Resistance heating element, ceramic heater, and sheath heater

Abstract

To provide a technology for improving the durability of a resistance heating element against temperature changes.SOLUTION: A resistance heating element is made of an alloy containing five or more metal elements each having a molar concentration of 5% to 35%, and generates heat when electricity is applied.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a resistance heating element, a ceramic heater, and a sheath heater. [Background technology]

[0002] BACKGROUND ART Resistive heating elements that generate heat when electricity is applied are known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-151934 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even with prior art such as that disclosed in Patent Document 1, there is still room for improvement in the technology for improving the durability of a resistance heating element against temperature changes.

[0005] An object of the present invention is to provide a technique for improving the durability of a resistance heating element against temperature changes. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0007] (1) According to one aspect of the present invention, there is provided a resistance heating element formed from an alloy containing five or more metal elements, each of which has a molar concentration of 5% to 35%, and which generates heat when electricity is applied.

[0008] According to this configuration, the alloy forming the resistance heating element contains five or more metal elements, each with a molar concentration of 5% to 35%. Because metal diffusion is suppressed in such an alloy, even when the alloy itself repeatedly expands and contracts due to temperature changes, the crystal grains are less likely to coarsen, and changes in electrical resistance are suppressed. This improves durability against temperature changes.

[0009] (2) In the resistance heating element of the above embodiment, the alloy may have a ratio of electrical resistivity at 1000°C to electrical resistivity at 25°C of 1.5 or less. According to this configuration, the alloy forming the resistance heating element has a ratio of electrical resistivity at 1000°C to electrical resistivity at 25°C of 1.5 or less. This makes it easy to control the output of the resistance heating element.

[0010] (3) In the resistance heating element of the above embodiment, the electrical resistivity of the alloy at 25°C may be 90 μΩ·cm or more. With this configuration, the electrical resistivity of the alloy at 25°C is 90 μΩ·cm or more. This allows for a large amount of heat to be generated with a small current.

[0011] (4) In the resistance heating element of the above embodiment, the alloy may contain at least one of chromium, aluminum, and silicon as the metal element. According to this configuration, each of chromium, aluminum, and silicon contained in the alloy forms a dense oxide film, thereby improving the oxidation resistance of the resistance heating element. This allows the resistance heating element to be used for a longer period of time in the atmosphere.

[0012] (5) According to yet another aspect of the present invention, there is provided a ceramic heater. This ceramic heater comprises an insulator made of ceramic and the resistance heating element of the above-described aspect, which is disposed on the surface of or inside the insulator. With this configuration, the resistance heating element of the ceramic heater has relatively high durability against temperature changes, which can extend the life of the ceramic heater.

[0013] (6) According to another aspect of the present invention, there is provided a sheath heater. This sheath heater comprises the resistance heating element of the above aspect, a tubular member made of metal and housing the resistance heating element therein, and an insulating material filled inside the tubular member between the resistance heating element and the tubular member. With this configuration, the resistance heating element included in the sheath heater has relatively high durability against temperature changes, which can extend the life of the sheath heater.

[0014] The present invention can be realized in various forms, for example, in the form of a method for manufacturing a resistive heating element, an apparatus including a resistive heating element, a method for manufacturing an apparatus including a resistive heating element, a computer program for executing the manufacture of a resistive heating element, etc. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of a ceramic heater including a resistance heating element according to a first embodiment. [Figure 2] FIG. 1 is a diagram illustrating a method for evaluating a resistance heating element. [Figure 3] FIG. 10 is a diagram showing the results of a first evaluation test of the resistance heating element. [Figure 4] FIG. 10 is a diagram showing the results of a second evaluation test of the resistance heating element. [Figure 5] FIG. 10 is a schematic diagram illustrating the configuration of a sheath heater including a resistance heating element according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment FIG. 1 is a schematic diagram of a ceramic heater including a resistance heating element according to a first embodiment. The ceramic heater 10 of this embodiment is a flat-plate-shaped member that generates heat when supplied with electricity, and the amount of heat generated can be controlled by adjusting the magnitude of the supplied current. The ceramic heater 10 is used, for example, as a heat source in semiconductor manufacturing equipment, analytical equipment, and the like. The ceramic heater 10 includes an insulator 11, a pair of lead wires 12 and 13, and a resistance heating element 1. FIG. 1 also shows a z-axis indicating a direction substantially perpendicular to either of a pair of main surfaces 11a and 11b of the flat-plate-shaped insulator 11, an x-axis perpendicular to the z-axis, and a y-axis perpendicular to both the z-axis and the x-axis.

[0017] The insulator 11 is a member having a flat plate shape, and in this embodiment, as shown in FIG. 1, is formed so that each of a pair of main surfaces 11a, 11b has a rectangular shape. The insulator 11 is made of ceramic. In this embodiment, the insulator 11 is made of alumina (Al2O3). Note that the material forming the insulator 11 is not limited to alumina. The material forming the insulator 11 may be any material having insulating properties. Furthermore, the shape of the insulator 11 is not limited to a flat plate shape.

[0018] 1, the pair of lead wires 12, 13 are arranged along the x-axis so as to sandwich the insulator 11. Each of the pair of lead wires 12, 13 is connected to a pair of ends 1a, 1b of the resistance heating element 1. The pair of lead wires 12, 13 is connected to an external power source (not shown) and supplies electricity to the resistance heating element 1.

[0019] The resistance heating element 1 is made of an alloy. The alloy that forms the resistance heating element 1 contains five or more metal elements, each with a molar concentration of 5% to 35%, and generates heat when current is applied. The alloy that forms the resistance heating element 1 of this embodiment contains at least one of chromium (Cr), aluminum (Al), and silicon (Si) as a metal element. Specifically, the alloy that forms the resistance heating element 1 is a high-entropy alloy containing aluminum, niobium (Nb), zirconium (Zr), hafnium (Hf), and titanium (Ti) in approximately equimolar amounts. Here, the expression "the alloy contains multiple metal elements in approximately equimolar amounts" means that the ratio of the number of moles of each of the multiple metal elements contained in the alloy is within ±1%. The resistance heating element 1 is an alloy in which these metal elements are in solid solution. Whether the resistance heating element 1 is an alloy in which these metal elements are in solid solution is identified by X-ray diffraction using an X-ray diffraction device.

[0020] In this embodiment, the ratio of the electrical resistivity at 1000°C to the electrical resistivity at 25°C of the alloy (AlNbZrHfTi) forming the resistance heating element 1 is 1.0, which is 1.5 or less, and the electrical resistivity hardly changes with temperature. The electrical resistivity of the alloy forming the resistance heating element 1 at 25°C is 211 μΩ·cm, which is 90 μΩ·cm or more, and it is possible to increase the amount of heat generated with a small current. In this embodiment, the resistance heating element 1 has a zigzag shape as shown in FIG. 1 and is disposed inside the insulator 11. Note that the position where the resistance heating element 1 is disposed is not limited to the inside of the insulator 11. It may also be disposed on the surface of the insulator 11, for example, on one of the pair of principal surfaces 11a and 11b of the insulator 11.

[0021] Next, a method for manufacturing the resistance heating element 1 will be described. To manufacture the resistance heating element 1, first, the five elemental metals aluminum, niobium, zirconium, hafnium, and titanium are placed in a copper container so that they have the same number of moles. The five elemental metals placed in the copper container are arc-melted in an argon atmosphere to produce an ingot of metal represented by the composition formula AlNbZrHfTi. The produced metal ingot is processed into a zigzag shape to produce the resistance heating element 1. Note that the method for manufacturing the resistance heating element 1 is not limited to this. High-frequency melting, the Bridgman method, metal additive manufacturing, etc. may also be used.

[0022] When manufacturing a ceramic heater 10 including a resistance heating element 1, a plurality of green sheets that will become the insulator 11 and lead wires 12 and 13 are prepared. The manufactured resistance heating element 1 is sandwiched between the plurality of green sheets, and the green sheets are fired to manufacture a heater member in which the resistance heating element 1 is disposed inside the insulator 11. Finally, the manufactured heater member is processed, and the lead wires 12 and 13 are connected to a pair of ends 1a and 1b of the resistance heating element 1, respectively, to manufacture the ceramic heater 10.

[0023] Next, evaluation tests of resistance heating elements will be described. Two types of evaluation tests conducted on multiple resistance heating elements made of different materials will be described. In the first evaluation test, the electrical resistivity ρ25 at 25°C and the electrical resistivity ρ1000 at 1000°C were calculated for each of nine types of resistance heating element samples, and the degree of change in electrical resistivity with temperature change was evaluated. In the second evaluation test, the degree of change in electrical resistance value when five types of resistance heating element samples were repeatedly heated and cooled by passing current was evaluated.

[0024] FIG. 2 is a diagram illustrating a method for evaluating a resistance heating element. Here, a method for measuring the electrical resistivity of a sample in the first evaluation test will be described. In measuring the electrical resistivity of a sample in the first evaluation test, a square timber measuring 0.5 mm in height (H), 0.5 mm in width (W), and 1.5 mm in length (L) was cut from the metal ingot forming each sample to prepare a measurement sample Spm. Next, as shown in FIG. 2, platinum wires Ld1, Ld2, Ld3, and Ld4, each with a diameter of 0.1 mm, were welded to four locations on the measurement sample Spm. Next, the potential difference between the platinum wires Ld2 and Ld3 was measured when a current was passed through the measurement sample Spm via the platinum wires Ld1 and Ld4. In this evaluation test, the electrical resistance of the measurement sample Spm was measured using the four-terminal method performed in this manner.

[0025] The electrical resistance value R measured by the four-terminal method shown in FIG. 2 can be calculated by the following formula (1). R = ρ × Lv / Sv (1) Here, ρ is the electrical resistivity (unit: Ω m) of the measurement sample Spm, Lv is the distance (unit: m) between the platinum wires Ld2 and Ld3 in the measurement sample Spm, and Sv is the cross-sectional area (unit: m) of the measurement sample Spm, which is expressed by the product of the vertical length and the horizontal length. 2 ) Using equation (1), when the left side is transformed so that the electrical resistivity ρ of the measurement sample Spm is on the left side, the following equation (2) is obtained. ρ=R×Sv / Lv (2) Therefore, the electrical resistivity ρ of the sample Sp can be calculated by using the electrical resistance value R of the measurement sample Spm measured by the four-terminal method and formula (2). The electrical resistivity ρ1000 at 1000°C was calculated by measuring the electrical resistance value R of the measurement sample Spm in an electric furnace heated to 1000°C in an argon atmosphere and using formula (2).

[0026] FIG. 3 shows the results of the first evaluation test of the resistance heating element. FIG. 3 shows the materials of each of the nine types of resistance heating element samples. Like the resistance heating element 1 of this embodiment, Samples 1 to 4 were each produced by arc-melting five types of metal elements weighed out to be equimolar. Samples 5 to 7 each used nickel (Ni), molybdenum (Mo), and tungsten (W). Sample 8 was produced by arc-melting metal elements weighed out to contain 26 wt% chromium and 7 wt% aluminum, with iron (Fe) as the balance. Sample 9 used SUS430. Of Samples 1 to 9, Samples 1 to 4 are alloys containing five or more metal elements, each with a molar concentration of 5% to 35%.

[0027] FIG. 3 shows the evaluation results, including the electrical resistivity ρ25 at 25°C, the electrical resistivity ρ1000 at 1000°C, and the ratio of the electrical resistivity ρ1000 to the electrical resistivity ρ25 (ρ1000 / ρ25). It was clear that the electrical resistivity ρ25 at 25°C shown in FIG. 3 was higher for Samples 1 to 4 and Sample 8 than for Samples 5 to 7, which were made of simple metals, and Sample 9, which was made of SUS430. It was also clear that the electrical resistivity ρ1000 at 1000°C was higher for Samples 1 to 4 and Sample 8 than for Samples 5 to 7, which were made of simple metals. It was clear that the ratio of the electrical resistivity ρ1000 to the electrical resistivity ρ25 was a relatively large value of 2 or more for Samples 5 to 7, which were made of simple metals, and Sample 9, which was made of SUS430, while it was 1.5 or less for Samples 1 to 4 and Sample 8. From these findings, it was revealed that Samples 1 to 4 and Sample 8 had relatively small changes in electrical resistivity due to temperature changes.

[0028] FIG. 4 shows the results of a second evaluation test of the resistance heating element. FIG. 4 shows the degree of change in electrical resistance when heating by current and cooling by air are repeated for each of Samples 1 to 4 and Sample 8, which have a relatively small change in electrical resistivity due to temperature change. In the second evaluation test, five types of samples, Samples 1 to 4 and Sample 8, were prepared by welding 2 mm diameter nickel wire to both ends of a 0.5 mm square, 15 mm long piece of lumber, heating the material to 1200°C in 1 second by applying a voltage in an argon atmosphere, holding the material at 1200°C for 10 minutes, and then cooling the material by air cooling. For each of the five types of samples, heating by current and cooling by air cooling were repeated 5000 times, and the electrical resistance R of the sample before the first heating and the electrical resistance R of the sample after 5000 heating and cooling cycles were measured. 5000 The rate of change ΔR was calculated using equation (3) as an index representing the durability of the electrical resistance against temperature change. ΔR=(R 5000 / R0-1)×100 (3) The rate of change ΔR shown in FIG. 4 indicates the increase or decrease in the electrical resistance value due to repeated heating and cooling, and when ΔR is a negative value, it indicates that the electrical resistance value is decreasing due to repeated heating and cooling.

[0029] 4, it was revealed that the absolute value of the rate of change ΔR of electrical resistance of Samples 1 to 4, which are alloys containing five kinds of metal elements in equimolar amounts, was smaller than the absolute value of the rate of change ΔR of Sample 8 (Fe-26 wt% Cr-7 wt% Al). In other words, it was revealed that each of Samples 1 to 4 has better durability against temperature changes in electrical resistance than Sample 8.

[0030] Sample 6 made of molybdenum and Sample 7 made of tungsten used in the above evaluation tests had low electrical resistivity at room temperature (25°C) as shown in Figure 3, and the electrical resistivity also changed significantly with temperature, making it difficult to control the output (heat generation).

[0031] Furthermore, Sample 8 used in the evaluation test described above, i.e., the resistance heating element made of Fe-26 wt% Cr-7 wt% Al, has a relatively high electrical resistivity at room temperature and, as shown in Figure 4, the temperature dependency of the electrical resistivity is small, making it easy to control the output. However, there were cases where aluminum migration occurred when electricity was passed through the resistance heating element, resulting in a non-uniform composition, and heat generation caused the crystal grains to coarsen, making the material embrittlement.

[0032] According to the resistance heating element 1 of this embodiment described above, the alloy forming the resistance heating element 1 contains five or more metal elements, each with a molar concentration of 5% to 35%. In such an alloy, metal diffusion is suppressed, so even when the resistance heating element 1 repeatedly expands and contracts due to temperature changes, the crystal grains are less likely to coarsen, and changes in electrical resistance are suppressed. This improves the durability of the resistance heating element 1 against temperature changes.

[0033] Furthermore, according to the resistance heating element 1 of this embodiment, the alloy forming the resistance heating element 1 is a solid solution of five or more metal elements. This makes the electrical resistivity relatively high, and allows the wire diameter of the resistance heating element 1 to be increased. This further improves the durability of the resistance heating element 1 against temperature changes.

[0034] Furthermore, according to the resistance heating element 1 of this embodiment, the alloy forming the resistance heating element 1 is less likely to have coarse crystal grains, which makes it possible to prevent the alloy from becoming brittle. This makes it possible to prevent damage to the resistance heating element 1 caused by stress due to expansion and contraction caused by temperature changes.

[0035] Furthermore, according to the resistance heating element 1 of this embodiment, the alloy forming the resistance heating element 1 has a ratio of the electrical resistivity at 1000°C to the electrical resistivity at 25°C of 1.5 or less. For example, if the temperature change of the electrical resistivity is large, the temperature of the resistance heating element changes due to the heat generated by the passage of current, and the amount of heat generated changes even if the same current is flowing. This can make it difficult to control the output. On the other hand, as described above, the temperature change of the electrical resistivity of the resistance heating element 1 of this embodiment is relatively small, making it easy to control the output of the resistance heating element 1.

[0036] Furthermore, according to the resistance heating element 1 of this embodiment, the electrical resistivity of the alloy at 25° C. is 90 μΩ·cm or more, which makes it possible to generate a large amount of heat with a small current.

[0037] Furthermore, according to the resistance heating element 1 of this embodiment, the alloy forming the resistance heating element 1 contains aluminum as a metallic element. Aluminum easily forms a dense oxide film, improving the oxidation resistance of the resistance heating element 1. This allows the resistance heating element 1 to be used for a longer period of time in the atmosphere.

[0038] Furthermore, according to the ceramic heater 10 of this embodiment, the resistance heating element 1 included in the ceramic heater 10 has relatively high durability against temperature changes, which allows the life of the ceramic heater 10 to be extended.

[0039] Second Embodiment 5 is a schematic diagram of a sheath heater including a resistance heating element according to the second embodiment. The resistance heating element according to the second embodiment is different from the resistance heating element 1 (FIG. 1) according to the first embodiment in that the device to which the resistance heating element is applied is different.

[0040] The sheathed heater 20 of the second embodiment is a generally cylindrical member that generates heat when supplied with electricity, and the amount of heat generated can be controlled by the magnitude of the current supplied. The sheathed heater 20 is used, for example, by being directly immersed in a solution to heat or keep the solution warm. The sheathed heater 20 includes a tubular member 21, a pair of terminal pins 22 and 23, a resistance heating element 2, and an insulating material 24.

[0041] The tubular member 21 is a substantially cylindrical member made of metal. Openings formed at both ends of the tubular member 21 are provided with mouth insulation 21a, 21b, respectively. The tubular member 21 houses the resistance heating element 2 and an insulating material 24.

[0042] The pair of terminal pins 22, 23 are provided on the mouth insulations 21a, 21b, respectively. The terminal pins 22, 23 are electrically conductive and protrude to the outside and inside of the tubular member 21. The pair of terminal pins 22, 23 are connected to an external power source (not shown) and supply electricity to the resistance heating element 2.

[0043] The resistance heating element 2 is made of an alloy. The alloy that forms the resistance heating element 2 contains five or more metal elements, each with a molar concentration of 5% to 35%, and generates heat when electricity is applied. The alloy that forms the resistance heating element 2 of this embodiment contains at least one of chromium, aluminum, and silicon as a metal element. Specifically, the alloy that forms the resistance heating element 2 is a high-entropy alloy containing aluminum, niobium, zirconium, hafnium, and titanium in equimolar amounts. The manufacturing method of the resistance heating element 2 is the same as that of the resistance heating element 1 of the first embodiment. In this embodiment, the resistance heating element 2 is formed to have a spiral shape, as shown in FIG. 5. The resistance heating element 2 of this embodiment is provided inside a tubular member 21. Both ends of the resistance heating element 2 are connected to terminal pins 22 and 23, respectively.

[0044] The insulating material 24 is filled inside the tubular member 21 between the resistance heating element 2 and the tubular member 21. The insulating material 24 is, for example, magnesia (MgO), and provides insulation between the resistance heating element 2 and the tubular member 21.

[0045] As described above, according to the resistance heating element 2 of this embodiment, the alloy forming the resistance heating element 2 contains five or more metal elements, each with a molar concentration of 5% to 35%. In such an alloy, metal diffusion is suppressed, so that crystal grains are less likely to coarsen, and changes in electrical resistance are suppressed. This improves the durability of the resistance heating element 2 against temperature changes.

[0046] Furthermore, according to the sheath heater 20 of this embodiment, the resistance heating element 2 included in the sheath heater 20 has relatively high durability against temperature changes, which allows the life of the sheath heater 20 to be extended.

[0047] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0048] [Variation 1] In the above-described embodiment, the alloy forming the resistance heating element is a high-entropy alloy containing aluminum, niobium, zirconium, hafnium, and titanium in equimolar amounts. The alloy forming the resistance heating element may contain five or more metal elements, each with a molar concentration of 5% to 35%.

[0049] [Variation 2] In the above-described embodiment, the ratio of the electrical resistivity at 1000°C to the electrical resistivity at 25°C of the alloy forming the resistance heating element is 1.0, which is 1.5 or less, and the electrical resistivity at 25°C is 211 μΩ·cm, which is 90 μΩ·cm or more. The ratio of the electrical resistivity at 1000°C to the electrical resistivity at 25°C and the electrical resistivity at 25°C are not limited to these numerical values. When the ratio of the electrical resistivity at 1000°C to the electrical resistivity at 25°C is 1.5 or less, output control of the resistance heating element can be easily performed. When the electrical resistivity at 25°C is 90 μΩ·cm or more, the amount of heat generated can be increased with a small current.

[0050] [Variation 3] In the first embodiment, the alloy forming the resistance heating element 1 contains aluminum as a metal element. The alloy forming the resistance heating element 1 does not have to contain chromium, aluminum, and silicon. Furthermore, the metal element contained in the alloy forming the resistance heating element 1 is not limited to aluminum, and may be chromium or silicon. Chromium and silicon form dense oxide films, so resistance heating elements formed from alloys containing chromium or silicon have improved oxidation resistance. This allows the resistance heating element to be used for a longer period of time in the atmosphere.

[0051] [Variation 4] In the first embodiment, the resistance heating element 1 is disposed inside the insulator 11 in the ceramic heater 10. However, the position of the resistance heating element 1 in the ceramic heater 10 is not limited to this. The resistance heating element 1 may be disposed on the surface of the insulator 11.

[0052] [Variation 5] In the first embodiment, the resistance heating element 1 is applied to a ceramic heater 10, and in the second embodiment, the resistance heating element 2 is applied to a sheath heater 20. Devices to which the resistance heating element is applied are not limited to these.

[0053] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0054] <Application example 1> A resistive heating element, It is made of an alloy, The alloy contains five or more metal elements, each of which has a molar concentration of 5% or more and 35% or less, It is characterized by generating heat when electricity is applied. Resistive heating element. <Application example 2> The resistance heating element according to Application Example 1, The alloy is characterized in that the ratio of the electrical resistivity at 1000°C to the electrical resistivity at 25°C is 1.5 or less. Resistance heating element. <Application example 3> The resistance heating element according to Application Example 1 or Application Example 2, The alloy has an electrical resistivity of 90 μΩ cm or more at 25°C. Resistance heating element. <Application Example 4> The resistance heating element according to any one of Application Examples 1 to 3, The alloy contains at least one of chromium, aluminum, and silicon as the metal element. Resistive heating element. <Application example 5> A ceramic heater, an insulator made of ceramic; and the resistance heating element according to any one of Application Examples 1 to 4, which is disposed on a surface of or inside the insulator. Ceramic heater. <Application Example 6> A sheath heater, The resistance heating element according to any one of Application Examples 1 to 4, a tubular member made of metal and accommodating the resistance heating element therein; an insulating material filled between the resistance heating element and the tubular member inside the tubular member, Sheath heater. [Explanation of symbols]

[0055] 1, 2...Resistance heating element 10...Ceramic heater 11...Insulator 11a, 11b...main surface 20...Sheath heater 21...Tubular member 24...Insulating material

Claims

1. A resistive heating element, It is made of an alloy, The alloy contains five or more metal elements, each of which has a molar concentration of 5% or more and 35% or less, It is characterized by generating heat when electricity is applied. Resistive heating element.

2. 2. The resistance heating element according to claim 1, The alloy is characterized in that the ratio of the electrical resistivity at 1000°C to the electrical resistivity at 25°C is 1.5 or less. Resistive heating element.

3. The resistance heating element according to claim 1 or 2, The alloy has an electrical resistivity of 90 μΩ cm or more at 25°C. Resistive heating element.

4. The resistance heating element according to claim 1 or 2, The alloy contains at least one of chromium, aluminum, and silicon as the metal element. Resistive heating element.

5. A ceramic heater, an insulator made of ceramic; and the resistance heating element according to claim 1 or 2, which is disposed on the surface of or inside the insulator. Ceramic heater.

6. A sheath heater, The resistance heating element according to claim 1 or 2; a tubular member made of metal and accommodating the resistance heating element therein; an insulating material filled between the resistance heating element and the tubular member inside the tubular member, Sheath heater.

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