JP2007335397A - Ceramic heater and glow plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic heater that can prevent corrosion by calcium component, while preventing defects such as a crack or the like resulting from thermal stress. <P>SOLUTION: A glow plug comprises a main clasp 2, a ceramic heater 4 and the like. The ceramic heater 4 has a base substrate 21 having a round-bar shape and extending in the direction of an axis in which a heating element 22 elongated in a horseshoe shape is held buried. The heating element 22 has at least one of silicide, nitride and carbide of molybdenum, and silicide, nitride and carbide of tungsten as a principal component. The base substrate 21 comprises silicon nitride as a principal component, rare earth component in an amount of 4 to 25% by mass, calculated as an oxide equivalent, chromium component in an amount of 1 to 8% by mass, calculated as a chromium silicide equivalent and aluminum component in an amount of 0.02 to 1.0% by mass, calculated as a nitride aluminum equivalent. The aluminum component suppresses erosion of the base substrate due to calcium component or the like included in engine oil. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, a heating element mainly composed of at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide is contained in a substrate mainly composed of silicon nitride. The present invention relates to an embedded ceramic heater and a glow plug including the ceramic heater.

  2. Description of the Related Art Conventionally, glow plugs used for diesel engine start-up assistance and the like include a cylindrical metal shell, a rod-shaped center shaft, a heater containing a heating element that generates heat when energized, an insulating member, an outer cylinder, and a caulking member. As a glow plug in recent years, a metal glow plug using a metal sheath heater as a heater and a ceramic glow plug using a heater as a ceramic heater are appropriately selected and used from the viewpoint of performance and cost required for a diesel engine.

  By the way, this ceramic glow plug generally has the following configuration. That is, a central shaft with one end projecting toward the rear end is disposed on the inner peripheral side of the metal shell, and a round bar-shaped ceramic heater is disposed on the front end side of the central shaft. An outer cylinder is joined to the tip of the metal shell, and a ceramic heater is held by the outer cylinder. On the other hand, on the rear end side of the metallic shell, an annular insulating member is inserted into the gap between the central shaft and the metallic shell, and a caulking member is provided on the rear end side of the insulating member so as to fix the central shaft.

  The ceramic heater is configured such that a heating element made of conductive ceramic is embedded and held in a base made of insulating ceramic. In recent years, various studies have been conducted on materials constituting the heating element and the base so as to withstand use under higher temperature conditions. For example, it is conceivable to employ a material mainly comprising at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide as a material constituting the heating element. ing. On the other hand, a material mainly composed of silicon nitride is known as a material constituting the substrate.

However, in general, the material constituting the heating element tends to have a larger thermal expansion coefficient than the material constituting the base. And if the difference in thermal expansion coefficient between the two is large, for example, the amount of thermal shrinkage will greatly differ in the process from the high temperature state to the cooling state, and the base will crack due to thermal stress, etc. There is a risk. In view of this, there is a technique in which a metal carbide such as tungsten carbide having a larger thermal expansion coefficient is contained in the material constituting the base in order to bring the thermal expansion coefficient of the base closer to the thermal expansion coefficient of the heating element (for example, Patent Document 1). Etc.).
Japanese Patent Laid-Open No. 10-25162

  However, although the above technique can suppress the occurrence of cracks due to the difference in thermal expansion coefficient, the following problems still remain. That is, engine oil is interposed in the engine to lubricate the contact surfaces between metals and reduce friction, and engine oil may enter the cylinder bore due to a malfunction of the piston ring. In this case, engine oil may adhere to the tip portion of the ceramic heater, and the base portion at the tip of the ceramic heater may be corroded by a calcium component or the like in the oil. Moreover, there is a risk of corrosion not only due to the adhesion of oil but also due to an air-fuel mixture or combustion gas containing oil components. And if corrosion progresses, a heat generating body will be exposed and oxidation will advance and there exists a possibility that the function of a glow plug may be impaired.

  Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to prevent a malfunction such as a crack caused by thermal stress and to prevent corrosion due to a calcium component or the like in oil. Is to provide.

  Hereinafter, each configuration suitable for solving the above-described problems will be described in terms of items. In addition, the effect etc. peculiar to the structure which respond | corresponds as needed are added.

Configuration 1. In the ceramic heater of this configuration, the heating element mainly composed of at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide is mainly composed of silicon nitride. A ceramic heater embedded in a substrate,
The substrate is
4 to 25% by mass of the rare earth component in terms of oxide,
While containing 1-8 mass% of chromium silicide in terms of chromium silicide,
The aluminum component is contained in an amount of 0.02 to 1.0% by mass in terms of aluminum nitride.

  Here, the “main component” refers to a component having the highest mass ratio in the material. Examples of the “rare earth component” include erbium (Er), ytterbium (Yb), yttrium (Y), and the like. The phrase “rare earth component in terms of oxide” is based on the fact that the present inventors use rare earth oxide as a raw material in the process of conceiving the present invention. Therefore, it does not mean that the rare earth component must always remain as an oxide.

In addition, chromium silicides include not only pure (narrowly defined) chromium silicide (CrSi ₂ ), but also chromium silicides such as solid solutions of chromium and tungsten silicides and solid solutions of chromium and vanadium silicides. The idea is that it only has to be. “Chromium silicide in terms of chromium silicide” is based on the fact that the inventors mainly use chromium silicide (CrSi ₂ ) as a raw material in the process of conceiving the present invention. is there. Therefore, it is desirable that “almost all of the added chromium component remains as silicide”, but only pure chromium silicide (CrSi ₂ ) must remain as chromium silicide. Absent.

Furthermore, “the aluminum component in terms of aluminum nitride” means that, as described above, in the process that the inventors have conceived of the present invention, the raw material is not alumina (Al ₂ O ₃ ) alone but aluminum nitride (AlN ) Is mainly used.

According to the above configuration 1, the heating element is mainly composed of at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide, and the base is mainly silicon nitride. Since it is a component, it can withstand use under higher temperature conditions (eg, 1200 ° C. or higher). Moreover, the base body of the ceramic heater of Configuration 1 contains 4 to 25% by mass of a rare earth component in terms of oxide. It is more desirable that “a rare earth component is contained in an amount of 4 to 15% by mass in terms of oxide”. This not only improves the sinterability when firing the ceramic heater, but also improves the thermal expansion coefficient of the substrate. Therefore, there is an advantage that the difference in thermal expansion coefficient between the heating element and the substrate can be reduced, and the occurrence of cracks due to thermal stress can be prevented. On the other hand, when the content of the rare earth component in terms of oxide is less than 4% by mass, there is a possibility that sintering does not occur well during firing. In addition, the improvement of the thermal expansion coefficient cannot be expected, and there is a risk that cracks may occur due to thermal stress. On the other hand, when the content of the rare earth component in terms of oxide exceeds 25% by mass, the thermal expansion coefficient is improved, but the rare earth element (RE), silicon (Si), nitrogen (N), and oxygen (O). The grain boundary crystal phase composed of the above is generated, and the oxidation resistance is lowered due to the presence of the crystal phase. Examples of such crystal phases include J phase (Er ₄ Si ₂ N ₂ O ₇ ), H phase (Er ₂₀ Si ₁₂ N ₄ O ₄₈ ), melilite phase (Er ₂ Si ₃ N ₄ O ₃ ) and the like. Can be mentioned.

  Further, the base body of the ceramic heater of Configuration 1 contains 1 to 8% by mass of chromium silicide in terms of chromium silicide. More preferably, it is “containing chromium silicide of 1.5 to 5% by mass in terms of chromium silicide”. Thereby, the thermal expansion coefficient of the substrate can be improved, and the difference in thermal expansion coefficient between the heating element and the substrate can be reduced. On the other hand, when the content of chromium silicide is less than 1% by mass in terms of chromium silicide, improvement of the thermal expansion coefficient cannot be expected, and cracks may occur due to thermal stress. On the other hand, if the chromium silicide content exceeds 8% by mass in terms of chromium silicide, the chromium component may aggregate. As a result, the coefficient of thermal expansion varies depending on the part, which may cause a decrease in strength.

  Furthermore, the ceramic heater substrate of Configuration 1 contains 0.02 to 1.0% by mass of an aluminum component in terms of aluminum nitride. It is more desirable that “the aluminum component is contained in an amount of 0.02 to 0.8% by mass in terms of aluminum nitride”. Thereby, the corrosion of the base | substrate by the calcium component etc. which are contained in engine oil is suppressed. On the other hand, when the content of the aluminum component is less than 0.02% by mass in terms of aluminum nitride, the corrosion inhibiting effect of the substrate cannot be sufficiently obtained. On the other hand, when the content of the aluminum component exceeds 1.0% by mass in terms of aluminum nitride, the strength of the substrate at a high temperature decreases. In addition, since the aluminum component is contained in the above specified amount, the aluminum component diffuses in the heating element during the firing process, and it becomes easy to match the sintering behavior of the heating element and the substrate, and as a result, in the sintering process. Can be further suppressed. In addition, the resistance value can be stabilized. In addition, the effect mentioned above is more reliably show | played by setting it as the structure "at least the surface (surface layer) site | part of the said base | substrate contains 0.02-1.0 mass% of aluminum components in conversion of aluminum nitride." It will be.

Configuration 2. In the ceramic heater of this configuration, the heating element mainly composed of at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide is mainly composed of silicon nitride. A ceramic heater embedded in a substrate,
The substrate is
4 to 25% by mass of rare earth oxide,
While containing 1-8% by mass of chromium silicide,
An aluminum component is contained in an amount of 0.2 to 1.0% by mass in terms of aluminum nitride.

  Here, the “main component” refers to a component having the highest mass ratio in the material. Examples of the “rare earth oxide” include oxides of erbium (Er), ytterbium (Yb), and yttrium (Y). The phrase “4 to 25% by mass of the rare earth oxide” is based on the fact that the inventors have used rare earth oxide as a raw material in the process conceived by the present inventors. The component is almost synonymous with 4 to 25% by mass in terms of oxide.

In addition, the term “chromium silicide” in Configuration 2 is not only pure (narrowly defined) chromium silicide (CrSi ₂ ), but also chromium silicides such as a solid solution of chromium and tungsten silicide and a solid solution of chromium and vanadium silicide. In other words, it means “chrome silicide” in a broad sense. That is, “1 to 8% by mass of chromium silicide” is based on the fact that chromium silicide (CrSi ₂ ) is mainly used as a raw material in the process of the inventors conceiving the present invention as described above. It is. Therefore, it is desirable that “almost all of the added chromium component remains as silicide”, but this does not necessarily mean that only pure chromium silicide (CrSi ₂ ) must remain. Therefore, “1-8% by mass of chromium silicide” is almost synonymous with “1-8% by mass of chromium silicide in terms of chromium silicide”.

Furthermore, “the aluminum component in terms of aluminum nitride” means that, as in the case of the above-described configuration 1, in the process that the inventors have conceived of the present invention, the raw material is not alumina (Al ₂ O ₃ ) alone. This is based on the fact that aluminum nitride (AlN) is mainly used.

According to the configuration 2, the heating element is mainly composed of at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide, and the base is mainly silicon nitride. Since it is a component, it can withstand use under higher temperature conditions (eg, 1200 ° C. or higher). Moreover, the base body of the ceramic heater of Configuration 2 contains 4 to 25% by mass of rare earth oxide. More desirably, it is “containing 4 to 15% by mass of rare earth oxide”. This not only improves the sinterability when firing the ceramic heater, but also improves the thermal expansion coefficient of the substrate. Therefore, there is an advantage that the difference in thermal expansion coefficient between the heating element and the substrate can be reduced, and the occurrence of cracks due to thermal stress can be prevented. On the other hand, when the content of the rare earth oxide is less than 4% by mass, there is a possibility that sintering does not occur well during firing. In addition, the improvement of the thermal expansion coefficient cannot be expected, and there is a risk that cracks may occur due to thermal stress. On the other hand, when the content of the rare earth oxide exceeds 25% by mass, the thermal expansion coefficient is improved, but it is composed of rare earth elements (RE), silicon (Si), nitrogen (N), and oxygen (O). A grain boundary crystal phase is generated, and the oxidation resistance decreases due to the presence of the crystal phase. Examples of such crystal phases include J phase (Er ₄ Si ₂ N ₂ O ₇ ), H phase (Er ₂₀ Si ₁₂ N ₄ O ₄₈ ), melilite phase (Er ₂ Si ₃ N ₄ O ₃ ) and the like. Can be mentioned.

  Further, the base of the ceramic heater of Configuration 2 contains 1 to 8% by mass of chromium silicide (chromium silicide in terms of chromium silicide). It is more desirable that “chromium silicide is contained in an amount of 1.5 to 5% by mass”. Thereby, the thermal expansion coefficient of the substrate can be improved, and the difference in thermal expansion coefficient between the heating element and the substrate can be reduced. On the other hand, when the content of chromium silicide is less than 1% by mass, an improvement in the thermal expansion coefficient cannot be expected, and cracks may occur due to thermal stress. On the other hand, when the content of chromium silicide exceeds 8% by mass, the chromium component may be aggregated. As a result, the coefficient of thermal expansion varies depending on the part, which may cause a decrease in strength.

  Furthermore, the base body of the ceramic heater of Configuration 2 contains 0.2 to 1.0% by mass of an aluminum component in terms of aluminum nitride. It is more desirable that “the aluminum component is contained in an amount of 0.3 to 0.8 mass% in terms of aluminum nitride”. Thereby, the corrosion of the base | substrate by the calcium component etc. which are contained in engine oil is suppressed. On the other hand, when the content of the aluminum component is less than 0.2% by mass in terms of aluminum nitride, there is a possibility that the corrosion inhibition effect of the substrate cannot be sufficiently obtained. On the other hand, when the content of the aluminum component exceeds 1.0% by mass in terms of aluminum nitride, the strength of the substrate at a high temperature decreases. In addition, since the aluminum component is contained in the above specified amount, the aluminum component diffuses in the heating element during the firing process, and it becomes easy to match the sintering behavior of the heating element and the substrate, and as a result, in the sintering process. Can be further suppressed. In addition, the resistance value can be stabilized. In addition, the effect mentioned above is more reliably show | played by setting it as the structure "at least the surface (surface layer) site | part of the said base | substrate contains 0.2-1.0 mass% of aluminum components in conversion of aluminum nitride." It will be.

  Configuration 3. The ceramic heater according to this configuration is characterized in that, in the above configuration 1, the substrate includes at least one of a solid solution of silicide of chromium and tungsten and a solid solution of silicide of chromium and vanadium.

As in the configuration 3, it is desirable that the base body contains at least one of chromium and tungsten silicide solid solution (CrW) Si and chromium and vanadium silicide solid solution (CrV) Si. The inclusion of such a solid solution means that a situation in which the chromium component aggregates at the interface between the heating element and the substrate does not occur so much. That is, in the ceramic heater including the solid solution as in the configuration 3, the occurrence of unevenness of the thermal expansion coefficient due to the aggregation of the chromium component can be suppressed, and the effect of preventing the strength of the base from being lowered can be achieved. In addition, since the solid solution is included as in the configuration 3, the thermal expansion coefficient is easily increased. In this sense, the solid solution of chromium and tungsten silicide (CrW) Si, the solid solution of chromium and vanadium silicide (CrV) Si, etc. are made of chromium rather than the case where only pure chromium silicide (CrSi ₂ ) remains. It is more desirable that it exists as a silicide. In order to configure as described above, tungsten silicide (WSi ₂ ) or vanadium silicide (VSi ₂ ) is added to the material constituting the substrate in the ceramic heater manufacturing process (powder mixing process before firing, etc.). It is desirable to add. Thus, by adding tungsten silicide or vanadium silicide, the above solid solution is formed during firing.

  Configuration 4. The ceramic heater of this configuration is characterized in that, in any one of configurations 1 to 3, a crystal phase composed of rare earth elements, silicon, nitrogen and oxygen does not exist on the surface of the base.

  As described above, when a grain boundary crystal phase composed of rare earth elements, silicon, nitrogen and oxygen is present, particularly when the grain boundary crystal phase is present on the surface of the substrate, the surface layer of the substrate is oxidized, There is concern about weakening, and in particular, the oxidation resistance at a high temperature of 1000 ° C. or higher is inferior. In this regard, according to the configuration 4, since the grain boundary crystal phase composed of rare earth elements, silicon, nitrogen and oxygen does not exist on the surface, it is difficult for the surface to be oxidized, resulting in oxidation resistance. Can be improved. Here, the surface (the same applies to the “surface” described in the “notes” in the sections 1 and 2) is specifically a ceramic heater that can be analyzed using a predetermined X-ray analyzer. (More specifically, refer to [Best Mode for Carrying Out the Invention] described later).

  Configuration 5. The ceramic heater of this configuration is characterized in that, in any one of the above configurations 1 to 4, at least one of a rare earth element monosilicate crystal phase and a rare earth element disilicate crystal phase is present on the substrate. .

The point that it is better not to have a crystal phase composed of rare earth elements, silicon, nitrogen and oxygen on the surface of the substrate has already been described in the configuration 4. On the other hand, as in the configuration 5, the substrate has a rare earth element. More preferably, a monosilicate crystal phase or a rare earth disilicate crystal phase exists. The presence of such a crystal phase improves the heat resistance and can improve the strength of the substrate under high temperature conditions. Examples of the rare earth element monosilicate crystal phase include Er ₂ SiO ₅ , and examples of the rare earth element disilicate crystal phase include Er ₂ Si ₂ O ₇ .

  Configuration 6. In the ceramic heater of this configuration, in any one of the above configurations 1 to 5, the substrate contains 2 to 10% by volume of silicon carbide.

  According to the configuration 6, since the substrate contains 2 to 10% by volume of silicon carbide, not only the sinterability at the time of firing the ceramic heater is improved, but also the thermal expansion coefficient of the substrate is improved. The difference in thermal expansion coefficient between the heating element and the substrate can be reduced. On the other hand, when the content of silicon carbide is less than 2% by volume, it is difficult to improve the thermal expansion coefficient, and it is difficult to improve the high-temperature strength. Moreover, when content of silicon carbide exceeds 10 volume%, there exists a possibility that the improvement of the sinterability at the time of baking may become insufficient, and there exists a possibility of causing the fall of insulation.

  Further, from the point of aiming at matching in the sintering process, the following configuration is desirable.

Configuration 7. In the ceramic heater of this configuration, the thermal expansion coefficient of the substrate is 3.3 × 10 ⁻⁶ / ° C. or higher and 4.0 × 10 ⁻⁶ / ° C. or lower in any of the above configurations 1 to 6. Features.

In general, the thermal expansion coefficient of a heating element mainly composed of at least one of molybdenum silicide, nitride and carbide and tungsten silicide, nitride and carbide is 3.7 × 10 ⁻⁶ / It is often about from ℃ to 3.8 × 10 ^-6 / ℃. On the other hand, when the thermal expansion coefficient of the substrate is 3.3 × 10 ⁻⁶ / ° C. or higher and 4.0 × 10 ⁻⁶ / ° C. or lower as in the configuration 7, There is a merit that the difference in thermal expansion coefficient can be further reduced and the occurrence of cracks due to thermal stress can be prevented more reliably.

  Of course, it is possible to use the ceramic heater as described below.

  Configuration 8. A glow plug comprising the ceramic heater according to any one of configurations 1 to 7.

  As in the configuration 8, by using the ceramic heater to form a glow plug, it is possible to provide a glow plug that does not cause the above-mentioned problems in the ceramic heater.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, an example of a glow plug including a ceramic heater according to the present invention will be described with reference to FIGS. FIG. 1 is a vertical cross-sectional view of the glow plug 1, and FIG. 2 is a partially enlarged cross-sectional view centering on the ceramic heater 4. In FIGS. 1 and 2, the lower side of the drawing will be described as the front end side of the glow plug 1 (ceramic heater 4), and the upper side will be described as the rear end side.

  As shown in FIG. 1, the glow plug 1 includes a metal shell 2, a middle shaft 3, a ceramic heater 4, insulating members 5 and 6, an outer cylinder 7, a caulking member 8, and the like. The metal shell 2 has a substantially cylindrical shape, and a male screw portion 11 for attaching the glow plug 1 to an engine cylinder head (not shown) is formed on the outer periphery of the central portion in the longitudinal direction. A hexagonal hook-shaped tool engaging portion 12 is formed on the outer periphery of the rear end portion of the metal shell 2, and a tool used when the glow plug 1 is screwed to the cylinder head is engaged. It is supposed to be combined.

  On the inner peripheral side of the metal shell 2, the other end of a metal-made round bar-shaped middle shaft 3 with one end protruding toward the rear end side is accommodated. A ring-shaped insulating member 5 is provided between the outer periphery of the intermediate shaft 3 and the inner periphery of the metallic shell 2, and the central axis of the central shaft 3 coincides with the central axis of the metallic shell 2 on the axis C <b> 1. Thus, the middle shaft 3 is fixed. Furthermore, another insulating member 6 is provided in a state where the central shaft 3 is inserted from the rear end side of the metal shell 2. The insulating member 6 includes a cylindrical portion 13 and a flange portion 14, and the cylindrical portion 13 is fitted in a gap between the middle shaft 3 and the metal shell 2. A substantially cylindrical caulking member 8 is fitted to the middle shaft 3 on the upper end side of the insulating member 6. The caulking member 8 is caulked by being pressed from the outer periphery of the body portion in a state where the front end surface thereof is in contact with the flange portion 14 of the insulating member 6. As a result, the insulating member 6 fitted between the middle shaft 3 and the metal shell 2 is fixed, and is prevented from coming off from the middle shaft 3.

  Further, a metal outer cylinder 7 is joined to the front end of the metal shell 2. More specifically, the outer cylinder 7 has a thick portion 15 on the rear end side, and a stepped engagement portion 16 is formed on the outer periphery of the rear end of the thick portion 15. And the inner periphery of the front end of the metal shell 2 is engaged with the engaging portion 16.

  A ceramic heater 4 is provided on the tip side of the middle shaft 3. The ceramic heater 4 includes a base 21 and a heating element 22 (see FIG. 2). That is, the base body 21 has a round bar shape whose tip is processed into a curved surface, and a heating element 22 having an elongated U shape is held in an embedded state therein. As for this ceramic heater 4, the outer periphery of the trunk | drum is hold | maintained by the said outer cylinder 7. FIG. A portion of the ceramic heater 4 on the rear end side of the outer cylinder 7 is housed in the metal shell 2, but the ceramic heater 4 is firmly positioned and fixed by the outer cylinder 7. For this reason, the metal shell 2 is not in contact with the metal shell 2.

  Further, the distal end of the middle shaft 3 is a small diameter portion 17, and the small diameter portion 17 is located at the approximate center in the longitudinal direction of the metal shell 2. In addition, an electrode ring 18 is fitted to the rear end of the ceramic heater 4, and the electrode ring 18 and the small diameter portion 17 of the middle shaft 3 are connected by a lead wire 19, and electrical continuity between the two is achieved. It has been.

  Next, details of the ceramic heater 4 will be described with reference mainly to FIG. The ceramic heater 4 is made of an insulating ceramic, has a round bar-like base body 21 having substantially the same diameter extending in the direction of the axis C1, and an elongated U-shaped heating element 22 made of conductive ceramic is embedded therein. (The material composition of these components will be described in detail later). The heating element 22 includes a pair of rod-shaped lead portions 23 and 24 as conductive portions, and a connecting portion 25 that connects the tip portions of the lead portions 23 and 24. The portion is a heat generating portion 26. The heat generating portion 26 is a part that functions as a so-called heat generating resistor, and has a substantially U-shape corresponding to the curved surface at the tip of the ceramic heater 4 formed in a curved surface. In this embodiment, the cross-sectional area of the heat generating part 26 is configured to be smaller than the cross-sectional area of the lead parts 23 and 24, and the heat generating part 26 positively generates heat mainly when energized. ing.

  The lead parts 23 and 24 are connected to both ends of the connecting part 25 and extend substantially parallel to each other toward the rear end of the ceramic heater 4. An electrode lead-out portion 27 protrudes in the outer peripheral direction at a position near the rear end of one lead portion 23 and is exposed on the outer peripheral surface of the ceramic heater 4. Similarly, the electrode lead-out portion 28 protrudes in the outer peripheral direction at a position near the rear end of the other lead portion 24 and is exposed on the outer peripheral surface of the ceramic heater 4. The electrode extraction portion 27 of the one lead portion 23 is located on the rear end side with respect to the electrode extraction portion 28 of the other lead 24 in the longitudinal direction (in the direction of the axis C1) of the ceramic heater 4.

  The exposed portion of the electrode lead-out portion 28 is in contact with the inner peripheral surface of the outer cylinder 7, so that the outer cylinder 7 and the lead portion 24 are electrically connected. Further, the electrode ring 18 described above is fitted in correspondence with the exposed portion of the electrode extraction portion 27, and the electrode extraction portion 27 comes into contact with the inner peripheral surface of the electrode ring 18, and the electrode ring 18 and the lead portion 23. And electrical continuity. That is, the center shaft 3 electrically connected to the electrode ring 18 via the lead wire 19 and the metal shell 2 engaged with and electrically connected to the outer cylinder 7 are connected to the ceramic heater 4 in the glow plug 1. It functions as an anode / cathode for energizing the heat generating portion 26 of the battery.

  In the present embodiment, in the ceramic heater 4, the heating element 22 is mainly composed of at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide. Yes. Of course, other components such as various sintering aids may be included. Further, in order to generate heat more actively in the heat generating part 26, the materials (mixing ratio) of both may be slightly different so that the conductivity of the lead parts 23 and 24 is higher than the heat generating part 26. Good. As a result, the heating element 22 can withstand use under higher temperature conditions (eg, 1200 ° C. or higher).

On the other hand, the substrate 21 is mainly composed of silicon nitride, the rare earth component is 4 to 25% by mass (more preferably 4 to 15% by mass) in terms of oxide, and the chromium silicide is 1 to 8% in terms of chromium silicide. % (More desirably 1.5 to 5% by mass) and an aluminum component in an amount of 0.02 to 1.0% by mass (more desirably 0.02 to 0.8% by mass) in terms of aluminum nitride. Yes. Examples of the “rare earth component” include erbium (Er), ytterbium (Yb), yttrium (Y), and the like. The phrase “rare earth component in terms of oxide” is based on the use of rare earth oxide as a raw material in the implementation process by the present inventors. Therefore, it does not mean that the rare earth component must always remain as an oxide. In addition, chromium silicides include not only pure (narrowly defined) chromium silicide (CrSi ₂ ), but also chromium silicides such as solid solutions of chromium and tungsten silicides and solid solutions of chromium and vanadium silicides. The idea is that it only has to be. The phrase “chromium silicide in terms of chromium silicide” is based on the fact that chromium silicide (CrSi ₂ ) is mainly used as a raw material in the implementation process by the present inventors as described above. Therefore, it is desirable that “almost all of the added chromium component remains as silicide”, but only pure chromium silicide (CrSi ₂ ) must remain as chromium silicide. Absent. Furthermore, “the aluminum component in terms of aluminum nitride” means that, as described above, in the implementation process by the present inventors, aluminum nitride (AlN) is mainly used as a raw material instead of alumina (Al ₂ O ₃ ) alone. It is based on being.

  In particular, at least the surface (surface layer) portion of the substrate 21 contains 0.02 to 1.0% by mass (more desirably 0.02 to 0.8% by mass) of an aluminum component in terms of aluminum nitride. Here, the “surface (surface layer)” specifically refers to a surface layer portion of the ceramic heater that can be analyzed using a predetermined X-ray analyzer. More specifically, as the X-ray analyzer here, trade name ROTAFLEX manufactured by Rigaku Corporation was used, and CuKα1 was used as the X-ray source. The applied voltage was set to 40 kV and the current was set to 100 mA. Further, the optical system was composed of a diverging slit 1 °, a scattering slit 1 °, a light receiving slit 0.3 mm, and a curved crystal monochromator. Further, as shown in FIG. 7, the X-ray incident direction was set to be parallel to the longitudinal direction of the ceramic heater 4 in a plan view of the ceramic heater 4 in a horizontal state. The reflection intensity was measured by irradiating the surface of the ceramic heater 4 at a scan mode of 2θ / θ and an angle of 2 ° from 20 ° to 80 ° at a rate of 6 ° / min at intervals of 0.01 °. The above numerical value on the “surface (surface layer)” indicates the measurement result under such conditions.

Further, the base 21 contains not only pure chromium silicide (CrSi ₂ ) but also at least one of a solid solution of chromium and tungsten silicide and a solid solution of chromium and vanadium silicide as chromium silicide. In the solid solution, tungsten silicide (WSi ₂ ) or vanadium silicide (VSi ₂ ) is added to the material constituting the substrate 21 in the manufacturing process of the ceramic heater 4 described later (powder mixing stage before firing, etc.). It is formed by.

In the present embodiment, the surface of the base 21 has a crystal phase [for example, J phase (Er ₄ Si ₂ N ₂ O ₇ ), H phase (Er ₂₀ Si] composed of rare earth elements, silicon, nitrogen and oxygen. ₁₂ N ₄ O ₄₈ ), melilite phase (Er ₂ Si ₃ N ₄ O ₃ ) etc.] are not present. Of course, the “surface” also refers to the result measured by the method using the X-ray analyzer described above.

On the other hand, the substrate 21 in the present embodiment has at least one of a rare earth element monosilicate crystal phase (Er ₂ SiO ₅ ) and a rare earth element disilicate crystal phase (Er ₂ Si ₂ O ₇ ). ing.

  Furthermore, the base 21 in the present embodiment contains 2 to 10% by volume of silicon carbide (SiC).

  The structure of the glow plug 1 centered on the ceramic heater 4 has been described above. However, in manufacturing the ceramic heater 4, the following manufacturing method is used in the present embodiment. Below, the manufacturing method of the ceramic heater 4 is demonstrated easily, referring FIGS. 3-6.

  FIG. 3 is a flowchart showing each manufacturing process of the ceramic heater 4. As shown in the figure, in the manufacturing process of the ceramic heater 4, the heating element molded body 31 (see FIG. 4) is first molded (S1). The heating element molded body 31 is a so-called precursor of the heating element 22 described above. The molding of the heating element molded body 31 will be described in more detail. As described above, at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide is used as a main component. A product in which an additive such as a sintering aid is mixed is made into a slurry in water and spray-dried to obtain a powder state. The heating element molded body 31 is produced by kneading the powder and a resin chip as a binder, performing injection molding, and then preliminarily heating and drying to ash (remove) a part of the binder. The

  As shown in FIG. 4, the produced heating element molded body 31 is a substantially U-shaped unfired connecting the unfired lead portions 33, 34 and the leading ends (left side in the drawing) of the lead portions 33, 34. The connection part 35 is provided. Furthermore, in the present embodiment, a support portion 39 that connects the rear ends of the lead portions 33 and 34 is also integrally formed. That is, the ceramic before firing has a low mechanical strength and the connecting portion 35 is relatively thin, so there is a concern that defects such as cracks and breakage may occur during the processing. In the present embodiment, the heating element molded body 31 is formed in an annular shape as a whole by the connecting portion 35, the lead portions 33 and 34, and the support portion 39, so that the load due to the weight of the lead portions 33 and 34 is supported by the connecting portion 35 and the support portion 39. In this way, it is dispersed at the portion 39, thereby preventing problems such as cracking of the connecting portion 35. In addition, since the support part 39 is cut | disconnected after baking, you may employ | adopt a thing thinner than the same figure from a viewpoint of performing a cutting | disconnection more easily. Of course, it is possible to adopt a configuration in which the support portion 39 is omitted.

Now, returning to the description of the manufacturing process of the ceramic heater 4, apart from the molding process of the heating element molded body 31, the half insulation molded body 40 constituting the half of the base body 21 is molded (S2 in FIG. 3). More specifically, first, powder of a material constituting the half-insulated molded body 40 is prepared. As described above, silicon nitride (average particle size 0.7 μm) as a main component, rare earth oxide, Cr compound powder such as average particle size 1.0 μm Cr ₂ O ₃ · CrSi ₂ ), average particle size 1.0 μm W nitride powder (or V compound powder) such as WO ₃ · WSi ₂ , silicon carbide powder having an average particle size of 1.0 μm and α or β silicon carbide powder as a crystal structure, alumina, aluminum nitride, etc. are mixed into silicon nitride. Wet mixing is carried out in ethanol for 40 hours, and then dried in a hot water bath to form a powder (granule). Then, after the insulating ceramic powder is used, the half-insulated molded body 40 is molded.

  A predetermined mold apparatus (not shown) is used for forming the half-insulated molded body 40. The mold apparatus includes, for example, an outer frame having an opening that has a frame shape, that is, a rectangular shape in plan view, and a lower mold and an upper mold that can move up and down with respect to the outer frame. Then, the lower mold convex portion is inserted through the opening of the outer frame, and the opening is filled with a predetermined amount of the above-mentioned insulating ceramic powder. From this state, the upper mold is moved downward and pressed with a predetermined pressure. Press. Thereby, as shown in FIG. 4, the half insulation molded body 40 in which the accommodation recessed part 48 was formed is obtained. Note that either the molding of the heating element molded body 31 (S1) or the molding of the half-insulated molded body 40 (S2) may be performed first.

  Next, the heating element molded body 31, the half-insulated molded body 40, and the holding body 61 (see FIG. 5) using the insulating ceramic powder are molded (S3 in FIG. 3). A predetermined mold apparatus (not shown) is also used for forming the holding body 61. As the mold apparatus, for example, an outer frame having a frame shape similar to the above, and a lower mold and an upper mold that can move up and down with respect to the outer frame are provided. Then, the lower mold convex portion is inserted into the opening of the outer frame, the half insulation molded body 40 is set thereon, and the accommodation concave portion 48 on the set half insulation molded body 40, The heating element molded body 31 is installed. Next, the above-mentioned insulating ceramic powder is filled in the opening, the upper mold is inserted through the opening to move the upper mold downward, and press-pressed with a predetermined pressure. Thereby, as shown in FIG. 5, a holding body 61 is obtained in which the heating element molded body 31 is held by the insulating molded body 60.

  Next, after forming the holding body 61, degreasing is performed (S4 in FIG. 3). That is, since the binder is still present in the obtained holding body 61, in order to ash the binder, that is, to remove it, calcination (degreasing and debinding process) for 1 hour at 800 ° C. in a nitrogen gas atmosphere is performed. Do.

  Thereafter, a release agent is applied to the entire outer surface of the holding body 61 (S5 in FIG. 3). Subsequently, the holding body 61 is subjected to a firing step (S6 in FIG. 3). In this step, firing is performed by a so-called hot press method. That is, by using a hot press machine (not shown) and pressurizing and heating the holding body 61 shown in FIG. 6A at 1800 ° C. for 1.5 hours at a hot press pressure of 25 MPa in a non-oxidizing atmosphere, A fired body 62 shown in 6 (b) is obtained. In the hot press firing furnace, a recess for correcting the shape was formed so that the fired fired body 62 has a substantially cylindrical shape (the shape conforming to the outer shape of the ceramic heater 4 described above is recessed). The carbon jig is used to perform hot press firing. At this time, the holding body 61 is pressurized under a uniaxial pressure condition as shown by an arrow in FIG.

  Then, the end surface cutting process which cut | disconnects the rear end side of the sintered body 62 is performed (S7 of FIG. 3). That is, the rear end side of the fired body 62 is cut with a diamond cutter or the like. Thereby, the support part 39 mentioned above is excised, and the baking body 62 which the rear-end surface of the lead parts 33 and 34 exposed from the end surface is obtained. This cutting is performed so that the lead part 23 and the lead part 24 of the heating element 22 are not short-circuited without passing through the heating part 26, and the cutting position is from the electrode extraction part 27. May be on the rear end side. That is, through this cutting step, the heating element molded body 31 constituted by the connecting portion 35, the lead portions 33 and 34 and the support portion 39 in the injection molding step is opened so as to be non-annular. It becomes. Of course, in the injection molding process, the end face cutting process is not necessary when a heating element molded body originally having no support portion is obtained.

  Thereafter, the finished body of the ceramic heater 4 described above is obtained by subjecting the fired body 62 to various polishing processes (S7 in FIG. 3). As the polishing process, the outer periphery of the fired body 62 is polished using a known centerless polishing machine, and the electrode extraction portions 27 and 28 are exposed from the outer peripheral surface, or the curved surface processing of the tip of the base 21 is performed. For example, there is R polishing to make the distance between the outer surface and the heat generating portion 26 uniform.

  As described above in detail, the base 21 of the ceramic heater 4 of the present embodiment contains 4 to 25% by mass of a rare earth component in terms of oxide. Thereby, not only the sinterability during firing is improved, but also the thermal expansion coefficient of the substrate 21 is improved. Therefore, there is an advantage that the difference in thermal expansion coefficient between the heating element 22 and the base 21 can be reduced, and the occurrence of cracks due to thermal stress can be prevented. On the other hand, when the content of the rare earth component in terms of oxide is less than 4% by mass, there is a possibility that sintering does not occur well during firing. In addition, the improvement of the thermal expansion coefficient cannot be expected, and there is a risk that cracks may occur due to thermal stress. On the other hand, when the content of the rare earth component in terms of oxide exceeds 25% by mass, the thermal expansion coefficient is improved, but the rare earth element (RE), silicon (Si), nitrogen (N), and oxygen (O). The grain boundary crystal phase composed of the above is generated, and the oxidation resistance is lowered due to the presence of the crystal phase.

  Moreover, the base | substrate 21 contains 1-8 mass% of chromium silicide in conversion of chromium silicide. Thereby, the thermal expansion coefficient of the base 21 is improved, and the difference in the thermal expansion coefficient between the heating element 22 and the base 21 can be reduced. On the other hand, when the content of chromium silicide is less than 1% by mass in terms of chromium silicide, improvement of the thermal expansion coefficient cannot be expected, and cracks may occur due to thermal stress. On the other hand, if the chromium silicide content exceeds 8% by mass in terms of chromium silicide, the chromium component may aggregate. As a result, the coefficient of thermal expansion varies depending on the part, which may cause a decrease in strength.

  Furthermore, the base 21 contains 0.02 to 1.0% by mass of an aluminum component in terms of aluminum nitride, both as a whole and on the surface. Thereby, the corrosion of the base | substrate 21 by the calcium component etc. which are contained in engine oil is suppressed. On the other hand, when the content of the aluminum component is less than 0.02% by mass in terms of aluminum nitride, the corrosion suppressing effect of the base 21 cannot be sufficiently obtained. On the other hand, when the content of the aluminum component exceeds 1.0% by mass in terms of aluminum nitride, the strength of the substrate 21 at a high temperature is lowered.

  At the same time, in this embodiment, tungsten silicide (or vanadium silicide) is mixed into the material constituting the base 21 to form a solid solution of chromium and tungsten silicide (or chromium and vanadium as a silicide of chromium). A solid solution of silicide). That is, a situation in which the chromium component is aggregated at the interface between the heating element 22 and the substrate 21 does not occur so much. As a result, the occurrence of uneven thermal expansion coefficient due to the aggregation of the chromium component can be suppressed, and the strength of the substrate 21 is reduced. Prevention can be achieved.

  In addition, in the present embodiment, since there is no crystalline phase composed of rare earth elements, silicon, nitrogen and oxygen on the surface of the base 21, it is difficult for the surface to be oxidized, resulting in acid resistance. It is possible to improve the productivity. Further, since at least one of the rare earth element monosilicate crystal phase and the rare earth element disilicate crystal phase is present in the substrate 21, the heat resistance is improved and the strength of the substrate under high temperature conditions is improved. be able to.

  In addition, since the base 21 contains 2 to 10% by volume of silicon carbide, not only the sinterability during firing is improved, but also the thermal expansion coefficient of the base 21 is improved, and the heating element The difference in thermal expansion coefficient between 22 and the substrate 21 can be reduced. On the other hand, when the content of silicon carbide is less than 2% by volume, it is difficult to improve the thermal expansion coefficient, and it is difficult to improve the high-temperature strength. Moreover, when content of silicon carbide exceeds 10 volume%, there exists a possibility that the improvement of the sinterability at the time of baking may become insufficient, and there exists a possibility of causing the fall of insulation.

  Next, in order to confirm the above-described effects, various samples were prepared under various conditions, and various experiments were performed to evaluate the characteristics of each sample.

First, W compound such as silicon nitride powder having an average particle size of 0.7 μm, Er ₂ O ₃ as a rare earth oxide, CrSi ₂ powder having an average particle size of 1.0 μm, WO ₃ · WSi ₂ having an average particle size of 1.0 μm Powder, silicon carbide powder with an average particle size of 1.0 μm and crystal structure of α or β and silicon dioxide powder, aluminum nitride and aluminum compound powder of alumina are blended, and this is mixed with ethanol using silicon nitride cobblestone Wet mixed in for 40 hours and then dried in hot water. Thereafter, the powder of the heater member thus obtained is processed as described above to prepare a ceramic heater, and separately from these ceramic heaters (substrates), under a nitrogen atmosphere at 1800 ° C. and 25 MPa. It baked with the hot press over 1.5 hours, and produced the plate-shaped sintered compact (test piece = TP) of 45 mm x 45 mm x 10 mm.

In this case, the ceramic heater (element) and the test piece were prepared after variously changing the blending ratio of the rare earth oxide (Er ₂ O ₃ ), the chromium silicide (CrSi ₂ ), and the aluminum component. And while measuring each component ratio regarding the base | substrate part of a ceramic heater, the crystal phase was also observed. For each component ratio, the ceramic heater was cut at a portion corresponding to the maximum heat generating portion (4 mm from the tip in this example), and an electron beam probe microanalyzer (EPMA) at a position 100 μm inside from the outer peripheral surface with respect to the cross section. JXA-8800 manufactured by JEOL Ltd.) was used to quantify rare earth components, chromium components, and aluminum components using a wavelength dispersive X-ray detector (WDS, acceleration voltage 20 kV, spot diameter 100 μm). The rare earth component is calculated from the quantified rare earth component in terms of rare earth oxide, the chromium silicide is calculated from the quantified chromium component in terms of chromium silicide (CrSi ₂ ), and the aluminum component is The content was calculated in terms of aluminum nitride (AlN).

Further, for each test piece, “thermal expansion coefficient” and “CaSO ₄ corrosion resistance at 1100 ° C. and 1150 ° C.” were evaluated. In addition, “high temperature continuous durability performance” and “ONOFF durability performance” were evaluated for ceramic heater elements. The results are shown in Table 1.

  In the table, in the column of crystal phase, “DS” mainly confirms rare earth element disilicate as the crystal phase, and “MS” mainly confirms rare earth element monosilicate as the crystal phase. “MS, DS” means that a mixture of rare earth monosilicate and disilicate is mainly confirmed as a crystalline phase. The term “melilite phase” means that the “melilite phase” is mainly confirmed, and it is neither monosilicate nor disilicate.

Further, the “thermal expansion coefficient” can be calculated based on the following equation (1).
Thermal expansion coefficient (ppm / ° C.) = − [(Standard sample length at 1000 ° C.−measured sample length at 1000 ° C.) / {Measured sample length at 30 ° C. × (1000 ° C.−30 ° C.)}] + 8.45 × 10 ^-6 (1)
However, in the above formula (1), “standard sample length at 1000 ° C.” means that the alumina having a thermal expansion coefficient of 8.45 × 10 ⁻⁶ / ° C. at 1000 ° C. is used as the standard sample. It means the length at 1000 ° C. The length of this standard sample at 30 ° C. is the same as the length of the measurement sample at 30 ° C.

In addition, “CaSO ₄ corrosion resistance” was evaluated as follows. That is, a sample obtained by processing the above test piece into 3 mm × 4 mm × 15 mm into an alumina crucible containing CaSO ₄ powder, and kept in air at 1100 ° C. for 20 hours, and held at 1150 ° C. for 20 hours. Each was taken out and then subjected to sandblasting to remove CaSO ₄ and the mass reduction rate was measured. In this case, when the mass reduction rate is less than 5%, an evaluation of “◯” is given. When the mass reduction rate is 5% to 20%, an evaluation of “△” is given, and when the mass reduction rate exceeds 20%. It was decided to evaluate “x”.

  Furthermore, the “high temperature continuous durability performance” of the ceramic heater element was evaluated as follows. That is, the heater was heated up so that the maximum surface temperature of the heater was 1350 ° C. (further, 1400 ° C.), and a continuous energization test was performed. And after energizing for 1000 hours, resistance value was first measured and resistance value change before and after a test was measured. After measuring the resistance value, the heater was cut along the axial direction, mirror-polished, and the presence or absence of migration (migration) of the sintering aid component (rare earth component, chromium, aluminum) in the vicinity of the heating element was observed with EPMA. In this case, when there was no resistance change and no migration, the evaluation of “◯” was made. When the resistance change was not so much, the evaluation of “△” was made when there was migration, and the resistance value was 10%. In the case where there was an increase and migration occurred, “x” was evaluated.

  In addition, the “ONOFF durability performance” of the ceramic heater element was evaluated as follows. That is, after applying a voltage to the heater, a voltage is applied so as to reach 1000 ° C. in 1 second, and the temperature reaches 1400 ° C. which is the maximum temperature while maintaining the rate of temperature increase. Fan cooling was performed for 1 second, and the test which made this 1 cycle was repeated, and the resistance value after 1000 cycles was measured. In this case, when there was almost no change in resistance after 1000 cycles (within 5%), an evaluation of “◯” was given. After 1000 cycles, there was a change in resistance, and the change was 5 to 10%. The evaluation of “Δ” was evaluated as “x” when the disconnection occurred within 1000 cycles.

表１において、希土類酸化物（Ｅｒ₂Ｏ₃）が６．０〜６．４質量％含有されてなり、かつ、クロムの珪化物がシリサイド換算で１．９〜２．３質量％含有されてなるサンプル１〜１０を参酌すると、Ａｌ成分が窒化アルミニウム換算で０．０２〜１．０質量％含有されてなるサンプル３〜９については、１１００℃、１１５０℃におけるＣａＳＯ₄耐食性が優れていることが明らかとなった。

In Table 1, the rare earth oxide (Er ₂ O ₃ ) is contained in an amount of 6.0 to 6.4% by mass, and chromium silicide is contained in an amount of 1.9 to 2.3% by mass in terms of silicide. In consideration of Samples 1 to 10, Samples 3 to 9 containing 0.02 to 1.0% by mass of an Al component in terms of aluminum nitride have excellent CaSO ₄ corrosion resistance at 1100 ° C. and 1150 ° C. Became clear.

On the other hand, when the content of the Al component was less than 0.02% by mass in terms of aluminum nitride (in the case of samples 1 and 2), the CaSO ₄ corrosion resistance was inferior. In particular, the CaSO ₄ corrosion resistance at 1100 ° C. was not significantly different, but the CaSO ₄ corrosion resistance at 1150 ° C. was when the Al component content was 0.01% by mass or less in terms of aluminum nitride. It turned out to be extremely inferior. That is, it became clear that the corrosion resistance in the high temperature region of 1150 ° C. was extremely excellent by adopting the configurations of Samples 3 to 9.

  On the other hand, when the content of the Al component exceeds 1.0 mass% in terms of aluminum nitride (in the case of sample number 10), the resistance value changes during high-temperature continuous durability, and disconnection also occurs in ONOFF durability. (See heater element evaluation).

In Table 1, chromium silicide is contained in an amount of 2.0 to 2.5% by mass in terms of silicide, and an Al component is contained in an amount of 0.07 to 0.11% in terms of aluminum nitride. In consideration of Samples 11 to 17, Samples 12 to 16 containing 4.0 to 25.0% by mass of rare earth oxide (Er ₂ O ₃ ) have excellent CaSO ₄ corrosion resistance and “high temperature continuous durability”. It became clear that it was excellent in terms of “performance” and “ONOFF durability performance”. On the other hand, the sample 11 containing only 3.0% by mass of the rare earth oxide (Er ₂ O ₃ ) has a low thermal expansion coefficient of 3.2 and “ONOFF durability performance” under high temperature conditions. It became clear that it was inferior in terms of. On the other hand, for sample 17 containing 27.0% by mass of rare earth oxide (Er ₂ O ₃ ), a melilite phase was confirmed as a crystal phase, and “high temperature continuous durability performance” and “ONOFF durability performance” were remarkably high. It became clear that it would be inferior.

Further, in Table 1, 5.9 to 6.1% by mass of rare earth oxide (Er ₂ O ₃ ) is contained, and Al component is contained in an amount of 0.07 to 0.09% by mass in terms of aluminum nitride. In consideration of the samples 18 to 24, the samples 19 to 23 containing 1.0 to 8.0% by mass of chromium silicide in terms of silicide are excellent in CaSO ₄ corrosion resistance and “high temperature continuous durability” It became clear that it was excellent in terms of “performance” and “ONOFF durability performance”. On the other hand, the sample 18 containing only 0.7% by mass of chromium silicide in terms of silicide has a low coefficient of thermal expansion of 3.2, and “ONOFF durability performance” under high temperature conditions. But it turned out to be inferior. On the other hand, the sample 24 containing chromium silicide in an amount of 10.0% by mass in terms of silicide is inferior in “high temperature continuous durability performance” and “ONOFF durability performance” at 1400 ° C. Became clear. Further, with respect to the sample 24, Cr agglomeration was observed at the resistor interface, and it is considered that the durability performance under high temperature was lowered.

Table 1 shows the results when Er ₂ O ₃ is used as the rare earth oxide. On the other hand, a test piece and a ceramic heater were produced in the same manner as described above, and various evaluations were performed in the same manner as described above, in order to examine whether or not the same effect was exhibited when other rare earth components were contained. . The results are shown in Table 2.

表２に示すように、希土類酸化物としてＥｒ₂Ｏ₃以外の化合物（例えば、サンプル２６＝酸化イットリウム（Ｙ₂Ｏ₃）、サンプル２７＝酸化イッテルビウム（Ｙｂ₂Ｏ₃）、サンプル２８＝Ｙ₂Ｏ₃、Ｙｂ₂Ｏ₃の混合物、サンプル２９＝Ｅｒ₂Ｏ₃、Ｙｂ₂Ｏ₃の混合物）を用いた場合であっても、Ｅｒ₂Ｏ₃と同様の作用効果が奏されることが明らかとなった。

As shown in Table 2, compounds other than Er ₂ O ₃ as the rare earth oxide (for example, sample 26 = yttrium oxide (Y ₂ O ₃ ), sample 27 = ytterbium oxide (Yb ₂ O ₃ ), sample 28 = Y ₂ Even when a mixture of O ₃ and Yb ₂ O ₃ and sample 29 = a mixture of Er ₂ O ₃ and Yb ₂ O ₃ are used, it is clear that the same effects as Er ₂ O ₃ are exhibited. It became.

Further, in Table 1 above, numerical evaluation is performed after converting the silicide of chromium into a silicide. This is because, as described above, in the process of manufacturing the ceramic heater, be based on the fact that by using mainly the chromium silicide (CrSi ₂₎ as a raw material, as the method of addition of the silicide, the chromium silicide (CrSi ₂ In addition to the above, tungsten silicide or vanadium silicide may be mixed. Therefore, for the case where tungsten silicide or vanadium silicide is mixed as a compounded silicide, a test piece and a ceramic heater were prepared in the same manner as described above, and various evaluations were performed in the same manner as described above. The results are shown in Table 3.

  In addition, the following method was employ | adopted as a confirmation method of a solid solution in a table | surface. That is, a sample of a cross-section is prepared by cutting the highest heating portion of the heater element (4 mm from the tip of the element in this example), and the cross-section of the cross-section is mirror-polished, and then the structure of the substrate portion is scanned with a scanning electron microscope (SEM). Observation and identification of chromium silicide particles. The chromium silicide particles were spot-analyzed by energy dispersive X-ray spectroscopy (EDS) at an observation magnification of 5000 times, and elemental analysis was performed. As a result, in the detected element, when tungsten or vanadium is detected in addition to chromium and silicon, it is determined that a solid solution is present.

表３において、サンプル３０は、クロムシリサイド（ＣｒＳｉ₂）に加えてタングステンシリサイドを混入させたものであって、得られたテストピース及びセラミックヒータには、クロムとタングステンのシリサイドの固溶体の存在が確認された。また、サンプル３１は、クロムシリサイド（ＣｒＳｉ₂）に加えてバナジウムシリサイドを混入させたものであって、得られたテストピース及びセラミックヒータには、クロムとバナジウムのシリサイドの固溶体の存在が確認された。尚、サンプル３２は、珪化物原料してクロムシリサイド（ＣｒＳｉ₂）のみを用いたものであって、得られたテストピース及びセラミックヒータには、クロムシリサイド（ＣｒＳｉ₂）の存在が確認された。

In Table 3, sample 30 is a mixture of chromium silicide (CrSi ₂ ) and tungsten silicide, and the obtained test piece and ceramic heater confirmed the presence of a solid solution of chromium and tungsten silicide. It was done. Sample 31 was mixed with vanadium silicide in addition to chromium silicide (CrSi ₂ ), and it was confirmed that the obtained test piece and ceramic heater had a solid solution of chromium and vanadium silicide. . The sample 32 used only silicide silicide (CrSi ₂ ) as a silicide raw material, and the presence of chromium silicide (CrSi ₂ ) was confirmed in the obtained test piece and ceramic heater.

As shown in Table 3, not only pure chromium silicide (CrSi ₂ ) has to remain, but a solid solution of chromium and tungsten silicide and a solid solution of chromium and vanadium silicide exist. It has also been clarified that the same effects can be obtained. The inclusion of such a solid solution means that a situation in which the chromium component aggregates at the interface between the heating element and the substrate does not occur so much. That is, a solid solution is formed by adding tungsten silicide and vanadium silicide in addition to chromium silicide (CrSi ₂ ) at the raw material stage, and in a ceramic heater containing the solid solution, the coefficient of thermal expansion due to aggregation of chromium components It can be said that the occurrence of unevenness can be suppressed and the strength of the substrate can be prevented from lowering.

From the results shown in Tables 1, 2 and 3 above, as materials constituting the substrate of the ceramic heater, the rare earth component is 4 to 25% by mass in terms of oxide, and the chromium silicide is 1 to 3 in terms of chromium silicide. In addition to containing 8% by mass and containing 0.02 to 1.0% by mass of the aluminum component in terms of aluminum nitride, the “thermal expansion coefficient” can be increased, and “CaSO at 1100 ° C. and 1150 ° C.” excellent ₄ corrosion resistance ", yet" high temperature continuous durability in the case of using as a ceramic heater ", revealed that becomes excellent in" ONOFF durability ".

Next, in order to confirm the influence of the content of silicon carbide in the substrate, the content of rare earth oxide (Er ₂ O ₃ ), chromium silicide, and Al component is made almost constant, and the content of silicon carbide Samples with various amounts were prepared, and the thermal expansion coefficient and “ONOFF durability performance” were evaluated in the same manner as described above. The results are shown in Table 4. The silicon carbide content was specified as follows. That is, a sample of a cross-section is prepared by cutting the highest heating portion of the heater element (4 mm from the tip of the element in this example), and the cross-section of the cross-section is mirror-polished, and then the structure of the substrate portion is scanned with a scanning electron microscope (SEM). The silicon carbide particles were observed and identified, and the area% was quantified and converted to volume%.

表４に示すように、希土類酸化物（Ｅｒ₂Ｏ₃）が６．０〜６．２質量％含有されてなり、かつ、クロムの珪化物がシリサイド換算で１．９〜２．１質量％含有されてなり、かつ、Ａｌ成分が窒化アルミニウム換算で０．０８〜０．１０質量％含有されてなるサンプル３３〜３７において、炭化珪素の含有量が多くなるほど、熱膨張係数が増大することが明らかとなった。すなわち、炭化珪素を所定量含有させることで、基体の熱膨張係数の向上が図られ、発熱体と基体との熱膨張係数の差を少なくすることができるという効果が奏される。これに対し、炭化珪素の含有量が１０体積％を超えるサンプル３７（１３．１体積％）の場合には、「ＯＮＯＦＦ耐久性能」が若干、劣ったものとなってしまった。

As shown in Table 4, the rare earth oxide (Er ₂ O ₃ ) is contained in an amount of 6.0 to 6.2% by mass, and the chromium silicide is 1.9 to 2.1% by mass in terms of silicide. In samples 33 to 37 that are contained and contain Al components in an amount of 0.08 to 0.10% by mass in terms of aluminum nitride, the thermal expansion coefficient may increase as the silicon carbide content increases. It became clear. That is, by containing a predetermined amount of silicon carbide, the thermal expansion coefficient of the substrate can be improved, and the difference in the thermal expansion coefficient between the heating element and the substrate can be reduced. On the other hand, in the case of Sample 37 (13.1% by volume) in which the content of silicon carbide exceeds 10% by volume, the “ONOFF durability performance” is slightly inferior.

Now, from the evaluation results in Table 1, etc., the point that the aluminum component needs to be contained in an amount of 0.02 to 1.0% by mass in terms of aluminum nitride has been described above. In this case, when alumina (Al ₂ O ₃ ) alone is used as a raw material and when aluminum nitride (AlN) is mainly used (for example, the mass ratio of AlN to 1 mass of Al ₂ O ₃ is 1). 3), a strength characteristic under a high temperature condition of 1400 ° C. was evaluated. The results are shown in Table 5. The “high temperature bending test at 1400 ° C.” was performed as follows. That is, a test piece of 3 mm × 4 mm × 40 mm was obtained in the same manner as described above, and the test piece was measured for 4 point bending strength (upper span 10 mm, lower span 30 mm) at 1400 ° C. according to JIS 1604.

表５に示すように、ＡｌＮを主として用いた場合のほうが、Ａｌ₂Ｏ₃単体を用いた場合よりも、１４００℃での高温曲げ強度が高いことが明らかとなった。すなわち、アルミニウム成分の添加に関しては、Ａｌ₂Ｏ₃のみではなく、Ａｌ₂Ｏ₃と、ＡｌＮとを混合添加することがより望ましく、その比率としては、例えばＡｌ₂Ｏ₃の質量が１に対してＡｌＮの質量比が３（或いはそれ以上）とすることがより望ましいといえる。こうすることで、ＪＩＳ １６０４に準じて１４００℃にて４点曲げ強度を測定した場合に、６００ＭＰａ以上（本例では６３９ＭＰａ）の高温曲げ強度を得ることができる。

As shown in Table 5, it was revealed that the high temperature bending strength at 1400 ° C. was higher when AlN was mainly used than when Al ₂ O ₃ was used alone. That is, regarding the addition of the aluminum component, it is more desirable to add not only Al ₂ O ₃ but also Al ₂ O ₃ and AlN, and the ratio is, for example, that the mass of Al ₂ O ₃ is 1 Therefore, it can be said that it is more desirable that the mass ratio of AlN is 3 (or more). By carrying out like this, when measuring 4 point bending strength at 1400 degreeC according to JIS1604, 600 MPa or more (this example 639 MPa) high temperature bending strength can be obtained.

  In addition, it is not limited to the description content of embodiment mentioned above, For example, you may implement as follows.

  (A) In the above embodiment, alumina is mixed in the powder constituting the holding body 61 (base 21), but this is nitrided after firing. Therefore, it is good also as mixing aluminum nitride only as an aluminum component, avoiding mixing of alumina, and conversely, it is possible to mix only alumina as an aluminum component without using aluminum nitride. However, if a large amount of alumina is mixed, a liquid phase is formed at 1350 to 1400 ° C., and there is a concern that the high-temperature strength is lowered. From this point of view, as described in the section of Table 5, it is desirable to mix aluminum nitride from the beginning.

  (B) The ceramic heater 4 of the above embodiment is embodied in the case of a round bar shape, that is, a circular cross section, but it is not always necessary to have a circular cross section. It may be a shape or a polygonal cross section. Further, it may be embodied as a so-called plate heater in which a plurality of insulating substrates are formed in a plate shape and a heating element is sandwiched therebetween.

  (C) In the above embodiment, the cross-sectional shape of the holding body 61 is substantially oval. However, the cross-sectional shape may be a circle, a rectangle, or a polygon. Good.

  (D) In the above embodiment, the holding body 61 is formed after the half-insulated molded body 40 is molded. However, such a step is omitted, and the periphery of the heating element molded body 31 is insulated. It is good also as obtaining a holding body by performing the press molding which hardens at a stretch with the powder which has a ceramic as a main component.

  (E) In the above embodiment, preliminary drying is performed on the heating element molded body 31, but the preliminary drying may be omitted.

  (F) Regarding the configuration of the ceramic heater, it can be used as a temperature sensor for detecting the temperature based on reading the change in the temperature resistance coefficient of the heating element from the voltage. That is, the base material according to the present invention may be used as the base of the temperature sensor.

It is a longitudinal cross-sectional view which shows the structure of the glow plug of this embodiment. It is a partial expanded sectional view of the glow plug mainly showing a ceramic heater. It is a flowchart which shows the manufacturing method of a ceramic heater. It is a perspective view explaining the process which installs a heat generating body molded object in the accommodation recessed part on a half insulation molded object. It is a perspective view which shows a holding body. (A) is sectional drawing which shows the press direction at the time of baking of a holding body, (b) is sectional drawing which shows the sintered body obtained. It is a perspective view explaining the irradiation direction of the X-ray in the case of measuring the surface of a base | substrate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Glow plug, 4 ... Ceramic heater, 21 ... Base | substrate, 22 ... Heating body.

Claims (8)

A heating element mainly composed of at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide is embedded in a substrate mainly composed of silicon nitride. A ceramic heater,
The substrate is
4 to 25% by mass of the rare earth component in terms of oxide,
While containing 1-8 mass% of chromium silicide in terms of chromium silicide,
A ceramic heater comprising 0.02 to 1.0 mass% of an aluminum component in terms of aluminum nitride. A heating element mainly composed of at least one of molybdenum silicide, nitride and carbide, and tungsten silicide, nitride and carbide is embedded in a substrate mainly composed of silicon nitride. A ceramic heater,
The substrate is
4 to 25% by mass of rare earth oxide,
While containing 1-8% by mass of chromium silicide,
A ceramic heater comprising 0.2 to 1.0% by mass of an aluminum component in terms of aluminum nitride.   3. The ceramic heater according to claim 1, wherein the base includes at least one of a solid solution of chromium and tungsten silicide and a solid solution of chromium and vanadium silicide. 4.   4. The ceramic heater according to claim 1, wherein a crystal phase composed of a rare earth element, silicon, nitrogen, and oxygen does not exist on the surface of the substrate. 5.   5. The ceramic heater according to claim 1, wherein at least one of a rare earth element monosilicate crystal phase and a rare earth element disilicate crystal phase is present on the substrate. 6.   The ceramic heater according to any one of claims 1 to 5, wherein the base contains 2 to 10% by volume of silicon carbide. 7. The ceramic according to claim 1, wherein the substrate has a coefficient of thermal expansion of 3.3 × 10 ⁻⁶ / ° C. or more and 4.0 × 10 ⁻⁶ / ° C. or less. heater.   A glow plug comprising the ceramic heater according to claim 1.

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