阅读说明：本技术 电阻体、蜂窝结构体及电加热式催化剂装置 (Resistor, honeycomb structure, and electrically heated catalyst device ) 是由 德野刚大 成濑淳一 高山泰史 于 2020-01-22 设计创作，主要内容包括：电阻体(1)具备多个导电性粒子(100)连接而成的粒子连续体(10)、和位于粒子连续体(10)的周围的基体(11)。粒子连续体(10)具有导电性粒子(100)彼此被面接合而成的面接合部(101)。作为导电性粒子(100),可以适宜使用硅粒子。面接合部(101)的平均边界线长度优选为0.5μm以上。(The resistor (1) is provided with a particle continuum (10) formed by connecting a plurality of conductive particles (100), and a substrate (11) positioned around the particle continuum (10). The particle continuous body (10) has a surface-bonded part (101) in which conductive particles (100) are surface-bonded to each other. As the conductive particles (100), silicon particles can be suitably used. The average boundary line length of the surface joint (101) is preferably 0.5 [ mu ] m or more.)

1. A resistor (1) comprising a particle continuum (10) formed by connecting a plurality of conductive particles (100), and a substrate (11) positioned around the particle continuum,

the particle continuum has a surface-bonded portion (101) in which the conductive particles are surface-bonded to each other.

2. The resistor body according to claim 1, wherein the conductive particles are silicon particles.

3. The resistor according to claim 1 or 2, wherein an average boundary line length of the surface joint portion is 0.5 μm or more.

4. The resistor body according to any one of claims 1 to 3, wherein the matrix includes borosilicate and cordierite.

5. The resistor according to any one of claims 1 to 4, wherein the resistance change rate after 50 hours at 1000 ℃ in the atmosphere is 200% or less.

6. A honeycomb structure (2) comprising the resistor according to any one of claims 1 to 5.

7. An electrically heated catalyst device (3) having the honeycomb structure according to claim 6.

Technical Field

The present application relates to a resistor, a honeycomb structure, and an electrically heated catalyst device.

Background

Conventionally, in various fields, a resistor is used for electrical heating. For example, in the field of vehicles, an electrically heated catalyst device is known in which a catalyst-supporting honeycomb structure is made of a resistor such as SiC and the honeycomb structure is heated by energization to generate heat.

As the resistor, for example, a ceramic resistor obtained by firing a mixture of silica particles, borosilicate glass, or boric acid and kaolin at 1250 to 1300 ℃.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2019-12682

Disclosure of Invention

In the conventional resistor, the conductive path is formed by point contact of silicon particles. Therefore, when a conventional resistor is exposed to a high-temperature oxidizing atmosphere of 1000 ℃, the contact portions of the silicon particles are oxidized to form an insulating oxide film. As a result, the conventional resistor has a problem that the conductive path is cut or narrowed at the contact portion between the silicon particles, and the resistance rapidly increases.

The purpose of the present application is to provide a resistor body capable of suppressing an increase in resistance even when exposed to a high-temperature oxidizing atmosphere of 1000 ℃.

One aspect of the present invention is a resistor including a particle continuum in which a plurality of conductive particles are connected, and a base located around the particle continuum,

the particle continuous body has a surface-bonded portion in which the conductive particles are surface-bonded to each other.

Another aspect of the present invention is a honeycomb structure including the resistor.

Still another aspect of the present invention is an electrically heated catalyst device including the above honeycomb structure.

The resistor can suppress an increase in resistance even when exposed to a high-temperature oxidizing atmosphere of 1000 ℃.

The honeycomb structure can suppress an increase in electrical resistance even when exposed to a high-temperature oxidizing atmosphere of 1000 ℃, and therefore can achieve a constant temperature rise rate.

The electrically heated catalyst device can suppress an increase in the electrical resistance of the honeycomb structure even when exposed to a high-temperature oxidizing atmosphere of 1000 ℃ in an exhaust gas environment, and therefore can achieve a constant temperature rise rate. Further, the above electrically heated catalyst device is also advantageous for improvement of thermal durability.

The parenthesized symbols in the claims indicate correspondence with specific means described in the embodiments described later, and do not limit the technical scope of the present application.

Drawings

The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. The attached drawings are as follows:

FIG. 1 is an explanatory view schematically showing a cross section of a resistor according to embodiment 1,

FIG. 2 is an explanatory view of a part of an EBSD image schematically showing a cross section of a resistor according to embodiment 1,

FIG. 3 is an explanatory view schematically showing a honeycomb structure of embodiment 2,

FIG. 4 is an explanatory view schematically showing an electrically heated catalyst device according to embodiment 3,

FIG. 5 is an EBSD image of the cross section of the resistor of sample 1 prepared in the experimental example,

FIG. 6 is an EBSD image of the cross section of the resistor of sample 1 prepared in the experimental example (different in magnification from FIG. 5),

fig. 7 is an EBSD image of a cross section of the resistor of sample 1C produced in the experimental example.

Detailed Description

The resistor of the present embodiment includes a particle continuous body in which a plurality of conductive particles are connected, and a base located around the particle continuous body, and the particle continuous body includes a surface bonding portion in which the conductive particles are surface-bonded to each other.

In the resistor of the present embodiment, since the particle continuum has the surface-bonded portion in which the conductive particles are surface-bonded to each other, the cut or the narrowing of the conductive path is less likely to occur in the surface-bonded portion even when the resistor is exposed to a high-temperature oxidizing atmosphere of 1000 ℃. Therefore, the resistor of the present embodiment can suppress an increase in resistance even when exposed to a high-temperature oxidizing atmosphere of 1000 ℃. Hereinafter, the resistor of the present embodiment will be described with reference to fig. 1 and 2.

(embodiment mode 1)

As illustrated in fig. 1, the resistor 1 includes a particle continuum 10 and a base 11. The particle continuous body 10 is configured by connecting a plurality of conductive particles 100. The particle continuous body 10 has a surface-bonded portion 101 in which the conductive particles 100 are surface-bonded to each other. Fig. 1 illustrates a particle continuous body 10 having a constricted portion 102 in a portion of a surface joint 101. Further, an arrow Y shown in fig. 1 refers to a conductive path.

The presence of the surface-bonded portion 101 in the particle continuous body 10 can be confirmed by performing electron back scattering diffraction (hereinafter, may be abbreviated as EBSD) on the cross section of the resistor 1. EBSD is known as a method of analyzing an orientation distribution of crystal grains by calculating a crystal orientation of a pattern continuously obtained based on information on a crystal structure of a measurement sample. Specifically, as illustrated in fig. 2, when the conductive particles 100 constituting the particle continuum 10 have the boundary line 101a therebetween by the crystal orientation analysis using the EBSD apparatus, the particle continuum 10 is determined to have the surface junction 101. In the EBSD image, it is considered that the boundary line 101a is seen in the surface junction 101 due to disturbance of crystal orientation of the material constituting the conductive particle 100 in the surface junction 101. Therefore, it is technically inaccurate to determine that the conductive particles 100 are not connected to each other because of the existence of the boundary line 101 a. This can be easily understood by comparing the SEM image with the EBSD image for the same site, and the like.

The average boundary line length of surface joint 101 obtained by EBSD may be set to 0.5 μm or more. With this configuration, the effect of suppressing the increase in resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ℃ can be easily obtained, and the oxidation resistance of the resistor body 1 can be reliably ensured. The average boundary line length may be set to preferably 1 μm or more, more preferably 2 μm or more, and further preferably 4 μm or more. The average boundary line length may be set to 10 μm or less from the viewpoint of productivity, uniformity in cell wall thickness when the resistor 1 is used in a honeycomb structure, and the like. As for the average boundary length, 5 fields of EBSD images are acquired for the cross section of the resistor 1, the length of the boundary 101a of the surface joint 101 is measured for all the particle continuants 10, and the average value of the obtained measurement values is obtained. Note that, since the boundary line 101a extending from the inside of the field of view to the outside of the field of view has an unknown length, the count is not performed. When the average boundary line length of the surface joint 101 is measured by EBSD, the plurality of particle continuants 10 do not enter 1 field of view if the magnification is excessively increased, and therefore the field of view is acquired so that the plurality of particle continuants 10 enter 1 field of view. Specifically, the EBSD image can be acquired within the range of 20 μm × 20 μm. The magnification can be set to 3500.

The resistance of the resistor used as a resistance heating element increases with use, and varies depending on the applicationUsually, the resistor is replaced when the resistance is about 3 times. Therefore, it is preferable to set the material structure at which the resistance is increased by 3 times as the threshold value. Specifically, the resistance is defined by R ═ ρ × L/a (where R [ Ω ])]: resistance, rho omega m]: resistivity, L [ m ]]: length, Am²]: cross sectional area). Since the surface junction 101 between the conductive particles 100 is narrowed, the resistance in the high-temperature oxidizing atmosphere is increased by the reduction in the cross-sectional area of the surface junction 101. Here, when the oxide film thickness of the material constituting the conductive particles used in the resistance heating element is set to 100nm, the conductive area of the surface junction 101 decreases, and the boundary length when the resistance is 3 times becomes 0.5 μm. More specifically, when the diameter of the surface junction 101 is 0.5 μm, the cross-sectional area of the surface junction 101 becomes 0.25 × 0.25 × 3.14 — 0.196 μm². When the surface junction 101 is oxidized from the outer surface to the inside of 0.1 μm, the diameter of the surface junction 101 becomes 0.3 μm, and the cross-sectional area of the surface junction 101 becomes 0.15 × 0.15 × 3.14 — 0.071 μm². That is, the cross-sectional area of the surface junction 101 becomes about 1/3 by oxidation, and the resistance increases by about 3 times. Therefore, by setting the average boundary line length of the surface joining portion 101 to 0.5 μm or more, the oxidation resistance of the resistor 1 can be ensured. As one of the above-mentioned means for setting the oxide film thickness to 0.1 μm, the following can be mentioned. For example, as described below, silicon is considered as a material constituting the conductive particles. The oxidation of silicon is performed by exposure to an oxidizing atmosphere at about 1000 ℃. The interface reaction becomes rate-controlling in the initial stage of oxidation, and oxidation occurs on the surface of about 40nm in a relatively short time. It is known that SiO, which is an oxide film on the surface of silicon, is oxidized at a wavelength of 40nm or more₂The membrane functions as a barrier to oxygen and thus the rate of oxidation is suppressed. Therefore, although the oxidation rate of silicon is stabilized, the oxidation proceeds to about 100nm in a dry environment, and a wet oxidation process is used to further oxidize the silicon. Therefore, if the resistor is used in a dry environment, the silicon surface can be set to be oxidized at 100nm during use.

The resistor 1 may have a configuration in which the number of surface joints 101 having a boundary line length of 0.5 μm or more is preferably 5 or more, more preferably 10 or more, and still more preferably 20 or more. With this configuration, the average boundary line length of the surface bonding portion 101 can be easily set to 0.5 μm or more, the effect of suppressing the increase in resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ℃ can be easily obtained, and the heat resistance of the resistor 1 can be easily improved. The number of the surface joints 101 having a boundary line length of 0.5 μm or more can be determined for each EBSD image acquired within the range of 20 μm × 20 μm as described above.

The conductive particles 100 may be composed of a surface oxidizable material. According to this configuration, even when the surface of the particle continuous body 10 is insulated by oxidation of the conductive particles 100, insulation by oxidation is not easily generated in the surface bonding portion 101. Therefore, according to this configuration, the resistor 1 can easily enjoy the effect of suppressing the increase in resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ℃. In this case, when the particle continuous body 10 has the constricted portion 102 in the portion of the surface joining section 101, the surface of the constricted portion 102 is particularly easily oxidized, and therefore, the effects of the above configuration can be sufficiently exhibited.

As a material constituting the conductive particles 100, for example, silicon particles (Si particles) or the like can be exemplified as a suitable material. Silicon is oxidized to form SiO on the surface₂A film. In the resistor 1, the conductive particles 100 may be made of silicon particles. It is considered that, in the material in which silicon particles play a main conductive path, the increase in resistance in a high-temperature oxidizing atmosphere at 1000 ℃ is caused by the disconnection or narrowing of the conductive path between the silicon particles due to the surface oxidation of the silicon particles. In contrast, in the resistor 1 having the above-described configuration, a sufficient bonding area is secured by the surface bonding portion 101 in which the silicon particles are surface-bonded to each other. When the surfaces of the silicon particles constituting the particle assembly 10 are oxidized, insulating SiO is formed on the surfaces of the particle assembly 10₂A thin film, but if oxidation proceeds to a certain extent or more, SiO₂The film becomes gas barrierTherefore, oxygen hardly enters the inside of the surface joint 101, and oxidation can be suppressed. Therefore, according to the above configuration, even when silicon particles are used as the conductive particles 100, the conductive paths are less likely to be cut or narrowed, and the oxidation resistance can be improved.

The matrix 11 is present around the particle continuum 10. As illustrated in fig. 1, the resistor 1 may include a plurality of particle continuous bodies 10, and the plurality of particle continuous bodies 10 may be electrically connected to each other directly or through the conductive phase 111. In this case, from the viewpoint of securing a conductive path or the like, it is preferable that the plurality of particle continuous bodies 10 do not include an oxide film formed by oxidizing a material constituting the conductive particles 100 in an initial state. Such a configuration can be realized by firing in an inert gas atmosphere such as an Ar gas atmosphere.

As illustrated in fig. 1, the base 11 may have a configuration including a conductive phase 111 and an insulating phase 112. The conductive phase 111 may include, for example, a conductive coating portion 111a that covers the surface of the particle continuum 10, and according to this configuration, the particle continuum 10 adjacent to each other via the conductive coating portion 111a are easily electrically connected to each other, which is advantageous for forming a conductive path. The conductive coating portion 111a may cover the entire surface of the particle continuous body 10 or may cover a part thereof. The conductive coating 111a may be made of, for example, borosilicate, from the viewpoint of formation of a conductive path between the particle assemblies 10. The conductive phase 111 may contain conductive particles alone, or may contain borosilicate or the like not covering the surface of the particle continuous body 10. Examples of the conductive particles that can be contained in the single body include silicon particles (Si particles), silicide particles, and the like. As the silicide particles, for example, particles selected from the group consisting of TiSi₂、TaSi₂And CrSi₂At least 1 of the constituent groups is preferably CrSi, for example, from the viewpoint of excellent balance between oxidation resistance and low volume expansion₂And the like. On the other hand, the insulating phase 112 may be made of, for example, insulating particles. The insulating particles include, for example, cordierite particlesAnd the like. Cordierite has a low thermal expansion coefficient as compared with alumina, mullite, or the like. Therefore, according to this configuration, the thermal expansion coefficient of the resistor 1 can be easily reduced. Further, cordierite melts at 1300 ℃ or higher, and therefore the material structure of the resistor 1 is densified, and oxygen hardly penetrates into the material. Therefore, according to this configuration, the oxidation resistance of the resistor 1 can be easily improved. The resistor 1 may include an air hole.

The substrate 11 is preferably made of borosilicate and cordierite. With this configuration, the balance between securing of the conductive path, lowering of the thermal expansion coefficient, improvement of the oxidation resistance due to inhibition of penetration of oxygen into the material by densification, and the like is excellent. The base 11 may further contain 1 or 2 or more kinds of fillers, materials for reducing thermal expansion coefficient, materials for increasing thermal conductivity, materials for improving strength, and the like, as necessary.

The resistor 1 may have a resistance change rate of 200% or less after being held at 1000 ℃ for 50 hours in the air. With this configuration, the oxidation resistance in a high-temperature oxidizing atmosphere of 1000 ℃ is improved. The resistance change rate is preferably 150% or less, more preferably 100% or less, and still more preferably 50% or less from the viewpoint of improvement in oxidation resistance or the like, and may be further preferably 35% or less, and still more preferably 30% or less from the viewpoint of easiness of maintenance of circuit elements in the electrically heated catalyst device or the like.

The resistance change rate was measured as follows. The resistivity of the sample of the resistor 1 was measured before (i.e., at the initial stage) and after 50 hours of holding at 1000 ℃ in the atmosphere. The resistivity of the resistor 1 is an average value of measured values (n is 3) measured by a four-terminal method. Then, the absolute value of the value calculated by the formula of 100 × { (resistivity after 50 hours at 1000 ℃) (initial resistivity before 50 hours at 1000 ℃)/(initial resistivity before 50 hours at 1000 ℃) is set as the rate of change in resistance.

The resistor 1 being at a temperature of 25-500 deg.CA resistivity of 0.0001-1 Ω · m in a temperature range and a resistance increase rate of 0/K-5.0 × 10^-4preferably,/K or less. According to this configuration, since the temperature dependency of the resistor 1 is small, the resistor 1 in which temperature distribution is less likely to occur in the interior during electrical heating and cracks are less likely to occur due to thermal expansion and contraction can be obtained. Further, according to the above configuration, since the resistor 1 can be heated early at a lower temperature during the electrical heating, it is useful as a material for a honeycomb structure that requires early heating for early activation of a catalyst.

The resistivity of the resistor 1 varies depending on the required specifications of a system using the resistor 1, but may be set to, for example, 0.5 Ω · m or less, more preferably 0.1 Ω · m or less, and still more preferably 0.05 Ω · m or less, from the viewpoint of lowering the resistance of the resistor 1. The resistivity of the resistor 1 may be set to preferably 0.0002 Ω · m or more, more preferably 0.0005 Ω · m or more, and even more preferably 0.001 Ω · m or more, from the viewpoint of an increase in the amount of heat generated during electrical heating.

The resistance increase rate of the resistor 1 may be preferably set to 0.001 × 10 from the viewpoint of facilitating suppression of the temperature distribution by the electrical heating, and the like^-6More preferably 0.01X 10,/K or more^-6More preferably 0.1X 10 or more in terms of/K^-6More than K. The resistance increase rate of the resistor 1 is preferably set to 100 × 10, because the resistance value most suitable for the electrical heating is present in the circuit, and the resistance increase rate is not changed^-6A value of less than or equal to K, more preferably 10X 10^-6A value of 1X 10 or less, more preferably 1K or less^-6and/K is less than or equal to.

The resistivity of the resistor 1 is an average value of measured values (n is 3) measured by a four-terminal method. The rate of increase in resistance of the resistor 1 can be calculated by measuring the resistivity of the resistor 1 by the above-described method and then by the following calculation method. First, the resistivity was measured at 3 points at 50 ℃, 200 ℃ and 400 ℃. The resistance increase rate was calculated by dividing the value obtained by subtracting the resistivity at 50 ℃ from the resistivity at 400 ℃ by the temperature difference between 400 ℃ and 50 ℃ of 350 ℃.

(embodiment mode 2)

The honeycomb structure of embodiment 2 will be described with reference to fig. 3. In addition, the same reference numerals as those used in the present embodiment among the reference numerals used in embodiment 2 and thereafter represent the same components and the like as those in the present embodiment unless otherwise specified.

As illustrated in fig. 3, the honeycomb structure 2 of the present embodiment includes the resistor 1 of embodiment 1. In this embodiment, specifically, the honeycomb structure 2 is composed of the resistor 1 of embodiment 1. Specifically, fig. 3 shows a structure having a plurality of cells 20 adjacent to each other, cell walls 21 forming the cells 20, and an outer peripheral wall 22 provided on an outer peripheral portion of the cell walls 21 and integrally holding the cell walls 21, in a honeycomb cross-sectional view perpendicular to a central axis of the honeycomb structure 2. A known structure may be applied to the honeycomb structure 2, and the structure is not limited to the structure of fig. 3. Fig. 3 shows an example in which the cell 20 has a square cross section, and the cell 20 may have a hexagonal cross section, for example. Fig. 3 shows an example in which the honeycomb structure 2 is formed in a cylindrical shape, and for example, the honeycomb structure 2 may be formed in a cross-sectional circular track shape or the like.

The honeycomb structure 2 of the present embodiment includes the resistor 1 of embodiment 1. Therefore, the honeycomb structure 2 of the present embodiment can suppress an increase in the electrical resistance of the honeycomb structure 2 even when exposed to a high-temperature oxidizing atmosphere of 1000 ℃. Since the amount of heat generation increases in proportion to the resistance, the honeycomb structure 2 according to the present embodiment can realize a constant temperature rise rate.

(embodiment mode 3)

An electrically heated catalyst device according to embodiment 3 will be described with reference to fig. 4. As illustrated in fig. 4, an electrically heated catalyst apparatus 3 of the present embodiment includes a honeycomb structure 2 of embodiment 2. Specifically, in the present embodiment, the electrically heated catalyst device 3 includes the honeycomb structure 2, an exhaust gas purifying catalyst (not shown) supported on the cell walls 21 of the honeycomb structure 2, a pair of electrodes 31 and 32 disposed to face each other on the outer peripheral wall 22 of the honeycomb structure 2, and a voltage applying unit 33 for applying and controlling a voltage to the electrodes 31 and 32. The electrodes 31 and 32 are applied with voltages through the rod-shaped electrode terminals 310 and 320, respectively. The electrically heated catalyst device 3 may be applied to a known configuration, and is not limited to the configuration shown in fig. 4. The voltage application may be any one of a dc voltage application, an ac voltage application, a pulse voltage application, and a combination thereof.

The electrically heated catalyst device 3 of the present embodiment has the honeycomb structure 2 of embodiment 2. Therefore, the electrically heated catalyst device 3 of the present embodiment can suppress an increase in the electrical resistance of the honeycomb structure 2 even when exposed to a high-temperature oxidizing atmosphere of 1000 ℃ in an exhaust gas environment, and thus can achieve a constant temperature rise rate. The electrically heated catalyst device 3 of the present embodiment is also advantageous in improving thermal durability.

(Experimental example)

Preparation of samples 1, 2, 3, 1C, 2C-

Silicon (Si) particles (average particle diameter 7 μm), boric acid, and cordierite were mixed in the mass ratio shown in table 1. Subsequently, 4 mass% of methylcellulose was added as a binder to the mixture, and water was added thereto and mixed. Next, the obtained mixture was pelletized by an extrusion molding machine, dried at 80 ℃ in a thermostatic bath, and then degreased. The degreasing conditions were set to atmospheric air/normal pressure, a degreasing temperature of 700 ℃ and a degreasing time of 3 hours.

Subsequently, the degreased fired body is subjected to pre-firing. The calcination conditions were set to Ar gas atmosphere/normal pressure, the calcination temperature and the calcination time shown in table 1 for 30 minutes. In table 1, the sample that was not subjected to the burn-in is described as "none" (specifically, sample 1C).

Subsequently, the obtained fired body is subjected to main firing. The conditions for main firing were set to Ar atmosphere and normal pressure, main firing temperature and firing time shown in table 1, and 30 minutes.

Subsequently, the obtained fired body is subjected to a pre-oxidation treatment (oxidative ripening). The conditions for the pre-oxidation were set to atmospheric atmosphere and atmospheric pressure, a treatment temperature of 1000 ℃ and a treatment time of 10 hours. Thus, the resistors of sample 1, sample 2, sample 3, sample 1C and sample 2C having a shape of 5mm × 5mm × 25mm were obtained.

Preparation of samples 3C and 4C-

Resistors of samples 3C and 4C were obtained in the same manner as in sample 1, except that a mixture obtained by mixing silicon particles, boric acid, and kaolin at the mass ratio shown in table 1 was used, that calcination was not performed, and that the pre-oxidation treatment was not performed.

(EBSD Observation)

The cross section EBSD of the resistor of each sample was observed. As the EBSD device, JEOL-JSM7100M manufactured by Japan Electron was used. Thus, the crystal orientation of silicon was detected, and EBSD images color-differentiated for each crystal orientation were obtained. In this experimental example, the observation results of the resistor of sample 1 are shown in fig. 5 as representative examples of sample 1, sample 2, and sample 3. The magnification of the EBSD image in fig. 5 is 3500. Fig. 6 shows the observation result (enlargement) of the resistor of sample 1. Fig. 6 is an enlarged view of the bonding portions between silicon particles, which facilitates observation of the bonding portions between silicon particles. The magnification of the EBSD image of fig. 6 is 10000 times. Fig. 7 shows the observation result of the resistor of sample 1C. The magnification of the EBSD image in fig. 7 is 3500. The triangular shapes shown on the right side of the EBSD images in fig. 5 and 7 show the crystal orientation of silicon.

As shown in fig. 5 and 6, it was confirmed that the resistor 1 of each of samples 1, 2, and 3 includes a grain continuum 10 in which silicon particles used as the conductive particles 100 as a raw material are connected to each other by sintering by high-temperature firing, and a substrate 11 disposed around the grain continuum 10. As shown in fig. 5 and 6, it was confirmed that the grain continuous body 10 had a surface-bonded portion 101 in which the silicon grains 100 were surface-bonded to each other in the resistor body 1 of the samples 1, 2, and 3. In the EBSD images of fig. 5 and 6, the matrix 11 is an area around the particle continuum 10. In this region, cordierite particles, borosilicate, silicon particles whose crystal orientation cannot be determined, and the like used in the raw material are included. It is considered that at least a part of the borosilicate is formed on the surface of the particle continuum 10 because boron is detected on the surface of the silicon particles constituting the particle continuum 10 by observation by a time-of-flight secondary ion mass spectrometry (TOF-SIMS) which is separately performed. The borosilicate is formed by reacting boric acid with the surface of silicon particles used as a raw material, and can be said to be derived from silicon and boric acid. From the above results, it can be said that the resistive element 1 of sample 1, sample 2, and sample 3 has a conductive path formed by silicon and borosilicate.

In contrast, as shown in fig. 7, it was confirmed that the silicon particles of the resistors of samples 1C and 2C were only in point contact with each other and were not in surface contact with each other. This is believed to be due to: the highest temperature of the firing temperature is lower than that in firing of sample 1 and the like, and therefore necking by sintering of silicon particles (chemical bonding by sintering of silicon particles) does not proceed sufficiently.

The average boundary line length of the surface joint of the resistor of sample 1 was determined by EBSD by the method described above. Fig. 5 shows the length of the boundary line of each surface joint (7) surrounded by a circle. As a result, the average boundary line length in the resistor of sample 1 was 1.2 μm. In addition, the number of surface joints 101 having a boundary line length of 0.5 μm or more in the EBSD surface joint was measured for the resistor of sample 1 by the above-described method. As a result, the number of the resistors of sample 1 is 7.

(measurement of resistivity)

The initial resistivity of the resistor of each sample was measured. The resistivity was measured by a four-terminal method using a thermoelectric property evaluation device (manufactured by Ulvac Riko Inc, "ZEM-2") for a 5mm × 5mm × 18mm square column sample. The measurement temperature in this measurement was 25 ℃. Subsequently, the resistor of each sample was held at 1000 ℃ for 50 hours in the air. Next, the resistivity of the resistor of each of the samples after holding was measured in the same manner as described above. Next, the resistance change rate of the resistor of each sample was measured by the above calculation formula. However, the resistors of samples 3C and 4C were held at 1000 ℃ for 10 hours in the air, and the resistivity of the resistor after holding was measured, and the rate of change in resistance was measured using the same.

Table 1 summarizes the conditions for producing the resistor and the measurement results for each sample.

From the above results, the following can be seen. The resistors of samples 1C, 2C, 3C and 4C were oxidized at the contact portions between the silicon particles when exposed to a high-temperature oxidizing atmosphere of 1000 ℃ to form SiO, which is an insulating oxide film₂The film breaks the conductive path, and the resistance increases sharply. This is believed to be due to: the silicon particles of the resistors are in point contact with each other.

In contrast, the resistors of samples 1, 2, and 3 can suppress a rapid increase in resistance even when exposed to a high-temperature oxidizing atmosphere of 1000 ℃. This is due to: since the particle continuum has a surface-bonded portion in which silicon particles are surface-bonded to each other, the conductive path is less likely to be cut or narrowed at the surface-bonded portion even when the particle continuum is exposed to a high-temperature oxidizing atmosphere of 1000 ℃.

In addition, when the average boundary line length of the surface-bonded portion obtained by EBSD is 0.5 μm or more, the effect of suppressing the increase in resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ℃ is easily obtained, and the heat resistance of the resistor 1 is easily improved. As a result of the resistors of samples 1C and 2C, the resistance when exposed to a high-temperature oxidizing atmosphere of 1000 ℃ tends to increase as the firing temperature decreases. This is believed to be due to: when the firing temperature is low, a particle continuum having a surface junction is not formed.

The present application is not limited to the above embodiments and experimental examples, and various modifications may be made without departing from the scope of the present application. The respective configurations shown in the embodiments and the experimental examples may be arbitrarily combined. That is, although the present application is described in terms of the embodiments, it is to be understood that the present application is not limited to the embodiments, configurations, and the like. The present application also includes various modifications and modifications within an equivalent range. In addition, various combinations or forms, and further, other combinations or forms including only one element, more than one element, or less than one element are also included in the scope and idea of the present application.