WO2021111869A1

WO2021111869A1 - Electrical resistor, honeycomb structure, and electrically heated catalyst device

Info

Publication number: WO2021111869A1
Application number: PCT/JP2020/042884
Authority: WO
Inventors: 剛大徳野; 泰史 ▲高▼山; 慎二冨田; 幸司笠井
Original assignee: 株式会社デンソー
Priority date: 2019-12-06
Filing date: 2020-11-18
Publication date: 2021-06-10
Also published as: JP2021089878A

Abstract

An electrical resistor (1) including silicon particles (10) and an oxide (11) including silicon and boron. The mass ratio of silicon to boron (Si/B) in the material overall is no more than 280 and the boron content in the material overall is at least 0.5% by mass. The electrical resistor (1) can also include fused silica or cordierite. A honeycomb structure (2) comprises the electrical resistor (1). An electrically heated catalyst device (3) has the honeycomb structure (2).

Description

Electric resistors, honeycomb structures, and electrically heated catalysts

Cross-reference of related applications

This application is based on Japanese Application No. 2019-220855 filed on December 6, 2019, and the contents of the description are incorporated herein by reference.

The present disclosure relates to an electric resistor, a honeycomb structure, and an electric heating type catalyst device.

Conventionally, electric resistors have been used for energizing and heating in various fields. For example, in the vehicle field, there is known an electric heating type catalyst device in which a honeycomb structure supporting a catalyst is composed of an electric resistor and the honeycomb structure is heated by energization heating.

Examples of this type of electric resistor include a mixture of silicon particles, boric acid, and kaolin in a mass ratio of 42: 4: 54 and a mass ratio of 40: 8: 52 in the preceding Patent Document 1. An electric resistor formed by firing a mixed mixture is described.

Japanese Unexamined Patent Publication No. 2019-12682

The electric resistor that generates heat when energized and heated is required to have oxidation resistance when used at high temperatures. However, when the conventional electric resistor is exposed to a high temperature oxidizing atmosphere of 1000 ° C., the electric resistance increases and the electric characteristics deteriorate.

The present disclosure describes an electric resistor capable of suppressing an increase in electric resistance even when exposed to a high-temperature oxidizing atmosphere of 1000 ° C., a honeycomb structure using the electric resistance, and electric heating using the honeycomb structure. It is an object of the present invention to provide a type catalyst device.

One aspect of the present disclosure comprises silicon particles and oxides containing silicon and boron.
The Si / B ratio, which is the mass ratio of silicon to boron in the entire material, is 280 or less.
The boron content in the whole material is 0.5% by mass or more.
It is in the electric resistor.

Another aspect of the present disclosure is a honeycomb structure including the above electric resistor.

Yet another aspect of the present disclosure is in an electrically heated catalyst device having the honeycomb structure.

The electric resistor has the above configuration. Therefore, the electric resistor can suppress an increase in electric resistance even when exposed to a high temperature oxidizing atmosphere of 1000 ° C.

The honeycomb structure includes the electric resistor. Therefore, the honeycomb structure can suppress an increase in electrical resistance even when exposed to a high-temperature oxidizing atmosphere of 1000 ° C., and can realize a constant temperature rise rate. Therefore, the honeycomb structure is suitable as a honeycomb structure of an electrically heated catalyst device.

The electroheating catalyst device has the honeycomb structure. Therefore, the electric heating type catalyst device can suppress an increase in the electric resistance of the honeycomb structure even when exposed to a high temperature oxidizing atmosphere of 1000 ° C. in an exhaust gas environment, and realizes a constant temperature rising rate. be able to. Further, the electric heating type catalyst device is also advantageous in improving thermal durability.

Note that the reference numerals in parentheses described in the claims indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the present disclosure.

The above objectives and other objectives, features and advantages of the present disclosure will be clarified by the following detailed description with reference to the accompanying drawings. The drawing is
FIG. 1 is an explanatory view schematically showing a cross section of the electric resistor according to the first embodiment. FIG. 2 is a diagram for explaining an estimation mechanism of the action and effect of the electric resistor according to the first embodiment, in which (a) is the electric resistor according to the first embodiment and (b) is the comparative embodiment. It is a figure which showed the electric resistor, and is FIG. 3 is an explanatory view schematically showing the honeycomb structure according to the second embodiment. FIG. 4 is an explanatory view schematically showing the electrically heated catalyst device according to the third embodiment. FIG. 5 is a diagram showing the relationship between the time (horizontal axis) held at 1000 ° C. in the air and the electrical resistivity (vertical axis) at 25 ° C. obtained in Experimental Example 1. FIG. 6 is a diagram showing the relationship between the boron content (horizontal axis) measured by ICP and the electrical resistance increase rate (vertical axis) obtained in Experimental Example 1. FIG. 7 is a diagram showing the relationship between the Si / B ratio (horizontal axis) obtained by ICP measurement and the electrical resistance increase rate (vertical axis) obtained in Experimental Example 1. FIG. 8 is a diagram showing the relationship between the silicon / boric acid compounding ratio (horizontal axis) and the mass increase rate (vertical axis) obtained in Experimental Example 2. FIG. 9 is a diagram showing the relationship between the silicon / boric acid compounding ratio (horizontal axis) and the electric resistance increase rate (vertical axis) obtained in Experimental Example 2.

(Embodiment 1)
The electric resistor of the first embodiment will be described with reference to FIGS. 1 and 2. As illustrated in FIG. 1, the electric resistor 1 of the present embodiment has silicon particles 10 and an oxide containing silicon and boron (hereinafter, may be appropriately referred to as “Si / B-containing oxide”) 11. And are configured to include.

In the electric resistor 1, the silicon particles 10 and the Si / B-containing oxide 11 form a conductive path. That is, in the electric resistor 1, the silicon particles 10 and the Si / B-containing oxide 11 function as a conductive phase. Specifically, as illustrated in FIG. 1, the electric resistor 1 can include a plurality of silicon particles 10 and include a silicon particle continuum 101 in which the silicon particles 10 are connected to each other. The silicon particle continuum 101 can have a constricted portion 101a at a portion where the silicon particles 10 are connected to each other. The Si / B-containing oxide 11 can exist so as to cover the surface of the silicon particle continuum 101. The electric resistor 1 may contain a single silicon particle 10 in which the silicon particles 10 are not connected to each other, or a Si / B-containing oxide 11 that covers the surface of the single silicon particle 10.

The electric resistor 1 has a Si / B ratio of 280 or less, which is the mass ratio of silicon to boron in the entire material, and the boron content in the entire material is 0.5% by mass or more. The Si / B ratio and the boron content can be measured by an ICP (Inductively Coupled Plasma) emission spectroscopic analyzer (hereinafter, the measurement may be appropriately referred to as "ICP measurement"). As the ICP emission spectroscopic analyzer, an ICP emission spectroscopic analyzer manufactured by Hitachi High-Tech Science Co., Ltd. (ICP-AES, AES is an abbreviation for Atomic Emission Spectroscopy) can be used. The boron content (mass%) and silicon content (mass%) contained in the entire material of the electric resistor 1 are measured by ICP measurement. The Si / B ratio can be calculated by dividing the silicon content (mass%) by the boron content (mass%).

When the electric resistor 1 contains silicon particles 10 and a Si / B-containing oxide 11 and is exposed to a high-temperature oxidizing atmosphere at 1000 ° C. by setting the Si / B ratio and the boron content within a specific range. However, the increase in electrical resistance can be suppressed. Hereinafter, the reason for this will be described with reference to FIG.

In the electric resistor 1 that generates heat by energization heating, it is important to control the electric resistance in order to control the rate of temperature rise. The calorific value W is calculated by the following formula based on the current I, the voltage E, and the electric resistance R.
W = E x I = I ² x R
Since the calorific value is proportional to the electric resistance in this way, it is necessary to keep the electric resistance constant in order to suppress a sudden increase in the calorific value when the electric resistor 1 is used. However, the conventional electric resistor 1 that does not satisfy the above regulation has a problem that the electric resistance increases when exposed to a high temperature oxidizing atmosphere of 1000 ° C. This is presumed to be due to the following reasons. Oxidation of silicon proceeds by being exposed to an oxidizing atmosphere of about 1000 ° C. Therefore, when the above regulation is not satisfied, as shown in FIG. 2B, the film thickness of the Si / B-containing oxide 11 on the surface of the silicon particles 10 is thin, so that oxidation proceeds on the surface of the silicon particles 10. Then, a thick SiO ₂ film grows. The grown SiO ₂ film causes narrowing or cutting of the conductive path between the silicon particles 10. As a result, the conventional electric resistor 1 has an increased electric resistance when exposed to a high temperature oxidizing atmosphere of 1000 ° C. On the other hand, when the above regulation is satisfied, as shown in FIG. 2A, since the film thickness of the Si / B-containing oxide 11 is thick, the oxidation of the surface of the silicon particles 10 is suppressed, and SiO ₂ is formed. Hard to grow. Therefore, narrowing or cutting of the conductive path between the silicon particles 10 is unlikely to occur, and the change in electrical resistance between the silicon particles 10 is suppressed. As a result, the electric resistor 1 satisfying the above regulation can suppress an increase in electric resistance even when exposed to a high temperature oxidizing atmosphere of 1000 ° C.

As will be described later in the experimental example, boric acid can be used as a boron source in the production of the electric resistor 1. In this case, the boron content corresponding to the boric acid blending amount at the time of production is not directly detected as the boron content of the electric resistor 1 by the ICP measurement, and the detected amount is smaller than the blending amount. It is considered that this is because when the amount of boric acid blended is small, the effect of boric acid evaporation during firing is large. Due to such a phenomenon, in order to form the Si / B-containing oxide 11 having a gas barrier property against oxygen gas around the silicon particles 10, the amount of boric acid blended should be increased in consideration of the amount of boron to evaporate. Is required. According to the results of EDX measurement and electron diffraction measurement of a transmission electron microscope (TEM), an amorphous region containing elements of Si, B, and O can be seen around the silicon particles 10. Therefore, the Si / B-containing oxide 11 is considered to be a borosilicate. Specifically, the Si / B-containing oxide 11 is preferably derived from at least silicon particles 10 and boric acid. According to this configuration, it becomes easier to suppress the mixing of the alkaline component as compared with the case where the Si / B-containing oxide 11 is derived from the silicon particles 10 and the borosilicate glass. Therefore, according to this configuration, it becomes easy to suppress the crystallization of the glass phase in the material, and the electric resistor 1 which is advantageous in reducing the coefficient of thermal expansion can be obtained.

When the Si / B ratio of the electric resistor 1 exceeds 280, the rate of increase in electric resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ° C. increases sharply. This is because the content of boron is smaller than that of the silicon particles 10, so that the gas barrier property is lowered, and the silicon particles 10 change to the _{insulating SiO 2 when exposed to a high temperature oxidizing atmosphere of 1000 ° C.} This is because the electrical junction is broken. The Si / B ratio is preferably 200 or less, more preferably 150 or less, and further, from the viewpoint of ensuring the effect of reducing the rate of increase in electrical resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ° C. Preferably, it can be 100 or less. Further, the Si / B ratio is preferably 5 or more, more preferably 8 from the viewpoint that the amount of silicon particles 10, which are the key to the development of conductivity, is relatively small when the amount of boron is too large. Above, more preferably, it can be 10 or more.

When the boron content of the electric resistor 1 is less than 0.5% by mass, the rate of increase in electrical resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ° C. increases sharply. The boron content is preferably 0.8% by mass or more, more preferably 1 from the viewpoint of ensuring the effect of reducing the rate of increase in electrical resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ° C. It can be 0.0% by mass or more, more preferably 2.0% by mass or more. Further, the boron content is preferably 8.0% by mass or less, more preferably from the viewpoint that the amount of silicon particles 10, which are the key to the development of conductivity, is relatively small when the amount of boron is too large. Can be 6.0% by mass or less, more preferably 4.0% by mass or less.

The electric resistor 1 can further contain fused silica. The molten silica melts during firing during the production of the electric resistor 1 to densify the material structure of the electric resistor 1. Therefore, according to this configuration, it becomes difficult for oxygen gas to permeate into the electric resistor 1, and the oxidation of the silicon particles 10 is suppressed. Therefore, according to this configuration, it becomes easy to reduce the rate of increase in electrical resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ° C. Further, since the molten silica is produced by melting the raw material silica at a high temperature, it contains almost no alkaline component. Therefore, according to this configuration, the alkaline component contained in the electric resistor 1 is reduced, and the crystallization of the glass phase is suppressed. Further, the molten silica has a low coefficient of thermal expansion (coefficient of thermal expansion of the molten silica: about 0.8 ppm / K). Therefore, according to this configuration, the coefficient of thermal expansion of the electric resistor 1 can be reduced, which is advantageous for improving the thermal shock resistance of the electric resistor 1.

The content of molten silica in the electric resistor 1 can be 85% by mass or less. According to this configuration, it becomes easy to secure the electrical conductivity, so that it becomes easy to obtain the electric resistor 1 suitable for the energization heating. The content of the molten silica can be preferably 80% by mass or less, more preferably 70% by mass or less, still more preferably 60% by mass or less, from the viewpoint of ensuring the above effect. .. The content of the molten silica is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, from the viewpoint of the balance between oxidation resistance and low thermal expansion. can do.

The electric resistor 1 can further include cordierite. Cordierite melts during firing during the production of the electric resistor 1 to densify the material structure of the electric resistor 1. Therefore, according to this configuration, it becomes difficult for oxygen gas to permeate into the electric resistor 1, and the oxidation of the silicon particles 10 is suppressed. Therefore, according to this configuration, it becomes easy to reduce the rate of increase in electrical resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ° C. Further, by adopting a configuration containing cordierite, it is possible to reduce or eliminate the amount of kaolin in the starting material. Cordierite has a lower coefficient of thermal expansion than alumina and mullite produced by firing kaolin (coefficient of thermal expansion of cordierite: about 1.8 to 2.0 ppm / K). Therefore, according to this configuration, the coefficient of thermal expansion of the electric resistor 1 can be reduced, which is advantageous for improving the thermal shock resistance of the electric resistor 1.

The content of cordierite in the electric resistor 1 can be 75% by mass or less. According to this configuration, it becomes easy to secure the electrical conductivity, so that it becomes easy to obtain the electric resistor 1 suitable for the energization heating. The content of cordierite is preferably 70% by mass or less, more preferably 68% by mass or less, still more preferably 60% by mass or less, still more preferably, from the viewpoint of ensuring the above effects. Can be 50% by mass or less. The content of cordierite is preferably 30% by mass or more, more preferably 35% by mass or more, still more preferably 40% by mass or more, from the viewpoint of the balance between oxidation resistance and low thermal expansion. Can be.

The above-mentioned fused silica and cordierite can function as an insulating phase in the electric resistor 1. Both the molten silica and cordierite can exist around the silicon particle continuum 101 whose surface is covered with the Si / B-containing oxide 11. Specifically, as illustrated in FIG. 1, the electric resistor 1 contains a silicon particle continuum 101 whose surface is covered with a Si / B-containing oxide 11 in the matrix 12, and is described above. Matrix 12 can be configured to contain at least one of fused silica and cordierite.

The electric resistor 1 can be configured such that the rate of increase in electrical resistance after holding at 1000 ° C. for 50 hours in the atmosphere is 250% or less. According to this configuration, it becomes easy to realize an electric resistor 1 capable of suppressing an increase in electric resistance even when exposed to a high-temperature oxidizing atmosphere of 1000 ° C. The rate of increase in electrical resistance is preferably 230% or less, more preferably 200% or less, still more preferably 150% or less, still more preferably in an electrically heated catalyst device, from the viewpoint of improving oxidation resistance and the like. From the viewpoint of easy maintenance of the circuit element, it can be 135% or less, and even more preferably 130% or less.

For the rate of increase in electrical resistance, the value measured as follows is used. For each sample of the electric resistor 1, the electrical resistivity before (that is, initial) holding at 1000 ° C. for 50 hours and after holding the sample are measured. The electrical resistivity of the electric resistor 1 is an average value of measured values (n = 3) measured by the four-terminal method at 25 ° C. Then, the value calculated by the formula of 100 × (electric resistivity after holding at 1000 ° C. for 50 hours) / (initial electrical resistivity after holding at 1000 ° C. for 50 hours) is the electric resistance increase rate. (%).

The electric resistor 1 can be configured to have an electric resistivity of 0.01 Ω · cm or more and 100 Ω · cm or less. According to this configuration, it becomes easy to select a circuit suitable for a hybrid car equipped with an electric heating type catalyst device, so that an electric resistor suitable as a honeycomb structure in the electric heating type catalyst device can be obtained. The electrical resistivity of the electric resistor 1 is an average value of measured values (n = 3) measured by the four-terminal method at 25 ° C.

The electrical resistivity of the electric resistor 1 is preferably 0.1 Ω · cm or more, more preferably 0., from the viewpoint of increasing the amount of heat generated during energization heating and making it easier to adopt a relatively simple electric circuit. It can be 3 Ω · cm or more, more preferably 0.5 Ω · cm or more. The electrical resistivity of the electric resistor 1 can be preferably 50 Ω · cm or less, more preferably 30 Ω · cm or less, and further preferably 10 Ω · cm or less from the viewpoint of reducing the electric resistance.

The electric resistor 1 can be configured such that the rate of increase in electric resistance is 0% / ° C. or higher and 0.5% / ° C. or lower. According to this configuration, the electric resistor 1 does not have the NTC characteristic (the characteristic that the electrical resistivity decreases as the temperature rises). An electric resistor having NTC characteristics is disadvantageous from the viewpoint of uniform heat generation because a larger amount of current flows into a locally heated part, which causes a temperature distribution. On the other hand, according to the above configuration, since the electric resistor 1 does not have the NTC characteristic, the electric resistor 1 that can easily realize uniform heat generation can be obtained.

The electrical resistivity increase rate of the electric resistor 1 is preferably larger than 0% / ° C. from the viewpoint of PTC characteristics (characteristics in which the electrical resistivity increases as the temperature rises), and ensures the PTC characteristics. From this point of view, it can be more preferably 0.05% / ° C. or higher, further preferably 0.06% / ° C. or higher, and even more preferably 0.07% / ° C. or higher. Further, the rate of increase in electric resistance of the electric resistor 1 is preferably increased from the viewpoint that when used as a honeycomb structure in an electric heating type catalyst device, the change in electric resistance does not become too large and it is easy to correspond to a circuit. It can be 0.5% / ° C. or lower, more preferably 0.4% / ° C. or lower, still more preferably 0.3% / ° C. or lower, and even more preferably 0.2% / ° C. or lower.

The rate of increase in electrical resistance of the electrical resistor 1 is calculated as follows. The electrical resistivity of the electric resistor 1 is measured at three points of 50 ° C., 200 ° C., and 400 ° C. The electrical resistivity of the electrical resistor 1 at each temperature is an average value of measured values (n = 3) measured by the four-terminal method. Then, the rate of increase in electrical resistance [% / ° C.] is calculated by the following formula. Measuring the electrical resistivity at 200 ° C. in addition to the electrical resistivity at 50 ° C. and 400 ° C. is meaningful for confirming whether the temperature dependence of the electrical resistivity has linearity.
Electrical resistance increase rate [% / ° C]
= {100 x (R _400- R ₅₀ ) / R ₅₀ [%]} / (400 [° C] -50 [° C])
However, in the above formula,
R ₄₀₀ is the electrical resistivity [Ω · cm] of the electrical resistor 1 at 400 ° C.
R ₅₀ is the electrical resistivity [Ω · cm] of the electrical resistor 1 at 50 ° C.

(Embodiment 2)
The honeycomb structure of the second embodiment will be described with reference to FIG. In addition, among the codes used in the second and subsequent embodiments, the same codes as those used in the above-described embodiments represent the same components and the like as those in the above-mentioned embodiments, unless otherwise specified.

As illustrated in FIG. 3, the honeycomb structure 2 of the present embodiment includes the electric resistor 1 of the first embodiment. Specifically, in the present embodiment, the honeycomb structure 2 is composed of the electric resistor 1 of the first embodiment. In FIG. 3, specifically, in a cross-sectional view of the honeycomb perpendicular to the central axis of the honeycomb structure 2, a plurality of cells 20 adjacent to each other, a cell wall 21 forming the cells 20, and an outer peripheral portion of the cell wall 21 are formed. An example is a structure having an outer peripheral wall 22 provided and integrally holding the cell wall 21. A known structure can be applied to the honeycomb structure 2, and the structure is not limited to the structure shown in FIG. FIG. 3 shows an example in which the cell 20 has a quadrangular cross section, but in addition, for example, the cell 20 may have a hexagonal cross section. Further, FIG. 3 shows an example in which the honeycomb structure 2 has a cylindrical shape, but in addition, for example, the honeycomb structure 2 may have a cross-sectional track shape or the like.

The honeycomb structure 2 of the present embodiment is configured to include the electric resistor 1 of the first embodiment. Therefore, the honeycomb structure 2 of the present embodiment can suppress an increase in electrical resistance even when exposed to a high-temperature oxidizing atmosphere of 1000 ° C. The calorific value increases in proportion to the electrical resistance. According to the honeycomb structure 2 of the present embodiment, the calorific value does not increase sharply, and a constant temperature rise rate can be realized. Therefore, the honeycomb structure 2 of the present embodiment is suitable as the honeycomb structure of the electric heating type catalyst device.

(Embodiment 3)
The electrically heated catalyst device of the third embodiment will be described with reference to FIG. As illustrated in FIG. 4, the electrically heated catalyst device 3 of the present embodiment has the honeycomb structure 2 of the second embodiment. In the present embodiment, specifically, the electric heating type catalyst device 3 includes a honeycomb structure 2, an exhaust gas purification catalyst (not shown) supported on the cell wall 21 of the honeycomb structure 2, and the honeycomb structure 2. It has a pair of

electrodes

31 and 32 arranged to face each other on the outer peripheral wall 22, and a voltage application unit 33 that applies and controls a voltage to the

electrodes

31 and 32. A voltage is applied to the electrode 31 and the electrode 32, respectively, through the rod-shaped electrode terminal 310 and the rod-shaped electrode terminal 320, respectively. The electric heating type catalyst device 3 can generate heat by energization through a pair of

electrodes

31 and 32 provided to the outer peripheral wall 22. The electrically heated catalyst device 3 can be heated to a temperature of, for example, 500 ° C. or higher from the viewpoint of fully exerting the function of the exhaust gas purification catalyst. A known structure can be applied to the electrically heated catalyst device 3, and the structure is not limited to the structure shown in FIG. Further, the form of voltage application may be any form or combination such as direct current, alternating current, pulsed voltage application and the like.

The electrically heated catalyst device 3 of the present embodiment has the honeycomb structure 2 of the second embodiment. Therefore, the electric heating type catalyst device 3 of the present embodiment can suppress an increase in the electric resistance of the honeycomb structure 2 even when exposed to a high temperature oxidizing atmosphere of 1000 ° C. in an exhaust gas environment, and the increase is constant. A temperature rate can be achieved. Further, the electrically heated catalyst device 3 of the present embodiment is also advantageous in improving the thermal durability.

(Experimental Example 1)
<Preparation of sample>
-Sample 1-
Silicon particles (average particle size 7 μm), boric acid and cordierite (average particle size 1.7 μm) were mixed at a mass ratio of 30:20:50. Then, 4% by mass of methyl cellulose was added as a binder to this mixture, water was added, and the mixture was mixed. Next, the obtained mixture was molded into pellets by an extrusion molding machine, dried at 80 ° C. in a constant temperature bath, and then degreased. The degreasing conditions were air atmosphere / normal pressure, degreasing temperature 700 ° C., and degreasing time 3 hours.

Next, the degreased fired body was calcined. The calcination conditions were an Ar gas atmosphere, normal pressure, a calcination temperature of 1250 ° C., and a calcination time of 30 minutes.

Next, the obtained fired body was main fired. The conditions for the main firing were an Ar gas atmosphere, normal pressure, a main firing temperature of 1350 ° C., and a main firing time of 30 minutes.

Next, the obtained fired body was subjected to a preliminary oxidation treatment (oxidation aging treatment). The conditions for pre-oxidation were atmospheric atmosphere / normal pressure, treatment temperature 1000 ° C., and treatment time 10 hours. As a result, an electric resistor of Sample 1 having a shape of 5 mm × 5 mm × 25 mm was obtained.

-Sample 2-
An electric resistor of Sample 2 was obtained in the same manner as in Sample 1 except that a mixture of silicon particles, boric acid and cordierite was used at a mass ratio of 30:10:60.

-Sample 3-
Sample 1 except that fused silica (average particle diameter 6.8 μm) was used instead of cordierite, and a mixture of silicon particles, boric acid, and fused silica mixed at a mass ratio of 30:20:50 was used. In the same manner as above, the electric resistor of sample 3 was obtained.

-Sample 4-
Sample 1 except that fused silica (average particle diameter 6.8 μm) was used instead of cordierite, and a mixture of silicon particles, boric acid, and fused silica mixed at a mass ratio of 30:10:60 was used. In the same manner as above, the electric resistor of sample 4 was obtained.

-Sample 1C-
An electric resistor of sample 1C was obtained in the same manner as in sample 1 except that a mixture of silicon particles, boric acid and cordierite in a mass ratio of 30: 4: 66 was used.

-Sample 2C-
Sample 1 except that fused silica (average particle size 6.8 μm) was used instead of cordierite, and a mixture of silicon particles, boric acid, and fused silica mixed at a mass ratio of 30: 4: 66 was used. In the same manner as above, an electric resistor of sample 2C was obtained.

<Si / B ratio, boron content>
For the electrical resistors of each sample, use an ICP emission spectrophotometer (“SPS-3520UV” manufactured by Hitachi High-Tech Science Co., Ltd.), and the boron content (mass%) and silicon content (mass%) contained in each material as a whole. Was measured. Then, for the electric resistors of each sample, the Si / B ratio, which is the mass ratio of silicon to boron in the entire material, was calculated.

<Electrical resistivity, electrical resistance increase rate>
The electrical resistivity of each sample was measured. The electrical resistivity of a prism sample having a size of 5 mm × 5 mm × 25 mm was measured by a four-terminal method using a thermoelectric characterization device (“ZEM-2” manufactured by ULVAC Riko Co., Ltd.). The measurement temperature in this measurement is 25 ° C. In addition, the electrical resistors of each sample were held in the air at 1000 ° C. for 50 hours. The condition of holding the product in the atmosphere at 1000 ° C. for 50 hours simulates the usage state of being exposed to a high temperature oxidizing atmosphere of 1000 ° C. In this example, as a reference, the electrical resistivity of each electric resistor before the preliminary oxidation treatment was measured in the same manner as described above. Then, in the same manner as described above, the electrical resistivity of the electrical resistor of each sample after the holding was measured. In this example, the electrical resistivity of the electrical resistivity of each sample after being subjected to the pre-oxidation treatment for 10 hours and before being held at 1000 ° C. for 50 hours is defined as the initial electrical resistivity. Next, using the initial electrical resistivity before holding at 1000 ° C. for 50 hours and the electrical resistivity after holding at 1000 ° C. for 50 hours, the electrical resistivity of the electric resistor of each sample is calculated by the above formula. The rate of increase was measured.

<Rate of increase in electrical resistance>
For the electrical resistivity of each sample, the electrical resistivity at 50 ° C. (R ₅₀ ), the electrical resistivity at 200 ° C. (R ₂₀₀ ), and the electrical resistivity at 400 ° C. (R ₄₀₀ ) according to the method for measuring the electrical resistivity described above. Was measured. Then, based on the above-mentioned calculation formula, the rate of increase in electrical resistance of the electrical resistor of each sample was calculated.

Table 1 summarizes the production conditions of the electric resistors of each sample, various measurement results, and the like.

According to Table 1, FIGS. 5 to 7, the following can be seen. The electrical resistivity of Sample 1C and Sample 2C, which did not have the configuration specified in the present disclosure, increased sharply when exposed to a high-temperature oxidizing atmosphere at 1000 ° C. On the other hand, the electric resistors of Samples 1 to 4 having the configuration specified in the present disclosure suppress a rapid increase in electrical resistivity even when exposed to a high temperature oxidizing atmosphere of 1000 ° C. I was able to.

According to Table 1, it can be seen that the mixing ratio of boric acid in Sample 1 is 5 times higher than that in Sample 1C, but the ratio of the boron content measured by ICP is not 5 times higher. .. That is, it can be seen that the amount of boric acid blended is not proportional to the boron content measured by ICP. It is considered that this is because when the amount of boric acid blended is small, the effect of boric acid evaporation during firing is large.

Further, from the above results, if the honeycomb structure of the electric heating type catalyst device is constructed by using the electric resistance of this example, it is possible to suppress the increase of the electric resistance even when exposed to a high temperature oxidizing atmosphere of 1000 ° C. Therefore, it can be said that a constant temperature rise rate can be realized. Further, according to the electric heating type catalyst device having a honeycomb structure composed of the electric resistors of this example, the electric resistance of the honeycomb structure increases even when exposed to a high temperature oxidizing atmosphere of 1000 ° C. in an exhaust gas environment. It can be said that a constant temperature rise rate can be realized because the temperature can be suppressed. Further, it can be said that such an electrically heated catalyst device is also advantageous in improving thermal durability.

(Experimental Example 2)

<Silicon / boric acid compounding ratio, mass increase rate, electrical resistance increase rate>
By increasing the boric acid content as compared with the conventional one and setting the Si / B ratio and the boron content as measured by ICP within the ranges specified in this disclosure, electricity when exposed to a high temperature oxidizing atmosphere at 1000 ° C. The reason why the increase in resistivity could be suppressed was further investigated. Specifically, the silicon / boric acid compounding ratio, which is the mass ratio of silicon to boric acid in the compounding raw material of the electric resistor, is changed, and the electric resistance before and after holding at 1000 ° C. for 50 hours in the air. The mass increase rate was calculated from the mass. The mass increase rate (%) was calculated from the formula of 100 × (mass of electric resistor after holding at 1000 ° C. for 50 hours) / (mass of electric resistor before pre-oxidation treatment). In addition, the above-mentioned silicon / boric acid compounding ratio was changed to obtain the above-mentioned increase rate of electrical resistance. The results are shown in FIGS. 8 and 9.

As shown in FIG. 8, it can be seen that the mass increase rate is large in the region where the silicon / boric acid compounding ratio is large, that is, the boric acid compounding amount is small with respect to the silicon compounding amount. This is because when the silicon particles are exposed to a high-temperature oxidizing atmosphere at 1000 ° C., oxidation is actively generated on the surface of the silicon particles, _{so that a large number of SiO 2} films are formed and the mass is increased. As a result, the conductive path between the silicon particles was narrowed or cut, and it is considered that the electrical resistance of Sample 1C and Sample 2C of Experimental Example 1 increased when exposed to a high-temperature oxidizing atmosphere at 1000 ° C. On the other hand, it can be seen that the mass increase rate is small in the region where the silicon / boric acid compounding ratio is small, that is, the boric acid compounding amount is large relative to the silicon compounding amount. This is because oxidation of the surface of the silicon particles was suppressed even when exposed to a high-temperature oxidizing atmosphere of 1000 ° C., and SiO ₂ was difficult to grow. As a result, narrowing or cutting of the conductive path between the silicon particles is unlikely to occur, and the samples 1 to 4 of Experimental Example 1 are said to have suppressed the increase in electrical resistance even when exposed to a high-temperature oxidizing atmosphere at 1000 ° C. Conceivable.

Further, according to FIG. 9, in the region where the silicon / boric acid compounding ratio is large, that is, the boric acid compounding amount is small with respect to the silicon compounding amount, the electric resistance increase rate is large and the silicon / boric acid compounding ratio is small. That is, it can be seen that the rate of increase in electrical resistance becomes smaller in the region where the boric acid compounding amount is larger than the silicon compounding amount. From this result, in order to suppress the increase in electric resistance when exposed to a high temperature oxidizing atmosphere of 1000 ° C., it is effective to increase the amount of boric acid compounded and increase the boron content contained in the electric resistor. It can be said that.

The present disclosure is not limited to each of the above embodiments and experimental examples, and various changes can be made without departing from the gist thereof. In addition, each configuration shown in each embodiment and each experimental example can be arbitrarily combined. That is, although the present disclosure has been described in accordance with the embodiments, it is understood that the present disclosure is not limited to the embodiments, structures, and the like. The present disclosure also includes various modifications and modifications within an equal range. In addition, various combinations and forms, as well as other combinations and forms that include only one element, more, or less, are also within the scope of the present disclosure.

Claims

Containing silicon particles (10) and oxides containing silicon and boron (11),
The Si / B ratio, which is the mass ratio of silicon to boron in the entire material, is 280 or less.
The boron content in the whole material is 0.5% by mass or more.
Electrical resistor (1).
The electric resistor according to claim 1, further comprising fused silica.
The electrical resistor according to claim 1 or 2, further comprising cordierite.
The electric resistor according to any one of claims 1 to 3, wherein the rate of increase in electrical resistance after holding at 1000 ° C. for 50 hours in the atmosphere is 250% or less.
The electric resistor according to any one of claims 1 to 4, wherein the electrical resistivity is 0.01 Ω · cm or more and 100 Ω · cm or less.
The electric resistor according to any one of claims 1 to 5, wherein the rate of increase in electrical resistance is 0% / ° C. or higher and 0.5% / ° C. or lower.
The electric resistor according to any one of claims 1 to 6, which is configured to be used for a honeycomb structure in an electrically heated catalyst device.
A honeycomb structure (2) including the electric resistor according to any one of claims 1 to 6.
An electrically heated catalyst device (3) having the honeycomb structure according to claim 8.