonding strength by including the same ceramic material as the ceramic sintered body in a predetermined ratio in this intermediate layer, we have developed a structure that can withstand permanent durability against thermal history. It is an object of the present invention to provide a ceramic heating element with high properties.

[Means for Solving the Problems] In order to achieve the above object, the ceramic heating element of the present invention includes a heating resistor made of a high melting point metal such as tungsten, molybdenum, rhenium, or an alloy thereof in a silicon nitride sintered body. In a ceramic heating element formed by embedding a wire, a) on the surface of the resistance wire constituting the resistance wire, the same metal element as the main constituent metal element of the resistance wire or its nitride;
A configuration in which an intermediate layer is formed of a non-oxide ceramic such as carbide, silicide, or silicified carbide. A configuration is adopted in which an intermediate layer is formed of a mixture of a non-oxide ceramic such as a compound or a silicified carbide compound, and a silicon nitride material.

In addition, in order to manufacture this ceramic heating element, c) a metal of the same metal element as the main constituent metal element of the resistance wire is coated on the surface of the heating resistance wire made of a high melting point metal such as tungsten, molybdenum, rhenium, or an alloy thereof. A mixed powder consisting of 20 to 100% (by weight) of powder or non-oxide ceramic powder such as its nitride, carbide, silicide, or silicided carbide, and 0 to 80% (by weight) of silicon nitride powder is deposited. A method was adopted in which this adherend was embedded in a molded body of silicon nitride powder and hot press fired.

In this invention, silicon nitride refers to silicon nitride with a content of 0 to 0.
30% by weight aluminum oxide powder (Aρzoi), M
Contains a sintering aid such as yttrium chloride (Y20.).

[Function and Effects of the Invention] The ceramic heating element of the present invention has a heat generating resistance wire formed from a high melting point metal such as tungsten, molybdenum, and rhenium or an alloy thereof buried therein. Since an intermediate layer made of a non-oxide ceramic such as the same metal element as the main constituent metal element of the heating resistance wire or its carbide, silicide, or silicided carbide is interposed on the surface, the heating resistance wire and the ceramic do not mix during firing. In addition to preventing the generation of reactive oxides, the main constituent elements of the heat-generating resistance wire and the same metal elements contained in the intermediate layer are melted together and integrated.This allows the bond between the intermediate layer and the heat-generating resistance wire to be integrated. It can be extremely strong. Furthermore, since the intermediate layer and the silicon nitride sintered body are both ceramics, they have good compatibility and are closely bonded. Therefore, due to the action of this intermediate layer, the heat-generating resistance wire and the ceramic can be closely bonded, and permanent durability can be obtained against the ceramic heat shoe. Furthermore, by using a mixture of a silicon nitride material and a non-oxide ceramic such as the same metal element as the main constituent metal element of the heating resistance wire or its carbide, silicide, or silicide carbide, for the intermediate layer. Since the silicon nitride and the silicon nitride of the silicon nitride sintered body are integrated, the bonding strength can be further increased, and the durability against thermal history can be further improved.

[Example] Next, the present invention will be explained based on an example shown in FIGS. 1 and 2.

The ceramic heating element 1 of the present invention includes a silicon nitride sintered body 2 which is an electrically insulating ceramic, and a silicon nitride sintered body 2 that is an electrically insulating ceramic.
It consists of a heating resistance wire 3 buried therein, and an intermediate layer 4 interposed at the interface between the silicon nitride sintered body 2 and the heating resistance wire 3.

The silicon nitride sintered body 2 has a cylindrical shape with a hemispherical tip 2A, an outer diameter of 3.5 mm, and a total length of about 60 mm.

The heating resistance wire 3 is a pair of tungsten electrode lead wires 31 buried in parallel in the rear side 22 of the sintered body 2.
and 32, and a heating coil 33 whose rear end is connected to the tip of each of the electrode lead wires and which is embedded in the front side portion 23 of the sintered body 2 in a substantially U-shape. The electrode lead wires 31 and 32 are tungsten wires with a wire diameter of 0.3 mm, and the heating coil 33 is made of a tungsten-rhenium alloy and is a thin wire with a wire diameter of 0.22 mm spirally wound with an inner diameter of 0.3 mm. The rear end of the electrode lead wire 31 is exposed at the exposed surface 31a on the side wall of the rear end portion 21 of the silicon nitride sintered body 2, and the rear end of the electrode lead line 32 is slightly behind the center of the silicon nitride sintered body 2. The exposed surface 32a'''C is exposed on the wall near the end.

In this embodiment, the intermediate layer 4 has an exposed surface 31a.

It is provided at the interface between the electrode lead line 31, 32 and the silicon nitride sintered body 2 in a portion close to the electrode lead line 32a.

The materials used for this intermediate layer 4 are: (a) Tungsten, which is the main constituent metal element of the electrode lead wires 31 and 32, or non-oxides such as tungsten nitrides, silicides, carbides, and silicide carbons; 100% (by weight) of ceramic; (b) 20 to 1 o of tungsten, which is the constituent metal element;
O (weight)% and silicon nitride material in trace amounts ~ 80 (weight)
%, (c) nitride of tungsten, which is the constituent metal element;
20 to less than 100% (by weight) of non-oxide ceramics such as silicides, carbides, and silicided carbides, and trace amounts to 80% (by weight) of silicon nitride materials.

(d) A mixture of tungsten, which is the constituent metal element, and a non-oxide ceramic such as tungsten nitride, silicide, carbide, or silicided carbide is 20 to less than 100% (by weight), and the silicon nitride material is There are four types: trace amount to 80% (by weight).

That is, in the above configuration, since all of the materials used for the intermediate layer 4 contain the same metal element as the metal element of the electrode lead wires 31 and 32, they are melted together and firmly bonded to each other during hot press firing. can.

Further, the intermediate layer 4 is made of a silicon nitride material and the electrode lead wire 3.
Since it has a coefficient of thermal expansion between 1.32 and 1.32, it alleviates the stress that occurs when subjected to thermal history.

In addition, if a silicon nitride material is included, the silicon nitride material in the intermediate layer 4 enters the silicon nitride sintered body 2 during hot press firing and prevents the firing from occurring. The bonding strength between 31.32 and the silicon nitride sintered body 2 is also extremely strong.

Further, even when the intermediate layer does not contain a silicon nitride material, the sintering aid contained in the silicon nitride material forms a glass layer and diffuses into the intermediate layer 4, so that the electrode lead wire 31.
The bonding strength between 32 and the silicon nitride sintered body 2 becomes stronger.

Next, a method for manufacturing the ceramic heating element 1 of the present invention will be explained.

(A) Bend the tungsten wire cut to a predetermined length to form electrode lead wires 31 and 32, and insert both ends of the tungsten-rhenium alloy heating coil 33 into the tips of the electrode lead wires 31 and 32 to wire the heating resistance wire. 3 is manufactured.

(b) A paste is produced by adding acetone and an organic binder to powder of tungsten, which is the main constituent metal element of the electrode lead wires 31 and 32, or tungsten nitride, silicide, carbide, silicide carbide, etc. This paste is applied to the electrode lead wires 31 and 32 and dried.

(c) Silicon nitride powder is press-molded to obtain a molded body in which a heat-generating resistance wire is embedded, and then calcined.

) Hot press firing is performed at 1800° C. for 30 minutes at a hot press pressure of 300 kg/cm” in a non-oxygen atmosphere.

(E) Shape shaping and electrode exposure by polishing.

(Experiment Example 1) 700 g of tungsten powder with an average particle size of 0.8 μm, 270 g of silicon nitride powder with an average particle size of 1.0 μm, and an average particle size of 0
．． 15 g of 8 μm aluminum oxide powder, average particle size 1.
Acetone and an organic binder were added to 15 g of 5 μm yttrium oxide powder to produce a paste to serve as an intermediate layer, and the paste was applied to tungsten electrode lead wires 31 and 32 in varying thicknesses.

A bonding strength measurement test and a thermal cycle test were conducted with seven types of coating thickness (4 μm to 450 μm), the thickness of the intermediate layer 4 after hot pressing (1.7 μm to 255 μm), and a non-coated one for comparison. , as shown in Table 1 below, the thickness of the intermediate layer is 2.0 μm to 200 μm, preferably 10 μm to
The result was that 50 μm was optimal.

[Table 1] ★...1/100 wire breakage (Experiment example 2) Acetone and an organic binder were added to tungsten carbide (WC) powder with an average particle size of 0.8 μm to produce a paste that would become the intermediate layer 4. , tungsten electrode lead wire 31.3
The above paste was applied to No. 2 to a thickness of 100 μm.

In the bonding strength measurement test, this ceramic heating element 1
The average strength was 1.88 kg/mm2, and no change in resistance was observed in the thermal cycle test, giving good results.

(Experimental Example 3) Acetone and an organic binder were added to tungsten silicide (WSiz) powder with an average particle size of 1.2 μm to produce a paste that would become the intermediate layer 4, and a tungsten electrode lead wire 31.
The paste was applied to No. 32 to a thickness of 100 μm.

This ceramic heating element 1 had an average strength of 1.93 kg/mm' in a joint strength measurement test, and no change in resistance was observed in a thermal cycle test, giving good results.

In the above embodiments, the effect of forming the intermediate layer on the electrode lead wire has been described, but when the intermediate layer according to the present invention is formed on the heating coil part, it is sufficient to withstand the thermal history caused by heating. Needless to say, it has a great durability effect.

In the bonding strength measurement test, nickel (N
i) Wires were brazed, a tensile load was applied, and the value obtained by dividing the measured load at cutting by the exposed area of the electrode wire was defined as the bonding strength.

The thermal cycle test was performed on the exposed electrode portion 31a of the ceramic heating element 1 to which the paste was applied to various thicknesses.

32a was fitted with a metal outer cylinder and energized for 1 minute to de-energized for 1 minute 10,000 times.The maximum temperature when energized was approximately 1200°C, and the exposed electrode portion 32a of the silicon nitride sintered body 2 was approximately 10,000 times. The temperature reached 350℃.

3 and 4 show a glow plug 100 for a diesel engine using the ceramic heating element 1 according to the present invention. This glow plug 100 has a metal support tube 3O fitted inside the tip of a cylindrical mounting fitting 20, and this support tube 30
Fitting the central part 11 of the ceramic heating element 1 into the
Insert the shaft center within the mounting bracket 2° and insert the coiled center electrode 40.
is arranged, and the tightly wound part 50 at the tip is fitted into the rear end part 21 of the ceramic heating element 1, and the mounting bracket 2
A mounting screw 24 and a hexagonal head 25 are formed on the outer periphery of the cylinder 0, and is mounted to the cylinder head of a diesel engine.

[Brief explanation of the drawing]

FIG. 1 is a front cross-sectional view of the ceramic heating element of the present invention, FIG. 2 is a cross-sectional view taken along the line A-B, and FIG. 3 is a cross-sectional view of a glow plug for a diesel engine using the ceramic heating element of the present invention. , FIG. 4 is an enlarged view of the main part. In the figure 1...Ceramic heating element 2...Silicon nitride sintered body 3...Heating resistance wire 4...Intermediate layer agent
Patent Attorney Kenji Ishiguro Figure 1 Figure 2 Figure 3 Figures 2 and 41

Claims (1)

[Claims] 1) A ceramic heat generating device in which a heat generating resistance wire made of a high melting point metal such as tungsten (W), molybdenum (Mo), rhenium (Re) or an alloy thereof is embedded in a silicon nitride sintered body. In the body, an intermediate layer made of a non-oxide ceramic such as the same metal element as the main constituent metal element of the resistance wire or its nitride, carbide, silicide, or silicide carbide is formed on the surface of the resistance wire. A ceramic heating element featuring 2) Tungsten, molybdenum,
In a ceramic heating element formed by embedding a heating resistance wire made of a high melting point metal such as rhenium or an alloy thereof, the surface of the resistance wire is coated with the same metal element as the main constituent metal element of the resistance wire, or its nitride or carbide. A ceramic heating element characterized in that an intermediate layer is formed of a mixture of a non-oxide ceramic such as a silicide or a silicided carbide, and a silicon nitride material. 3) Metal powder of the same metal element as the main constituent metal element of the resistance wire, or its nitride, carbide, silicide, A ceramic characterized by depositing a mixed powder of non-oxide ceramic powder such as silicide carbide and silicon nitride powder, embedding this adherend in a molded body of silicon nitride powder, and hot press firing. Method of manufacturing heating elements.