JP2023092016A - Corrosion-resistant silicon carbide heating elements and method for manufacturing the same - Google Patents

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

The present invention relates to a corrosion-resistant silicon carbide heating element and a method for manufacturing a corrosion-resistant silicon carbide heating element.

Conventionally, heat generating elements made of silicon carbide (silicon carbide heat generating elements) have been known. A heat treatment is performed on an object to be treated (see Patent Document 1, etc.).

JP 2010-126427 A

It is known that the silicon carbide heat generating element deteriorates with time due to long-term use, and it is known that the deterioration with time is particularly susceptible to the use environment of the silicon carbide heat generating element.

As a cause of deterioration of the silicon carbide heating element, silicon carbide (SiC), which is the main component of the heating element, reacts with oxygen (O ₂ ) in a high-temperature atmospheric atmosphere of 800° C. or higher to form silicon dioxide (SiO ₂ ). is mentioned.

In addition, in a high-temperature steam-containing atmosphere, silicon dioxide (SiO ₂ ) 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)

Furthermore, in a high-temperature steam-containing atmosphere, silicic acid (Si(OH) ₄ ) is produced from the silicon dioxide (SiO ₂ ) as shown in the following reaction formula (3).
_SiO2 + _2H2O →Si(OH) ₄ (3)
As described above, it is considered that silicon carbide reacts with water vapor, particularly in a high-temperature water vapor-containing atmosphere, and progresses in corrosion and dissolution, thereby accelerating its deterioration.

Silicon carbide heating elements are widely used as a heat source for firing electronic components such as MLCCs (multilayer ceramic capacitors), and for firing in the process of synthesizing positive electrode materials for lithium ion secondary batteries. Firing treatments such as these may be carried out in an atmosphere containing water vapor, especially in the process of synthesizing the positive electrode material of a lithium ion secondary battery. Since the firing is often performed in the presence of water vapor, the life of the silicon carbide heating element tends to be shortened.

The present inventors came up with the idea of a silicon carbide heating element provided with a protective film in order to suppress deterioration due to the high-temperature steam.

As the protective film, silicates of ytterbium (Yb) such as Yb ₂ SiO ₅ and Yb ₂ Si ₂ O ₇ which have low reactivity with high-temperature steam and have thermal expansion coefficients close to that of silicon carbide (ytterbium silicate ) was considered.
However, the melting point of ytterbium silicate such as Yb ₂ SiO ₅ and Yb ₂ Si ₂ O ₇ exceeds 1800° C., whereas the heat resistance temperature of silicon carbide is about 1400° C. It is difficult to melt Yb ₂ SiO ₅ , Yb ₂ Si ₂ O ₇ or the like to form a film.

Plasma PVD (Plasma Physical Vapor Deposition), EB-PVD (Electron Beam Physical Vapor Deposition), etc. are methods for forming a protective film made of Yb ₂ SiO ₅ or Yb ₂ Si ₂ O ₇ at a low temperature. was also considered, but all of them require special equipment and require high costs for their manufacture.

Thus, conventionally, it has been difficult to form an ytterbium silicate-containing film on the surface of a silicon carbide base material easily and at low cost with excellent fixability.

Under such circumstances, the present invention provides a novel corrosion-resistant silicon carbide heating element that has an ytterbium silicate-containing film with excellent fixability on the surface of a silicon carbide base material and that can be manufactured simply and at low cost. It is an object of the present invention to provide a method of manufacturing a corrosion-resistant silicon carbide heating element.

In order to solve the above technical problems, the inventors of the present application conducted extensive studies and found that instead of melting Yb ₂ SiO ₅ or Yb ₂ Si ₂ O ₇ or the like, Yb ₂ O ₃ and SiO ₂ After coating at least a portion of the silicon carbide heating element with the slurry containing Yb 2 SiO 5 or Yb 2 SiO 5 or Yb ₂ SiO ₅ or Yb 2 SiO 5 or It was found that a protective film containing Yb ₂ Si ₂ O ₇ can be formed, and that such a protective film can exhibit excellent fixability to a silicon carbide substrate. Based on this finding, the present invention was completed. came to.

That is, the present invention
(1) A corrosion-resistant silicon carbide heating element having a protective film on at least a part of the surface of a silicon carbide substrate, the protective film comprising:
Yb ₂ O ₃ 25-85% by mass,
Yb ₂ SiO ₅ 10 to 50% by mass,
Yb ₂ Si ₂ O ₇ 0 to 20% by mass,
_SiO2 2 to 10% by mass
A corrosion-resistant silicon carbide heating element, characterized by containing
(2) The corrosion-resistant silicon carbide heating element according to (1) above, wherein the protective film has a thickness of 30 to 200 μm;
(3) The silicon carbide substrate has a silicon carbide content of 98% by mass or more, has a plurality of pores with an average pore diameter of 1 to 30 μm on the surface, and has a porosity of 10% or more. The corrosion-resistant silicon carbide heating element according to the above (1) or (2), which is
(4) A method for manufacturing a corrosion-resistant silicon carbide heating element according to any one of (1) to (3) above,
After applying the slurry containing Yb ₂ O ₃ and SiO ₂ to at least part of the silicon carbide substrate,
A method for manufacturing a corrosion-resistant silicon carbide heating element is provided, which is characterized by heat treatment at 1000 to 1350°C.

ADVANTAGE OF THE INVENTION 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 with excellent fixability as a protective film on the surface of a silicon carbide base material and that can be easily manufactured at low cost. In addition, it is possible to provide a method for manufacturing a corrosion-resistant silicon carbide heating element.

1 is a schematic diagram showing a form example of a corrosion-resistant silicon carbide heating element according to the present invention; FIG. 1 is a schematic diagram showing an example of the form of a silicon carbide substrate that constitutes a corrosion-resistant silicon carbide heating element according to the present invention; FIG. 1 is a schematic diagram showing a form example of a corrosion-resistant silicon carbide heating element according to the present invention; FIG. FIG. 3 is a diagram showing an observation image of a cross section of a corrosion-resistant silicon carbide heating element obtained in an example; FIG. 4 is an enlarged view of an observed image in the vicinity of the outer peripheral surface in the cross section of the corrosion-resistant silicon carbide heating element obtained in the example. FIG. 4 is an enlarged view of an observed image at the central portion of the cross section of the corrosion-resistant silicon carbide heating element obtained in Example. FIG. 5 is a diagram showing evaluation results of the steam resistance ability of corrosion-resistant silicon carbide heating elements obtained in Examples and silicon carbide heating elements obtained in Comparative Examples.

First, a corrosion-resistant silicon carbide heating element according to the present invention will be described.
A corrosion-resistant silicon carbide heating element according to the present invention is a corrosion-resistant silicon carbide heating element in which a protective film is provided on at least a part of the surface of a silicon carbide substrate, the protective film comprising:
Yb ₂ O ₃ 25-85% by mass,
Yb ₂ SiO ₅ 10 to 50% by mass,
Yb ₂ Si ₂ O ₇ 0 to 20% by mass,
SiO ₂ 2-10% by mass
It is characterized by containing

A corrosion-resistant silicon carbide heating element according to the present invention is used in a state in which at least a portion of the surface of a silicon carbide substrate is provided with a protective film, and functions as a heating element by generating heat when energized, Its shape may be solid or hollow, but it is preferably hollow cylindrical.

FIG. 1 is a schematic diagram showing an example of a form of a corrosion-resistant silicon carbide heating element according to the present invention. It is composed of E and E.
A corrosion-resistant silicon carbide heating element according to the present invention is used, for example, as the heat generating portion M shown in FIG.

A corrosion-resistant silicon carbide heating element according to the present invention includes a silicon carbide substrate and a protective film provided on at least a portion of the silicon carbide substrate.

In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film contains Yb ₂ O ₃ in an amount of 25 to 85% by mass, preferably 25 to 75% by mass, more preferably 25 to 60% by mass. % is more preferable.

In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film contains Yb ₂ SiO ₅ in an amount of 10 to 50% by mass, preferably 20 to 50% by mass, more preferably 30 to 50% by mass. % is more preferable.

In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film contains Yb ₂ Si ₂ O ₇ in an amount of 0 to 20% by mass, preferably 5 to 20% by mass. It is more preferable to contain 20% by mass.

In the corrosion-resistant silicon carbide heating element according to the present invention, the content ratio of Yb ₂ SiO ₅ and Yb ₂ Si ₂ O ₇ in the protective film satisfies the above stipulations, respectively, so that the protective film and the silicon carbide substrate It is possible to effectively suppress deterioration of the silicon carbide substrate due to high-temperature steam while suppressing damage to the silicon carbide substrate and the protective film due to the difference in thermal expansion coefficient.

In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film preferably contains Yb ₂ SiO ₅ and Yb ₂ Si ₂ O ₇ in a total content of 10 to 70% by mass, preferably 40 to 70% by mass. It is more preferable to contain.

In the corrosion-resistant silicon carbide heat generating element according to the present invention, the total content of Yb ₂ SiO ₅ and Yb ₂ Si ₂ O ₇ in the protective film satisfies the above-mentioned stipulations. It is possible to more effectively suppress deterioration of the silicon carbide substrate due to high-temperature steam while suppressing damage to the silicon carbide substrate and the protective film due to a difference in coefficient of thermal expansion from that of the silicon carbide substrate.

In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film contains SiO ₂ in an amount of 2 to 10% by mass, preferably 5 to 10% by mass.

In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film contains 37 to 100 mass of Yb ₂ O ₃ , Yb ₂ SiO ₅ , Yb ₂ Si ₂ O ₇ and SiO ₂ in total. It preferably contains 70 to 100% by mass, and more preferably consists of only Yb ₂ O ₃ , Yb ₂ SiO ₅ , Yb ₂ Si ₂ O ₇ and SiO ₂ .

In the corrosion-resistant silicon carbide heating element according to the present invention, the content of each component such as Yb ₂ O ₃ , Yb ₂ SiO ₅ , Yb ₂ Si ₂ O ₇ and SiO ₂ in the protective film is determined by the surface of the corrosion-resistant silicon carbide heating element. means a value obtained by the following method using a measurement sample obtained by scraping off the protective film provided on the .
(1) Measurement of X-ray diffraction (XRD) spectrum The X-ray diffraction (XRD) spectrum of the measurement sample is measured under the following conditions.
X-ray diffractometer: Fully automatic horizontal multi-purpose X-ray diffractometer SmartLab manufactured by Rigaku Corporation
Goniometer: SmartLab
X-ray voltage: 40 kV
X-ray current: 30mA
Measurement angle range (2θ): 10° to 90°
Measurement step: 0.001°
Scanning speed: 5°/minute (2) Quantification of each component by RIR (Reference Intensity Ratio) method The X-ray diffraction spectrum data obtained in (1) was analyzed using Rigaku's "integrated powder X-ray analysis software PDXL2. 2”, and the RIR (Reference Intensity Ratio) method using an ICDD card specifies the amount of each component constituting the protective film.
The ICDD card numbers of Yb ₂ O ₃ , Yb ₂ SiO ₅ , Yb ₂ Si ₂ O ₇ and SiO ₂ are as follows.
Yb ₂ O ₃ : 01-075-6636
Yb ₂ SiO ₅ : 00-040-0386
Yb ₂ Si ₂ O ₇ : 01-082-0734
_SiO2 : 01-083-1831

In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film is provided on at least a part of the surface of the silicon carbide substrate, and preferably covers 36 to 100% of the surface.
When the corrosion-resistant silicon carbide heating element according to 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 substrate. More preferably, they are provided on the entire outer peripheral surface and the entire inner peripheral surface of the silicon carbide substrate.

In the corrosion-resistant silicon carbide heating element according to the present invention, the protective film preferably has a thickness of 30 to 200 μm, more preferably 50 to 200 μm.

In the corrosion-resistant silicon carbide heating element according to the present invention, since the thickness of the protective film is within the above range, it is possible to easily exhibit corrosion resistance against high-temperature steam over a long period of time.

In the present application documents, the lower limit and upper limit of the range of the thickness of the protective film are each obtained by observing the vertical cross section of the corrosion-resistant silicon carbide heating element according to the present invention at 10 locations with a scanning electron microscope. It means the arithmetic average value of the minimum film thickness of the protective film and the arithmetic average value of the maximum film thickness of the protective film in the observed image.

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% by mass or more (98 to 100% by mass), and preferably 99% by mass or more (99 to 100% by mass). % by mass), more preferably 100% by mass.
In the corrosion-resistant silicon carbide heating element according to the present invention, since the content of silicon carbide constituting the silicon carbide substrate satisfies the above-described regulation, the object to be treated can be heat-treated with high efficiency.

In the corrosion-resistant silicon carbide heating element according to the present invention, the content ratio of silicon carbide in the silicon carbide base material is obtained by scraping off a predetermined amount of the silicon carbide base material constituting the corrosion-resistant silicon carbide heating element to obtain a measurement sample. It means a value measured according to the provisions of "Method for quantifying silicon carbide" in the remarks of JIS R 6124.14.

In the corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide substrate suitably has a plurality of pores on its surface, and the pores preferably have an average pore diameter of 1 to 30 μm. It is more preferably 5 to 30 μm, even more preferably 20 to 30 μm.

In the corrosion-resistant silicon carbide heat generating element according to the present invention, the silicon carbide substrate has a plurality of pores that satisfy the above-mentioned regulations on the surface, so that part of the protective film penetrates into the silicon carbide substrate. However, due to the so-called anchor effect, the strong adhesion of the protective film to the silicon carbide substrate can be easily exhibited.

In addition, in the corrosion-resistant silicon carbide heating element according to the present invention, the average pore diameter on the surface of the silicon carbide substrate is determined by the mercury intrusion method specified in JIS R 1655 in the silicon carbide substrate cut from the corrosion-resistant silicon carbide heating element. Means the desired value.

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%, even more preferably 10 to 30%. More preferred.

In the corrosion-resistant silicon carbide heating element according to the present invention, the porosity of the silicon carbide base material satisfies the above-described regulation, so that the adhesion of the protective film to the silicon carbide base material can be more easily improved. can.

In addition, in the corrosion-resistant silicon carbide heating element according to the present invention, the porosity of the surface of the silicon carbide substrate is determined by the mercury injection method specified in JIS R1655 in the silicon carbide substrate cut out from the corrosion-resistant silicon carbide heating element. value.

In the corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide base material that satisfies the above regulations for pore size and porosity is obtained, for example, by adding a binder and water to silicon carbide (SiC) powder and kneading them to obtain silicon carbide. It can be produced by molding into a shape corresponding to the shape of the heating portion of the heating element, drying it, and then sintering it at a temperature of 2100 to 2400° C. in a nitrogen gas atmosphere.

FIG. 2(a) is a schematic diagram showing an example of the form of the silicon carbide substrate constituting the corrosion-resistant silicon carbide heating element according to the present invention. , as a cross section perpendicular 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 base material b. .

On the other hand, FIG. 3(a) shows a form example of a corrosion-resistant silicon carbide heating element according to the present invention, in which protective films c are provided on the outer and inner surfaces of the silicon carbide substrate b shown in FIG. 2(a). It is a schematic view, in which a hollow cylindrical corrosion-resistant silicon carbide heating element M 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 FIG. It can be seen that a part of the protective film c provided on each surface penetrates into and adheres to the plurality of pores h formed on the surface of the silicon carbide base material b.

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.

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

Next, a method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention will be described.
A method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention is a method for manufacturing a silicon carbide heating element according to the present invention,
After applying the slurry containing Yb ₂ O ₃ and SiO ₂ to at least part of the silicon carbide substrate,
It is characterized by heat treatment at 1000 to 1350°C.

In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide substrate may be the same as those described above.

In the method of manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, a slurry containing Yb ₂ O ₃ and SiO ₂ is applied to at least a portion of a silicon carbide substrate.

In the manufacturing method of the corrosion-resistant silicon carbide heating element according to the present invention, the Yb ₂ O ₃ concentration and the SiO ₂ concentration in the slurry that becomes the coating liquid are adjusted appropriately according to the concentration of each component in the protective film to be obtained. do it.

In the method for manufacturing the corrosion-resistant silicon carbide heating element according to the present invention, the concentration of Yb ₂ O ₃ in the slurry serving as the coating liquid is preferably 65 to 80% by mass in terms of solid content.

In the method for manufacturing the corrosion-resistant silicon carbide heating element according to the present invention, the SiO ₂ concentration in the slurry serving as the coating liquid is preferably 7 to 14% by mass in terms of solid content.

In the method for manufacturing the corrosion-resistant silicon carbide heating element according to the present invention, the slurry serving as the coating liquid contains, as components other than Yb ₂ O ₃ and SiO ₂ , a dispersant for the purpose of dispersing the components in the coating liquid, and a heating element. A binder (for example, an acrylic emulsion) or the like can be included for the purpose of ensuring the strength of the coating film before processing (before baking).

The dispersion medium that constitutes the slurry is not particularly limited, but water is preferable in consideration of the environment and workability.

In the method of manufacturing the corrosion-resistant silicon carbide heating element according to the present invention, the slurry that serves as the coating liquid can be prepared by mixing each constituent component in the dispersion medium.
The solid content concentration in the slurry is preferably 70 to 80% by mass.
Moreover, the viscosity of the slurry is preferably 100 to 800 Pa·s.

In the method of manufacturing the corrosion-resistant silicon carbide heating element according to the present invention, the method of applying the slurry as the coating liquid to the silicon carbide substrate is not particularly limited. It may be applied by a spray method of blowing, or a dipping method of immersing the silicon carbide substrate in the slurry.

In the method of manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, a slurry containing Yb ₂ O ₃ and SiO ₂ is applied to at least a portion of a silicon carbide substrate.
The position and range of application of the slurry may be determined according to the formation position and range of the protective film to be obtained.

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 substrate having a hollow cylindrical shape, slurry is applied by a brush coating method or a spray method. is preferred, and when protective films are to be provided on both the outer peripheral surface and the inner peripheral surface of the silicon carbide substrate having a hollow cylindrical shape, it is preferable to apply the slurry by a dipping method.

In the method of manufacturing the corrosion-resistant silicon carbide heating element according to the present invention, the coating process may be performed multiple times in order to obtain a protective film having a predetermined thickness.

In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, it is preferable to appropriately dry the slurry after applying the slurry.

In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide substrate having the slurry applied to at least a portion of the surface thereof is heat-treated at 1000 to 1350.degree.

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 substrate having the slurry applied to at least a portion of the surface is 1000 to 1350°C, and 1100 to 1350°C. It is preferably 1250 to 1350°C, more preferably 1250 to 1350°C.

In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide base material having the slurry applied to at least a portion of the surface thereof is heat-treated at a temperature within the above range. It is possible to form a protective film simply and at low cost without using a special heating device while suppressing breakage of the base material due to exceeding the heat-resistant temperature of .

In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, the time for heat-treating the silicon carbide substrate having the slurry applied to at least part of the surface thereof is preferably 1 to 30 minutes, and preferably 3 to 30 minutes. 20 minutes is more preferable, and 5 to 10 minutes is even more preferable.

In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, the silicon carbide base material having the slurry applied to at least a part of the surface thereof is heat-treated for a time within the above range, whereby the silicon carbide base material is It is possible to easily form a protective film having excellent adhesion (fixability) to the surface.

In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, the atmosphere in which the silicon carbide base material having the slurry applied to at least a part of the surface thereof is heat-treated is not particularly limited, but an inert gas atmosphere. Examples of the inert gas include nitrogen gas, argon gas, helium gas, etc. Nitrogen gas is preferred.

In the method for manufacturing a corrosion-resistant silicon carbide heating element according to the present invention, the moisture concentration in the atmosphere when heat-treating the silicon carbide substrate having the slurry applied to at least a portion of the surface thereof is 1000 ppm by mass or less. is preferred.

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

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited by the following examples.

(Example 1)
(1) Formation of Substrate Bonded Material 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 (content of silicon carbide: 98% by mass, distributed on the surface) An average pore diameter of 20 μm and a porosity (opening ratio) of 23%) were prepared.
By joining SiC/C end portions 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 to both ends of the silicon carbide base material, the base material joined body ( 20 mm outer diameter x 10 mm inner diameter x 900 mm total length).
(2) Preparation of Coating LiquidW. R. 17.5% by mass of colloidal silica suspension (grade: Ludox HS-40) manufactured by Grace, 65% by mass of Yb ₂ O ₃ powder (grade: 3N) manufactured by Nippon Yttrium Co., Ltd., and 17.5% by mass of deionized water. A raw material mixture in the form of slurry was obtained by weighing and mixing each material in a mortar for 5 minutes so as to obtain 5% by mass.
To the obtained raw material mixture, further, as a binder, a 1.5% by mass aqueous solution of Metolose manufactured by Shin-Etsu Chemical Co., Ltd. (grade: SM-400), 90% by mass of the raw material mixture, and 10% of the dispersant. A slurry-like coating liquid was prepared by mixing so as to obtain a mass %.
(3) Application of coating liquid The substrate bonded body prepared in (1) was allowed to stand still for 90 minutes so that the entire substrate bonded body was immersed in the coating liquid prepared in (2). The entire surface and inner peripheral surface were impregnated with the coating liquid.
(4) Heat treatment After the substrate bonded body is pulled out of the coating liquid and sufficiently dried, it is baked in an air atmosphere at 1300° C. for 4 minutes in a heat treatment furnace to obtain corrosion-resistant silicon carbide heat generation. A joint was obtained in which the ends were joined to both ends of the body.
A protective film was formed on the entire outer peripheral surface and the inner peripheral surface of the joint, and it was visually confirmed that no peeling or the like had occurred. It contained 26% by mass of Yb ₂ O ₃ , 48% by mass of Yb ₂ SiO ₅ , 17% by mass of Yb ₂ Si ₂ O ₇ and 9% by mass of SiO ₂ .
Also, a part of the corrosion-resistant silicon carbide heating element constituting the above-mentioned joint was cut out, and as shown in the schematic diagram on the left side of FIG. Each observation image obtained is shown on the right side of FIG.
5 and 6 are enlarged views of SEM observation images (magnification: 100 times, backscattered electron images) in the vicinity of the outer peripheral surface and in the central portion of the corrosion-resistant silicon carbide heating element.
From FIG. 6, it can be seen that the silicon carbide base material has pores shown in dark black in the figure.
Further, from FIG. 5, a protective film shown in white is formed in layers on the outer peripheral surface of the silicon carbide substrate shown in gray, and a part of this protective film is formed on the surface of the silicon carbide substrate. It can be seen that it is formed in close contact with the base material by entering into the plurality of formed pores.
The thickness of the protective film was 35 to 190 μm.

(Example 2)
In the same manner as in Example 1, except that in Example 1 (4), the baking treatment was performed by heating at 1100° C. for 4 minutes instead of performing the baking treatment by heating at 1300° C. for 4 minutes. , a bonded product in which the ends were bonded to both ends of the corrosion-resistant silicon carbide heating element was obtained.
A protective film was formed on the entire outer peripheral surface and the inner peripheral surface of the joint, and it was visually confirmed that no peeling or the like had occurred. It contained 80% by mass of Yb ₂ O ₃ , 13% by mass of Yb ₂ SiO ₅ , 3% by mass of Yb ₂ Si ₂ O ₇ and 4% by mass of SiO ₂ .
A part of the corrosion-resistant silicon carbide heating element was cut out and its cross section was observed with a scanning electron microscope. entered the pores on the surface of the silicon carbide substrate and was formed in close contact with the silicon carbide substrate.

(Comparative example 1)
In Example 1, the substrate-bonded product prepared in "(1) Formation of substrate-bonded product" was performed without performing the "(2) Coating liquid preparation" step and the "(3) Coating liquid application" step. , and a bonded product in which the ends were bonded to both ends of the silicon carbide heating element was obtained by treating in the same manner as in Example 1, except that the silicon carbide heating element was directly subjected to the "(4) heat treatment" step.

(Comparative example 2)
In the step of "(2) preparation of coating liquid" in Example 1, W.W. R. Grace's colloidal silica suspension (grade: Ludox HS-40) is 38.9% by mass, Nippon Yttrium Co., Ltd.'s Yb ₂ O ₃ powder (grade: 3N) is 48.1% by mass, and ion-exchanged water is A bonded product in which the ends were bonded to both ends of the silicon carbide heating element was obtained by the same treatment as in Example 1, except that each was weighed out so as to be 13.0% by mass.
A protective film was formed on the outer and inner peripheral surfaces of the bonded product, but it was visually observed that it was partially not fixed and peeled off. When the fixed portion of the protective film was scraped off and measured, the protective film contained Yb ₂ O ₃ 0% by mass (not detected), Yb ₂ SiO ₅ 79% by mass, Yb ₂ Si ₂ O ₇ 4% by mass, It contained 17% by mass of SiO ₂ .
In addition, when a portion of the corrosion-resistant silicon carbide heating element where the protective film was fixed was cut out and its cross section was observed with a scanning electron microscope, a protective film having a thickness of 10 to 25 μm was formed on the surface. rice field.
Table 1 shows the characteristics of the corrosion-resistant silicon carbide heating element and the protective film of the silicon carbide heating element obtained in each example and comparative example.
In Table 1, regarding "protective film fixability", if the protective film is formed on the entire outer peripheral surface and inner peripheral surface of the silicon carbide base material and it is visually observed that no peeling has occurred, "O" is given. When peeling of the film was observed on part of the outer peripheral surface and the inner peripheral surface of the silicon carbide base material, it was evaluated as "x".

<Evaluation of water vapor resistance>
Two each of the bonded products obtained by the method described in Example 1 and Comparative Example 1 were prepared (hereafter, the bonded products obtained by the method described in Example 1 were referred to as Example 1(a) and Example 1 (b), and the bonded products obtained by the method described in Comparative Example 1 are referred to as bonded products according to Comparative Examples 1(a) and 1(b)). An electrode was provided at the end of each of the joints to make it possible to conduct electricity.
Each of the joints in the energizable state was placed in a box-type test furnace (furnace width: 180 mm, furnace height: 180 mm, furnace length: 300 mm). , respectively.
Electricity is applied to each joint, and the temperature in the box test furnace is raised to 1050 while maintaining the surface load density of the corrosion-resistant silicon carbide heating element or silicon carbide heating element of each joint at 2 W/cm ² . C. and the amount of water vapor in the electric furnace was controlled to 82.8 g/ ^m.sup.3 (dew point 50.degree. C.).
In the above continuous operation, the rate of increase in resistance value (resistance increase rate) was measured when the resistance value of the joint at the start of energization was taken as 100%.

As shown in FIG. 7, the corrosion-resistant silicon carbide heating elements constituting the bonded products according to Examples 1(a) and 1(b) are those in which a protective film having a specific composition is provided on the surface of the silicon carbide substrate. Therefore, even if the furnace is continuously operated for 2000 hours, the resistance increase rate is suppressed to within 30%, and the corrosion deterioration of the silicon carbide heating element due to high-temperature steam can be suppressed over a long period of time. It turns out that

On the other hand, as shown in FIG. 7, the silicon carbide heat generating elements constituting the bonded products according to Comparative Examples 1(a) and 1(b) are not provided with a protective film having a specific composition on the surface, so that the , the resistance increase rate rises sharply when the operating time exceeds 1000 hours, and the resistance increase rate rises with the passage of time. It turns out to be irrepressible.

ADVANTAGE OF THE INVENTION 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 with excellent fixability as a protective film on the surface of a silicon carbide base material and that can be easily manufactured at low cost. In addition, it is possible to provide a method for manufacturing a corrosion-resistant silicon carbide heating element.

Claims (4)

A corrosion-resistant silicon carbide heating element provided with a protective film on at least a part of the surface of a silicon carbide substrate, the protective film comprising:
Yb ₂ O ₃ 25-85% by mass,
Yb ₂ SiO ₅ 10 to 50% by mass,
Yb ₂ Si ₂ O ₇ 0 to 20% by mass,
_SiO2 2 to 10% by mass
A corrosion-resistant silicon carbide heating element comprising: 2. The corrosion-resistant silicon carbide heating element according to claim 1, wherein said protective film has a thickness of 30 to 200 μm. The silicon carbide substrate has a silicon carbide content of 98% by mass or more, has a plurality of pores with an average pore diameter of 1 to 30 μm on the surface, and has a porosity of 10% or more. A corrosion-resistant silicon carbide heating element according to claim 1 or claim 2. A method for manufacturing a corrosion-resistant silicon carbide heating element according to any one of claims 1 to 3,
After applying the slurry containing Yb ₂ O ₃ and SiO ₂ to at least part of the silicon carbide substrate,
A method for manufacturing a corrosion-resistant silicon carbide heating element, characterized by heat-treating at 1000 to 1350°C.

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