JP6869839B2 - Ceramic heater and glow plug - Google Patents

Description

The present invention relates to ceramic heaters and glow plugs.

Conventionally, as a ceramic heater used for glow plugs and the like, it is known that a heat generating resistor made of a conductive ceramic is embedded and held in a substrate made of an insulating ceramic.
In such a ceramic heater, in general, the material constituting the heat generation resistor tends to have a larger coefficient of thermal expansion than the material constituting the substrate. If the difference in the coefficient of thermal expansion between the two is large, for example, the amount of heat shrinkage will be significantly different in the process from the high temperature state to the cooling state, and the substrate or the heat generating resistor will crack due to the thermal stress. There is a risk that it will end up.
Therefore, in Patent Document 1, in order to bring the coefficient of thermal expansion of the substrate closer to the coefficient of thermal expansion of the heating element, it is studied to include a metal siliceous material having a larger coefficient of thermal expansion in the material constituting the substrate. Specifically, _{a metal siliceate such as WSi 2} is contained in the substrate.

JP-A-2007-335397

However, although the coefficient of thermal expansion of the substrate and the coefficient of thermal expansion of the heating element are close to _each other, the heat between silicon nitride, which is the main component of the insulating ceramic constituting the substrate, and WSi 2 and the like existing in the grain boundary phase of silicon nitride. The expansion difference becomes large, and as a result, cracks may occur due to thermal stress starting from the grain boundary.
The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the durability of the ceramic heater by adjusting the type and amount of the silicified product, and it can be realized as the following form. It is possible.

(1) A ceramic heater having an insulating ceramic substrate and a conductive ceramic heating resistor embedded in the substrate.
The conductive ceramic contains tungsten carbide and silicon nitride as main components.
The insulating ceramic has a silicon nitride crystal as a main phase, and has a rare earth element compound and a silicified product represented by _{W 5} Si ₃ or Mo ₅ Si _{3 in the grain boundary phase.}
In the X-ray diffraction chart of the substrate, the peak intensity on the (101) plane of the silicon nitride crystal is defined as the peak intensity X, and the peak intensity on the (411) plane of the _{W 5} Si ₃ or Mo ₅ Si _{3 crystal is peaked.} A ceramic heater characterized in that the value of peak intensity Y / peak intensity X, which is the ratio of peak intensity, is 0.05 or more and 0.4 or less when the intensity is Y.

In the ceramic heater having this configuration, _{since the substrate contains a predetermined amount of W 5} Si ₃ or Mo ₅ Si ₃ , the difference in the coefficient of thermal expansion between the substrate and the heat generating resistor becomes small, and the main phase of the substrate is used. The difference in thermal expansion from the constituent silicon nitride can also be reduced, and the durability of the ceramic heater is improved.

(2) In the X-ray diffraction chart of the substrate _{, when the peak intensity of the WSi 2} or MoSi ₂ crystal on the (101) plane is the peak intensity Z, the peak intensity is the ratio of the peak intensity X to the peak intensity Z. The ceramic heater according to (1), wherein Z / peak intensity X is 0.05 or less.

In the ceramic heater having this configuration, the _{amount of WSi 2} or MoSi ₂ contained in the substrate is small, and it is suppressed that the grain boundaries are excessively expanded by _{WSi 2} or MoSi _{2 and become the starting point of destruction.} Therefore, the strength and durability of the ceramic heater are improved.

(3) The average circle-equivalent diameter of one or more particles selected from the group consisting of _{W 5} Si ₃ , WSi ₂ , Mo ₅ Si ₃ , and MoSi ₂ contained in the insulating ceramic, or aggregates of the particles. The ceramic heater according to (1), characterized in that it is 0.05 μm or more and 0.90 μm or less.

In the ceramic heater having this configuration, the difference in the coefficient of thermal expansion between the substrate and the heat generating resistor can be reduced while maintaining the mechanical properties of the ceramic heater at room temperature and high temperature, and the durability can be improved.

(4) The item according to any one of (1) to (3), wherein crystals of _{Er 2} Si ₂ O ₇ and / or Yb ₂ Si ₂ O _{7 are further present in the grain boundary phase.} Ceramic heater.

In the ceramic heater having this configuration, the heat resistance of the grain boundaries is improved, the softening of the ceramic heater at high temperature is suppressed, and the strength at high temperature is improved.

(5) A glow plug comprising the ceramic heater according to any one of (1) to (4) and a tubular main metal fitting for holding the rear end portion of the ceramic heater inside. ..

In the glow plug having this configuration, since the base of the ceramic heater used _{contains a predetermined amount of W 5} Si ₃ or Mo ₅ Si ₃ , the difference in the coefficient of thermal expansion between the base and the heat generating resistor becomes small. The difference in thermal expansion from the silicon nitride that constitutes the main phase of the substrate can also be reduced, and the durability as a glow plug is improved.

According to the present invention, it is possible to realize a ceramic heater or glow plug having improved strength and durability.

It is sectional drawing which shows an example of a glow plug. FIG. 5 is an enlarged cross-sectional view showing an enlarged portion of the glow plug shown in FIG. 1 including a ceramic heater. FIG. 3 is an enlarged cross-sectional view showing a part of the ceramic heater shown in FIG. 2 in an enlarged manner. FIG. 4A is an explanatory diagram illustrating an example of a method for manufacturing a ceramic heater. FIG. 4B is an explanatory view showing a molded body formed in the process of manufacturing the ceramic heater.

A1. Configuration of Glow Plugs FIG. 1 is a schematic view showing an example of glow plugs of the first embodiment. FIG. 2 is an enlarged cross-sectional view showing a portion of the glow plug 1 shown in FIG. 1 including a ceramic heater 40. The line CL illustrated in FIGS. 1 and 2 indicates the central axis of the glow plug 1. The cross section shown in FIGS. 1 and 2 is a cross section including the central axis CL.

Hereinafter, the central axis CL is also referred to as "axis CL", and the direction parallel to the central axis CL is also referred to as "axis direction". The radial direction of the circle centered on the central axis CL is also simply referred to as the "diameter direction", and the circumferential direction of the circle centered on the central axis CL is also referred to as the "circumferential direction". Of the directions parallel to the central axis CL, the downward direction in FIG. 1 is called the first direction D1. The first direction D1 is a direction from the terminal member 80, which will be described later, toward the ceramic heater 40. The second direction D2 and the third direction D3 in the figure are directions perpendicular to each other, and both are directions perpendicular to the first direction D1. Hereinafter, the first direction D1 is also referred to as a tip direction D1, and the direction opposite to the first direction D1 is also referred to as a rear end direction D1r. Further, the front end direction D1 side in FIG. 1 is referred to as the front end side of the glow plug 1, and the rear end direction D1r side in FIG. 1 is referred to as the rear end side of the glow plug 1.

As shown in FIG. 1, the glow plug 1 includes a main metal fitting 20, a center pole 30, a ceramic heater 40, an O-ring 50, an insulating member 60, and a metal outer cylinder 70 (hereinafter, also simply referred to as “outer cylinder 70”). ), The terminal member 80, and the connecting member 90.

The main metal fitting 20 is a tubular member having a through hole 20A extending along the central axis CL. The main metal fitting 20 includes a tool engaging portion 28 formed at an end portion on the rear end direction D1r side, and a male screw portion 22 provided on the tip end direction D1 side of the tool engaging portion 28. The tool engaging portion 28 is a portion that engages with a tool (not shown) when the glow plug 1 is attached or detached. The male screw portion 22 includes a screw thread for screwing into a female screw formed in a mounting hole of an internal combustion engine (not shown). The main metal fitting 20 is made of a conductive material (for example, a metal such as carbon steel).

The center pole 30 is housed in the through hole 20A of the main metal fitting 20. The center pole 30 is a round bar-shaped member. The center pole 30 is made of a conductive material (eg, stainless steel). The rear end portion 39, which is the end portion on the rear end direction D1r side of the center pole 30, projects from the opening 20B on the rear end direction D1r side of the main metal fitting 20 toward the rear end direction D1r.

An O-ring 50 is provided between the outer surface of the center pole 30 and the inner surface of the through hole 20A of the main metal fitting 20 in the vicinity of the opening 20B. The O-ring 50 is made of an elastic material (for example, rubber). A ring-shaped insulating member 60 is attached to the opening 20B of the main metal fitting 20. The insulating member 60 includes a tubular portion 62 and a flange portion 68 provided on the D1r side in the rear end direction of the tubular portion 62. The tubular portion 62 is sandwiched between the outer surface of the center pole 30 and the inner surface of the portion forming the opening 20B of the main metal fitting 20. The insulating member 60 is made of, for example, a resin. The main metal fitting 20 supports the center pole 30 via the O-ring 50 and the insulating member 60.

The terminal member 80 is arranged on the D1r side in the rear end direction of the insulating member 60. The terminal member 80 is a cap-shaped member and is made of a conductive material (for example, a metal such as nickel). A flange portion 68 of the insulating member 60 is sandwiched between the terminal member 80 and the main metal fitting 20. The rear end 39 of the center pole 30 is inserted into the terminal member 80. By crimping the terminal member 80, the terminal member 80 is fixed to the rear end portion 39. With such a structure, the terminal member 80 and the center pole 30 are electrically connected.

The outer cylinder 70 is fixed to the opening 20C on the D1 side in the tip direction of the main metal fitting 20. The outer cylinder 70 is fixed to the opening 20C by, for example, press fitting or welding. The outer cylinder 70 is a tubular member having a through hole 70A extending along the central axis CL. The outer cylinder 70 is made of a conductive material (for example, stainless steel).

A ceramic heater 40 that generates heat when energized is inserted into the through hole 70A of the outer cylinder 70. The ceramic heater 40 is a rod-shaped member arranged so as to extend along the central axis CL. The outer cylinder 70 holds the outer peripheral surface of the central portion of the ceramic heater 40 in a state where the tip portion 41 of the ceramic heater 40 is exposed. The rear end 49 of the ceramic heater 40 is housed in the through hole 20A of the main metal fitting 20.

A connecting member 90 is fixed to the rear end 49 of the ceramic heater 40. The connecting member 90 is a cylindrical member having a through hole extending along the central axis CL, and is made of a conductive material (for example, stainless steel). The rear end 49 of the ceramic heater 40 is press-fitted on the D1 side of the connecting member 90 in the tip direction. The tip portion 31, which is the end portion of the center pole 30 on the tip end direction D1 side, is press-fitted to the rear end direction D1r side of the connecting member 90. With such a structure, the center pole 30 and the connecting member 90 are electrically connected.

A2. Configuration of Ceramic Heater 40 Next, the ceramic heater 40 will be described with reference to FIGS. 2 and 3. 2 and 3 show the details of the ceramic heater 40 of the first aspect. FIG. 2 shows a more detailed cross-sectional view of the outer cylinder 70, the connecting member 90, the ceramic heater 40, and the like. FIG. 3 shows an enlarged cross-sectional view obtained by further enlarging a part of the cross-sectional view shown in FIG.

As shown in FIG. 2, the ceramic heater 40 includes a round bar-shaped base 110 extending along the axial direction from the rear end side to the front end side, and a substantially U-shaped heat generating resistor 120 embedded inside the base 110 (hereinafter referred to as a heat generating resistor 120). , Simply referred to as "resistor 120"). The ceramic heater 40 is formed by firing the material.

The substrate 110 is made of an insulating ceramic. The insulating ceramic has _{a crystal of silicon nitride (Si 3} N ₄ ) as a main phase, and a rare earth element compound and a silicified product represented by _{W 5} Si ₃ or Mo ₅ Si _{3 are used in the grain boundary phase.} Have.
The rare earth element in the rare earth element compound is not particularly limited, but is selected from, for example, Yb (ytterbium), Y (yttrium), and Er (erbium), and preferably Yb (ytterbium) and Er (erbium). Rare earth elements are _{derived from ytterbium oxide (Yb 2} O ₃ ), yttrium oxide (Y ₂ O ₃ ), erbium oxide (Er ₂ O ₃ ), etc. as sintering aids. Examples of the rare earth element compound include Er ₂ Si ₂ O ₇ , Yb ₂ Si ₂ O ₇ , Y ₂ Si ₂ O ₇ , and Er ₂ Si ₂ O ₇ and / or Yb ₂ Si ₂ O _7. Especially preferable. In the _{ceramic heater 40 having Er 2} Si ₂ O ₇ and / or Yb ₂ Si ₂ O ₇ in the grain boundary phase, the heat resistance of the grain boundaries is improved, the softening of the ceramic heater 40 at high temperature is suppressed, and the softening of the ceramic heater 40 at high temperature is suppressed. Strength is improved.

The component ratio of the rare earth element in the substrate 110 is not particularly limited, but is preferably 5.5 to 11.5% by mass when the entire substrate is 100% by mass. This is because when the component ratio of the rare earth element is within this range, the characteristics such as room temperature strength, high temperature strength, and durability of the ceramic heater 40 are improved.
The component ratio of W (tungsten) or Mo (molybdenum) in the substrate 110 is not particularly limited, but is preferably 0.8 to 7.5% by mass when the entire substrate is 100% by mass. This is because when the component ratio of W or Mo is within this range, the characteristics such as room temperature strength, high temperature strength, and durability of the ceramic heater 40 are improved. The components of W or Mo are derived from _{tungsten oxide (WO 3} ) and molybdenum oxide (MoO _{3) as sintering aids.}
The ratio of each component is a metal equivalent value that is quantified by cutting the ceramic heater (sintered body) 40, polishing the cross section, and using an electron probe microanalyzer (EPMA).

In the present embodiment, in the X-ray diffraction chart on the substrate 110, the peak intensity on the (101) plane of the silicon nitride crystal is defined as the peak intensity X, and the peak on the (411) plane of _{the W 5} Si ₃ or Mo ₅ Si _{3 crystal.} When the intensity is peak intensity Y, the value of peak intensity Y / peak intensity X, which is the ratio of peak intensity, is 0.05 or more and 0.4 or less. When the value of the peak intensity Y / peak intensity X is in this range, the substrate 110 _{contains a predetermined amount of W 5} Si ₃ or Mo ₅ Si ₃ , and the coefficient of thermal expansion between the substrate 110 and the resistor 120. The difference between the above and the silicon nitride constituting the main phase of the substrate 110 can be reduced, and the durability of the ceramic heater 40 can be improved.
Here, the peak intensities X and Y will be described. The peak intensity X is the peak intensity on the (101) plane of the silicon nitride crystal. Specifically, the peak intensity near 2θ = 33.6 ° is defined as the peak intensity X.
On the other hand, the peak intensity Y is the peak intensity on the (411) plane of the crystal of _{W 5} Si ₃ or Mo ₅ Si _3. Both the (411) planes of the W ₅ Si ₃ or Mo ₅ Si ₃ crystal have a peak near 2θ = 42.7 °. That is, since _{both (411) planes of the W 5} Si ₃ or Mo ₅ Si ₃ crystal have the same space group I4 / mcm and the lattice constants are almost the same, the peaks cannot be separated. In the present embodiment, the peak intensity near 42.7 ° is defined as the peak intensity Y.
For each peak in this embodiment, the peak when the X-ray source is CuKα1 and the wavelength is 1.5460 Å is used. The same applies hereinafter.

In the present embodiment, in the X-ray diffraction chart on the substrate 110 _{, when the peak intensity on the (101) plane of the WSi 2} or MoSi ₂ crystal is the peak intensity Z, the peak intensity is the ratio of the peak intensity X to the peak intensity Z. Z / peak intensity X is not particularly limited, but is preferably 0.05 or less.
When the value of peak intensity Z / peak intensity X is in this range, the _{amount of WSi 2} or MoSi ₂ contained in the substrate 110 becomes small, and the grain boundaries are excessively expanded by _{WSi 2} or MoSi _{2 to serve as the starting point of destruction.} Is suppressed. Therefore, the strength and durability of the ceramic heater 40 are improved.
Here, the peak intensity Z will be described. Both the (101) planes of the WSi ₂ or MoSi ₂ crystal have a peak near 2θ = 30.1 °. That is, since _{both (101) planes of the WSi 2} or MoSi ₂ crystal have the same space group I4 / mmm and the lattice constants are almost the same, the peaks cannot be separated. In the present embodiment, the peak intensity near 30.1 ° is defined as the peak intensity Z.

In the present embodiment, the average circle-equivalent diameter of one or more particles selected from the group consisting of _{W 5} Si ₃ , WSi ₂ , Mo ₅ Si ₃ , and MoSi _{2 contained in the substrate 110, or the aggregates of the particles is} Although not particularly limited, it is preferably 0.05 μm or more and 0.90 μm or less. When the average circle-equivalent diameter of the particles or aggregates is in this range, the difference in the coefficient of thermal expansion between the substrate 110 and the resistor 120 is reduced while maintaining the mechanical properties of the ceramic heater 40 at room temperature and high temperature. , Durability can be improved.
Here, a method for measuring the diameter equivalent to the average circle will be described. _{In order to obtain the average circle-equivalent diameter of particles such as W 5} Si ₃ contained in the substrate 110 or aggregates, the cross section of the ceramic heater 40 is mirror-polished and 10,000 times by FE-SEM. Observe with. With respect to the tissue photograph obtained by this observation, 5 arbitrary different places are cut out in a unit area (9 μm × 12 μm), each tissue photograph is made into two gradations, and then analyzed by image analysis software to obtain an average circle equivalent diameter. ..

The resistor 120 is made of conductive ceramic. The conductive ceramic forming the resistor 120 contains tungsten carbide (WC) and silicon nitride as main components. The resistor 120 may contain a sintering aid or the like in addition to tungsten carbide and silicon nitride. The content of the sintering aid and the like is preferably 10% by mass or less, for example, when the entire resistor 120 is 100% by mass. Further, when the total amount of tungsten carbide and silicon nitride is 100% by mass, tungsten carbide is preferably 60 to 85% by mass, while silicon nitride is preferably 15 to 40% by mass. ..

The tip of the substrate 110 (that is, the tip 41 of the ceramic heater 40) is gradually tapered toward the tip. The electrical conductivity of the resistor 120 is higher than the electrical conductivity of the substrate 110. The resistor 120 generates heat when energized.

As shown in FIG. 2, the resistor 120 has a first conductive portion 122 and a second conductive portion 123 formed as two lead portions, and a heat generating portion connected to the first conductive portion 122 and the second conductive portion 123. 121 and electrode extraction portions 124 and 125 are included. The first conductive portion 122 and the second conductive portion 123 are a pair of conductive portions extending from the rear end 110A side of the substrate 110 toward the tip 110B side. Each of the first conductive portion 122 and the second conductive portion 123 extends parallel to the axis CL from the rear end portion 49 of the ceramic heater 40 to the vicinity of the front end portion 41. The first conductive portion 122 and the second conductive portion 123 are arranged at positions substantially symmetrical with respect to the central axis CL. The direction from the first conductive portion 122 to the second conductive portion 123 is the third direction D3.

The heat generating portion 121 is made of conductive ceramic and is a portion embedded in the base 110 at the tip portion 41 of the ceramic heater 40. The end portion of the first conductive portion 122 on the D1 side in the tip direction direction and the tip end of the second conductive portion 123. It is configured to connect with the end on the direction D1 side. The heat generating portion 121 includes a first resistance portion 121A extending from the first conductive portion 122 toward the tip side, a second resistance portion 121B extending from the second conductive portion 123 toward the tip side, and a first resistance portion 121A and a second resistance portion 121B. It is provided with a connecting portion 121C for connecting the tip end side of the above. The shape of the heat generating portion 121 is a folded shape, and specifically, it has a substantially U shape that is curved according to the curved outer surface shape of the tip portion 41 of the ceramic heater 40.

The heat generating portion 121 is made of the same conductive ceramic material as the first conductive portion 122 and the second conductive portion 123, which are a pair of conductive portions. The cross-sectional area of the heat generating portion 121 is smaller than the cross-sectional area of each of the first conductive portion 122 and the second conductive portion 123. Specifically, the cross-sectional area at any position of the heat generating portion 121 is smaller than the cross-sectional area at any position of each of the first conductive portion 122 and the second conductive portion 123. Therefore, the electric resistance per unit length of the heat generating portion 121 is larger than the electric resistance per unit length of the first conductive portion 122 and the second conductive portion 123. Therefore, when the resistor 120 is energized, the temperature of the heat generating portion 121 rises rapidly as compared with the temperatures of the first conductive portion 122 and the second conductive portion 123. The "cross-sectional area" of the resistor 120 is the area of the cross section perpendicular to the direction of the conduction path (the direction in which the current flows).

The first electrode extraction portion 124 is connected to the portion on the D1r side in the rear end direction of the first conductive portion 122. The first electrode extraction portion 124 is a member extending along the radial direction, the inner end portion is connected to the first conductive portion 122, and the outer end portion is exposed to the outer surface of the ceramic heater 40. The exposed portion of the first electrode extraction portion 124 is in contact with the inner peripheral surface of the outer cylinder 70. With such a structure, the outer cylinder 70 and the first conductive portion 122 are electrically connected to each other.

The second electrode extraction portion 125 is connected to the portion on the D1r side in the rear end direction of the second conductive portion 123. The second electrode take-out portion 125 is a member extending along the radial direction, and is arranged on the rear end direction D1r side of the first electrode take-out portion 124. The inner end of the second electrode take-out portion 125 is connected to the second conductive portion 123, and the outer end is exposed to the outer surface of the ceramic heater 40. The exposed portion of the second electrode extraction portion 125 is in contact with the inner peripheral surface of the connecting member 90. With such a structure, the connecting member 90 and the second conductive portion 123 are electrically connected.

A3. Manufacture of Ceramic Heater Next, a method of manufacturing the ceramic heater 40 will be described.
In the method of manufacturing the ceramic heater 40, first, the material of the resistor 120 is produced. Specifically, a slurry is produced by mixing a powder of a conductive compound, silicon nitride, a sintering aid, and water. From the produced slurry, powder is produced by spray drying. By kneading the produced powder and the binder with a kneader, a mixture is produced as a material for the resistor 120 shown in FIG. 2 and the like. As the conductive compound, various compounds described above can be adopted.

After producing the material of the resistor 120 in this way, a molded product is produced by molding the produced mixture. As a molding method, for example, injection molding is adopted. As described above, the unfired resistor (hereinafter referred to as "unfired resistor") is formed. In addition, another molding method (for example, press molding) may be adopted.

FIG. 4A shows an exploded perspective view of an unfired ceramic heater, which will be described later. The member 120Z in the figure indicates an unfired resistor (hereinafter referred to as “unfired resistor 120Z”). As shown in the figure, the unfired resistor 120Z includes unfired conductive portions 122Z and 123Z, unfired heat generating portions 121Z, and unfired electrode extraction portions 124Z and 125Z.

Further, the material for the substrate 110 is produced. Specifically, a slurry is produced by mixing an insulating ceramic (silicon nitride) powder, a sintering aid, and water. From the produced slurry, powder is produced by spray drying. By kneading the produced powder and the binder with a kneader, a mixture is produced as a material for the substrate 110.
In this embodiment, at least one of _{ytterbium oxide (Yb 2} O ₃ ), yttrium oxide (Y ₂ O ₃ ), erbium oxide (Er ₂ O ₃ ) and the like, which are sintering aids containing rare earth elements, is used. Be done. In the present embodiment, at least one of _{tungsten oxide (WO 3} ) and molybdenum oxide (MoO ₃ ), which are sintering aids containing W or Mo, is further used. In addition to these sintering aids, for example, aluminum oxide (Al ₂ O ₃ ), aluminum nitride (AlN), titanium oxide (TiO ₂ ), silicon carbide (SiC), magnesium oxide (MgO), etc. are used in combination. can do.
The content of the sintering aid is not particularly limited, but can be, for example, 5 to 20% by mass with respect to the total amount of the starting material (total amount of silicon nitride powder and sintering aid 100% by mass).

After producing the material of the substrate 110 in this way, an unfired molded product is formed by molding the produced mixture. The member 40Z shown in FIG. 4B shows a molded body to be molded (hereinafter referred to as “molded body 40Z”). The exploded perspective view of FIG. 4 (A) shows two portions 110Y and 110Z obtained by bisecting a portion of the molded product 40Z shown in FIG. 4 (B) corresponding to the substrate 110 in a plane passing through the central axis CL. And the molded unfired resistor 120Z. The first portion 110Z has a first recess 111Z for accommodating a part of the unfired resistor 120Z. Although not shown, the second portion 110Y also has a similar recess. The unfired resistor 120Z is sandwiched between these portions 110Y and 110Z.

Such a molded body 40Z is molded as follows. The unfired resistor 120Z molded by the method described above is placed at a predetermined position in a molding die (not shown). Then, the material of the substrate produced by kneading is molded by injection molding so as to cover the unfired resistor 120Z. As a result, the molded body 40Z shown in FIG. 4 (B) is molded.

In addition, another molding method may be adopted. For example, the first portion 110Z is press-molded. Then, the first portion 110Z is arranged at a predetermined position in a molding die (not shown). Next, the unfired resistor 120Z is fitted into the first recess 111Z of the first portion 110Z. Next, the space corresponding to the second portion 110Y in the molding die is filled with the substrate material produced by the above-mentioned method, and the molded body 40Z is molded by press molding.

It should be noted that the generation of the material of the substrate can be executed at an arbitrary timing prior to the molding of the molded body 40Z. For example, it may be before or after the production of the material of the resistor 120, or before or after the molding of the unfired resistor 120Z.

After the molded body 40Z is molded in this way, calcining is performed in order to remove the binder from the molded body 40Z. The calcining is performed, for example, at a temperature of 400 degrees Celsius or higher and 800 degrees Celsius or lower. After calcining, a cold isotropic press (CIP) may be performed.

After the calcined body 40Z is calcined in this way, the molded body 40Z is fired. As a result, a sintered member (also referred to as a fired body) is generated. As the firing method, for example, a normal pressure firing method is adopted. When the normal pressure firing method is adopted, for example, at a temperature of 1500 ° C. or higher and 1800 ° C. or lower, in a non-oxidizing atmosphere with a pressure of 0.1 MPa or higher and 1 MPa or lower (preferably, the nitrogen partial pressure is 0.05 MPa or higher). Then, firing is performed. The normal pressure firing method can fire a large amount of molded body 40Z at low cost.

The "peak intensity Y / peak intensity X" and "peak intensity Z / peak intensity X" in the present invention can be controlled by adjusting the amount of the sintering aid, the partial pressure of nitrogen at the time of firing, and the like. ..
Specifically, increasing the amount of the sintering aid increases "peak intensity Y / peak intensity X" and "peak intensity Z / peak intensity X", and decreasing the amount of the sintering aid increases "peak". "Intensity Y / Peak intensity X" and "Peak intensity Z / Peak intensity X" decrease. Further, when the nitrogen partial pressure is relatively low, the "peak intensity Y / peak intensity X" decreases while the "peak intensity Z / peak intensity X" increases, and when the nitrogen partial pressure is relatively high, the "peak""Intensity Y / Peak intensity X" increases while "Peak intensity Z / Peak intensity X" decreases.

As the firing method, another method may be adopted. For example, a gas pressure firing method, a hot isostatic pressing method (HIP), a hot press method, or the like can be adopted. When the gas pressure firing method is adopted, for example, firing is performed at a temperature of 1500 ° C. or higher and 1950 ° C. or lower in a non-oxidizing atmosphere at a pressure of 5 MPa or higher and 12 MPa or lower. When the hot isostatic pressing method (HIP) is adopted, for example, the primary firing is performed by the normal pressure firing method or the gas pressure firing method. After that, firing (secondary firing) is performed at a temperature of 1450 ° C. or higher and 1900 ° C. or lower in a nitrogen atmosphere at a pressure of 12 MPa or higher and 200 MPa or lower. When the hot press method is adopted, for example, in a non-oxidizing atmosphere of 0.1 MPa or more and 1 MPa or less, at a temperature of 1450 degrees Celsius or more and 1900 degrees Celsius or less, under uniaxial pressure of 10 MPa or more and 50 MPa or less. Firing is performed.

After the molded body 40Z is fired in this way, the fired body (not shown) obtained by firing the molded body 40Z is polished. As a result, the outer shape of the fired body is processed into a predetermined shape.

The present invention will be described in more detail with reference to Examples.

1. 1. Fabrication of Ceramic Heater The mixture as the material of the resistor 120 was made into an unfired resistor 120Z by injection molding. The unfired resistor 120Z was placed at a predetermined position in the molding die. Then, the material of the substrate 110 produced by kneading was press-molded so as to cover the unfired resistor 120Z to obtain a molded body 40Z. After degreasing the molded body 40Z, it was calcined. After calcining, a cold isotropic press (CIP) was performed. Then, the molded body 40Z was fired at normal pressure and polished to obtain a ceramic heater 40.
In Examples and Comparative Examples, one of the sintering aids of the substrate 110 was ytterbium oxide, so that the rare earth element compound of the grain boundary phase in the substrate 110 of the ceramic heater 40 was the compound shown in Table 1. Selected from yttrium and erbium oxide. Further, in Examples and Comparative Examples, when "W" is described in the column of "W or Mo" in Table 1, tungsten oxide is used as a sintering aid and is described as "Mo". In this case, molybdenum oxide was used as the sintering aid.
The amounts of rare earth elements, W and Mo were controlled by adjusting the amount of the above-mentioned sintering aid. Regarding the ratio of these elemental components, the ceramic heater (sintered body) 40 is cut, the cross section is surface-polished, and an electron probe microanalyzer (EPMA) is used to quantify the metal equivalent value. Yes, not the content at the time of manufacture. The ratio of the elemental components was calculated by assuming an analysis area of 15 kV−φ20 μm and assuming that the analysis area was a dense homogeneous solid solution, and theoretically correcting the standard sample intensity (ZAF method).

2. Test 2.1 Peak intensity Y / peak intensity X value (abbreviated as "Y / X" in Table 1)
For each peak, the peak when the X-ray source was CuKα1 and the wavelength was 1.5460 Å was used.
The peak intensity X is the peak intensity on the (101) plane of the silicon nitride crystal, and this peak intensity was specifically measured using a peak near 2θ = 33.6 °.
The peak intensity Y was measured using a peak near 2θ = 42.7 °.

2.2 Value of peak intensity Z / peak intensity X (abbreviated as "Z / X" in Table 1)
For each peak, the peak when the X-ray source was CuKα1 and the wavelength was 1.5460 Å was used.
The peak intensity X was specifically measured using a peak near 2θ = 33.6 ° in the same manner as described above.
The peak intensity Z was measured using a peak near 2θ = 30.1 °.

2.3 Average circle equivalent diameter In any cross section of the ceramic heater 40, the cross section was mirror-polished and observed by FE-SEM at a magnification of 10000. With respect to the tissue photograph obtained by this observation, 5 arbitrary different places are cut out in a unit area (9 μm × 12 μm), each tissue photograph is made into two gradations, and then analyzed by image analysis software (WinROOF manufactured by Mitani Shoji Co., Ltd.). Then, the diameter equivalent to the average circle was calculated.
The average circle-equivalent diameter relates to one or more particles selected from the group consisting of _{W 5} Si ₃ , WSi ₂ , Mo ₅ Si ₃ , and MoSi _{2 contained in the substrate 110, or an aggregate of the particles.} ..

2.4 Room temperature strength In the measurement of the room temperature strength of the ceramic heater 40, 10 samples of the ceramic heater 40 were used for each Example and each Comparative Example. A three-point support bending test (distance between fulcrums = 12 mm, crosshead speed = 0.5 mm / min) was performed, and the maximum bending stress at the time of breaking was calculated. The average bending stress of the bending stress of 10 samples was adopted as the room temperature strength of the ceramic heater. This test was carried out according to JIS R 1601. The evaluation was as follows.

◎ (Extremely good): 750 MPa or more ○ (Good): 700 MPa or more and less than 750 MPa × (Defective): Less than 700 MPa

2.5 High-temperature strength For the measurement of the high-temperature strength of the ceramic heater 40, five samples of the ceramic heater 40 were used for each Example and each Comparative Example. A 4-point support bending test (distance between external fulcrums = 30 mm, distance between internal fulcrums = 10 mm, crosshead speed = 0.5 mm / min) was performed in an environment of 1300 ° C., and the maximum bending stress when broken was calculated. .. The average bending stress of the bending stresses of the five samples was adopted as the high temperature strength of the ceramic heater. This test was performed according to JIS R 1604. The evaluation was as follows.

◎ (Extremely good): 250 MPa or more ○ (Good): 200 MPa or more and less than 250 MPa × (Defective): Less than 200 MPa

2.6 ON / OFF durability The durability of the glow plug 1 was evaluated by repeating the ON state and the OFF state as follows.

[ON state] The temperature of the maximum heat generating portion of the glow plug was raised to 1000 ° C. in 1 sec, and then the maximum temperature was further raised to 1250 ° C. and stopped.
[OFF state] Air-cooled for 30s.

The evaluation was as follows.
◎ (Extremely good): Disconnection over 60,000 cycles ○ (Good): Disconnection over 25,000 cycles and below 60,000 cycles △ (Yes): Disconnection over 8,000 cycles and below 25,000 cycles × (No): 8000 cycles or less Disconnection

3. 3. Test results The test results are also shown in Table 1.
Examples 1 to 10 having a siliceate represented by W ₅ Si ₃ or Mo ₅ Si ₃ and having a peak intensity Y / peak intensity X value of 0.05 or more and 0.4 or less have room temperature intensity and high temperature. The evaluation was "○" or higher (good or higher) in all performances of strength and ONOFF durability.
On the other hand, in _{Comparative Example 1 which does not have the silicified product represented by W 5} Si ₃ or Mo ₅ Si ₃ , the evaluation of all the performances of room temperature strength, high temperature strength, and ONOFF durability is "x" ( It was bad).
In Comparative Examples 2 and 3 in which the values of peak intensity Y / peak intensity X were out of the range of 0.05 or more and 0.4 or less, the evaluation of room temperature intensity was “x” or more (defective). Further, in Comparative Examples 2 and 3, the evaluation of ONOFF durability was "Δ" (possible).
From these results, _{when it has a silicified product represented by W 5} Si ₃ or Mo ₅ Si ₃ and the value of peak intensity Y / peak intensity X is 0.05 or more and 0.4 or less, the room temperature intensity is determined. It was confirmed that all of the high temperature strength and ONOFF durability were excellent.
The reason why the characteristics of the comparative example are inferior is presumed as follows.
In Comparative Example 1, since the substrate material does not contain tungsten oxide as a sintering aid, it is presumed that the sinterability of the ceramic heater was lowered, and as a result, the room temperature strength was lowered. In Comparative Example 1, since no include silicide represented by W ₅ Si ₃ to the substrate, no effect on the thermal expansion, ONOFF durability is presumed to have become lower.
In Comparative Example 2, since the substrate material contained an excess of tungsten oxide as a sintering aid, the particle size of the silicified product was increased, and as a result, it is presumed that the room temperature strength was lowered due to the influence of the coarse particles. .. Further, it is presumed that the ON / OFF durability was lowered because the ratio _{of W 5} Si _{3 was excessive in the substrate.}
In Comparative Example 3, since the substrate material contains less tungsten oxide as a sintering aid, it is presumed that the sinterability of the ceramic heater is lowered, and as a result, the room temperature strength is lowered. Further, since the amount of silicified product produced is small, the effect on thermal expansion is small, and it is presumed that the evaluation of ONOFF durability is "Δ" (possible).

Next, the peak intensity Z / peak intensity X will be examined. It was confirmed that Examples 1 to 8 and 10 in which the peak intensity Z / peak intensity X was 0.05 or less were superior in ON / OFF durability as compared with Example 9 in which the intensity ratio was larger than 0.05. Was done.
In Example 9, _{it is presumed that the WSi 2} ratio was large, the effect on thermal expansion was excessive, and the evaluation of ONOFF durability remained at “◯” (good).

Next, the average circle-equivalent diameter of one or more particles selected from the group consisting of _{W 5} Si ₃ , WSi ₂ , Mo ₅ Si ₃ , and MoSi ₂ contained in the substrate 110, or aggregates of the particles, will be examined. Examples 1 to 8 in which the average circle-equivalent diameter of the particles or aggregates of the particles is 0.05 μm or more and 0.90 μm or less are superior in room temperature strength as compared with Example 10 in which this value is larger than 0.90 μm. It was confirmed that
In Example 10, the average circle-equivalent diameter is large, and as compared with Examples 1 to 8, the silicates are agglomerated without being dispersed, so that the strength at room temperature is lowered, and the evaluation of the room temperature strength is “◯”. It is presumed that it stopped at (good).

Next, the rare earth element compounds of the grain boundary phase will be examined. _{In Examples 1 to 6 and 9 to 10 in which crystals of Yb 2} Si ₂ O 7 were present in the grain boundary phase, the evaluation of high temperature strength was "⊚" (extremely good). _{In Example 7 in which crystals of Er 2} Si ₂ O ₇ were present in the grain boundary phase, the evaluation of high temperature strength was “⊚” (extremely good).
On the other hand, in _{Example 8 in which crystals of Y 2} Si ₂ O ₇ were present in the grain boundary phase, the evaluation of high temperature strength was “◯” (good).
From this result, it was confirmed that the high temperature strength was extremely excellent when crystals of _{Er 2} Si ₂ O ₇ and / or Yb ₂ Si ₂ O _{7 were present in the grain boundary phase.} It is presumed that such a result is obtained because the crystals of the rare earth element compounds of Er and Yb have higher heat resistance than the crystals of the rare earth element compounds of Y.

<Other Embodiments (Modified Examples)>
The present invention is not limited to the above examples and embodiments, and can be implemented in various embodiments without departing from the gist thereof.

1 ... Glow plug 20 ... Main metal fitting 20A ... Through hole 20B ... Opening 20C ... Opening 22 ... Male screw part 28 ... Tool engaging part 30 ... Center pole 31 ... Tip part 39 ... Rear end part 40 ... Ceramic heater 40Z ... Molding Body (member)
41 ... Front end 49 ... Rear end 50 ... O-ring 60 ... Insulating member 62 ... Cylindrical portion 68 ... Flange portion 70 ... Outer cylinder 70 ... Metal outer cylinder 70A ... Through hole 80 ... Terminal member 90 ... Connecting member 110 ... Base 120 ... Heat generation resistor (resistor)
120Z ... Unfired resistor (member)
121 ... Heat generation unit 121A ... First resistance unit 121B ... Second resistance unit 121C ... Connecting unit 121Z ... Heat generation unit 122 ... First conductive unit 123 ... Second conductive unit CL ... Axis line

Claims (5)

A ceramic heater having an insulating ceramic substrate and a conductive ceramic heating resistor embedded in the substrate.
The conductive ceramic contains tungsten carbide and silicon nitride as main components.
The insulating ceramic has a silicon nitride crystal as a main phase, and has a rare earth element compound and a silicified product represented by _{W 5} Si ₃ or Mo ₅ Si _{3 in the grain boundary phase.}
In the X-ray diffraction chart of the substrate, the peak intensity on the (101) plane of the silicon nitride crystal is defined as the peak intensity X, and the peak intensity on the (411) plane of the _{W 5} Si ₃ or Mo ₅ Si _{3 crystal is peaked.} A ceramic heater characterized in that the value of peak intensity Y / peak intensity X, which is the ratio of peak intensity, is 0.05 or more and 0.4 or less when the intensity is Y. In the X-ray diffraction chart of the substrate _{, when the peak intensity of the WSi 2} or MoSi ₂ crystal on the (101) plane is the peak intensity Z, the peak intensity Z / peak is the ratio of the peak intensity X to the peak intensity Z. The ceramic heater according to claim 1, wherein the intensity X is 0.05 or less. _{One or more particles selected from the group consisting of W 5} Si ₃ , WSi ₂ , Mo ₅ Si ₃ , and MoSi ₂ contained in the insulating ceramic, or an aggregate of the particles having an average equivalent circle diameter of 0.05 μm. The ceramic heater according to claim 1, wherein the ceramic heater has a diameter of 0.90 μm or less. The ceramic heater according to any one of claims 1 to 3, wherein crystals of _{Er 2} Si ₂ O ₇ and / or Yb ₂ Si ₂ O ₇ are further present in the grain boundary phase. The ceramic heater according to any one of claims 1 to 4,
A glow plug including a tubular main metal fitting that holds the rear end portion of the ceramic heater inside.

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