DE19757752A1 - Sintered ceramic-embedded refractory metal heating element - Google Patents

Abstract

A novel ceramic heating device consists of a heating element (11) which is formed of a refractory (melting point >= 2000 deg C) metal-containing material and an inorganic conductive material and which is embedded in a sintered body (14) of insulating ceramic containing silicon nitride, silicon carbide and 0.01-10 vol.% of one or more group IIIa, IVa and Va element nitrides. Preferably, a pair of refractory metal leads (12, 13) is connected to the element (11) and is embedded in the sintered body (14). Also claimed is production of the above ceramic heating device by embedding the heating element (11), connected to a pair of leads (12, 13), in a powder of the insulating ceramic material and then sintering, preferably at >1750 deg C.

Description

Background of the Invention

The present invention relates to a ceramic heater comprising a high temperature heating sintered body is formed in a glow plug and the like for the ignition of various heaters and burners and for Auxiliary starting of a diesel engine is used and a manufacturing process the same.

A glow plug is used, for example, as an auxiliary heating source (preheating source) when starting of a diesel engine. A conventionally known glow plug This type generally has a structure in which a metal heater is made Ni-Cr (nickel-chrome), Fe-Cr (iron-chrome) or the like in a heat resistant insulating powder such as MgO (magnesia) is embedded in the heat resistant insulating powder embedded metal heater with a heat resistant metal sheath is covered.

In a glow plug of this type, the rise time must reach 800 ° C be shortened, the peak and saturation temperatures must be set higher and the afterglow time must be extended to today's To comply with exhaust gas regulations. To achieve these conditions, the heating  Part of the heating element a high-melting metal can be used. The man The tel part is not made from a metal, but from one at a high temperature usable ceramics.

For example, Japanese Patent Laid-Open No. 55-126989 discloses kera mix heater used in the above-mentioned glow plug, the Structure in which a high-melting metal such as W (tungsten) in an insulating Silicon nitride ceramic, the excellent oxidation resistance and heat has shock resistance, is embedded.

However, cracking occurs in this ceramic heater during sintering tion, peeling and the like takes place or the resistance of the heating part becomes insta bil, since between the metal and the insulating ceramic (especially on the Metal side) a reaction layer is formed like a tungsten silicide layer. Because of the manufacturing problems described above, the temperature at Sintering of the ceramics can not be increased so much, and the ceramics is under Ver sintered using a hot press.

Even in hot press sintering, the maximum sintering temperature is at most 1,750 ° C. If the ceramic is sintered at a higher temperature, the Form a reaction layer such as a tungsten silicide layer between the Me tall and the insulating ceramic confirmed.

It is difficult to get silicon nitride based ceramics at 1,750 ° C or less sintering unless the amount of sintering aid is increased or low melting sintering aids can be selected. If the amount of sintering aids is increased or the low-melting auxiliary is selected, deteriorate however, the high temperature properties of the silicon nitride-based ceramics. Furthermore, a silicon nitride-based ceramic can be used at 1,750 ° C or less not be completely sintered.

To form a reaction layer such as the above tungsten silicide layer prevent, Japanese Patent Laid-Open No. 61-179084 discloses the structure in which the surface of a resistance heating element made of W (tungsten) or Mo (Molybdenum) is covered with an oxide-free ceramic.  

However, this structure requires an additional step of covering the upper area of the resistance heating element with the oxide-free ceramic, resulting in high Manufacturing costs leads. It is also difficult to achieve that the surface surface of the spiral W is uniformly covered with an oxide-free ceramic.

Summary of the invention

It is an object of the present invention to provide the ceramic heater in which a reaction layer on a high-melting metal can be prevented and the resistance of a refractory metal is kept stable, and a To provide methods of making the same.

It is another object of the present invention to provide a ceramic heater device that can be easily manufactured at low cost, and a method for Manufacture to deliver same.

In order to achieve the above objects, according to the invention, a ceramic heater Device supplied with a heating element made of a material that is high contains melting metal with a melting point of 2,000 ° C or more, and a material including an inorganic conductor is formed, and one sintered body made of an insulating ceramic, one of silicon nitride and Contains silicon carbide materials, with the heating element in the sintered body is embedded, the insulating ceramic comprising at least one type of nitride that of groups IIIA, IVA and VA in a periodic table of the elements in one Ratio of 0.01 vol .-% to 10 vol .-% contains.

Brief description of the drawings

Fig. 1 is a sectional view showing a ceramic heater according to an embodiment of the present invention;

Fig. 2 is a sectional view showing another structure of the ceramic Heizvor direction in Fig. 1;

FIG. 3 is an exploded view showing yet another structure of the ceramic heater in FIG. 1;

Fig. 4 is a sectional view showing still another structure of the ceramic heater in Fig. 1; and

Fig. 5 is a sectional view showing still another structure of the ceramic heater in Fig. 1.

Description of the preferred embodiment

The present invention will be carried out with reference to the accompanying drawings Lich described.

Fig. 1 shows a ceramic heater according to an embodiment of the prior invention. In Fig. 1, there is a ceramic heater 10 from egg NEM heating element 11 made of a high-melting metal with a melting point of 2,000 ° C or more, lines 12 and 13 which are connected to the two ends of the heating elements 11 and made of a high-melting metal a melting point of 2,000 ° C or more, and a sintered body by 14 made of an insulating ceramic based on silicon nitride or silicon carbide. The heating element 11 and the lines 12 and 13 are embedded in the sintered body 14 made of the insulating ceramic. The structure shown in FIG. 1 is a ceramic heater in a glow plug disclosed in, for example, Japanese Utility Model Laid-Open No. 61-115857, and a detailed description thereof is omitted.

According to the present invention, a hochschmel shielded tungsten halogen metal as described above, having a melting point of 2,000 ° C or more element than the Heizele 11 and the lines 12 and 13 are used, and the heating element 11 and the lines 12 and 13 are in the sintered Body 14 made of an insulating ceramics based on silicon nitride or silicon carbide embedded, whereby the ceramic heater 10 is produced. During production, at least one type of nitride from groups IIIA, IVA and VA of the periodic table of the elements is contained in an insulating ceramic powder based on silicon nitride or silicon carbide in a proportion of 0.01% by volume to 10% by volume, and is sintered at a temperature higher than, for example, 1,750 ° C. Under these sintering conditions, a reaction layer on the high-melting metal can be reduced to a cross-sectional thickness of 20 μm or less (0 to 20 μm). The reaction layer is desirably 0 µm, ie it is not formed. However, the reaction layer with a thickness of 20 µm or less does not pose any problems in practical use.

This point is explained in more detail below. That is, the metal constituting the heating element 11 and the leads 12 and 13 must be a refractory metal having a melting point of 2,000 ° C or more, and preferably 2,200 ° C or more, in order to cause the heating element 11 to while of heating by the heater to generate heat of 1,400 ° C or more, and to set the sintering temperature higher than 1,750 ° C. Examples of this refractory metal are W, Mo, Nb (niobium), Hf (hafnium) and Ir (iridium). The melting point of W is 3,400 ° C and that of Mo is 2,617 ° C.

In this case, the sintered body based on silicon nitride is produced from an insulating ceramic which contains silicon nitride (Si ₃ N ₄ ) as the main component, ie a ceramic based on silicon nitride which contains so-called sintering aids. Silicon nitride contains an inevitable impurity such as oxygen, which has been mixed in the manufacturing process or the like. Preferably used silicon nitride has a high purity from the viewpoint of sintering properties, migration and the like. Known sintering aid systems which are represented by an yttrium oxide-aluminum oxide system, an yttrium oxide system or an ytterium oxide system can be used. With regard to the high-temperature oxidation resistance and the high-temperature strength, sintering aids based on yttrium oxide or ytterbium oxide are preferably used.

Silicon nitride decomposes (sublimed) at around 2,000 ° C. The Sin mentioned above The temperature is 1,750 ° C or more, which must be lower than the Subli mation temperature. Of course, the sintering temperature must be lower than the melting temperature of a metal used.

In this case, the sintered body based on silicon carbide is isolated from an isolie ceramics that contain silicon carbide (SiC) as the main component, d. H. a ceramic based on silicon carbide, which contains so-called sintering aids. Silicon carbide preferably used has from the point of view of Sin  tere properties, migration and the like a high purity. Known Sin Auxiliary systems by an alumina system or a boron carbon system can be used.

Silicon carbide is known to decompose (sublime) at about 2,400 ° C. The sintering temperature is preferably set lower than the decomposition temperature, e.g. B. to about 2,100 to 2,200 ° C. The sinter must also be carried out at the same time temperature should be lower than the melting point of the metal.

The present applicant found that even when a ceramic was sintered at a temperature greater than 1750 ° C, by including a Group IIIA, IVA or VA nitride in the periodic table of the elements in an insulating ceramic on silicon nitride or silicon carbide Based on a proportion of 0.01 vol.% To 10 vol.%, A reaction layer on a high-melting metal can be reduced to a cross-sectional thickness of 20 μm or less. The present invention uses this to manufacture the ceramic heater 10 in which the refractory metal is embedded in the insulating ceramic.

It is believed that the advantage described above is obtained because the Group IIIA, IVA or VA nitride decomposition (sublimation) of silicon nitride or Prevents silicon carbide and reacts with the refractory metal, i. H. Sili cification, prevented.

Examples of the group IIIA, IVA and VA nitrides are NdN, YN, TiN, ZrN, NbN and TaN. One or more types of nitrides can be obtained from these examples be chosen as you like. According to the experiment, TaN was able to have the thinnest reaction form a layer on a high-melting metal.

If the Group IIIA, IVA or VA nitride content is less than 0.01 vol. %, the reaction layer becomes thicker than 20 µm. Results of various experiments elements showed that when the reaction layer becomes thicker than 20 µm, in the The sintered body produced from the insulating ceramic shows microcracks. When this sintered body is used as a ceramic heater the durability is very low.

If the content of the nitride is more than 10% by volume or more, the oxidation resistance of the sintered body itself decreases. When this sintered body is used as a ceramic heater, the durability becomes poor. Regarding the oxidation resistance, an oxidation test was carried out in the atmosphere at 1400 ° C for 144 hours, and it was found that the properties of the ceramic heater were disadvantageous when the weight gain by oxidation was larger than 1.5 mg / cm ² .

According to these results, the content must be 0.01 vol% to 10 vol%. Taking into account the oxidation resistance and the high temperature resistance The content is preferably about 1% by volume.

More specifically, when the group IIIA, IVA or VA nitride is contained in the periodic table of the elements in the insulating ceramic based on silicon nitride or silicon carbide in a proportion of 0.01% by volume to 10% by volume, the reaction layer can be reduced to 20 µm or less cross-sectional thickness on the refractory metal. Accordingly, the resistance of the heating element 11 and the lines 12 and 13 made of the refractory metal is stabilized, and the sintered body 14 does not break, resulting in a long service life of the ceramic heater 10 . This can be understood to mean that the Group IIIA, IVA or VA nitride prevents decomposition of silicon nitride or silicon carbide and prevents reaction with the refractory metal, ie silicification.

According to the present invention, since the ceramic can be sintered at a temperature higher than 1750 ° C, sintering aids based on yttrium and ytterbi um, which are difficult to sinter at about 1700 ° C, can be contained in the sintered body based on silicon nitride be used. Therefore, the ceramic heater 10 , which has excellent high temperature properties and oxidation resistance, can be obtained by sintering. Conventionally, a high-melting metal cannot be embedded and sintered in the silicon carbide-based sintered body. In the present invention, however, since reaction with the refractory metal can be prevented, the silicon carbide material can be sintered at a high temperature.

The sintering temperature of the insulating ceramic must be a temperature that is higher than 1,750 ° C, decomposition (sublimation) of silicon nitride or silicon carbide ver prevents and is lower than the melting point of the refractory metal.  

It should be noted that the present invention is not limited to that described above Embodiment is limited. The shape, structure and the like of the glow plug ze, which is not fully set out, and those of each part in the glow Ceramic heater used can be suitably modified and to be changed.

For example, the ceramic heater may have a conventional shape and structure that is well known. Fig. 2 shows the ceramic heater 10 , in which a U-shaped heating element 11 'made of a material including an inorganic conductive material is embedded in the distal end, and the lines 12 and 13 made of refractory metal, which of the go out at both ends of the heating element 11 ', in which sintered body 14 are embedded from an insulating ceramic. In this case, the same effect as that of the ceramic heater in Fig. 1 can be obtained by forming the leads 12 and 13 from a refractory metal.

Fig. 3 shows the ceramic heater of a glow plug, which is disclosed, for example, in Japanese Patent Laid-Open No. 59-230285. In this case, the ceramic heater is formed by sandwiching the heating element 11 and the lines 12 and 13 made of a high-melting metal between annealed (semi-sintered) bodies 14 a and 14 b made of a ceramic powder and sintering the entire structure. Even in the ceramic heater 10 having this structure, the same effect as that of the ceramic heater in Fig. 1 can be obtained.

Fig. 4 shows the ceramic heater 10 , are connected to the control heating elements 15 and 16 for controlling the temperature of the heating element 11 made of a high-melting metal between the heating element 11 and the lines 12 and 13 made of a high-melting metal. The structure obtained was embedded in the sintered body 14 made of an insulating ceramic. The ceramic heater 10 having this structure is disclosed, for example, in Japanese Patent Laid-Open No. 58-110919. The same effect as that of the ceramic heater in Fig. 1 can be obtained.

Fig. 5 shows the ceramic heater 10 having the same structure as that in Fig. 4, which is disclosed in, for example, Japanese Patent Laid-Open No. 4-257615. The ceramic heater shown in FIG. 5 also has the same effect as that of the ceramic heater in FIG. 1.

example 1

Table 1 shows an example in which insulating ceramics based on silicon nitride were sintered using a hot press.  

Table 1

Table 1 shows the example in which the types and amounts of sintering aids have been modified, and at least one type of group IIIA, IVA and nitrides VA of the Periodic Table of the Elements was used. Table 1 also shows that Thickness of reaction layers on refractory metals at that time point and the oxidation weight increases per unit area at a 144 h long oxidation test in the air at 1,400 ° C. The relative densities were through the Archimedes process after removing the embedded melt metals found.

Example 2

Table 2 shows an example in which insulating ceramics based on silicon carbide were sintered using a hot press.  

Table 2

In example 2, the types and amounts of sintering aids and nitrides were changed of Groups IIIA, IVA and VA in the Periodic Table of the Elements were used. Table 2 shows the thicknesses of the reaction layers on refractory metals at this time and the oxidation weight increases per unit area a 144 h long oxidation test in the atmosphere at 1400 ° C.

Example 3

230 g silicon nitride, 20 g yttrium oxide, 10.5 g TaN and a silicon nitride ball were placed in a silicon nitride jar and using acetone for 24 h long mixed. A slurry formed by mixing was applied for 24 hours Dried to room temperature and ground in a mortar to contain a TaN of the ceramic powder based on silicon nitride. Using this A columnar raw body was obtained from the powder by a uniaxial press provides a W-coil (tungsten-coil) with a purity of 99.95% and egg Embed a diameter of 0.2 mm in the middle. Gas pressure sintering was used 1,650 ° C to 1,950 ° C, a step size of 50 ° C and a pressure of 0.93 MPa executed. Table 3 shows the densities in the sintered body, the thicknesses of the Reaction layers on the W coil and the oxidation weight increases pro Unit area during a 144 h long oxidation test in the atmosphere 1,400 ° C.

Table 3

Example 4

Similar to Example 3, a silicon nitride-based ceramic powder containing TaN became produced. A W wire with a purity of 99.95% and a diameter water of 0.2 mm was attached to a U-shaped heating element (sintered body), the 33 Vol .-% TiN and the rest of ceramic based on silicon nitride, connected. The structure obtained was transferred to the pulp produced by a uniaxial press  embedded to form three columnar raw bodies. After that was a pressureless sintering at 1,850 ° C. The relative densities were 97.9%, 97.4% and 98.1%, respectively.

A sintered body with a relative density of 97.9% underwent a 144 h long oxidation test in the atmosphere at 1,400 ° C. The oxidation weight gain at this time was 0.7 mg / cm ² . A sintered body with a specific gravity of 97.4% was cut, embedded in a resin and polished. The thickness of a reaction layer was observed using a scanning electron microscope (SEM) with an energy dispersion X-ray analyzer (EDX). Based on the analysis of the EDX, a section in which both W and Si were present was defined as a reaction layer. The thickness was a uniform 8 µm. A sintered body with a specific gravity of 98.1% was processed to form a lead section. A metal case was attached to the sintered body to make a glow plug. As characteristics of the glow plug, the rise time to 800 ° C was 3.3 s and the saturation temperature was 1430 ° C.

Example 5

230 g silicon nitride, 15 g yttrium oxide, 10 g TaN and a silicon nitride ball were placed in a silicon nitride jar and using isopropyl alcohol 24 mixed for h. A slurry formed by mixing was applied for 24 hours Dried to room temperature and ground in a mortar to contain a TaN of the ceramic powder based on silicon nitride. Using this A columnar raw body was obtained from the powder by a uniaxial press represents a W coil with a purity of 99.95% and a diameter of 0.2 mm in the middle. The resulting structure was at 1,850 ° C hot pressed.

The same evaluation as in Example 4 was carried out. The thickness of a reaction layer was 8 μm, and the oxidation weight gain in a 144 h long oxidation test in the atmosphere at 1400 ° C. was 0.5 mg / cm ² . A glow plug was manufactured using this sintered body. As a feature of the glow plug, the rise time to 800 ° C was 3.0 s, and the saturation temperature was 1,450 ° C.

As described above, according to the present invention, a becomes high melting metal with a melting point of 2,000 ° C or more or materi al, which includes an inorganic conductor as the material of the heating element used. A high-melting metal with a melting point of 2,000 ° C or more is used as the wiring material. When embedding the heater and the line in a sintered body made of an insulating ceramic silicon nitride or silicon carbide-based is in the insulating ceramic powder based on silicon nitride or silicon carbide at least one type of nitrides Groups IIIA, IVA and VA of the Periodic Table of the Elements in a proportion of Contain 0.01 vol .-% to 10 vol .-%. The structure obtained is at a tempera higher than 1,750 ° C (e.g. about 1,800 ° C for silicon nitride and about 2,100 ° C to 2,200 ° C for silicon carbide) sintered. As a result, a reaction layer can build up the refractory metal to a thickness of 20 µm or less (0 to 20 µm) are formed. Because of this, the following can be excellent Effects are achieved.

That is, decomposition of silicon nitride or silicon carbide can occur during sintering Ceramic heater can be prevented from reacting with the melting the metal like silicification (formation of a reaction layer like a tungsten sili cid layer) can be prevented, and the reaction layer on the high melting metal can re to a cross-sectional thickness of 20 microns or less be reduced. Therefore the resistance of the heating element and the line, which are each made of the high-melting metal, are stabilized. Since the insulating ceramic does not break, the operating time of the heating element can be extended be extended.

Because the ceramic heater at a temperature of more than 1,750 ° C can be sintered, as described above, can be made in the sintered body for example, an insulating ceramic based on silicon nitride, an yttrium oxide system or an ytterbium oxide system as a sintering aid which is difficult to sinter  be applied. Accordingly, one formed from the sintered body Heating element can be obtained, the high temperature properties and Resistance to oxidation is excellent. In a sintered body from one insulating ceramic based on silicon carbide can be the high-melting metal not embedded in the conventional way and sintered at more than 1,750 ° C the. According to the present invention, however, since reaction with the high melting metal can be prevented, the ceramic based on silicon carbide be sintered at high temperature.

In particular, as for one made from an insulating ceramic sintered ceramic body, forming a reaction layer like a wolf ramsilicid layer on an embedded portion of a high-melting Me talls can be prevented, the resistance can be kept stable, and the sin temperature can be set higher. Because of this, sinters tools that cannot be sintered in a conventional manner at 1,700 ° C, can be used, and the amount of sintering aids can be reduced. A Heating element made of a ceramic based on silicon carbide with a high sintering temperature temperature can also be produced. In addition, pressureless sintering or Gas pressure sintering can be carried out.

Claims (8)

1. Ceramic heater, characterized in that it comprises:
a heating element ( 11 , 11 ') formed from a material containing a refractory metal having a melting point of not less than 2,000 ° C and an inorganic conductive material; and
a sintered body ( 14 ) made of an insulating ceramic containing one of silicon nitride and silicon carbide materials, said heating element being embedded in said sintered body,
wherein the insulating ceramic contains at least one type of nitrides of groups IIIA, IVA and VA in a periodic table of the elements in a proportion of 0.01 vol.% to 10 vol.%. 2. A heater according to claim 1, wherein said ceramic heater direction by sintering a powder of the insulating ceramic, in which said Heating element is embedded, formed at a temperature higher than 1,750 ° C becomes. 3. The heater of claim 1, further comprising:
a pair of leads ( 12 , 13 ) connected to two end portions of said heating elements and made of a refractory metal having a melting point of not less than 2,000 ° C, and wherein said heating element and said leads are embedded in said sintered body. 4. The heater of claim 3, further comprising:
a pair of control heaters ( 15 , 16 ) connected between said heater and end portions of said conduits and made of a refractory metal having a melting point of not less than 2,000 ° C to control a temperature of said heater, and
said heating element, said control heating elements and said lines are embedded in said sintered body. 5. A method of manufacturing a ceramic heater, characterized in that it comprises the steps of:
Forming at least one heating element ( 11 , 11 ') using a material containing a high-melting metal with a melting point of not less than 2,000 ° C. and an inorganic conductive material,
Embedding said heating element and a pair of leads ( 12 , 13 ) connected to two ends of said heating element in an insulator of the ceramic powder, one of silicon nitride and
Contains silicon carbide materials, wherein the insulating ceramic powder contains at least one type of nitrides of groups IIIA, IVA and VA in a periodic table of the elements in a proportion of 0.01 vol% to 10 vol%; and sintering the insulating ceramic powder in which said heating element and said lines are embedded. 6. The method of claim 5, wherein the step of embedding said heater and conduits comprises the steps of:
Containing at least one kind of group IIIA, IVA and VA nitrides of the periodic table of the elements in the insulating ceramic powder in a proportion of 0.01 vol% to 10 vol%; and
Embedding said heating element and said lines in the insulating ceramic powder containing the nitride. 7. The method of claim 5, wherein the step of sintering the isolate the ceramic powder the step of sintering the insulating Ceramic powder, embedded in said heating element and said lines are included, at a temperature higher than 1,750 ° C. The method of claim 5, further comprising the step of forming Lines made of a high-melting metal with a melting point of not less than 2,000 ° C.