JP2017195078A - Ceramic heater and glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve both of the enhancement in oxidation resistance of a base included in a ceramic heater, and the increase in sinterability.SOLUTION: A ceramic heater comprises: a base including silicon nitride as a primary component and additionally, a rare earth element, and provided to extend in an axial direction; and a conductive part including two extending parts buried in the base and extending along the axial direction in parallel with each other and a joint portion. In a section orthogonal to the axial direction, where the two extending parts appear, the content of the rare earth element in the base in a center portion of the ceramic heater is higher than that in the base in a surface layer portion; the content of the rare earth element in the base of the center portion is 0.6-2.0 atm%.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a ceramic heater and a glow plug using the ceramic heater.

  Conventionally, a glow plug having a ceramic heater has been used as a glow plug used for starting assistance of a diesel engine. As a configuration of the ceramic heater, a configuration is known in which a ceramic heating element having conductivity is arranged inside a ceramic base having insulation properties. The base and the heating element are produced by sintering a ceramic material containing silicon nitride. Since the sinterability of silicon nitride is low, the sintering aid is generally improved by using a sintering aid mixed with a ceramic material. In addition, as such a sintering aid, a sintering aid containing a rare earth element may be used (see, for example, Patent Documents 1 and 2). By using the rare earth element, the melting point of the glass phase existing at the grain boundary between the main phases made of silicon nitride can be increased, and the oxidation resistance of the substrate can be improved.

International Publication No. 2012/073476 Pamphlet JP 2008-293804 A

A substrate made of a ceramic material using a rare earth element as a sintering aid has a coating of silicon dioxide (SiO ₂ ) or the like on the substrate surface under a very high temperature environment (for example, a high temperature environment higher than 1000 ° C.). As a result, oxidation resistance is improved. However, in a relatively low temperature environment (for example, in a low temperature environment of 1000 ° C. or lower), there is a problem that the oxidation of the substrate proceeds and the oxidation resistance of the substrate decreases because such a film is not formed. For this oxidation, for example, oxynitride such as melilite type rare earth oxide (Y ₂ SI ₃ ON ₄ ) is considered to contribute, and the amount of rare earth elements contained in the sintering aid should be reduced. Thus, the amount of oxynitride produced can be suppressed, and a decrease in the oxidation resistance of the substrate in a low temperature environment can be suppressed. On the other hand, when the amount of rare earth elements contained in the sintering aid is reduced, the problem that the sinterability deteriorates cannot be solved. Such a problem may occur not only in ceramic heaters used in glow plugs but also in any ceramic heater used in ignition heater devices, various sensor devices, and the like. For this reason, there is a demand for a technique that can achieve both improvement in the oxidation resistance and sinterability of the substrate.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to an aspect of the present invention, a base body containing silicon nitride as a main component and further containing a rare earth element and extending in the axial direction, and embedded in the base body and extending along the axial direction with each other There is provided a ceramic heater provided with two extending portions provided and a conductive portion including a connecting portion that connects tip portions of the two extending portions. In the ceramic heater, in the cross section in which the two extending portions appear perpendicular to the axial direction, the content of the rare earth element in the base at the center of the ceramic heater is the surface of the base of the ceramic heater. The content of the rare earth element is higher than the content of the rare earth element, and the content of the rare earth element in the substrate at the center is 0.6 atm% or more and 2.0 atm or less.
According to the ceramic heater of this embodiment, the rare earth element content in the substrate at the center of the ceramic heater is higher than the rare earth element content in the substrate at the surface layer of the ceramic heater. That is, the rare earth element content in the central substrate is relatively high. In addition, the rare earth element content in the substrate at the center of the ceramic heater is 0.6 atm% or more. For this reason, sufficient liquid phase can be supplied at the time of baking, and sinterability can be improved. In addition, since the content rate of the rare earth element in the substrate at the center of the ceramic heater is 2.0 atm% or less, a decrease in the oxidation resistance of the substrate in a low temperature environment can be suppressed. On the other hand, since the rare earth element content in the substrate of the surface layer portion is relatively low, a reduction in oxidation resistance of the surface layer portion in a low temperature environment can be suppressed. Since the oxidation resistance of the surface layer portion of the substrate greatly affects the oxidation resistance of the entire substrate, the ceramic heater of the above embodiment can improve the oxidation resistance of the entire substrate in a low temperature environment. Therefore, according to the ceramic heater of the said form, the improvement of the oxidation resistance of a base | substrate and the improvement of sinterability can be made compatible.

  (2) In the ceramic heater of the above aspect, the conductive portion includes a heat generating portion formed by a tip side portion and the connecting portion in each extending portion, and a rear end in each extending portion connected to the heat generating portion. Two lead portions each formed by a side portion, and the cross section may be a cross section in which the heat generating portion appears. According to the ceramic heater of this form, both the oxidation resistance and the sinterability of the substrate can be improved at the cross section where the heat generating portion appears, that is, at the portion where the substrate can be heated at a higher temperature than other portions. Therefore, it is possible to improve both the oxidation resistance and the sinterability of the entire substrate including other portions of the substrate.

  (3) In the ceramic heater of the above aspect, the rare earth element content in the substrate of the surface layer portion is 65% or more and 90% or less of the rare earth element content in the substrate of the center portion. It may be a feature. According to the ceramic heater of this embodiment, the rare earth element content in the surface layer base is 65% or more and 90% or less of the rare earth element content in the central base, so that it is out of this range. Thus, the balance between the sinterability and oxidation resistance of the substrate can be improved. When the relative rare earth element content is lower than 65%, the liquid phase amount is insufficient at the time of sintering, so fine pores are generated in the grain boundary portion, and it is assumed that the sinterability is lowered. . On the other hand, when the relative rare earth element content is higher than 90%, it is presumed that the base layer of the surface layer is oxidized and cracked in a low temperature environment, and the oxidation resistance in the low temperature environment is lowered. The

  (4) In the ceramic heater of the above aspect, the rare earth element may be at least one selected from erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). According to this form of the ceramic heater, the crystallization of the grain boundary phase can be promoted to improve the oxidation resistance under a high temperature environment.

  (5) In the ceramic heater of the above aspect, the rare earth element may be ytterbium (Yb). According to this form of the ceramic heater, the crystallization of the grain boundary phase can be further promoted, and the oxidation resistance under a high temperature environment can be further improved. In addition, since ytterbium (Yb), which is relatively easily available, is used, the manufacturing cost of the ceramic heater can be kept low.

  (6) In the ceramic heater of the above aspect, the rare earth element content in the substrate of the surface layer portion may be 0.5 atm% or more and 1.05 atm% or less. According to the ceramic heater of this embodiment, since the rare earth element content in the substrate of the surface layer portion of the ceramic heater is 0.5 atm% or more and 1.05 atm% or less, the oxidation resistance of the substrate in a low temperature environment is reduced. Further suppression is possible.

  The present invention can be realized in various forms other than the ceramic heater. For example, it can be realized in the form of a glow plug, a ceramic heater manufacturing method, a glow plug manufacturing method, and the like.

It is sectional drawing which shows the structure of the glow plug to which the ceramic heater as one Embodiment of this invention is applied. FIG. 2 is a partially enlarged cross-sectional view of a glow plug with the heater shown in FIG. 1 as the center. It is sectional drawing of a heater. It is a process table | surface which shows the manufacturing procedure of a glow plug. It is explanatory drawing which shows the processing content of process P120 typically. It is explanatory drawing which shows typically the processing content of process P125.

A. Embodiment:
A1. Device configuration:
FIG. 1 is a cross-sectional view showing a configuration of a glow plug to which a ceramic heater according to an embodiment of the present invention is applied. FIG. 1 shows a cross section of the glow plug 100 including the axis C <b> 1 of the glow plug 100. A cross section of a ceramic heater 4 (hereinafter simply referred to as “heater 4”) to be described later is schematically shown in FIG. The glow plug 100 has a rod-like appearance, and mainly includes a metal shell 2, a middle shaft 3, an insulating member 5, a pin terminal 8, an outer cylinder 7, a heater 4, and an electrode ring 18. Yes. In FIG. 1, the X axis is set parallel to the axis C1 of the glow plug 100, and the Y axis and the Z axis are set perpendicular to the X axis. Hereinafter, the side where the heater 4 is provided along the axis C1 in the glow plug 100 is referred to as “front end side”, and the side where the middle shaft 3 is disposed along the axis C1 is referred to as “rear end side”. Call.

  The metal shell 2 is a metal member having a substantially cylindrical appearance with a shaft hole 9. On the outer peripheral surface of the metal shell 2, a tool engagement portion 12 is formed on the rear end side, and a male screw portion 11 is formed on the center portion. The tool engaging portion 12 has an external shape (for example, a hexagonal shape) that can be engaged with a predetermined tool. When the glow plug 100 is attached to a cylinder head of an engine (not shown) or the like, Engaged. When the glow plug 100 is attached to a cylinder head of an engine (not shown), the male screw portion 11 is screwed into a female screw formed on the cylinder head.

  The middle shaft 3 is a metal round bar-like member, and is accommodated in the shaft hole 9 of the metal shell 2 such that a part of the rear end side protrudes from the rear end of the metal shell 2. One end of the electrode ring 18 is fitted on the distal end side of the middle shaft 3. The middle shaft 3 is electrically connected to the heater 4 via the electrode ring 18.

  The insulating member 5 has a cylindrical external shape having a flange portion 6 on the rear end side, and is formed of an insulating material. The front end side of the insulating member 5 is fitted into the shaft hole 9 from the rear end side of the metal shell 2, and the flange portion 6 is in contact with the rear end surface of the tool engaging portion 12. A part of the rear end side of the middle shaft 3 is inserted into the shaft hole of the insulating member 5, and the insulating member 5 has both the axis of the metal shell 2 and the axis of the middle shaft 3 aligned with the axis C 1 of the glow plug 100. The middle shaft 3 is fixed so that The rear end surface of the flange portion 6 is in contact with the front end surface of the pin terminal 8. The insulating member 5 electrically insulates between the metal shell 2 and the middle shaft 3 and between the metal shell 2 and the pin terminal 8.

  The pin terminal 8 has a substantially cylindrical external shape, and is caulked so as to surround the rear end portion of the central shaft 3 protruding from the rear end of the metal shell 2 in contact with the flange portion 6. As the pin terminal 8 is caulked in this way, the insulating member 5 fitted between the middle shaft 3 and the metal shell 2 is fixed, and the insulation member 5 is prevented from coming off from the middle shaft 3.

  The outer cylinder 7 is a metal member having a substantially cylindrical outer shape having a shaft hole 10, and is joined to the distal end side of the metal shell 2. A thick portion 15 and an engaging portion 16 are formed on the rear end side of the outer cylinder 7. The engaging portion 16 is arranged on the rear end side with respect to the thick portion 15, and the outer peripheral diameter is smaller than the outer peripheral diameter of the thick portion 15. The engaging portion 16 is fitted in the shaft hole 9 of the metal shell 2. The thick portion 15 is welded to the front end side of the metal shell 2 and is disposed on the front end side of the metal shell 2. The outer cylinder 7 holds the heater 4 in the shaft hole 10 so that the axis of the heater 4 coincides with the axis C1 of the glow plug 100. The outer cylinder 7 corresponds to a “metal cylinder” in the claims.

  The heater 4 has a cylindrical appearance with a curved end, and is fitted in the shaft hole 10 of the outer cylinder 7. A part of the front end side of the heater 4 protrudes from the outer cylinder 7 to the front end side, and is exposed to a combustion chamber (not shown) when the glow plug 100 is attached to a cylinder head or the like of an engine (not shown). A part of the rear end side of the heater 4 protrudes from the outer cylinder 7 and is accommodated in the shaft hole 9 of the metal shell 2. The detailed configuration of the heater 4 will be described later. The heater 4 is molded from a ceramic molding material mainly composed of silicon nitride. The electrode ring 18 is fitted into the rear end of the heater 4.

  FIG. 2 is a partially enlarged sectional view of the glow plug with the heater shown in FIG. 1 as the center. In FIG. 2, the same components as those in FIG. The heater 4 includes a base 21 and a conductive portion 22. The base 21 is made of an insulating ceramic. The base body 21 has a substantially cylindrical external shape extending along the axis C1 and having a curved tip. A conductive portion 22 is embedded in the base 21.

  The conductive portion 22 includes two extending portions 31 and 32, a connecting portion 33, and two electrode portions 27 and 28. The two extending portions 31 and 32 are rod-shaped members each made of a conductive ceramic, and are disposed inside the base body 21. The two extending portions 31 and 32 are arranged so that their longitudinal directions are parallel to each other, and their axis lines (axis lines) C11 and C12 are parallel to the axis line C1 of the glow plug 100. The two extending portions 31 and 32 are arranged such that the three axes C1, C11, and C12 are positioned on one virtual plane.

  The extending portion 31 includes a distal end side portion 311 located on the distal end side and a rear end side portion 312 located on the rear end side and continuing to the distal end side portion 311. The diameter of the front end portion 311 is smaller than the diameter of the rear end portion 312. The electrode portion 27 is disposed at a position near the rear end of the rear end side portion 312. The electrode portion 27 is formed integrally with the rear end side portion 312 and is formed so as to protrude in the outer peripheral direction (Y-axis direction). In the electrode portion 27, the end portion opposite to the side continuous with the rear end side portion 312 is exposed on the surface of the base 21 and is in contact with the inner peripheral surface of the electrode ring 18. In this way, the electrode ring 18 and the extending portion 31 are electrically connected.

  The other extension part 32 has the same configuration as the extension part 31. That is, the extending portion 32 includes a front end side portion 321 and a rear end side portion 322, and includes the electrode portion 28 at a position near the rear end of the rear end side portion 322. In the electrode portion 28, the end opposite to the side continuous with the rear end side portion 322 is exposed on the surface of the base 21 and is in contact with the inner peripheral surface of the outer cylinder 7. In this way, the outer cylinder 7 and the extending portion 32 are electrically connected.

  The connecting portion 33 extends substantially in the Y-axis direction, and is connected to the distal end of the distal end side portion 311 and the distal end of the distal end side portion 321, respectively. The diameter of the connecting portion 33 is substantially equal to the diameter of the distal end side portion 311 and the diameter of the distal end side portion 321.

  The configuration of the conductive portion 22 including the extended portion 31, the extended portion 32, and the connecting portion 33 can be rephrased as follows. In other words, the conductive portion 22 has two lead portions 312 and 322 having a relatively large diameter composed of the two rear end portions 312 and 322, and a diameter composed of the two tip end portions 311 and 321 and the connecting portion 33. And a small heat generating portion 35. Hereinafter, the two lead portions are also referred to as two lead portions 312 and 322 by using the reference numerals of the two rear end side portions 312 and 322.

  The two lead portions 312 and 322 are both connected to the heat generating portion 35 and guide current to the heat generating portion 35. As described above, since the diameter of the heat generating portion 35 is smaller than the diameter of the two lead portions 312 and 322, heat is likely to be generated, and the temperature is raised to, for example, 1000 ° C. or more. The heater 4 guides the current supplied via the pin terminal 8, the central shaft 3, and the electrode ring 18 to the heat generating part 35 via the electrode part 27 and the lead part 312, and via the lead part 322 and the electrode part 28. By flowing to the outer cylinder 7 and the metal shell 2, the heat generating portion 35 generates heat and the temperature rises. The heat generating part 35 is heated to a temperature of, for example, 1000 ° C. or more during use.

  As will be described later, the ceramic material which is the base material of the base 21 used in manufacturing the heater 4 contains a rare earth element. Therefore, the finished substrate 21 also contains rare earth elements. In the heater 4 of the present embodiment, the rare earth element content in the base 21 at the center of the heater 4 and the rare earth content in the base 21 at the surface layer of the heater 4 are different from each other. Hereinafter, the content rate will be described with reference to FIG.

  FIG. 3 is a cross-sectional view of the heater 4. In FIG. 3, the AA cross section in FIG. 2 is shown. The AA cross section is a cross section that is perpendicular to the axis C <b> 1 and includes the heat generating portion 35. The outer shape of the cross section of the heater 4 is substantially circular. In the present embodiment, the diameter of the heater 4 is approximately 3 mm (millimeter).

  In the cross section shown in FIG. 3, two tip side portions 311 and 321 of the heat generating portion 35 appear. These two tip side portions 311 and 321 are arranged so as to have a point-symmetric relationship with respect to the center of gravity p2 of the heater 4.

In the heater 4 of this embodiment, the rare earth element content αa in the base 21 of the central portion Sa of the heater 4 is higher than the rare earth content αb in the base 21 of the surface layer portion Sb of the heater 4. In the present embodiment, the content αa is 0.6 atm% (atomic reference concentration) or more and 2.0 atm% or less. In addition, the relationship shown to following formula (1) may hold | maintain between said two content rate (alpha) b and (alpha) a.
0.65 ≦ αb / αa ≦ 0.9 (1)

  In the present embodiment, the content αb is preferably 0.5 atm% or more and 1.4 atm% or less. When the content αb is 0.5 atm% or more and 1.4 atm% or less, the oxidation resistance in a low temperature environment can be improved. Furthermore, the content rate αb is preferably 0.5 atm% or more and 1.05 atm% or less.

In the present embodiment, the central portion Sa of the heater 4 and the surface layer portion Sb of the heater 4 mean the region Ar2 provided in the first region SA and the region Ar1 provided in the second region SB, respectively, as shown in FIG. To do. The region Ar1 and the region Ar2 are both circular regions and have the same area. The first region SA indicates a portion of the base 21 that is located between the distal end side portion 311 of the extending portion 31 and the distal end side portion 321 of the extending portion 32. The second area SB indicates a portion of the base body 21 excluding the first area SA. The region Ar1 described above is not limited to the position shown in FIG. 3 as long as the entire range of the region Ar1 is included in the second region SB. Similarly, the above-described region Ar2 is not limited to the position shown in FIG. 3 as long as the entire range of the region Ar2 is included in the first region SA. The two regions Ar1 and Ar2 are not limited to a circular shape as long as their areas are equal to each other, and may be any shape such as a rectangle. The areas of the two regions Ar1 and Ar2 are each preferably 100 μm ² (square micrometer) or more.

  In the present embodiment, the central portion Sa (region Ar2) of the heater 4 has a circular shape having a radius of a predetermined length r1 (25 μm (micrometer)) centered on the center of gravity p2 of the heater 4 in the first region SA. It is an area. In the present embodiment, the surface layer portion Sb (region Ar1) of the heater 4 has a predetermined length centered on a point p1 located on the inner side from the outer peripheral surface Sf1 of the heater 4 by a predetermined distance d1 in the second region SB. This is a circular region having a radius of r1. In the present embodiment, the predetermined distance d1 is 100 μm.

  In the present embodiment, the rare earth element contained in the substrate 21 is at least one selected from erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Of these elements, erbium (Er) and ytterbium (Yb) are preferable from the viewpoint of production cost and stable availability. Furthermore, ytterbium (Yb) is more preferable from the viewpoint of oxidation resistance.

  Hereinafter, a method for manufacturing the glow plug 100 having the above configuration will be described with reference to FIGS.

A2. Manufacturing method of glow plug 100:
FIG. 4 is a process chart showing the manufacturing procedure of the glow plug 100. First, a molding material for the conductive portion 22 is produced (process P105), and a molding material for the base body 21 is produced (process P110). Note that these two steps P105 and P110 may be performed in the reverse order. Moreover, these two processes P105 and P110 may be performed simultaneously. In the present embodiment, the molding material of the conductive portion 22 is a pellet whose main component is ceramic (mainly silicon nitride, tungsten carbide, sintering aid). For example, a ceramic and a binder are used with a kneader. It can be prepared by kneading and then pelletizing. Moreover, in this embodiment, a binder is not specifically limited, For example, plastic resins, such as a polypropylene, wax, a dispersing agent, a plasticizer, etc. can be used 1 type or in mixture of 2 or more types. . In this embodiment, the sintering aid includes at least one rare earth element selected from the above-mentioned rare earth elements, that is, erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Note that the sintering aid may include alumina, aluminum nitride (AlN), molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ) silica (SiO ₂ ), and the like in addition to the rare earth oxide.

  In this embodiment, the molding material of the base 21 is a pellet mainly composed of ceramic (mainly silicon nitride and a sintering aid). For example, the ceramic and the binder are mixed with a kneader. It can be prepared by kneading and then pelletizing. The binder and the sintering aid are the same as the sintering aid for the conductive portion 22 described above. Here, the amount of the rare earth element in the sintering aid in Step P110 is such that when the heater 4 is completed, the rare earth element content in the base 21 at the center of the heater 4 is 0.6 atm% or more. The content is adjusted. Such an amount can be determined and set by experiment, for example.

  The intermediate molded body 200 of the conductive part is manufactured by injection molding using the molding material obtained in the process P105 (process P115). In the present embodiment, the “intermediate molded body 200 of the conductive portion” means a member that becomes the conductive portion 22 through a degreasing and firing process described later. Instead of injection molding, the intermediate molded body 200 of the conductive part may be produced by any molding method such as powder press molding and cast molding.

  An intermediate formed body of the half-shaped base 21 is formed on one side of the intermediate formed body 200 of the conductive part obtained in the process P115 (process P120). The remaining part of the intermediate molded body of the base body 21 is formed on the other surface side of the intermediate molded body 200 of the conductive portion to obtain the intermediate molded body of the heater 4 (process P125). In steps P120 and P125, both are performed by injection molding using the molding material obtained in step P110. In addition, it may replace with injection molding and may produce with arbitrary shaping | molding methods, such as powder press molding and casting molding.

  FIG. 5 is an explanatory diagram schematically showing the processing content of the process P120. FIG. 6 is an explanatory diagram schematically showing the processing content of the process P125. As shown in FIG. 5, in the process P120, first, the intermediate molded body 200 of the conductive part is disposed in the cavity 420 formed in the lower mold 400 so as to cover the upper half of the intermediate molded body 200 of the conductive part. An upper mold 500 is disposed. The intermediate molded body 200 of the conductive portion 22 has an appearance shape substantially similar to the conductive portion 22. That is, the intermediate molded body 200 of the conductive portion includes a lead correspondence portion 212 corresponding to the lead portion 312, a lead correspondence portion 222 corresponding to the lead portion 322, a heat generation correspondence portion 235 corresponding to the heat generation portion 35, and two electrodes. Two electrode corresponding portions 227 and 228 corresponding to the portions 27 and 28 are provided. The two lead corresponding portions 212 and 222 become the two lead portions 312 and 322 through processes such as degreasing, baking, polishing, and cutting described later. Similarly, the heat generation corresponding portion 235 and the two electrode corresponding portions 227 and 228 become the heat generation portion 35 and the two electrode portions 27 and 28 through processes such as degreasing, baking, polishing and cutting, which will be described later. Further, the intermediate molded body 200 of the conductive portion includes a rear end connecting portion 250. The rear end connecting portion 250 connects the ends of the two lead corresponding portions 212 and 222 on the opposite side of the heat generating corresponding portion 335 in the intermediate molded body 200 of the conductive portion. The rear end connecting portion 250 is provided in order to prevent the relative positions of the two lead corresponding portions 212 and 222 from shifting and facilitate the handling of the intermediate molded body 200.

  The cavity 420 formed in the lower mold 400 is formed in a shape that can accommodate the lower half of the intermediate molded body 200 of the conductive portion 22. The upper mold 500 has a hollow rectangular parallelepiped external shape in which the mating surface side with the lower mold 400 is opened. One end face Sf5 in the longitudinal direction of the upper mold 500 is provided with an injection hole for filling the molding material with the molding material. After arranging the intermediate molded body 200, the lower mold 400, and the upper mold 500 of the conductive part as described above, the molding material obtained in the process P110 is injected into the upper mold 500, and the half-shaped The intermediate molded body of the base body 21 is molded on one side surface (the upper surface side in FIG. 5) of the intermediate molded body 200 of the conductive portion. In this way, an intermediate molded body 700 shown in FIG. 6 is obtained.

  In Step P125, the intermediate molded body 700 obtained in Step P120 is turned upside down and placed in the cavity 620 of the new lower mold 600 in the posture shown in FIG. Next, the upper mold 500 is disposed so as to cover the upper half of the intermediate molded body 700. The cavity 620 formed in the lower mold 600 is formed in a shape that can just accommodate the portion of the intermediate molded body of the half-shaped base 21 in the intermediate molded body 700. The upper mold 500 is the same as the upper mold 500 shown in FIG. After placing the intermediate molded body 700, the lower mold 600, and the upper mold 500 as described above, the molding material obtained in the process P110 is injected into the upper mold 500, and the upper half of the intermediate molded body 700 is injected. The remainder of the intermediate molded body of the base body 21 is formed. In this way, an intermediate molded body of the heater 4 is obtained. In the present embodiment, the “intermediate molded body of the heater 4” means a member that becomes the heater 4 through processes such as degreasing, baking, polishing, and cutting described later.

  As shown in FIG. 4, when the intermediate molded body of the heater 4 is obtained in the process P125, the intermediate molded body of the heater 4 is degreased (process P130). Since the intermediate molded body of the heater 4 contains a binder, the binder is removed by heating (preliminary firing). For example, the intermediate formed body of the heater 4 may be heated at 800 ° C. for 60 minutes in a nitrogen atmosphere. After the step P130, main firing is performed (step P135). In the main baking, the heating is performed at a higher temperature than the so-called temporary baking in the process P130. For example, heating is performed so that the temperature is raised to about 1850 ° C. at the maximum. Further, in the main firing, the firing may be performed at 1 atm or less and in a nitrogen atmosphere at 1 atm or more and 7 atm or less.

  Here, in the present embodiment, the rare earth element content αa in the central portion Sa is obtained by volatilizing the rare earth element from the surface layer portion Sb of the heater 4 (intermediate molded body of the heater 4) in the main firing (process P135). It is adjusted to be higher than the rare earth element content αb in the surface layer portion Sb. Thus, the firing conditions for volatilizing the rare earth element from the surface layer portion Sb so that the content rate αa in the center portion Sa is higher than the content rate αb in the surface layer portion Sb can be obtained by experiments. For example, the heater is adjusted by appropriately adjusting the firing conditions such as the maximum temperature, the time for maintaining the maximum temperature, the pressure in the furnace when the maximum temperature is reached after nitrogen gas is introduced, and the time for maintaining the nitrogen gas introduction temperature. 4 is measured, and the content of rare earth elements in the surface layer portion Sb and the central portion Sa of the heater 4 is measured. In this way, the adjustment of the firing conditions and the measurement of the rare earth element content can be repeatedly performed to identify the firing conditions that satisfy the above formula (1).

  After the main firing, polishing and cutting are performed (process P140). The electrode portions 27 and 28 are exposed from the surface of the base 21 by the polishing process. Further, the rear end portion of the fired body obtained in the process P135, that is, the portion corresponding to the rear end connecting portion 250 is removed by the cutting process. The heater 4 is completed by the processes P105 to P140 described above. Thereafter, each component of the glow plug 100 shown in FIG. 1 is assembled (process P145), and the glow plug 100 is completed. In addition, a well-known method is employable as a manufacturing method of each structure parts, such as the metal shell 2. Steps P105 to P140 described above correspond to the method for manufacturing the heater 4.

  According to the heater 4 of the present embodiment described above, the rare earth element content αa in the base 21 of the central portion Sa of the heater 4 is compared with the rare earth content αb in the base 21 of the surface layer Sb of the heater 4. high. In addition, the rare earth element content αa in the base 21 of the central portion Sa of the heater 4 is 0.6 atm% or more. Therefore, a sufficient liquid phase can be supplied at the time of firing, and the sinterability in the base 21 of the central portion Sa of the heater 4 can be improved. In addition, since the rare earth element content αa in the base 21 of the central portion Sa of the heater 4 is 2.0 atm% or less, it is possible to suppress a decrease in oxidation resistance of the base 21 in a low temperature environment. On the other hand, since the rare earth element content αb in the base 21 of the surface layer portion Sb is relatively low, it is possible to suppress a decrease in oxidation resistance of the surface layer portion Sb in a low temperature environment. Since the oxidation resistance of the surface layer portion Sb in the substrate 21 greatly affects the oxidation resistance of the entire substrate 21, according to the heater 4 of the present embodiment, the oxidation resistance of the entire substrate 21 can be improved. Therefore, according to the heater 4 of the said embodiment, the improvement of the oxidation resistance of the base | substrate 21 and the improvement of sinterability can be made compatible. In addition, since the rare earth element used in the sintering aid is at least one selected from erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), it promotes crystallization of the grain boundary phase. Thus, the oxidation resistance in a high temperature environment can be improved.

B. Example:
The same or similar heater as the heater 4 of the above-described embodiment was produced as a sample, and an oxidation resistance test and a sinterability test were performed on these samples. In the oxidation resistance test, the oxidation resistance at 1300 ° C. (high temperature environment) and the oxidation resistance at 800 ° C. (low temperature environment) were evaluated. Table 1 below shows the test results of the oxidation resistance test and the sinterability test. In Table 1, in addition to the oxidation resistance and sinterability test results (evaluation results), the rare earth type for each sample, the rare earth element content αa in the central portion Sa, and the rare earth elements in the surface layer portion Sb Content rate αb and the ratio αa / αb of these content rates are described.

B1.1300 ° C. oxidation resistance test:
In the 1300 ° C. oxidation resistance test, first, nine heaters (samples 1 to 9) similar to the heater 4 of the embodiment described above were produced. Among samples 1 to 9, the rare earth element in sample 7 was erbium (Er), and the rare earth element in other samples 1 to 7, 8, and 9 was ytterbium (Yb). Moreover, the combinations of the content rates αa and αb of the samples 1 to 9 were made different from each other by making the firing conditions of the samples 1 to 9 different.

In addition, these nine samples 1-9 differ from the heater 4 of embodiment mentioned above in the point which does not have the electrode parts 27 and 28. FIG. Other configurations and manufacturing methods are the same as those of the heater 4 of the above-described embodiment. When the electrode portions 27 and 28 are present, oxidation proceeds from the electrode portions 27 and 28 exposed on the outer peripheral surface Sf <b> 1 of the heater 4 to oxidize the conductive portion 22, and the oxidation resistance of the base 21 cannot be accurately specified. For this reason, Samples 1 to 9 were prepared by omitting the electrode portions 27 and 28. Next, the weight and surface area of the produced samples 1 to 9 were measured. Next, samples 1 to 9 were heated at a predetermined temperature for a predetermined period. Specifically, it was heated at 1300 ° C. for 50 hours. Then, the weight of the samples 1-9 after a heating was measured. And oxidation resistance was evaluated according to the variation | change_quantity of the weight per unit area before and behind a heating. Specifically, the smaller the amount of change in weight per unit area, the higher the oxidation resistance, and the larger the amount of change, the lower the oxidation resistance. As the oxidation of silicon nitride proceeds, the weight per unit area in the substrate 21 increases. Therefore, a large change in weight before and after heating means that the oxidation of silicon nitride is more advanced, which indicates that the oxidation resistance of the substrate is low. In Table 1 above, when the change in weight per unit area is 0.20 g / cm ² or less, it is evaluated as “◯ (highest)” and is larger than 0.20 g / cm ^{2 and} 0.28 g / cm 2. When it was below, it was evaluated as “Δ (second highest)”, and when it was larger than 0.28 g / cm ² , it was evaluated as “× (lowest)”.

  In addition, three types of heaters 4 (samples 10 to 12) as comparative examples were produced, and the oxidation resistance test and the sinterability test were also performed on these samples 10 to 12, and each performance was evaluated. The sample 10 of the comparative example differs from the heater 4 of the above-described embodiment in that the rare earth element content αa in the central portion Sa is not 0.6 atm% or more. The sample 11 of the comparative example differs from the heater 4 of the above-described embodiment in that the rare earth element content αa in the central portion Sa is not 2.0 atm% or less. The sample 12 of the comparative example differs from the heater 4 of the above-described embodiment in that the rare earth element content rate αa in the central portion Sa is lower than the rare earth element content rate αb in the surface layer portion Sb.

  In the evaluation results of the 1300 ° C. oxidation resistance test, among the samples 1 to 9, the other samples 1 to 6 and 9 other than the samples 7 and 8 had the highest “◯” evaluation. Samples 7 and 8 were the second highest “Δ”. The reason why Samples 1 to 9 were comparatively high in this way was that the rare earth element content αa in the base 21 of the central portion Sa of the heater 4 was 0.6 atm% or more. In addition, regarding the samples 11 and 12 of the comparative example, since the content rate αa of the central portion Sa is 0.6 atm% or more, it is estimated that the oxidation resistance evaluation was “◯”. On the other hand, about the sample 10 of a comparative example, content rate (alpha) a of center part Sa is less than 0.6 atm%. Therefore, since the rare earth element (Yb) in the central portion Sa is small, it is presumed that the evaluation of oxidation resistance under a high temperature environment is “x”.

  Here, paying attention to Sample 3 and Sample 7, the two samples are different in the rare earth type, and the contents αa and αb are equal to each other. As a result of evaluating the oxidation resistance, the sample 3 was “◯” while the sample 6 was “Δ”. From this evaluation result, it can be understood that ytterbium (Yb) is more preferable than erbium (Er) as a rare earth element contained in the sintering aid from the viewpoint of oxidation resistance in a high temperature environment.

  The rare earth element content αa in the central portion Sa and the rare earth element content αb in the surface layer portion Sb of each sample 1 to 12 were measured as follows. That is, twelve types of heaters having the same firing conditions at the time of preparing each sample are prepared separately from each sample 1 to 12, and these twelve types of samples are respectively perpendicular to the axis C1 in the heat generating portion 35. The content of rare earth elements was measured for each of the center portion Sa and the surface layer portion Sb in the cross section that appeared after cutting using an electron beam microanalyzer (EPMA). Note that the rare earth element content may be measured by energy dispersive X-ray analysis (EDS) instead of EPMA.

B2.800 ° C. oxidation resistance test:
In the 800 ° C. oxidation resistance test, 12 types (12 pieces) of heaters (samples 1 to 12) similar to the samples 1 to 12 used in the 1300 ° C. oxidation resistance test were prepared. Next, samples 1 to 12 were heated at a predetermined temperature for a predetermined period. Specifically, it was heated at 800 ° C. for 50 hours. Then, the cross section of the samples 1-12 after a heating was observed and oxidation resistance was evaluated. Specifically, the smaller the progress of oxidation from the surface, the higher the oxidation resistance, and the higher the progress of oxidation, the lower the oxidation resistance. In Table 1 above, when the progress of oxidation was less than 20 μm from the surface, it was evaluated as “◎ (highest)”, and when the progress of oxidation was 20 μm or more and less than 30 μm from the surface, “◯ (second highest)” ”And evaluated as“ △ (third highest) ”when the oxidation trial is 30 μm or more and less than 50 μm from the surface, and“ × (lowest) when the progress of oxidation is 50 μm or more from the surface ) ”.

  In the evaluation results of the 800 ° C. oxidation resistance test, among samples 1 to 9, samples 1 to 4 and 6 to 8 had the highest “◎” evaluation. Sample 5 was the second highest “◯”. Sample 9 was the third highest “Δ”. As described above, the samples 1 to 9 were relatively highly evaluated because the relative content of the rare earth element αb in the base 21 of the surface layer portion Sb was relatively reduced, and the decrease in oxidation resistance under a low temperature environment was suppressed. This is presumed to have been made. For the sample 10 of the comparative example, since the content rate αa of the central portion Sa is higher than the content rate αb of the surface layer portion Sb, it is assumed that the oxidation resistance evaluation was “◯” for the same reason as described above. Is done. On the other hand, in the sample 12 of the comparative example, the content rate αa of the center portion Sa is lower than the content rate αb of the surface layer portion Sb. Therefore, since the surface layer portion Sb contains a large amount of rare earth elements (Yb), it is presumed that the oxidation of the surface layer portion Sb has progressed under a relatively low temperature environment, and the oxidation resistance evaluation has become “x”. .

  Moreover, about the sample 11 of a comparative example, although content rate (alpha) a of center part Sa is higher than content rate (alpha) b of surface layer part Sb, content rate (alpha) a of center part Sa is over 2.0 atm%. Therefore, since a large amount of rare earth element (Yb) is present in the central portion Sa, it is presumed that the oxidation progressed under a relatively low temperature environment, and the oxidation resistance evaluation was “x”.

  Here, focusing on the samples 1 to 6, the samples 1 to 4 and 6 in which the content αb of the surface layer portion Sb is 1.05 atm% or less have an oxidation resistance evaluation of “◎”, whereas the surface layer portion Sample 5 in which the Sb content αb was 1.3 had an oxidation resistance test of “◯”. From the evaluation results, the content αb of the surface layer portion Sb is preferably 0.5 atm% or more and 1.05 atm% or less.

B3. Sinterability test:
In the sinterability test, nine heaters were first manufactured according to the method for manufacturing the heater 4 of the above-described embodiment. In addition, three heaters similar to the comparative example of the oxidation resistance test described above were produced. These 12 heaters are different from the 12 samples 1 to 12 in the oxidation resistance test described above in that the electrode portions 27 and 28 are included, and the manufacturing method including other configurations and firing conditions is as follows. It is the same as the samples 1 to 12 described above. As described above, in order to adjust the content rate αa of the central portion Sa to be higher than the content rate αb of the surface layer portion Sb, adjustment of the firing conditions is an important point and whether the conductive portion 22 is included. No or no impact. Therefore, in the sinterability test, samples corresponding to the above-described samples 1 to 12 are also referred to as samples 1 to 12. Next, relative density was measured about 12 samples 1-12. In this example, density measurement was performed by Archimedes method, and the relative density was obtained from the measured value and the theoretical density value. And it was judged that the higher the relative density, the higher the sinterability. It can be estimated that the higher the relative density is, the fewer voids generated in the grain boundary portion, and thus the higher the sinterability (the property of being baked). In this example, the maximum firing temperature in the main firing was 1850 ° C. or lower, and the pressure in the furnace at that time was 7 atm or lower. In Table 1 above, when the relative density is 98% or more, it is evaluated as “◯ (highest)”, and when it is 97% or more and less than 98%, it is evaluated as “Δ (second highest)”. When it was less than%, it was evaluated as “× (lowest)”.

  In the evaluation results of the sinterability test, among the samples 1 to 12, the other samples 1 to 7, 9, 11, and 12 other than the samples 8 and 10 had the highest “◯” evaluation. Sample 8 was the second highest “Δ”. The reason why the samples 1 to 9 were evaluated to be relatively high in this way is presumed to be because the rare earth element content αa in the central portion Sa is relatively high at 0.6 atm% or more. Also in the samples 11 and 12 of the comparative example, since the rare earth element content αa in the central portion Sa is relatively high at 0.6 atm% or more, it is estimated that the sinterability evaluation was “◯”. On the other hand, regarding the sample 10 of the comparative example, the rare earth element content αa in the central portion Sa is relatively low at 0.50 atm%, and therefore, the sinterability evaluation is estimated to be “x”. The

  Here, the content ratio (αb / αa) of the sample 8 is 60.0%, which is smaller than the content ratios of the other samples 1 to 6. When the content ratio is relatively low at 60.0%, the liquid phase amount is insufficient at the time of sintering, so fine pores are generated in the grain boundary portion, and it is assumed that the sinterability is lowered. As can be understood from the comparison between Samples 1 to 6 and Samples 7 and 8, the ratio of the two contents (αb / αa) satisfies the above formula (1). Can be improved.

C. Variations:
C1. Modification 1:
In the above-described embodiment and examples, the central portion Sa and the surface layer portion Sb when defining the two content ratios αa and αb are the central portion Sa in the cross section in which the two tip side portions 311 and 321 appear in the heat generating portion 35. However, the present invention is not limited to this. Instead of the two tip side portions 311 and 321, the center portion and the surface layer portion in the cross section where the two rear end side portions 312 and 322 appear may be used. That is, in general, the two content ratios αa and αb may be defined by the center portion Sa and the surface layer portion Sb in the cross section where the two extending portions 31 and 32 appear.

C2. Modification 2:
In the said embodiment and Example, each extension part 31 and 32 was each formed from the single member (intermediate molded object), However, This invention is not limited to this. Each extending portion may be constituted by a plurality of types of members. For example, in the extended portion 31, a member corresponding to the front end side portion 311 and a member corresponding to the rear end side portion 312 may be configured by different types of members. In this configuration, for example, the content of tungsten carbide in the member corresponding to the front end side portion 311 is made lower than the content of tungsten carbide in the member corresponding to the rear end side portion 312, so that the specific resistance of the front end side portion 311 is reduced. It is also possible to make it easier to generate heat. In such a configuration, a portion from the boundary between the member corresponding to the front end side portion 311 and the member corresponding to the rear end side portion 312 to the connecting portion 33 corresponds to a subordinate concept of the front end side portion in the claims.

C3. Modification 3:
In the above-described embodiment and examples, the center portion Sa of the heater 4 is the circular region Ar2 having a radius of the predetermined length r1 centered on the center of gravity p2 of the heater 4, but the present invention is not limited to this. An area having an arbitrary shape such as a rectangle centered on the center of gravity of the heater 4 may be used. Moreover, the area | region of the arbitrary positions in 1st area | region SA which does not center on the gravity center of the heater 4 may be sufficient.

  Further, in the above-described embodiments and examples, the surface layer portion Sb of the heater 4 has a circular shape with a predetermined length r1 centered on a point p1 located at a predetermined distance d1 from the outer peripheral surface Sf1 of the heater 4 as a radius. Although the region is Ar1, the present invention is not limited to this. It may be a region between a circumference that is a set of points that enter a predetermined distance from the outer peripheral surface Sf1 and the outer peripheral surface Sf1. Moreover, it is good also as an area | region including outer peripheral surface Sf1. Furthermore, the area | region of the arbitrary positions in 2nd area | region SB may be sufficient.

C4. Modification 4:
In the above-described embodiment and examples, the conductive material in the molding material of the conductive portion 22 is tungsten carbide. However, any conductive material such as molybdenum silicide or tungsten silicide can be used instead. .

C5. Modification 5:
In the above embodiment, the heater 4 is a ceramic heater used for the glow plug 100. However, instead of the glow plug 100, the heater 4 is used as a heater for igniting a burner, a heater for a gas sensor, or a DPF (Diesel particulate filter). It may be a ceramic heater.

  The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit of the present invention. For example, the technical features in the present embodiment and the modified examples corresponding to the technical features in the embodiments described in the column of the summary of the invention are to solve part or all of the above-described problems, or In order to achieve part or all of the above effects, replacement or combination can be appropriately performed. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 2 ... Metal fitting 3 ... Medium shaft 4 ... Heater 5 ... Insulating member 6 ... Flange part 7 ... Outer cylinder 8 ... Pin terminal 9, 10 ... Shaft hole 11 ... Male screw part 12 ... Tool engaging part 15 ... Thick part 16 ... Engagement Joint part 18 ... Electrode ring 21 ... Base 22 ... Conductor 27, 28 ... Electrode part 31, 32 ... Extension part 33 ... Connection part 35 ... Heat generating part 100 ... Glow plug 200 ... Intermediate molded body 212, 222 ... Lead corresponding part 227 ... Electrode corresponding part 235 ... Heat generation corresponding part 250 ... Rear end connecting part 311 ... Front end side part 312 ... Rear end side part (lead part)
321 ... Front end side part 322 ... Rear end side part (lead part)
335 ... Heat generation corresponding part 400 ... Lower mold 420 ... Cavity 500 ... Upper mold 600 ... Lower mold 620 ... Cavity 700 ... Intermediate molded body Ar1, Ar2 ... Area C1, C11, C12 ... Axis Sa ... Center part Sb ... Surface layer Part Sf1 ... outer peripheral surface Sf5 ... end face d1 ... distance p1 ... point p2 ... center of gravity

Claims (7)

A base body containing silicon nitride as a main component and further containing a rare earth element and extending in the axial direction; two extending portions embedded in the base body and extending along the axial direction; and the two A ceramic heater comprising a conductive portion including a connecting portion that connects the distal end portions of the extending portion;
In the cross section perpendicular to the axial direction and where the two extending portions appear, the content of the rare earth element in the substrate at the center of the ceramic heater is the content of the rare earth element in the substrate at the surface layer of the ceramic heater. Higher than the rate,
The rare earth element content in the substrate in the center is 0.6 atm% or more and 2.0 atm% or less.
A ceramic heater characterized by that. The ceramic heater according to claim 1,
The conductive portion includes a heat generating portion formed by a front end side portion and the connecting portion in each extending portion, and two leads formed by a rear end side portion in each extending portion connected to the heat generating portion. And
The cross section is a cross section in which the heat generating portion appears.
A ceramic heater characterized by that. In the ceramic heater according to claim 1 or 2,
The content of the rare earth element in the substrate of the surface layer portion is 65% or more and 90% or less of the content of the rare earth element in the substrate of the center portion.
A ceramic heater characterized by that. In the ceramic heater according to any one of claims 1 to 3,
The rare earth element is at least one selected from erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
A ceramic heater characterized by that. The ceramic heater according to claim 4, wherein
The rare earth element is ytterbium (Yb).
A ceramic heater characterized by that. In the ceramic heater according to any one of claims 1 to 5,
The rare earth element content in the substrate of the surface layer portion is 0.5 atm% or more and 1.05 atm% or less.
A ceramic heater characterized by that. A glow plug comprising a ceramic heater and a metal cylinder holding the ceramic heater,
The ceramic heater is the ceramic heater according to any one of claims 1 to 6,
A glow plug characterized by that.

Images