JP6081836B2 - Ceramic heater - Google Patents

Description

  The present invention relates to a ceramic heater used in various sensors or measuring equipment such as a combustion-type in-vehicle heating device, an oil fan heater, a glow plug of an automobile engine, and an oxygen sensor.

  For example, a ceramic heater is known as a heater used in various sensors or measuring devices such as a combustion-type in-vehicle heating device, an oil fan heater, a glow plug of an automobile engine, an oxygen sensor, and the like. As a ceramic heater, the ceramic heater of patent document 1 is mentioned, for example. The ceramic heater described in Patent Document 1 includes a rod-shaped ceramic material, a heating element provided inside the ceramic material, and a lead provided outside the ceramic material and electrically connected to the heating element. ing. The ceramic heater is electrically connected to the metal pipe through a lead. Generally, the lead and the metal pipe are connected by joining the lead and the metal with a brazing material.

JP-A-7-55145

  However, in the ceramic heater described in Patent Document 1, when the lead and the metal pipe are joined by the brazing material, the heat generated by the ceramic heater may escape to the outside through the brazing material. there were. As a result, it has been difficult to improve the heating rate of the ceramic heater.

  This invention is made | formed in view of this problem, The objective is to provide the ceramic heater which improved the temperature increase rate.

The ceramic heater according to one aspect of the present invention includes a ceramic base, a heating element embedded in the ceramic base, a lead-out portion electrically connected to the heating base, and a brazing material layer bonded to the ceramic base. and a has been fitting, the gap there Ri in the brazing material layer, voids are facing at least one of the boundary between the boundary and the brazing material layer between the said brazing material layer ceramic substrate bracket It is characterized by.

  According to the ceramic heater of one embodiment of the present invention, the heat conduction in the brazing material layer can be suppressed due to the presence of voids in the brazing material layer. As a result, it is possible to suppress the heat generated by the ceramic heater from escaping to the outside through the brazing material. As a result, the temperature increase rate of the ceramic heater can be improved.

It is sectional drawing of one Embodiment of the ceramic heater of this invention. It is principal part sectional drawing of the ceramic heater shown in FIG. It is principal part sectional drawing which shows the modification 1 of the ceramic heater of this invention. It is principal part sectional drawing which shows the modification 2 of the ceramic heater of this invention. It is principal part sectional drawing which shows the modification 3 of the ceramic heater of this invention. It is principal part sectional drawing which shows the modification 4 of the ceramic heater of this invention. It is principal part sectional drawing which shows the modification 5 of the ceramic heater of this invention.

  Hereinafter, a ceramic heater 10 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a ceramic heater 10 of the present invention. As shown in FIG. 1, the ceramic heater 10 is bonded to the ceramic substrate 1, the heating element 5 embedded in the ceramic substrate 1, the lead-out portion 6 electrically connected to the heating element 5, and the ceramic substrate 1. The bracket 3 is included. A brazing filler metal layer 2 is provided between the ceramic base 1 and the metal fitting 3, and a void 4 is formed in the brazing filler metal layer 2.

  The ceramic substrate 1 is made of, for example, a ceramic sintered body formed in a rod shape or a plate shape. Examples of the ceramic sintered body include ceramics having electrical insulation properties such as oxide ceramics, nitride ceramics, and carbide ceramics. Specifically, alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics, or the like can be used. In particular, the ceramic substrate 1 is preferably made of silicon nitride ceramics. Silicon nitride ceramics are excellent in that silicon nitride as a main component has high strength, high toughness, high insulation, and high heat resistance.

The ceramic substrate 1 made of silicon nitride ceramic is, for example, 5 to 15% by mass of rare earth such as Y ₂ O ₃ , Yb ₂ O ₃ or Er ₂ O ₃ as a sintering aid with respect to silicon nitride as a main component. Element oxide, 0.5-5% by mass of Al ₂ O ₃ , and SiO ₂ are mixed so that the amount of SiO ₂ contained in the sintered body is 1.5-5% by mass, and formed into a predetermined shape Then, it can be obtained by hot press firing at 1650 to 1780 ° C.

  The length of the ceramic substrate 1 is set to 20 to 50 mm, for example, and the diameter of the ceramic substrate 1 is set to 3 to 5 mm, for example.

When the ceramic substrate 1 is made of silicon nitride ceramics and the heating element 5 is made of molybdenum (Mo) or tungsten (W), the ceramic substrate 1 includes MoSi ₂ and WSi _2. Etc. are preferably mixed and dispersed. Thereby, the thermal expansion coefficient of the silicon nitride ceramics which is a base material can be brought close to the thermal expansion coefficient of the heating element 5, and the durability of the heater can be improved.

  The heating element 5 is embedded in the ceramic substrate 1. The heating element 5 has a folded shape, and a lead-out portion 6 is connected to each end. The heating element 5 is a resistor for generating heat, and generates heat when a current flows. The lead-out unit 6 is a member for electrically connecting the heating element 5 and an external power source, and one end is connected to the heating element 5 and the other end is drawn to the surface of the ceramic substrate 1. .

  As the heating element 5 and the lead-out portion 6, a material mainly composed of carbides such as W, Mo or titanium (Ti), nitrides or silicides can be used. Further, the heating element 5 may contain the same material as that of the ceramic substrate 1 in order to bring the coefficient of thermal expansion close to that of the ceramic substrate 1. The heating element 5 is set to have a high resistance value, and generates heat most in the vicinity of the middle point of folding. On the other hand, the lead-out portion 6 generates a resistance value per unit length by reducing the content of the forming material of the ceramic base 1 less than that of the heating element 5 or increasing the cross-sectional area of the heating element 5. It is lower than the body 5.

  The metal fitting 3 is a member for holding the ceramic substrate 1. The metal fitting 3 is a cylindrical member, and is provided so as to surround the end portion of the ceramic substrate 1. In other words, the ceramic substrate 1 is inserted inside the metal fitting 3. The metal fitting 3 is made of, for example, stainless steel or iron (Fe) -nickel (Ni) -cobalt (Co) alloy.

  The metal fitting 3 and the ceramic substrate 1 are joined by the brazing material layer 2. The brazing material layer 2 is provided so as to surround the end portion of the ceramic substrate 1. In other words, the brazing filler metal layer 2 is provided on the entire periphery of the end portion of the ceramic substrate 1. Thereby, the metal fitting 3 and the ceramic base body 1 are firmly fixed.

  In order to provide the brazing material layer 2 on the ceramic substrate 1, the glass component may be baked on the inner surface of the ceramic substrate 1 before brazing. Thereby, the brazing filler metal layer 2 can be provided satisfactorily. When the metal fitting 3 functions as an electrode, it is only necessary to give conductivity to the base by mixing a glass component with a metal such as Ni and to electrically connect the lead-out portion 6 and the base. Thereby, the derivation | leading-out part 6, the brazing filler metal layer 2, and the metal fitting 3 can be electrically connected.

  As the brazing filler metal layer 2, silver (Ag) -copper (Cu) brazing, Ag brazing, Cu brazing or the like containing 5 to 20% by mass of a glass component can be used. Since the glass component has good wettability with ceramics and has a large coefficient of friction, the bonding strength between the brazing material layer 2 and the ceramic substrate 1 or the bonding strength between the brazing material layer 2 and the metal fitting 3 can be improved.

  The thickness of the brazing material layer 2 can be set to 50 to 150 μm, for example. Here, in the ceramic heater 10 of the present embodiment, the brazing filler metal layer 2 has a gap 4 as shown in FIG. The void 4 can be formed by including a glass component in the brazing material layer 2. Specifically, the void 4 is formed by foaming of nitrogen or oxygen contained in the glass component of the brazing filler metal layer 2 during heating during brazing. In other words, the void 4 in the present embodiment is a hole formed by foaming of nitrogen or oxygen. In other words, the gap 4 in the present embodiment is a bubble containing nitrogen or oxygen. As described above, in the ceramic heater 10 according to the present embodiment, since the gap 4 is provided in the brazing material layer 2, the heat generated by the heating element 5 escapes to the metal fitting 3 through the brazing material layer 2. This can be suppressed. As a result, the heating rate of the ceramic heater 10 can be improved.

  In addition, as shown in FIG. 3, the gap 4 is preferably provided so as to be in contact with the ceramic base 1 or the metal fitting 3. Thereby, the thermal stress generated between the ceramic substrate 1 and the brazing material layer 2 or the thermal stress generated between the metal fitting 3 and the brazing material layer 2 can be reduced.

  In order for the gap 4 to contact the ceramic substrate 1 or the metal fitting 3, the following method can be used. Specifically, a glass component base may be provided on the ceramic substrate 1 or the metal fitting 3 before brazing. Thus, nitrogen or oxygen contained in the glass component of the base foams during heating during brazing, so that the gap 4 is in contact with the ceramic substrate 1 or the metal fitting 3.

  Further, as shown in FIG. 4, it is preferable that a plurality of the gaps 4 are provided so as to contact the ceramic base 1 or the metal fitting 3. The presence of the plurality of gaps 4 can further reduce the thermal stress generated between the ceramic base 1 and the brazing material layer 2 or the thermal stress generated between the metal fitting 3 and the brazing material layer 2.

Moreover, as shown in FIG. 5, it is preferable that the size of the gap 4 is mixed. In the case where only the gap 4 is small, it is difficult to effectively obtain the effect of suppressing heat conduction in the brazing filler metal layer 2 caused by providing the gap 4. On the other hand, when only the gap 4 is large, it is difficult to improve the bonding strength between the ceramic base 1 and the metal fitting 3. Since the size of the gap 4 is mixed, the bonding strength between the ceramic base 1 and the metal fitting 3 can be improved while effectively suppressing heat conduction in the brazing material layer 2. The size of the gap 4 is large, for example, 0.1 to 0.5 mm, and small, for example, about 0.01 mm.

  Further, as shown in FIG. 6, it is preferable that most of the gaps 4 are provided so as to be in contact with the ceramic substrate 1. The heat conduction in the brazing filler metal layer 2 can be further suppressed by disposing the gap 4 at a place closer to the ceramic base 1 having the heating element 5 as a heat source therein. As a result, the temperature increase rate of the ceramic heater 10 can be further improved.

  As shown in FIG. 1, when the heating element 5 is provided on the tip side of the ceramic heater 10, the gap 4 is biased toward the rear end side of the ceramic heater 10 in the brazing material layer 2 as shown in FIG. 7. Preferably present. On the rear end side of the ceramic heater 10, the temperature of the metal fitting 3 is often lower than the temperature of the brazing material layer 2, and thermal stress is likely to occur between the metal fitting 3 and the brazing material layer 2. Durability can be improved by providing many gaps 4 on the rear end side.

  Next, the manufacturing method of the ceramic heater of this invention is demonstrated.

  First, an electrically conductive ceramic paste that becomes a heating element 5 and a lead-out portion 6 including an electrically conductive ceramic powder and a resin binder is prepared, and an insulating ceramic paste that becomes a ceramic substrate 1 including an insulating ceramic powder and a resin binder, etc. Is made.

  Next, using a conductive ceramic paste, a molded body (formed body A) of a conductive ceramic paste having a predetermined pattern to be the heating element 5 is formed by an injection molding method or the like. Then, in a state where the molded body A is held in the mold, the conductive ceramic paste is filled in the mold to form a conductive paste molded body (molded body B) having a predetermined pattern to be the lead-out portion 6. As a result, the molded body A and the molded body B connected to the molded body A are held in the mold.

  Next, in a state where the molded body A and the molded body B are held in the mold, a part of the mold is replaced with one for molding the ceramic base 1, and then the insulating property that becomes the ceramic base 1 in the mold. Fill with ceramic paste. Thereby, the molded body (molded body D) of the ceramic heater in which the molded body A and the molded body B are covered with the molded body of the insulating ceramic paste (molded body C) is obtained.

  Next, the obtained molded body D is fired at a temperature of 1650 ° C. to 1780 ° C., for example, at a pressure of 30 MPa to 50 MPa, thereby producing the heating element 5, the lead-out portion 6 and the ceramic substrate 1 inside the mold. be able to. The firing is preferably performed in a non-oxidizing gas atmosphere such as hydrogen gas.

Next, a brazing filler metal layer 2 is formed between the ceramic substrate 1 and the metal fitting 3. For example, in the case of Ag—Cu brazing containing a glass component, brazing is performed at 800 to 1000 ° C. Here, the voids 4 can be provided in the brazing filler metal layer 2 by setting the temperature rising rate of 700 ° C. or higher as the brazing condition to 4 to 8 ° C./min and the pressure to 1 to 1 × 10 ³ Pa. it can. This is because nitrogen or oxygen contained in the glass component can be foamed at a stroke by increasing the temperature rising rate. By increasing the heating rate further, the voids can be increased and increased. Moreover, nitrogen or oxygen can be easily foamed by lowering the pressure.

  The glow plug of the present invention can be obtained by the above method.

  The ceramic heater of the example of the present invention was produced as follows.

First, a conductive ceramic paste containing 50% by mass of tungsten carbide (WC) powder, 35% by mass of silicon nitride (Si ₃ N ₄ ) powder, and 15% by mass of a resin binder is injection-molded into a mold to produce a heating element. 5 was produced.

  Next, in a state where the molded body A is held in the mold, the above-described conductive paste that becomes the lead-out portion 6 is filled in the mold, thereby connecting the molded body A and forming the lead-out portion 6. Body B was formed.

Next, 85% by mass of silicon nitride (Si ₃ N ₄ ) powder and ytterbium (Yb) oxide (Yb ₂ ) as a sintering aid while the molded body A and the molded body B are held in the mold. An insulating ceramic paste containing 10% by mass of O ₃ ) and 5% by mass of WC for bringing the coefficient of thermal expansion close to the heating element 5 and the lead-out part 6 was injection molded into a mold. As a result, a molded body D having a configuration in which the molded body A and the molded body B were embedded in the molded body C to be the ceramic substrate 1 was formed.

  Next, after putting the obtained molded body D into a cylindrical carbon mold, it was sintered by hot pressing at 1700 ° C. and a pressure of 35 MPa in a non-oxidizing gas atmosphere composed of nitrogen gas. . Four types of samples were produced using the obtained sintered body.

Sample A is set in a sintered body with a metal fitting 3 made of SUS430 at a predetermined position and joined using a brazing material made of Ag and Cu to which 13% by mass of a glass component is added, and the ceramic heater 10 shown in FIG. Was made. When brazing, using a vacuum furnace, the pressure in the heating process from 700 ° C. to 850 ° C. and the pressure in the heating process at 850 ° C. is set to 1 × 10 ³ Pa, and the heating rate from 700 ° C. to 850 ° C. is set. The rate was 5 ° C / min.

Sample B was baked at 1000 ° C. by applying a base made of a glass component containing Ni on the surface of the sintered body and the inner diameter side of the metal member made of SUS430. The metal fitting 3 was set at a predetermined position on the sintered body and joined using a brazing material made of Ag and Cu to produce a ceramic heater 10 shown in FIG. As the conditions of the vacuum furnace, the pressure in the heating step from 700 ° C. to 850 ° C. and the heating step at 850 ° C. was 1 × 10 ³ Pa, and the heating rate from 700 ° C. to 850 ° C. was 5 ° C./min.

Sample C was baked at 1000 ° C. by applying a base made of a glass component containing Ni on the surface of the sintered body and the inner diameter side of the metal member made of SUS430. The metal fitting 3 was set at a predetermined position to the sintered body and joined using a brazing material made of Ag and Cu, and the ceramic heater 10 shown in FIG. 5 was produced. The pressure in the heating step from 700 ° C. to 850 ° C. and the heating step at 850 ° C. was 1 × 10 ¹ Pa as the vacuum furnace conditions, and the heating rate from 700 ° C. to 850 ° C. was 8 ° C./min.

Sample D was baked at 1000 ° C. by applying a base made of a glass component containing Ni on the surface of the sintered body. A ceramic heater 10 shown in FIG. 6 was manufactured by setting the metal fitting 3 made of SUS430 at a predetermined position and joining the sintered body with a brazing material made of Ag and Cu. The pressure in the heating step from 700 ° C. to 850 ° C. and the heating step at 850 ° C. was 1 × 10 ² Pa as the vacuum furnace conditions, and the heating rate from 700 ° C. to 850 ° C. was 6 ° C./min.

As a conventional product, a ceramic heater is manufactured by setting a metal member made of SUS430 to a predetermined position on a sintered body and bonding using a brazing material made of Ag and Cu to which 5% by mass of glass is added. did. As the conditions of the vacuum furnace, a temperature raising step from 700 ° C. to 850 ° C. and 85
The pressure in the heating process at 0 ° C. was 1 × 10 ⁴ Pa, and the rate of temperature increase from 700 ° C. to 850 ° C. was 2.5 ° C./min.

  The pressure in the vacuum furnace was adjusted by flowing argon gas into the vacuum furnace.

  With respect to each of 10 samples A to D, the occurrence position and size of the void 4 and the number of voids of 0.01 mm or more were investigated.

  In the measurement, the metal fitting 3 was divided into two in the longitudinal direction, one of them was polished, and a cross section including the ceramic base 1, the brazing filler metal layer 2 and the metal fitting 3 was observed at a magnification of 50 times using an SEM.

  In sample A, there are many voids 4 between the ceramic substrate 1 and the metal fitting 3, and the size is 0.01 to 0.1 mm. The number of voids of 0.01 mm or more is 3 to 7 per 1 cm in the longitudinal direction. It was a piece.

  In the sample B, the gap 4 is often in contact with the ceramic substrate 1 or the metal fitting 3 and has a size of 0.01 to 0.2 mm. The number of gaps of 0.01 mm or more is 5 per cm in the longitudinal direction. There were ~ 12.

  In the sample C, the positions of the gaps 4 are often in contact with the ceramic substrate 1 or the metal fitting 3 and the size is 0.01 to 0.5 mm. The number of the gaps of 0.01 mm or more is 10 per cm in the longitudinal direction. There were ~ 22.

  In sample D, the position of the gap 4 is often in contact with the metal fitting 3 and the size is 0.01 to 0.3 mm. The number of gaps of 0.01 mm or more is 8 to 20 per 1 cm in the longitudinal direction. there were.

  In the conventional product, the gap 4 is located between the ceramic substrate 1 and the metal fitting 3, and the size is less than 0.01 mm, and there is no gap of 0.01 mm or more.

  The results are shown in Table 1.

  Using these samples, the time required for the highest heat generating portion to reach 1200 ° C. and the power consumption when the highest heat generating portion maintained 1200 ° C. were measured. Ten samples A to D and each of the conventional products were measured and compared by average value.

  In the ceramic heater of Sample A, the time to reach 1200 ° C. averaged 17 seconds, and the power consumption at 1200 ° C. averaged 32 W.

  The ceramic heater of Sample B averaged 16 seconds to reach 1200 ° C., and the average power consumption at 1200 ° C. was 32 W.

  The ceramic heater of sample C had an average time to reach 1200 ° C. of 15 seconds, and the average power consumption at 1200 ° C. was 30 W.

  The ceramic heater of sample D had an average time to reach 1200 ° C. of 15.5 seconds, and the average power consumption at 1200 ° C. was 30.5 W.

  On the other hand, in the conventional product, the time to reach 1200 ° C. averaged 20 seconds, and the power consumption at 1200 ° C. averaged 35 W.

  From the above results, it was confirmed that the heating rate of the ceramic heater can be improved by using the present invention. Moreover, it has confirmed that the power consumption of a ceramic heater can be reduced by using this invention.

1: Ceramic base body 2: Brazing material layer 3: Metal fitting 4: Gaps 5: Heating element 6: Deriving part 10: Ceramic heater

Claims (6)

A ceramic base, a heating element embedded in the ceramic base, a lead-out portion electrically connected to the heating base, and a metal fitting joined to the ceramic base via a brazing filler metal layer. the layers Ri gap there, the air gap, the ceramic heater, characterized in that facing the at least one boundary between the boundary and the brazing material layer and the metal of the said brazing material layer ceramic substrate. The ceramic heater according to claim 1 , wherein there are a plurality of the gaps. The ceramic heater according to claim 2 , wherein the plurality of gaps are mixed in large and small sizes. The gap, the ceramic heater according to any one of claims 1 to 3, characterized in that are biased to the boundary between the said brazing material layer ceramic substrate. The ceramic heater according to any one of claims 1 to 4 , wherein the ceramic heater has a heat generating portion on a front end side, and the gap is biased toward a rear end side of the brazing material layer. . The ceramic heater according to any one of claims 1 to 5 , wherein the brazing material layer contains a glass component.

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