HEATER

Abstract

 A heater including a ceramic body having a columnar shape or a tubular shape, a heating resistor in the ceramic body, a metal tube in which the whole of the ceramic body is disposed, and an insulating member disposed between at least a portion of the ceramic body and the metal tube. The insulating member includes a tubular portion in contact with an outer circumferential surface of the ceramic body at an inner circumferential surface thereof and in contact with an inner circumferential surface of the metal tube at an outer circumferential surface thereof.

Description

Technical Field

[0001] The present invention relates to heaters used as heaters for heating fluid or heaters for heating gas, for example.

Background Art

[0002] A ceramic sheathed heater described in Japanese Unexamined Patent Application Publication No.10-247584 (hereinafter, referred to as Patent Literature 1) is known as a heater used as a heater for heating fluid or a heater for heating gas. The ceramic sheathed heater described in Patent Literature 1 includes a closed-bottom tubular body formed of metal and a ceramic body disposed in the closed-bottom tubular body. The ceramic body includes a heating resistor therein. The ceramic sheathed heater includes an insulating powder between the closed-bottom tubular body and the ceramic body.

[0003] The ceramic sheathed heater described in Patent Literature 1 may be used in a circumstance where external vibrations are transferred to the ceramic sheathed heater. In such a case, the vibrations may cause the insulating powder to move inside the closed-bottom tubular body with respect to the ceramic body. Thus, the insulating powder may be unevenly dispersed such that the insulating powder exists in a larger amount at a certain position and exists in a smaller amount at a certain position. As a result, the ceramic body and the closed-bottom tubular body may partly come in contact with each other at the position where the insulating powder exists in the smaller amount. If the heating resistor generates heat in such a state, a surface of the ceramic body may have a difference in temperature, because the portion of the ceramic body in contact with the closed-bottom tubular body has higher heat dissipation properties than the portion in contact with the insulating powder. In particular, if the ceramic sheathed heater generates heat of a temperature higher than a widely employed temperature, higher thermal stress may occur on the ceramic body, leading to a reduction in durability of the ceramic sheathed heater.

[0004] The present invention was made in view of the above-described problem. It is an object of the present invention to reduce the thermal stress on the ceramic body so as to improve the durability of the ceramic sheathed heater.

Summary of Invention

[0005] A heater includes a ceramic body having a columnar shape or a tubular shape, a heating resistor in the ceramic body, a metal tube in which the ceramic body is disposed, and an insulating member disposed between the ceramic body and the metal tube. The insulting member includes a tubular portion in contact with an outer circumferential surface of the ceramic body at an inner circumferential surface thereof and in contact with an inner circumferential surface of the metal tube at an outer circumferential surface thereof.

Brief Description of Drawings

[0006] 

Fig. 1 is a cross-sectional view illustrating a heater according to an embodiment.

Fig. 2 is a cross-sectional view illustrating a heater according to a first modification.

Fig. 3 is a cross-sectional view illustrating a heater according to a second modification.

Description of Embodiments

[0007] Hereinafter, a heater 100 according to an embodiment is described with reference to the drawings.

[0008] As illustrated in Fig. 1, the heater 100 includes a ceramic body 1 having a columnar shape, a heating resistor 2 in the ceramic body 1, a metal tube 3 in which the whole of the ceramic body 1 is disposed, and an insulating member 4 including a tubular portion 40 and disposed between the ceramic body 1 and the metal tube 3.

<Configuration of Ceramic Body>

[0009] The ceramic body 1 is configured to protect the heating resistor 2. The shape of the ceramic body 1 is a columnar shape or a tubular shape. Examples of the columnar shape include a cylinder and a prism. The columnar shape discussed herein may look like a plate shape depending on the direction of view. In the heater 100 of the present embodiment, the ceramic body 1 has a columnar shape having an oblong main surface. Examples of the tubular shape include a circular tubular shape and a square tubular shape.

[0010] The ceramic body 1 is a sintered body obtained by sintering an insulating ceramic material shaped into a predetermined shape. Examples of the insulating ceramic body include an alumina sintered body, a silicon nitride sintered body, and an aluminum nitride sintered body. In particular, the alumina sintered body is preferably employed from a productivity perspective. When the ceramic body 1 has the columnar shape, the ceramic body 1 may have a main surface having a length of 30 mm and a width of 3 mm and may have a thickness of 1 mm in a direction perpendicular to the main surface, for example.

<Configuration of Heating Resistor>

[0011] The heating resistor 2 is a resistor configured to generate heat by using a current flowing therein. The heating resistor 2 is disposed in the ceramic body 1. In other words, the heating resistor 2 is buried in the ceramic body 1. In addition, the shape of the heating resistor 2 is linear. The heating resistor 2 of the heater 100 according to the present embodiment has a bent portion at a position closer to a first end of the ceramic body 1 than to the center and is connected to two lead-out portions 5 at a second end side. The lead-out portions 5 are configured to electrically connect the heating resistor 2 with an external power supply. The lead-out portions 5 each have a first end connected to the heating resistor 2 and a second end positioned outside the ceramic body 1. The second end of each lead-out portion 5 positioned outside the ceramic body 1 is connected to an electrode 6 on the surface of the ceramic body 1.

[0012] The heating resistor 2 and the lead-out portions 5 are each formed of a metal material. Examples of the metal material include W, Mo, and Re. The heating resistor 2 may have a width of 0.3 mm, an entire length of 30 mm, and a thickness of 25 µm, for example. The lead-out portions 5 each may have a width of 0.7 mm, an entire length of 10 mm, and a thickness of 30 µm, for example.

<Configuration of Electrode>

[0013] The electrodes 6 are each configured to electrically connect the lead-out portion 5 with a lead 7. The electrodes 6 are disposed on two positions of an outer surface of the ceramic body 1 at the second end side. Specifically, the electrode 6 is disposed on each main surface of the ceramic body 1. The electrodes 6 each have a square shape when viewed in a direction parallel to the main surface of the ceramic body 1. The electrodes 6 each may have a length of 5 mm measured in a direction parallel to the longitudinal direction of the ceramic body 1, a length of 2.5 mm measured in a direction perpendicular to the longitudinal direction of the ceramic body 1, and a thickness of 20 µm, for example. The electrodes 6 are each electrically connected to the heating resistor 2 through the lead-out portion 5. The electrodes 6 are each formed of W, Mo, or Re, for example.

<Configuration of Lead>

[0014] The leads 7 are configured to conduct electricity from an external power supply to the heating resistor 2. The leads 7 are separately disposed for the corresponding electrodes 6. The leads 7 each have a first end connected to the electrode 6 and a second end positioned outside the metal tube 3. A portion of each lead 7 positioned outside the metal tube 3 is connected to an external power supply (not illustrated). The lead 7 and the electrode 6 are connected to each other with a brazing filler metal 8. Examples of the brazing filler metal 8 include a silver brazing filler metal, a gold-copper brazing filler metal, and a silver-copper brazing filler metal. The lead 7 is formed of Ni, for example. The lead 7 is covered by an insulating tube 9 except for the portion connected to the electrode 6 and the portion connected to the external power supply. The tube 9 is formed of a resin material, for example. In particular, the tube 9 is preferably formed of a fluoropolymer having high heat resistance.

[0015] If the leads 7 are linear, the leads 7 each may have a diameter of 0.4 mm and a length of 50 mm, for example. The tubes 9 used for the corresponding leads 7 each may have an outer diameter of 1 mm and a length of 45 mm, for example In addition, the portion of the lead 7 that is not covered by the tube 9 and positioned adjacent to the electrode 6 may have a length of about 2 mm, for example.

<Configuration of Metal Tube>

[0016] The metal tube 3 is configured to heat an object to be heated while being in contact with the object. The object to be heated by the heater 100 is a liquid such as water and oil, or a gas such as air and nitrogen, for example. In the heater 100 according to the present embodiment, the metal tube 3 has a circular tubular shape. The whole of the ceramic body 1 is disposed in the metal tube 3. In other words, the metal tube 3 has an inner diameter larger than the outer diameter of the ceramic body 1 such that a gap having an enough size to accommodate the insulating member 4 having an insulating cover 10 and the tubular portion 40 is formed between the inner circumferential surface of the metal tube 3 and the outer circumferential surface of the ceramic body 1. A first end of the metal tube 3 is closed by a metal lid 11. The metal lid 11 has a disc shape having a diameter equal to the outer diameter of the metal tube 3.

[0017] The metal tube 3 may have an inner diameter of 4 mm, an outer diameter of 5 mm, and a length of 40 mm, for example. The metal tube 3 is formed of a metal material such as stainless steel, aluminum, copper, or titanium, for example. In particular, stainless steel is preferably used in view of processability, strength, and heat resistance.

<Configuration of Insulating Cover>

[0018] The insulating cover 10 is configured to provide insulation between the leads 7 and the metal tube 3 and insulation between the electrodes 6 and the metal tube 3. The insulating cover 10 surrounds the electrodes 6 together with the first end of each lead 7. In the heater 100 according to the present embodiment, the insulating cover 10 is a sheet-like member. The insulating cover 10 is formed of an insulating material such as a fluoropolymer, for example. The insulating cover 10 may have a thickness of about 0.2 mm and a length of about 6 mm, for example. The insulating cover 10 is not necessarily limited to the sheet-like member. The insulating cover 10 may be a tubular member, for example. In addition, in the present embodiment the insulating cover 10 is a solid member, but the configuration of the insulating cover 10 is not limited thereto. The insulating cover 10 may be a semisolid member such as a gel, or may be a hardened semisolid member, for example.

<Configuration of Insulating Member>

[0019] The insulating member 4 is configured to prevent the ceramic body 1 from being in contact with the metal tube 3. The insulating member 4, which includes a tubular portion 40 is in contact with an outer circumferential surface of the ceramic body 1 at an inner circumferential surface thereof and in contact with an inner circumferential surface of the metal tube 3 at an outer circumferential surface thereof. The insulating member 4 is formed of a ceramic material such as alumina and aluminum nitride. The insulating member 4 may be an inorganic hardened product obtained, for example, by inserting the ceramic body 1 into the metal tube 3, filling a space between the ceramic body 1 and the metal tube 3 with a solution including an inorganic adhesive, water, and the above-described ceramic material (alumina or alumina nitride, for example) in the form of powder, and then drying the solution so as to be hardened such that the ceramic material and the component of the inorganic adhesive are in contact with each other and combined strongly due to mutual influence. Examples of the inorganic adhesive include water dispersible silica sol and water dispersible alumina sol.

[0020] When the insulating member 4 is formed of an inorganic adhesive, the insulating member 4 preferably has porosity larger than that of the ceramic body 1. This configuration enables, when thermal stress occurs in the heater 100 at a position inner than the metal tube 3, the insulating member 4 to change its shape to absorb the thermal stress. This reduces the possibility that the ceramic body 1 will have a crack. The porosity is compared by the following method. Specifically, the insulating member 4 and the ceramic body 1 are each cut to have a cross section. Then, the porosity is calculated by determining a ratio of an area of voids per unit area.

[0021] In addition, an organic adhesive such as an epoxy resin and a silicon resin, for example, may also be used as a material of the insulating member 4. The material of the insulating member 4 may be suitably selected depending on the usage environment of the heater 100. The insulating member 4 formed of the above-described inorganic adhesive is preferably employed, because such an insulating member 4 is able to withstand temperatures of up to about 800°C.

[0022] The dimension of the insulating member 4 may be set such that the tubular portion 40 has an inner diameter of 3 mm x 1 mm, which is the same as the outer diameter of the ceramic body 1, and an outer diameter of 4 mm, which is the same as the inner diameter of the metal tube 3, and a length of 20 mm, for example.

[0023] In the heater 100 according to the present embodiment instead of the insulating powder, which is unevenly dispersed due to vibrations such that the insulating powder exists in a larger amount at a certain position and exists in a smaller amount at a certain position, the insulating member 4 is disposed between the metal tube 3 and the ceramic body 1, preventing the uneven dispersion. This reduces the possibility that the metal tube 3 and the ceramic body 1 will partly come in contact with each other, and thus reduces the possibility that the surface of the ceramic body 1 will have a large difference in temperature. Thus, the possibility that the thermal stress will occur on the ceramic body 1 is reduced. As a result, the durability of the heater 100 is improved.

[0024] In addition, the insulating member 4 is preferably a joining layer as described above. In such a case, the insulating member 4 enables the ceramic body 1 and the metal tube 3 to be connected to each other, improving the contact between the insulating member 4 and the ceramic body 1 and the contact between the insulating member 4 and the metal tube 3. This allows heat to be readily transferred from the ceramic body 1 to the metal tube 3. As a result, temperature rise performance of the heater 100 is improved. The above-described inorganic adhesive or organic adhesive may be used as an adhesive. Thus, the inorganic hardened product using the inorganic adhesive enables the ceramic body 1 and the metal tube 3 to be connected to each other.

[0025] In addition, as described above, the insulating member 4 preferably includes a ceramic powder. This increases the strength of the insulating member 4. As a result, the heater 100 has higher long-term reliability. In addition, it is preferable that the ceramic powder in the insulating member 4 and the main component of the ceramic body 1 be formed of the same ceramic material. This reduces a difference in thermal expansion between the insulating member 4 and the ceramic body 1. As a result, generation of thermal stress in the heater 100 while the temperature increases or decreases is reduced.

[0026] As described above, the contact between the metal tube 3 and the ceramic body 1 is not preferable in view of durability of the heater 100. This is based on the following reason. If the ceramic body 1 has a crack due to thermal stress caused by a difference in thermal expansion between the ceramic body 1 and the metal tube 3, the crack may be developed to reach the heating resistor 2 in the ceramic body 1. In such a case, a resistance value of the heating resistor 2 may change. This may prevent the heater 100 from generating heat of a predetermined temperature.

[0027] Compared to this, since the tubular portion 40 of the insulating member 4 and the metal tube 3 are in contact with each other in the heater 100 according to the present embodiment, even if the crack occurs on the insulating member 4, development of the crack is suppressed at an interface between the insulating member 4 and the ceramic body 1. In addition, since the metal tube 3 and the ceramic body 1 are disposed away from each other, the surface of the ceramic body 1 will not have a large difference in temperature, resulting in a reduction in occurrence of the crack.

[0028] Thus, the possibility that the resistance value of the heating resistor 2 will change due to the crack is reduced, resulting in a reduction of the possibility that the heater 100 will not be able to generate heat of a predetermined temperature. However, if the crack in the insulating member 4 is developed in the insulating member 4 and the insulating member 4 is largely deformed, the thermal stress due to a difference in thermal expansion between the insulating member 4 and the ceramic body 1 may locally concentrate on the ceramic body 1. In such a case, the ceramic body 1 may have a crack. In view of this, the insulating member 4 also preferably has the configuration that reduces the crack development. This is described later

[0029] In addition, in the heater 100 according to the present embodiment, the metal lid 11 closing the first end of the metal tube 3 and the ceramic body 1 define a space 12 therebetween. This reduces thermal stress generated in the ceramic body 1 when a portion of the ceramic body 1 at the first end side is thermally expanded by the heat generated by the heating resistor 2, since contact between the ceramic body 1 and the metal lid 11 due to a difference in thermal expansion between the ceramic body 1 and the metal lid 11 is prevented. This reduces the possibility that the ceramic body 1 will have a crack, improving durability of the heater 100. The space 12 may have a length of 0.2 to 2 mm in the longitudinal direction of the ceramic body 1, for example. In particular, since the length of the space 12 is 0.2 mm or more, the ceramic body 1 and the metal lid 11 are less likely to come in contact with each other even when the ceramic body 1 and the metal lid 11 are thermally expanded by heat generated by the heater 100.

<First Modification>

[0030] A first modification of the heater 100 is described. In the heater 100 according to the above-described embodiment, the insulating member 4 has a tubular shape having open ends but the shape of the insulating member 4 is not limited thereto. Specifically, the insulating member 4 may be closed at one end, another end, or both the ends. In other words, the insulating member 4 may have the tubular portion 40 and a portion closing an opening at one end or at another end of the tubular portion 40, or portions closing openings at both the ends. As illustrated in Fig. 2, in the heater 100 according to the first modification, the first end of the insulating member 4 is in contact with the entire inner surface of the metal lid 11. In addition, the second end of the insulating member 4 is positioned in the opening of the metal tube 3 at the second end side. At the second end side of the metal tube 3, the insulating member 4 surrounds the ceramic body 1 together with the insulating cover 10, the electrodes 6, and the portions of the tubes 9 covering the leads 7, and is in contact with a second-end-side portion of the ceramic body 1 without any gap therebetween. Since the insulating member 4 covers the whole of the ceramic body 1, the ceramic body 1 is air-tightly sealed. As a result, the ceramic body 1 in the heater 100 has improved environmental resistance.

[0031] In this modification, the heater 100 includes the insulating cover 10 as in the above-described embodiment, but the configuration of the heater 100 is not limited thereto. Specifically, the insulating cover 10 may be eliminated from the heater 100, and the insulating member 4 may directly cover the electrodes 6. The insulating member 4 covering the whole of the ceramic body 1 together with the electrodes 6 provides insulation between the electrodes 6 and the metal tube 3.

[0032] In addition, in this modification, unlike the above-described embodiment, the heater 100 does not include the space 12, but the configuration of the heater 100 is not limited thereto. The heater 100 according to this modification may include the space 12 as in the above-described embodiment. This configuration reduces the thermal stress caused by the difference in thermal expansion between the ceramic body 1 and the metal lid 11.

[0033] The insulating member 4 in this modification may be produced as described below. Specifically, the leads 7 are disposed on the electrodes 6 on the ceramic body 1 and are connected thereto with a silver-copper brazing filler metal or a silver brazing filler metal. Then, the insulating cover 10 formed of a fluoropolymer is disposed to cover the electrodes 6 and the brazed portion. The ceramic body 1 to which the electrodes 6, the leads 7, and the insulating cover 10 are attached as described above is disposed in the metal tube 3, and then a slurry solution is filled in the metal tube 3 to the upper surface so as not to have air bubbles between the ceramic body 1 and the metal tube 3. The slurry solution is obtained by mixing an inorganic adhesive and water with ground ceramic such as alumina and alumina nitride, for example (ceramic powder). After the filling, water in the slurry solution is evaporated slowly by preliminary drying at 100°C or less for about 30 minutes. The preliminary drying is preferably performed at a temperature of 70 to 80°C, because if the drying is performed at 100°C or more, water is boiled to generate air bubbles, leading to a decrease in strength and deterioration in external appearance. After the preliminary drying, drying is performed at 250°C for 30 minutes to dry and harden the inorganic adhesive component. As a result, the insulating member 4 is produced. As in the heater 100 according to the above-described embodiment, the insulating member 4 may be formed of ceramic or may be formed of an organic adhesive.

<Second Modification>

[0034] A second modification of the heater 100 is described. In the heater 100 according to the above-described embodiment, the insulating member 4 is composed of one component, but the configuration of the insulating member 4 is not limited thereto. Specifically, the tubular portion 40 of the insulating member 4 may include a first portion 41 and a second portion 42 each having a tubular shape. As illustrated in Fig. 3, in the heater 100 according to the second modification, the tubular portion 40 of the insulating member 4 includes the first portion 41 and the second portion 42. The first portion 41 is positioned at the first end side of the metal tube 3, and the second portion 42 is positioned at the second end side of the metal tube 3. The first portion 41 and the second portion 42 each have a tubular shape, and an end surface of the first portion 41 and an end surface of the second surface 42 are in contact with each other. As described above, since the insulating member 4 includes a plurality of portions, if one of the portions (the first portion 41, for example) has a crack, the development of the crack stops between the two portions (the first portion 41 and the second portion 42), reducing the possibility that the crack will develop to reach another portion (the second portion 42, for example). This reduces the possibility that the crack in the insulating member 4 will develop in the insulating member 4 to largely deform the insulating member 4.

[0035] In addition, in this modification, the heating resistor 2 is disposed on the first end side of the ceramic body 1, and the first portion 41 surrounds an entire portion of the ceramic body 1 corresponding to the heating resistor 2. Since the first portion 41 surrounds the heating resistor 2, most of the heat generated by the heating resistor 2 is transferred to the first portion 41. In addition, since the insulating member 4 includes separate portions of the first portion 41 and the second portion 42, an interface exists between the first portion 41 and the second portion 42, reducing the amount of heat transferred from the first portion 41 to the second portion 42. This reduces the possibility that the heat generated by the heating resistor 2 will be transferred to the second portion 42 and escape to the second end side of the heater 100.

[0036] The first portion 41 and the second portion 42 may be formed of the same material, but may be formed of different materials. When the first portion 41 and the second portion 42 are formed of different materials, the first portion 41 preferably has higher thermal conductivity than the second portion 42, for example. The first portion 41 having higher thermal conductivity enables the heat generated by the heating resistor 2 to transfer rapidly to the metal tube 3. In addition, the second portion 42 having lower thermal conductivity reduces the possibility that the heat generated by the heating resistor 2 will be released to the outside from the side of the leads 7. This configuration enables the heater 100 to have a higher rate of temperature rise.

[0037] The thermal conductivity of the first portion 41 may be made higher than that of the second portion 42 by allowing the first portion 41 and the second portion 42 to have different amounts of the ceramic powder in the inorganic adhesive, for example. More specifically, if the inorganic adhesive is water dispersible silica sol and the ceramic is alumina, for example, the amount of alumina in the first portion 41 may be made larger than that in the second portion 42. Alternatively, the thermal conductivity may be adjusted by allowing the first portion 41 and the second portion 42 to include different ceramic powders or different inorganic adhesives.

[0038] Alternatively, the thermal conductivity of the first portion 41 may be made higher than that of the second portion 42 by adjusting a proportion of air bubbles in the inorganic adhesive to be larger in the second portion 42 than in the first portion 41, for example. The thermal conductivity of the second portion 42 is able to be made smaller by increasing the amount of air bubbles in the inorganic adhesive. In addition, the increase in the amount of air bubbles in the second portion enables the second portion to readily absorb the thermal stress, reducing the possibility that the generated thermal stress will be applied to the lead 7, for example. As a result, the heater 100 has higher long-term reliability.

[0039] In this modification, the heater 100 includes the insulating cover 10 as in the above-described embodiment, but the configuration of the heater 100 is not limited thereto. Specifically, the insulating cover 10 may be eliminated from the heater 100, and the insulating member 4 may directly cover the electrodes 6. The insulating member 4 covering the whole of the ceramic body 1 together with the electrodes 6 provides insulation between the electrodes 6 and the metal tube 3.

[0040] In this modification, unlike the above-described embodiment, the heater 100 does not include the space 12, but the configuration of the heater 100 is not limited thereto. The heater 100 according to this modification preferably has the space 12 as in the above-described embodiment. This configuration reduces the thermal stress caused by the difference in thermal expansion between the ceramic body 1 and the metal lid 11.

[0041] The first portion 41 and the second portion 42 may be produced as described below. Initially, an electrode ceramic body 1 to which the electrodes 6, the leads 7, and the insulating cover 10 are attached is inserted into the metal tube 3 with the opening at the first end closed by the metal lid 11. Then, a portion of the metal tube 3 at the first end side is filled with a slurry solution obtained by mixing an inorganic adhesive and water with ground ceramic such as alumina and nitride aluminum, for example (ceramic powder). Then, water in the slurry solution is evaporated slowly at 100°C or less for 30 minutes, and then the slurry solution is hardened by drying in a high-temperature environment to form the first portion 41. Then, a slurry solution obtained by mixing an inorganic adhesive and water with ground ceramic such as alumina and nitride aluminum, for example, is filled. Then, water in the slurry solution is evaporated slowly at 100°C or less for 30 minutes, and then the slurry solution is hardened by drying in a high temperature environment to form the second portion 42. As in the heater 100 according to the above-described embodiment, the insulating member 4 may be formed of ceramic or an organic adhesive.

Reference Signs List

[0042] 

100

heater

1

ceramic body

2

heating resistor

3

metal tube

4

insulating member

40

tubular portion

41

first portion

42

second portion

5

lead-out portion

6

electrode

7

lead

8

brazing filler metal

9

tube

10

insulating cover

11

metal lid

12

space

Claims

1. A heater comprising:

a ceramic body having a columnar shape or a tubular shape;

a heating resistor in the ceramic body;

a metal tube in which the ceramic body is disposed; and

an insulating member disposed between the ceramic body and the metal tube, the insulting member including a tubular portion in contact with an outer circumferential surface of the ceramic body at an inner circumferential surface thereof and in contact with an inner circumferential surface of the metal tube at an outer circumferential surface thereof.

2. The heater according to Claim 1, wherein the tubular portion includes a first portion and a second portion each having a tubular shape, and the first portion is disposed at a first end side of the ceramic body and the second portion is positioned at a second end side of the ceramic body.

3. The heater according to Claim 1 or 2, wherein the heating resistor is disposed on a first end side of the ceramic body, and the first portion surrounds an entire portion of the ceramic body corresponding to the heating resistor.

4. The heater according to any one of Claims 1 to 3, further comprising a metal lid closing an end of the metal tube, wherein the metal lid and the ceramic body define a space therebetween.

5. The heater according to any one of Claims 1 to 4, wherein the ceramic body and the metal tube are connected to each other by the insulating member.

6. The heater according to any one of Claims 1 to 5, wherein the insulating member has larger porosity than the ceramic body.

7. The heater according to any one of Claims 1 to 6, wherein the insulating member comprises a ceramic material identical to a main component of the ceramic body.

8. The heater according to any one of Claims 1 to 7, wherein the insulating member is an inorganic hardened product.

9. The heater according to any one of Claims 1 to 7, wherein the insulating member is a joining layer including an organic adhesive.

10. The heater according to Claim 9, wherein the joining layer includes a ceramic powder.

Drawing