Corrosion-resistant silicon carbide heating element and method for manufacturing the corrosion-resistant silicon carbide heating element

Abstract

To provide a corrosion-resistant silicon carbide heating element, capable of being manufactured easily at low cost, the heating element having a ytterbium silicate-containing film with excellent fusing properties as a protective film on a surface of a silicon carbide substrate.SOLUTION: A corrosion-resistant silicon carbide heating element has a protective film provided on at least a portion of a surface of a silicon carbide substrate, the protective film comprising 25-85 mass% of Yb2O3, 10-50 mass% of Yb2SiO5, 0-20 mass% of Yb2Si2O7, and 2-10 mass% of SiO2. Preferably, the thickness of the protective film is 30 to 200 μm.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a corrosion-resistant silicon carbide heating element and a method for producing the corrosion-resistant silicon carbide heating element. [Background technology]

[0002] Heating elements made of silicon carbide (silicon carbide heating elements) have been known for some time. In such heating elements, electricity is passed through the end of a rod-shaped heating element and heat is dissipated from the heating element placed in a furnace, thereby heat-treating the workpiece (see Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-126427 A DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0004] It is known that the silicon carbide heating element deteriorates over time when used for a long period of time, and that the deterioration over time is particularly susceptible to the influence of the environment in which the silicon carbide heating element is used.

[0005] One of the causes of deterioration of silicon carbide heating elements is the reaction of silicon carbide (SiC), the main component of the heating element, with oxygen (O2) in a high-temperature air atmosphere of 800°C or more, generating silicon dioxide (SiO2).

[0006] Moreover, in a high-temperature water vapor-containing atmosphere, it is believed that silicon dioxide (SiO2) is produced from silicon carbide (SiC) in the same manner as described above, as shown in the following reaction formula (1) or (2). SiC+2H2O→SiO2+CH4(1) SiC+4H2O→SiO2+CO2+4H2(2)

[0007] Furthermore, in a high-temperature water vapor-containing atmosphere, it is believed that silicic acid (Si(OH)4) is produced from the silicon dioxide (SiO2) as shown in the following reaction formula (3). SiO2+2H2O→Si(OH)4(3) As described above, it is believed that silicon carbide reacts with water vapor, particularly in a high-temperature water vapor-containing atmosphere, and the deterioration of the silicon carbide is accelerated by the progression of corrosion and dissolution.

[0008] Silicon carbide heating elements are widely used as a heat source in the firing process of electronic components such as MLCCs (multilayer ceramic capacitors) and in the firing process during the synthesis of positive electrode materials for lithium-ion secondary batteries. However, these firing processes may be carried out in an atmosphere containing water vapor. In particular, in the synthesis process of positive electrode materials for lithium-ion secondary batteries, a large amount of water vapor is generated from the raw material powder that is to be fired, and firing is often carried out in the presence of a large amount of water vapor in the furnace, which can shorten the lifespan of the silicon carbide heating elements.

[0009] The present inventors have come up with the idea of ​​providing a silicon carbide heating element with a protective film in order to suppress the deterioration caused by the high-temperature water vapor.

[0010] As the protective film, a material made of ytterbium (Yb) silicate (ytterbium silicate) such as Yb2SiO5 or Yb2Si2O7, which has low reactivity with high-temperature water vapor and a thermal expansion coefficient close to that of silicon carbide, was considered. However, while the melting point of ytterbium silicates such as Yb2SiO5 and Yb2Si2O7 exceeds 1800°C, the heat resistance temperature of silicon carbide is about 1400°C, making it difficult to melt Yb2SiO5, Yb2Si2O7, etc. on the surface of a silicon carbide substrate and form a film thereon.

[0011] Methods that have been considered for forming protective films made of Yb2SiO5 or Yb2Si2O7 at low temperatures include plasma PVD (plasma physical vapor deposition) and EB-PVD (electron beam physical vapor deposition), but both require special equipment and are expensive to manufacture.

[0012] As described above, it has been conventionally difficult to easily and inexpensively form an ytterbium silicate-containing film with excellent adhesion on the surface of a silicon carbide substrate.

[0013] Under these circumstances, an object of the present invention is to provide a novel corrosion-resistant silicon carbide heating element that has an ytterbium silicate-containing film with excellent adhesion on the surface of a silicon carbide substrate, and that can be produced simply and at low cost, and to provide a method for producing the corrosion-resistant silicon carbide heating element. [Means for solving the problem]

[0014] In order to solve the above technical problems, the present inventors conducted intensive research and found that, instead of melting Yb2SiO5 or Yb2Si2O7, etc., a slurry containing Yb2O3 and SiO2 can be applied to at least a portion of a silicon carbide heating element, and then heat-treated at a relatively low temperature of 1000 to 1350°C, thereby easily and at low cost forming a protective film containing Yb2SiO5 or Yb2Si2O7 on the surface of a silicon carbide substrate, and that such a protective film can exhibit excellent adhesion to the silicon carbide substrate. Based on this finding, the present invention was completed.

[0015] That is, the present invention provides (1) A corrosion-resistant silicon carbide heating element having a protective film provided on at least a part of a surface of a silicon carbide base material, the protective film being: Yb2O325~85% by mass, Yb2SiO510~50% by mass, Yb2Si2O70~20% by mass, SiO2 2~10% by mass A corrosion-resistant silicon carbide heating element comprising: (2) The corrosion-resistant silicon carbide heating element according to the above (1), wherein the protective film has a thickness of 30 to 200 μm. (3) The corrosion-resistant silicon carbide heating element according to (1) or (2) above, wherein the silicon carbide base material has a silicon carbide content of 98% by mass or more, has a plurality of pores on the surface thereof with an average pore diameter of 1 to 30 μm, and has a porosity of 10% or more. (4) A method for producing the corrosion-resistant silicon carbide heating element according to any one of (1) to (3) above, After applying a slurry containing Yb2O3 and SiO2 to at least a portion of a silicon carbide substrate, Heat treatment at 1000~1350℃ A method for producing a corrosion-resistant silicon carbide heating element, comprising: This provides: Effect of the Invention

[0016] According to the present invention, it is possible to provide a novel corrosion-resistant silicon carbide heating element that has an ytterbium silicate-containing film having excellent adhesion on the surface of a silicon carbide base material as a protective film, which can be easily and inexpensively produced, and also to provide a method for producing the corrosion-resistant silicon carbide heating element. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing an example of a corrosion-resistant silicon carbide heating element according to the present invention; [Diagram 2] 1 is a schematic diagram showing an example of a form of a silicon carbide substrate constituting a corrosion-resistant silicon carbide heating element according to the present invention. [Diagram 3] 1 is a schematic diagram showing an example of a corrosion-resistant silicon carbide heating element according to the present invention; [Figure 4] FIG. 2 is a diagram showing an observed image of a cross section of a corrosion-resistant silicon carbide heating element obtained in an example. [Diagram 5] FIG. 2 is an enlarged view of an observation image of the vicinity of the outer circumferential surface in a cross section of a corrosion-resistant silicon carbide heating element obtained in an example. [Figure 6] FIG. 2 is an enlarged view of an observation image of the center part in a cross section of the corrosion-resistant silicon carbide heating element obtained in an example. [Figure 7]FIG. 11 is a diagram showing the evaluation results of the water vapor resistance of the corrosion-resistant silicon carbide heating elements obtained in the examples and the silicon carbide heating elements obtained in the comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] First, the corrosion-resistant silicon carbide heating element according to the present invention will be described. The corrosion-resistant silicon carbide heating element according to the present invention is a corrosion-resistant silicon carbide heating element having a protective film provided on at least a part of the surface of a silicon carbide base material, the protective film being: Yb2O325~85% by mass, Yb2SiO510~50% by mass, Yb2Si2O70~20% by mass, SiO22~10% by mass The present invention is characterized in that it contains:

[0019] The corrosion-resistant silicon carbide heating element of the present invention is used with a protective film provided on at least a portion of the surface of a silicon carbide base material, and generates heat when electricity is passed through it to function as a heating element.The shape of the heating element may be either solid or hollow, although it is preferably hollow cylindrical.

[0020] FIG. 1 is a schematic diagram showing an example of a corrosion-resistant silicon carbide heating element according to the present invention. The corrosion-resistant silicon carbide heating element H shown in the figure is composed of a heating portion M and end portions E, E joined to both ends of the heating element M. The corrosion-resistant silicon carbide heating element according to the present invention is used, for example, as the heating part M shown in FIG. 1. In this case, the heating part M usually has a hollow cylindrical shape as shown in the figure.

[0021] The corrosion-resistant silicon carbide heating element according to the present invention has a silicon carbide base material and a protective film provided on at least a portion of the surface of the silicon carbide base material.

[0022] In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film contains 25 to 85 mass %, preferably 25 to 75 mass %, and more preferably 25 to 60 mass % of Yb2O3.

[0023] In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film contains 10 to 50 mass %, preferably 20 to 50 mass %, and more preferably 30 to 50 mass % of Yb2SiO5.

[0024] In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film contains 0 to 20 mass % of Yb2Si2O7, preferably 5 to 20 mass %, and more preferably 10 to 20 mass %.

[0025] In the corrosion-resistant silicon carbide heating element of the present invention, the content ratios of Yb2SiO5 and Yb2Si2O7 in the protective film each satisfy the above-mentioned regulations, thereby making it possible to effectively suppress deterioration of the silicon carbide base material due to high-temperature water vapor while suppressing damage to the silicon carbide base material or protective film caused by the difference in thermal expansion coefficient between the protective film and the silicon carbide base material.

[0026] In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film preferably contains 10 to 70 mass %, and more preferably 40 to 70 mass %, of Yb2SiO5 and Yb2Si2O7 in total.

[0027] In the corrosion-resistant silicon carbide heating element of the present invention, since the total content of Yb2SiO5 and Yb2Si2O7 in the protective film satisfies the above-mentioned regulation, damage to the silicon carbide base material or the protective film due to the difference in thermal expansion coefficient between the protective film and the silicon carbide base material can be suppressed, while deterioration of the silicon carbide base material due to high-temperature water vapor can be more effectively suppressed.

[0028] In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film contains 2 to 10 mass % of SiO2, and preferably contains 5 to 10 mass %.

[0029] In the corrosion-resistant silicon carbide heating element of the present invention, the protective film preferably contains 37 to 100 mass% of Yb2O3, Yb2SiO5, Yb2Si2O7 and SiO2 in total, more preferably 70 to 100 mass%, and even more preferably consists of only Yb2O3, Yb2SiO5, Yb2Si2O7 and SiO2.

[0030] In the corrosion-resistant silicon carbide heating element according to the present invention, the content ratios of each of the constituent components, such as Yb2O3, Yb2SiO5, Yb2Si2O7 and SiO2, in the protective film refer to values ​​obtained by the following method using a measurement sample obtained by scraping off the protective film provided on the surface of the corrosion-resistant silicon carbide heating element. (1) Measurement of X-ray diffraction (XRD) spectrum The X-ray diffraction (XRD) spectrum of the above measurement sample is measured under the following conditions. X-ray diffraction equipment: Rigaku Corporation fully automated horizontal multipurpose X-ray diffraction equipment SmartLab Goniometer: SmartLab X-ray voltage: 40kV X-ray current: 30mA Measurement angle range (2θ): 10°~90° Measurement step: 0.001° Scanning speed: 5° / min (2) Quantitation of each component using the RIR (Reference Intensity Ratio) method The X-ray diffraction spectrum data obtained in (1) is analyzed using Rigaku Corporation's "Integrated Powder X-ray Analysis Software PDXL2.2," and the amount of each component that makes up the protective film is identified by the RIR (Reference Instensity Ratio) method using an ICDD card. The ICDD card numbers for Yb2O3, Yb2SiO5, Yb2Si2O7 and SiO2 are as follows: Yb2O3:01-075-6636 Yb2SiO5:00-040-0386 Yb2Si2O7:01-082-0734 SiO2:01-083-1831

[0031] In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film is provided on at least a portion of the surface of the silicon carbide base material, and is preferably provided over a range of 36 to 100% of the surface. When the corrosion-resistant silicon carbide heating element of the present invention has a hollow cylindrical shape, the protective film is preferably provided on the entire outer peripheral surface of the hollow cylindrical silicon carbide base material, and more preferably provided on the entire outer peripheral surface and the entire inner peripheral surface of the hollow cylindrical silicon carbide base material.

[0032] In the corrosion-resistant silicon carbide heating element according to the present invention, the thickness of the protective film is preferably 30 to 200 μm, and more preferably 50 to 200 μm.

[0033] In the corrosion-resistant silicon carbide heating element according to the present invention, by having the thickness of the protective film within the above range, corrosion resistance against high-temperature water vapor can be easily exhibited for a long period of time.

[0034] In the present application, the lower limit and upper limit of the thickness range of the protective film respectively refer to the arithmetic mean value of the minimum thickness and the arithmetic mean value of the maximum thickness of the protective film in each observed image when 10 points on a vertical cross section of the corrosion-resistant silicon carbide heating element according to the present invention are observed with a scanning electron microscope.

[0035] In the corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide base material preferably has a silicon carbide content of 98 mass % or more (98 to 100 mass %), more preferably 99 mass % or more (99 to 100 mass %), and even more preferably 100 mass %. In the corrosion-resistant silicon carbide heating element according to the present invention, the content of silicon carbide constituting the silicon carbide base material satisfies the above-mentioned regulation, so that the object to be treated can be heat-treated with high efficiency.

[0036] In the corrosion-resistant silicon carbide heating element according to the present invention, the content of silicon carbide in the silicon carbide base material means a value measured in accordance with the provision of "Method for determining silicon carbide content" in the remarks of JIS R 6124.14 after scraping off a predetermined amount of the silicon carbide base material constituting the corrosion-resistant silicon carbide heating element to prepare a measurement sample.

[0037] In the corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide base material suitably has a plurality of pores on the surface, and the average pore diameter of the pores is preferably 1 to 30 μm, more preferably 5 to 30 μm, and even more preferably 20 to 30 μm.

[0038] In the corrosion-resistant silicon carbide heating element of the present invention, the silicon carbide base material has a plurality of pores on its surface that satisfy the above-mentioned specifications, so that a portion of the protective film penetrates into the silicon carbide base material, and the so-called anchor effect makes it possible to easily exhibit strong adhesion of the protective film to the silicon carbide base material.

[0039] In the corrosion-resistant silicon carbide heating element according to the present invention, the average pore size on the surface of the silicon carbide substrate means a value determined by the mercury intrusion method defined in JIS R 1655 on a silicon carbide substrate cut out from the corrosion-resistant silicon carbide heating element.

[0040] In the corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide substrate preferably has a porosity of 10% or more, more preferably 10 to 50%, and even more preferably 10 to 30%.

[0041] In the corrosion-resistant silicon carbide heating element according to the present invention, the open area ratio of the silicon carbide base material satisfies the above-mentioned regulation, so that the adhesion of the protective film to the silicon carbide base material can be more easily improved.

[0042] In the corrosion-resistant silicon carbide heating element according to the present invention, the porosity in the surface of the silicon carbide substrate means a value determined by the mercury intrusion method defined in JIS R1655 for a silicon carbide substrate cut out from the corrosion-resistant silicon carbide heating element.

[0043] In the corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide base material satisfying the above-mentioned pore size and porosity requirements can be produced, for example, by kneading silicon carbide (SiC) powder with a binder and water, forming the mixture into a shape corresponding to the shape of the heating part of the silicon carbide heating element, drying the mixture, and then sintering the mixture at a temperature of 2100 to 2400°C in a nitrogen gas atmosphere.

[0044] FIG. 2(a) is a schematic diagram showing an example of the form of a silicon carbide substrate constituting the corrosion-resistant silicon carbide heating element of the present invention, in which a hollow cylindrical silicon carbide substrate b is shown as a vertical cross-sectional view with respect to its longitudinal direction. FIG. 2(b) is an enlarged view of the dashed line portion in FIG. 2(a), and as shown in the figure, a plurality of pores h are formed on the surface and inside of the silicon carbide substrate b.

[0045] On the other hand, FIG. 3(a) is a schematic diagram showing an example of a corrosion-resistant silicon carbide heating element according to the present invention, in which a protective film c is provided on the outer and inner surfaces of the silicon carbide base material b shown in FIG. 2(a), and in the same figure, the corrosion-resistant silicon carbide heating element M in a hollow cylindrical shape is shown as a vertical cross-sectional view with respect to its longitudinal direction. FIG. 3(b) is an enlarged view of the dashed line portion in FIG. 3(a). As shown in the figure, in the silicon carbide substrate b having a hollow cylindrical shape, a portion of the protective film c provided on each of the outer and inner surfaces thereof penetrates into and is in close contact with a plurality of pores h formed on the surface of the silicon carbide substrate b.

[0046] The corrosion-resistant silicon carbide heating element according to the present invention can be easily manufactured by the manufacturing method according to the present invention.

[0047] According to the present invention, it is possible to provide a corrosion-resistant silicon carbide heating element that exhibits high corrosion resistance against high-temperature water vapor for a long period of time and can be manufactured simply and at low cost.

[0048] Next, a method for producing the corrosion-resistant silicon carbide heating element according to the present invention will be described. The method for producing a corrosion-resistant silicon carbide heating element according to the present invention is a method for producing a silicon carbide heating element according to the present invention, After applying a slurry containing Yb2O3 and SiO2 to at least a portion of a silicon carbide substrate, Heat treatment at 1000~1350℃ It is characterized by the above.

[0049] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, examples of the silicon carbide substrate include those similar to those described above.

[0050] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, a slurry containing Yb2O3 and SiO2 is applied to at least a portion of a silicon carbide substrate.

[0051] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the Yb2O3 concentration and the SiO2 concentration in the slurry that becomes the coating liquid may be appropriately adjusted according to the concentration of each component in the protective film to be obtained.

[0052] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the Yb2O3 concentration in the slurry that becomes the coating liquid is preferably 65 to 80 mass % in terms of solid content.

[0053] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the SiO2 concentration in the slurry that becomes the coating liquid is preferably 7 to 14 mass % in terms of solid content.

[0054] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the slurry serving as the coating liquid may contain, as components other than Yb2O3 and SiO2, a dispersant for dispersing components in the coating liquid, a binder (e.g., an acrylic emulsion) for ensuring the strength of the coating film before heat treatment (before baking), and the like.

[0055] The dispersion medium constituting the slurry is not particularly limited, but is preferably water in consideration of environmental aspects and workability.

[0056] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the slurry that serves as the coating liquid can be prepared by mixing the respective components in a dispersion medium. The solid content in the slurry is preferably 70 to 80% by mass. The viscosity of the slurry is preferably 100 to 800 Pa·s.

[0057] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the method for applying the slurry to be used as the coating liquid to the silicon carbide substrate is not particularly limited, and in addition to a brush coating method in which the slurry is applied by brushing, a spray method in which the slurry is sprayed, or a dipping method in which the silicon carbide substrate is immersed in the slurry may be used for application.

[0058] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, a slurry containing Yb2O3 and SiO2 is applied to at least a portion of a silicon carbide substrate. The position and area to which the slurry is applied may be determined according to the position and area on which the protective film is to be formed.

[0059] In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, when a protective film is to be provided on the outer peripheral surface of the silicon carbide base material having a hollow cylindrical shape, it is preferable to apply the slurry by a brushing method or a spraying method, and when a protective film is to be provided on both the outer peripheral surface and the inner peripheral surface of the silicon carbide base material having a hollow cylindrical shape, it is preferable to apply the slurry by a dipping method.

[0060] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, a coating process may be carried out multiple times to obtain a protective film of a predetermined thickness.

[0061] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, after the slurry is applied, it is preferable to carry out an appropriate drying treatment.

[0062] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, a silicon carbide base material having the above-mentioned slurry applied to at least a portion of its surface is heat-treated at 1000 to 1350°C.

[0063] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the temperature at which the silicon carbide base material having the above slurry applied to at least a portion of its surface is heat-treated is 1000 to 1350°C, preferably 1100 to 1350°C, and more preferably 1250 to 1350°C.

[0064] In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, the temperature for heat treating the silicon carbide base material having the above-mentioned slurry applied to at least a portion of its surface is within the above-mentioned range, so that a protective film can be formed simply and at low cost without using a special heating device, while suppressing damage to the base material due to the temperature exceeding the heat resistance temperature of the silicon carbide base material.

[0065] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the time for heat treating the silicon carbide base material having the slurry applied to at least a portion of its surface is preferably 1 to 30 minutes, more preferably 3 to 20 minutes, and even more preferably 5 to 10 minutes.

[0066] In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, by setting the time for heat treating the silicon carbide substrate having the slurry applied to at least a portion of its surface within the above-mentioned range, a protective film having excellent adhesion (fixability) to the silicon carbide substrate can be easily formed.

[0067] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the atmosphere in which the silicon carbide base material having the above-mentioned slurry applied to at least a portion of its surface is heat-treated is not particularly limited, but is preferably an inert gas atmosphere. Examples of the inert gas include nitrogen gas, argon gas, helium gas, etc., and nitrogen gas is preferred.

[0068] In the method for producing a corrosion-resistant silicon carbide heating element according to the present invention, the moisture concentration in the atmosphere when the silicon carbide base material having the above slurry applied to at least a portion of its surface is heat-treated is preferably 1000 ppm by mass or less.

[0069] According to the present invention, it is possible to provide a method for simply and inexpensively producing a corrosion-resistant silicon carbide heating element having an ytterbium silicate-containing film with excellent adhesion on the surface of a silicon carbide substrate.

[0070] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples in any way.

[0071] Example 1 (1) Formation of substrate bond As a silicon carbide substrate, a recrystallized SiC substrate having a hollow cylindrical shape with an outer diameter of 20 mm, an inner diameter of 10 mm, and a total length of 300 mm (silicon carbide content of 98% by mass, an average pore diameter of the multiple pores distributed on the surface of 20 μm, and a porosity (open area ratio) of 23%) was prepared. A SiC / C end portion having a hollow cylindrical shape of outer diameter 20 mm × inner diameter 10 mm × total length 300 mm was joined to each end of the silicon carbide substrate to obtain a substrate joint (outer diameter 20 mm × inner diameter 10 mm × total length 900 mm) on which a coating film was to be formed. (2) Preparation of coating solution A 17.5% by mass colloidal silica suspension (grade: Ludox HS-40) manufactured by WR Grace, 65% by mass Yb2O3 powder (grade: 3N) manufactured by Japan Yttrium Co., Ltd., and 17.5% by mass ion-exchanged water were weighed out and mixed in a mortar for 5 minutes to obtain a slurry-like raw material mixture. The obtained raw material mixture was further mixed with a 1.5 mass % aqueous solution of Metolose (grade: SM-400) manufactured by Shin-Etsu Chemical Co., Ltd. as a binder so that the raw material mixture was 90 mass % and the dispersant was 10 mass %, thereby preparing a slurry-like coating liquid. (3) Coating liquid application The substrate assembly produced in (1) was left to stand for 90 minutes so that the entire assembly was immersed in the coating liquid prepared in (2), thereby impregnating the entire outer and inner surfaces of the substrate assembly with the coating liquid. (4) Heat treatment The substrate bonded body was pulled out of the coating liquid and thoroughly dried, and then baked in a heat treatment furnace at 1300°C for 4 minutes in an air atmosphere to obtain a bonded body whose ends were bonded to both ends of the corrosion-resistant silicon carbide heating element. It was visible that a protective film was formed on the entire outer and inner surfaces of the bonded article and that no peeling or the like had occurred. When a portion of this protective film was scraped off and measured, it was found to contain 26% by mass of Yb2O3, 48% by mass of Yb2SiO5, 717% by mass of Yb2Si2O, and 9% by mass of SiO2. In addition, a part of the corrosion-resistant silicon carbide heating element constituting the above-mentioned bonded body was cut out, and the vicinity of the outer circumferential surface and the central part in the cross section were observed with a scanning electron microscope (SEM) as shown in the schematic diagram on the left side of FIG. 4, and the obtained observation images are shown on the right side of FIG. 4. 5 and 6 show enlarged SEM images (magnification: 100 times, backscattered electron images) of the vicinity of the outer circumferential surface and the center of the corrosion-resistant silicon carbide heating element, respectively. It can be seen from FIG. 6 that pores, which are indicated in dark black in the figure, are formed in the silicon carbide substrate. FIG. 5 also shows that a protective film, shown in white, is formed in a layer shape on the outer peripheral surface of the silicon carbide substrate, shown in gray, and that part of this protective film penetrates into a plurality of pores formed on the surface of the silicon carbide substrate and is formed in close contact with the substrate. The thickness of the protective film was 35 to 190 μm.

[0072] Example 2 In Example 1(4), a joint having ends joined to both ends of a corrosion-resistant silicon carbide heating element was obtained in the same manner as in Example 1, except that the baking treatment was performed by heating at 1100°C for 4 minutes instead of heating at 1300°C for 4 minutes in Example 1(4). It was visible that a protective film was formed on the entire outer and inner surfaces of the bonded article and that no peeling or the like had occurred. When a portion of this protective film was scraped off and measured, it was found to contain 80% by mass of Yb2O3, 13% by mass of Yb2SiO5, 73% by mass of Yb2Si2O, and 4% by mass of SiO2. In addition, when a portion of the above corrosion-resistant silicon carbide heating element was cut out and the cross section was observed under a scanning electron microscope, it was confirmed that a protective film having a thickness of 50 to 120 μm was formed on the surface, and that part of this protective film had penetrated into the pores in the surface of the silicon carbide base material and was formed in close contact with the silicon carbide base material.

[0073] Comparative Example 1 In Example 1, the steps "(2) Preparation of coating liquid" and "(3) Application of coating liquid" were not performed, and the substrate bonded product prepared in "(1) Formation of substrate bonded product" was directly subjected to the "(4) Heat treatment" step, but the same process as in Example 1 was performed to obtain a bonded product having ends bonded to both ends of the silicon carbide heating element.

[0074] Comparative Example 2 In the "(2) Preparation of coating solution" step of Example 1, a colloidal silica suspension manufactured by WR Grace (grade: Ludox HS-40) was weighed out to be 38.9 mass%, Yb2O3 powder manufactured by Nippon Yttrium Co., Ltd. (grade: 3N) was weighed out to be 48.1 mass%, and ion-exchanged water was weighed out to be 13.0 mass%, respectively. By carrying out the same process as in Example 1, a bonded product having ends bonded to both ends of a silicon carbide heating element was obtained. A protective film was formed on the outer and inner surfaces of the joint, but it was visually confirmed that some parts of the protective film were not fixed and peeled off. When the fixed parts of the protective film were scraped off and measured, the protective film contained 30 mass% Yb2O (not detected), 579 mass% Yb2SiO, 74 mass% Yb2Si2O, and 17 mass% SiO2. Furthermore, when a portion of the corrosion-resistant silicon carbide heating element where the protective film was fixed was cut out and the cross section was observed under a scanning electron microscope, it was found that a protective film having a thickness of 10 to 25 μm had been formed on the surface. Table 1 shows the properties of the corrosion-resistant silicon carbide heating elements and the protective film of the silicon carbide heating elements obtained in each of the examples and comparative examples. In Table 1, for "protective film adhesion," the evaluation was given as "O" when it was visually confirmed that the protective film was formed over the entire outer and inner surfaces of the silicon carbide substrate and was not peeling off, and the evaluation was given as "X" when it was visually confirmed that the protective film was peeling off from part of the outer and inner surfaces of the silicon carbide substrate.

[0075] [Table 1]

[0076] <Evaluation of water vapor resistance> Two bonded articles were prepared by the methods described in Example 1 and Comparative Example 1. (Hereinafter, the bonded articles obtained by the method described in Example 1 will be referred to as bonded articles according to Example 1(a) and Example 1(b), and the bonded articles obtained by the method described in Comparative Example 1 will be referred to as bonded articles according to Comparative Example 1(a) and Comparative Example 1(b).) Electrodes were provided on the ends of each of the bonded articles to enable electrical current to flow. Each of the joined bodies in the above-mentioned electrically conductive state was arranged so that the corrosion-resistant silicon carbide heating element or the silicon carbide heating element was contained in a box-shaped test furnace (inner furnace width 180 mm, inner furnace height 180 mm, inner furnace length 300 mm). Electricity is passed through each of the above-mentioned joints, and the surface load density of the corrosion-resistant silicon carbide heating element or silicon carbide heating element of each of the above-mentioned joints is 2 W / cm 2 While maintaining the temperature inside the box-type test furnace at 1050°C, the amount of steam inside the electric furnace was 82.8 g / m 3 The temperature was controlled so that the dew point was 50°C, and continuous operation was carried out. During the above continuous operation, the rate of increase in resistance (resistance increase rate) was measured, assuming that the resistance value of the joined material at the start of energization was 100%.

[0077] As can be seen from FIG. 7, the corrosion-resistant silicon carbide heating element constituting the bonded article of Example 1(a) and Example 1(b) has a protective film having a specific composition provided on the surface of a silicon carbide base material, and therefore even when operated continuously for 2000 hours in a furnace, the resistance increase rate is suppressed to within 30%, and it is understood that corrosion deterioration of the silicon carbide heating element due to high-temperature steam can be suppressed for a long period of time.

[0078] On the other hand, from FIG. 7, it can be seen that the silicon carbide heating elements constituting the bonded bodies according to Comparative Example 1(a) and Comparative Example 1(b) do not have a protective film having a specific composition on their surfaces, and therefore when they are operated continuously in a furnace, the resistance increase rate increases sharply when the operating time exceeds 1000 hours, and the resistance increase rate increases over time, so that the corrosion deterioration of the silicon carbide heating element due to high-temperature steam cannot be suppressed. [Industrial Applicability]

[0079] According to the present invention, it is possible to provide a novel corrosion-resistant silicon carbide heating element that has an ytterbium silicate-containing film having excellent adhesion on the surface of a silicon carbide base material as a protective film, which can be easily and inexpensively produced, and also to provide a method for producing the corrosion-resistant silicon carbide heating element.

Claims

1. A corrosion-resistant silicon carbide heating element having a protective film provided on at least a part of a surface of a silicon carbide base material, the protective film comprising: Yb ２ O ３ 25~85% by mass, Yb ２ SiO ５ 10~50 mass %, Yb ２ Si ２ O ７ 0~20% by mass, SiO ２ 2~10% by mass Contains The thickness of the protective film is 30 to 200 μm. A corrosion-resistant silicon carbide heating element characterized by:

2. 2. The corrosion-resistant silicon carbide heating element according to claim 1, wherein the silicon carbide base material has a silicon carbide content of 98 mass% or more, has a plurality of pores on the surface thereof with an average pore diameter of 1 to 30 μm, and has a porosity of 10 to 50%.

3. A method for producing the corrosion-resistant silicon carbide heating element according to claim 1 or 2, comprising the steps of: Yb ２ O ３ and SiO ２ and applying a slurry containing the above to at least a portion of a silicon carbide substrate, Heat treatment at 1000 to 1350°C The present invention relates to a method for producing a corrosion-resistant silicon carbide heating element.

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