JPH09245940A - Ceramic heat generation body, and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cracking or peeling at a ceramic part caused by a differential thermal expansion coefficient between metal and ceramic in a ceramic heat generation body, prevent generation of a reaction layer, maintain resistance stability, and secure durability to repeated use. SOLUTION: A heater base material 11 is formed of one sort of metal, or two or three sorts of alloy of W, Re, Mo, Ta, Nb, Ni, Cr. An outer shell 30 in which the heater base material 11 is embedded is formed of insulation ceramic mainly comprising silicon nitride or silicon carbide. A middle layer 31 to embed the heater base material 11 around it in the outer shell 30 is formed of ceramic including a compound including one, two, or three elements of Al, Ce, Y, Mg, Ca, in which an element 0, or 0 and N are coupled with them, or especially assistant components, and this is sintered in an atmospheric pressure, or sintered in a pressurized atmosphere to form a ceramic heat generation body 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heating element used in a high temperature state, for example, as a heating source in various heating equipment, an ignition source in combustion equipment, a glow plug for starting assistance in a diesel engine, and the manufacture thereof. Regarding the method.

[0002]

2. Description of the Related Art In a conventional glow plug for a diesel engine, a heater material made of nickel chromium (Ni-Cr) or iron chromium (Fe-Cr) is used in a sheath made of heat-resistant metal and magnesia (MgO). The heater part is constructed by embedding in a heat resistant insulating powder such as the above.

Recently, in such a glow plug,
It is desired to comply with exhaust gas regulations, and it is necessary to shorten the time required to reach 800 ° C., increase the peak temperature and saturation temperature, and lengthen the afterglow time after engine start. In order to meet these demands, it is necessary to form the heater material in the heater part with a high-melting-point metal material, and the sheath can also be formed with a ceramic material that can be used at a higher temperature than the metal material. It is considered. For example, as described in Japanese Patent Laid-Open No. 61-235613, a refractory metal material such as tungsten (W) or molybdenum (Mo) is added to silicon nitride or sialon having excellent oxidation resistance and thermal shock resistance. There is known a so-called ceramic heater which is formed by embedding it in an insulating ceramic such as silicon carbide and sintering it.

[0004]

However, in the above-mentioned conventional ceramic heater, there is a difference in the coefficient of thermal expansion between the metal material and the insulating ceramics, and there is a problem that tungsten silicide is present between the metal material and the insulating ceramics. Since such a reaction layer is generated, the ceramic part may be cracked, peeled off, or the resistance becomes unstable during sintering. For this reason, the temperature at the time of sintering cannot be raised to a very high temperature, so that hot press sintering is currently performed. Further, even if sintered by such hot pressing, the heat generation of the heating element is repeated, so that the heater material and the ceramic may be cracked or separated due to the difference in the coefficient of thermal expansion between the metal material and the ceramic. There are many.

Here, the reaction layer produced during the above-mentioned sintering is produced as follows. That is, in a ceramic heater, in particular, one in which W or Mo is embedded as a heating element in silicon nitride, ceramics, especially a ceramic-heating element interface due to a sintering reaction in a silicon nitride atmosphere during hot pressing. Reactants (here WSi, W
O2) is produced.

When such a reaction substance is generated, it is diffused from the boundary between the ceramic and the heating element to the inside of the heating element, causing a minute crack or an internal defect due to a transition. And
When the ceramic heater under such a condition is exposed to a heat cycle or a high temperature atmosphere, oxidation of the heating element is promoted. The thus-oxidized heating element expands in volume and presses the ceramics surrounding the heating element, so that the ceramics is likely to be cracked from the inside. Further, when the heating element is oxidized, the resistance value changes, and the amount of heat generated varies.

Further, in Japanese Patent Laid-Open No. 7-135068, in order to prevent disconnection of the heating element (heater base material) due to repeated use of the ceramic heater, TiN having a larger thermal expansion coefficient than the heater base material is disclosed. A structure in which a heater base material is coated with such a substance is also known. Further, Japanese Patent Laid-Open No. 61-179084 discloses a technique of coating the surface of a resistance heating element (heater base material) made of tungsten or molybdenum with a non-oxide ceramic.

However, the former Japanese Patent Laid-Open No. 7-135 mentioned above.
With the heater in the 068 publication, heating and cooling about 100 times is good, but when repeated about several thousand to tens of thousands times like a glow plug, cracks occur in the ceramics. Further, as in the latter Japanese Patent Laid-Open No. 61-179084, when coating with a simple non-oxide ceramics, when embedded in silicon nitride or silicon carbide and sintered,
The surface of the heater base material becomes polka dots, and due to so-called poor wetting, a gap is created at the interface between the heater base material and the ceramic that is the coating layer. When such a gap is formed between the heater base material and the coating layer, the metal of the heater base material is oxidized or the ceramics of the outer shell is cracked.

Further, in these conventional manufacturing methods, in order to prevent the diffusion of the coating layer covering the heater base material, which is a heating element, into the ceramics constituting the outer shell, one of the hot sintering methods of ceramics is used. It was essential to perform sintering by press sintering. However, since such hot press sintering is mechanical pressure sintering, it is possible to form the ceramic heating element only in a cross-sectional shape such as a substantially elliptical shape that can obtain uniform overpressure. However, there is a problem that the molding shape is limited. That is, it is impossible to form such a circular cross-sectional shape that is advantageous at the time of assembling with other parts incorporating such a ceramic heating element.

Therefore, it has been conventionally considered to form an elliptical ceramic heating element into a desired shape by cutting after molding, but the above-mentioned molded product by hot press sintering is very hard. However, since the number of processing steps for post-processing increases and the cost increases, it is desired to take measures to prevent such cracking and peeling of the ceramics in consideration of such points.

The present invention has been made in view of the above-mentioned circumstances, and cracks and peels in the ceramic portion due to the difference in the thermal expansion coefficient between the metal material serving as the heater base material and the ceramic serving as the outer shell of the ceramic heating element. Etc. and the formation of a reaction layer such as tungsten silicide can be prevented, resistance stability is maintained, and pressureless sintering is a sintering method that does not pressurize, or pressurizing with gas pressure for sintering. A ceramic heating element which can be formed by pressure sintering in an atmosphere and does not cause cracking or peeling between the heater base material and the ceramic of the outer shell even when the ceramic heating element is repeatedly used, and its production. Aim to get a way.

[0012]

In order to meet such a demand, in the ceramic heating element according to the present invention, the heater base material is made of one kind of metal selected from W, Re, Mo, Ta, Nb, Ni and Cr. Alternatively, it is formed of two or three kinds of alloys, and the outer shell in which the heater base material is embedded is formed of insulating ceramics containing silicon nitride or silicon carbide as a main component, and is formed around the heater base material. The intermediate layer between the buried outer shell is made of Al, Ce, Y, Mg, Ca.
It is formed by a compound containing one kind, two kinds or three kinds of elements, and the element O or O and N are connected to the element.

Further, the method for manufacturing a ceramic heating element according to the present invention uses a heater base material made of one kind of metal selected from W, Re, Mo, Ta, Nb, Ni and Cr, or two or three kinds of alloys. A sol containing one kind, two kinds or three kinds of elements of Al, Ce, Y, Mg and Ca,
Coating as an intermediate layer, heat treatment in a nitrogen atmosphere or an ammonia atmosphere, Al, Ce, Y, M
g or Ca, plasma-coated with an oxide or oxynitride containing one or more elements, and then embedded in a ceramic containing silicon nitride or silicon carbide as a main component, Normal pressure sintering or atmospheric pressure sintering is performed.

According to the present invention, by providing an intermediate layer having a component that can be an auxiliary agent of ceramics between the ceramics of the outer shell and the heater base material, the heater base material and the ceramics of the outer shell are made of a metal material. Prevents cracking and peeling in the outer ceramics part due to the difference in thermal expansion coefficient, and also prevents the formation of a reaction layer such as tungsten silicide, maintaining resistance stability as a heating element, and further sintering under normal pressure or atmosphere. It is possible to perform pressure sintering. Further, according to the ceramic heating element thus obtained, even if it is repeatedly used, cracking or peeling does not occur between the heater base material and the ceramic of the outer shell.

The outer shape of the ceramic heating element may be formed to have a circular cross section, but is not limited thereto. The outer shell of such a ceramic heating element is formed by either normal pressure sintering or atmospheric pressure sintering instead of conventional hot press sintering. The heater base material is
It is formed of one kind of metal selected from W, Re, Mo, Ta, Nb, Ni and Cr, or two or three kinds of alloys of two or more kinds. The intermediate layer contains, except for Si, one or more of Al, Ce, Y, Mg, and Ca, which are auxiliary agents for bonding with ceramics, and two or three elements of which more than one element are contained. It is formed by a compound in which O or O and N are linked. This intermediate layer is formed by coating the sol, followed by heat treatment in a nitrogen atmosphere or an ammonia atmosphere, or by plasma coating an oxide or an oxynitride.

[0016]

1 and 2 show one embodiment of a ceramic heating element and a method for manufacturing the same according to the present invention. In these drawings, in this embodiment, a case where a ceramic heating element is used for the glow plug 10 for a diesel engine will be described. In such a glow plug 10 for a diesel engine, a heater base material 11 composed of a heating element 21 and lead portions 22 and 23 thereof is embedded in an outer shell 30 made of an insulating ceramic such as silicon nitride (Si3 N4). Rod-shaped ceramic heater 12
And a metal holder 13 having a substantially tubular shape that holds the heater 12 at its tip.

The metal holder 13 is made of a material resistant to creep, for example, carbon steel such as S45C or a similar material. On the rear end side of the holder 13, a rod-shaped external connection terminal 15 is fitted and held via an insulating bush 14 made of insulating ceramics. Reference numeral 16 is a lead wire for electrically connecting the inner end of the external connection terminal 15 to one lead portion 23 on the rear end surface of the ceramic heater 12.
An insulating tube 16a is fitted in the. 19
Is a metal cap provided at the rear end of the heater 12.

Reference numeral 17 denotes a metal auxiliary pipe which is fitted in the central portion of the ceramic heater 12 and holds it at the tip of the holder 13. Further, the auxiliary pipe 17 is fitted on the rear end side of the heater 12 and is attached to the other lead portion 22.
A part 18a of the metal ring 18 electrically connected to is connected, and the body is grounded. Reference numeral 13a in the drawing denotes a screw portion formed on the outer periphery of the holder 13, which is screwed into a screw hole (not shown) on the engine cylinder head side so that the tip of the heater 12 is projected into the auxiliary combustion chamber (combustion chamber) of the engine. It is for mounting so that.

According to the present invention, in the ceramic heater 12 used in the glow plug 10 as described above, as shown in FIG.
As shown in (a) and (b), the heater substrate 11 (21,
22, 23) to W, Re, Mo, Ta, Nb, Ni,
An outer shell 3 formed of one kind of metal or two or three kinds of alloys of Cr and burying the heater base material 11 therein.
0 is formed of insulating ceramics containing silicon nitride (or silicon carbide) as a main component, and intermediate layers 31 and 31 between the outer periphery of the heater base material 11 and the outer shell 30 in which it is embedded are It is formed by a compound containing one kind, two kinds or three kinds of elements of Al, Ce, Y, Mg and Ca, and the element O or O and N are connected to this.

Here, in the above-mentioned material of the heater base material 11, W, Re, Mo, Ta, N which are refractory metals are used.
The purity of b, Ni, Cr, or an alloy thereof is not particularly limited, but is preferably 95% by weight or more in order to prevent the melting point from lowering, and is processed into a shape such as a wire or a flat plate for use as a heater. Is desirable. The alloy is not particularly limited in composition as long as it is an alloy based on the above-mentioned high melting point metal,
Suitable alloys include W-Mo, W-Re, Ni-Cr
And so on.

The feature of the present invention is that the above-mentioned intermediate layer 31 is present between the heater base material 11 and the outer shell 30 in which the intermediate base material 31 is embedded. The reason is that a silicide such as tungsten silicide is used. Preventing generation, stabilizing resistance, relaxing the difference in thermal expansion between ceramics and metal,
This is to prevent cracks on the ceramic side forming the outer shell 30. And as a result of repeating various experiments, this middle layer 3
It has been found that it is necessary that 1,31 have a composition that serves as a sintering aid for the silicon nitride or silicon carbide of the outer shell 30. That is, containing one kind, two kinds or three kinds of elements selected from Al, Ce, Y, Mg and Ca,
They must be compounds associated with the elements O or O and N.

Although the reason for being such a substance is not clear, it has good wettability with, for example, silicon nitride or silicon carbide, and has a thermal expansion coefficient smaller than that of the metal of the heater substrate 11, It is considered to be larger than the silicon nitride or silicon carbide of the shell 30. The thickness of the intermediate layers 31 and 31 is not particularly limited, but is preferably 5 μm or more in order to reduce the difference in thermal expansion and to avoid the reaction between the metal and Si which is the ceramic component of the outer shell 30. Further, the outer shell 30 has heat resistance required for the ceramic heater 12, which is a ceramic heating element,
It should be silicon nitride or silicon carbide because of its characteristics such as oxidation resistance and thermal shock resistance.

Next, a method for manufacturing the ceramic heater 12 which is the ceramic heating element according to the present invention will be described. Intermediate layer 3 between the heater substrate 11 (21, 22, 23)
1. As a method for coating the sol on the heater substrate 11 made of a metal material, known methods such as brush coating, dip coating, and spin coating can be used. The film thickness of such a coating is 5 μm depending on the usage environment of the heater 12 and other conditions.
It is desirable to make the above.

However, in dip coating and spin coating, the thickness of one coating is 0.
Since the thickness is as thin as about 5 μm, drying and coating may be repeated several times to increase the thickness of the coating to a desired thickness. The upper limit of the coating thickness is
If the thickness is too thick, the coating will take time and cost, and the coating itself will be cracked.

On the other hand, the form of the sol for obtaining the above-mentioned intermediate layer 31 is not particularly limited, but examples thereof include a sol prepared by hydrolysis of alkoxide and a sol in which colloids are dispersed. Incidentally, the solvent of such sol, drying is fast, good surface roughness is obtained,
An organic solvent is desirable because it provides good adhesion after drying.

The coated sol improves the adhesion between the coating film (intermediate layer 31) and the heater base material 11, increases the oxidation resistance of the heater base material 11, and increases the thermal expansion coefficient. In order to make the outer shell 30 intermediate between the ceramics and the metal, heat treatment is performed to form an oxide or an oxynitride. The treatment temperature at this time varies depending on the type of metal and the type of sol, but a temperature of 200 ° C. or higher is required. However, if the heat treatment is performed at an excessively rapid heating rate, cracks may occur, so the heating rate should be 200
C./h or less is desirable.

The heat treatment is performed in a nitrogen or ammonia atmosphere. By doing so, when N and O are present in the sol, oxides and oxynitrides are produced depending on the metal and the processing conditions. The heater material 11 coated by the above-described method is embedded in the ceramic powder that constitutes the outer shell 30 made of silicon nitride or silicon carbide, and is uniaxially pressed or CIP (Cold Isostatic).
Press and perform atmospheric pressure sintering or atmospheric pressure sintering to perform ceramic heating element (ceramic heater 1).
2) is manufactured. Here, ceramics made of silicon nitride or silicon carbide means silicon nitride ceramics or silicon carbide ceramics containing an auxiliary component.

According to the present invention as described above, W,
Heater substrate 1 made of one kind of metal selected from Re, Mo, Ta, Nb, Ni and Cr, or two or three kinds of alloys
1 (21, 22, 23) on Al, Ce, Y, Mg, C
Similar to the case where an oxide or oxynitride containing one, two or three elements of a is plasma-coated as the intermediate layer 31 and then coated, a silicon nitride or silicon carbide ceramic. The powder is embedded, uniaxial pressing or CIP is performed, and normal pressure sintering or atmospheric pressure sintering is performed to manufacture a ceramic heating element.

Here, the plasma coating can be performed by a known method. The oxide or oxynitride that performs such coating is Al
2 O3, MgAl2 O4, CeO2, etc. can be exemplified, but not only crystalline but Al, Ce, Y, M
It may be amorphous as long as it contains one, two, or three elements of g and Ca.

According to the present invention as described above, by providing the intermediate layer 31 having a component that can be an auxiliary agent of ceramics between the ceramics which becomes the outer shell 30 and the heater material 11, the thermal expansion of the metal and the ceramics can be achieved. It is possible to prevent cracking and peeling of the outer ceramics part due to the difference in coefficient, to prevent the formation of a reaction layer such as tungsten silicide, to maintain resistance stability, and to perform normal pressure sintering or atmospheric pressure sintering. Is. And according to the ceramic heating element 12 thus obtained, even if it is repeatedly used,
No cracking or peeling occurs between the heater base material 11 and the ceramic outer shell 30.

It is needless to say that the present invention is not limited to the structure described in the above-mentioned embodiment, and the shape, structure, etc. of each part can be appropriately modified or changed. For example, in the above-described embodiment, the case where the ceramic heating element is used for the glow plug for the diesel engine has been described, but the present invention is not limited to this, and a heater for CVD (chemical vapor deposition) or a petroleum fan heater. It can be applied to a heater or the like. Also, as for the material, shape, structure, etc. of each part, as is widely known, appropriate modifications can be considered.

[0032]

【Example】

(Example 1) Magnesium ethoxide: aluminum butoxide: butanol: water were mixed at 1: 1: 5: 2 and refluxed at 60 ° C for 1 hour to form a sol. Also,
A sol was dip-coated on a heater substrate 11 made of a metal material such as W, Re, Mo, Ta, Nb, Ni, Cr or a W-Re or Ni-Cr alloy. And 8
Drying at 0 ° C. and dip coating were repeated 10 times to obtain a coating having a thickness of about 10 μm. Then 2
The intermediate layer 31 was formed by performing heat treatment in a nitrogen stream at a temperature rising rate of 00 ° C./h, 800 ° C. × 1 h.

Heater substrate 1 manufactured by the above operation
1 was embedded in a ceramic powder made of silicon nitride containing an auxiliary agent and pressure-sintered in an atmosphere, and a ceramic heating element 12
Was manufactured. After that, 11.5 V was applied to such a heating element for 10 seconds, the heating cycle was stopped for 30 seconds and air cooling was performed 20,000 times. The heat generation temperature at that time is 13
A durability test of whether or not the temperature reached up to 00 ° C. and the presence or absence of cracks in the silicon nitride outer shell 30 after this test were observed.

For comparison, five ceramic heating elements having W as a heater base material, which were not coated with the above-mentioned coating and were manufactured by a conventional method of hot pressing, were prepared as comparative samples, and the same results were obtained. The test was conducted. Table 1 shows the test results.

[0035]

[Table 1] In addition, Comparative Example No. The durability of No. 5 is "x" because of disconnection due to the absence of the intermediate layer.

(Example 2) Al-O3 and Ti were added to W-Re.
N was plasma coated. After that, the same test as in Example 1 described above was performed. In Example 2 as described above, the Al2 O3 coating had no problem in durability and cracking. However, with TiN coating,
After 2230 cycles, the temperature did not rise to 1300 ° C. and the silicon carbide outer shell 30 was cracked after the test.

[0037]

As described above, according to the ceramic heating element of the present invention, by providing the intermediate layer having a component which can be an auxiliary agent of the ceramic between the ceramic of the outer shell and the heater, It is possible to prevent cracking and peeling of the ceramic portion due to the difference in the coefficient of thermal expansion from ceramics, prevent the formation of a reaction layer such as tungsten silicide, and maintain resistance stability.

Furthermore, according to the method for manufacturing a ceramic heating element of the present invention, it is possible to perform atmospheric pressure sintering or atmospheric pressure sintering without the need for conventional hot press sintering. Further, according to the ceramic heating element manufactured in this manner, even if this is repeatedly used, no cracking or peeling occurs between the heater and the ceramic. Further, due to these effects, hot pressing can be omitted, so that a ceramic heating element that is inexpensive and has excellent durability can be obtained.

In particular, according to the present invention, a glow plug having a circular cross section, which is advantageous when assembling with other parts, is subjected to normal pressure sintering or atmospheric pressure sintering without performing conventional hot press sintering. There is an advantage that can be obtained at.

[Brief description of drawings]

FIG. 1 shows an embodiment of a ceramic heating element and a method for manufacturing the same according to the present invention. (A) is a sectional view of a ceramic heater used in a glow plug for a diesel engine, (b) is its I-I line. FIG.

FIG. 2 is a cross-sectional view for explaining the overall configuration of a diesel engine glow plug to which the present invention is applied.

[Explanation of symbols]

10 ... Glow plug for diesel engine, 11 ... Heater base material, 12 ... Ceramic heater (ceramic heating element), 13 ... Metal holder, 21 ... Heating element, 22, 23
... Lead part, 30 ... Ceramic outer shell, 31 ... Intermediate layer.

Claims (5)

[Claims] 1. A heater base material comprising W, Re, Mo, Ta,
The outer shell is made of one kind of metal selected from Nb, Ni and Cr, or two or three kinds of alloys, and the outer shell for embedding the heater base material is made of insulating ceramics containing silicon nitride or silicon carbide as a main component. In addition, an intermediate layer between the heater base material and the outer shell that buries the heater base material is formed of one of Al, Ce, Y, Mg, and Ca.
A ceramic heating element which is formed by a compound containing two or three kinds of elements and having the elements O or O and N bound to them. 2. W, Re, Mo, Ta, Nb, Ni, C
A heater base made of one metal of r or two or three alloys, and a sol containing one, two, or three elements of Al, Ce, Y, Mg, Ca Manufacture of ceramic heating element characterized by being coated as a layer, heat-treated in a nitrogen atmosphere or an ammonia atmosphere, then embedded in a ceramic containing silicon nitride or silicon carbide as a main component and pressure-sintered. Method. 3. The method for producing a ceramic heating element according to claim 2, wherein atmospheric pressure sintering is performed instead of atmospheric pressure sintering. 4. W, Re, Mo, Ta, Nb, Ni, C
An oxide or acid containing one kind, two kinds or three kinds of elements of Al, Ce, Y, Mg and Ca in a heater base material made of one kind of metal of r or two kinds or three kinds of alloys. A method for manufacturing a ceramic heating element, which comprises plasma-coating a nitride, burying it in ceramics containing silicon nitride or silicon carbide as a main component, and sintering at atmospheric pressure. 5. The method for manufacturing a ceramic heating element according to claim 4, wherein atmospheric pressure sintering is performed instead of atmospheric pressure sintering.