JP2019186100A - Electric resistor, honeycomb structure, and electrically heated catalyst device - Google Patents

Abstract

To provide an electric resistor capable of improving thermal shock resistance, a honeycomb structure using the same, and an electrically heated catalyst device using the same.SOLUTION: An electric resistor 1 includes: borosilicate 10; Si-containing particles 11; a β-spodumene solid solution; and at least one kind 12 of β-quartz solid solutions. A coefficient of thermal expansion of the electric resistor 1 can be 0.5 ppm/K or more and 3 ppm/K or less. A honeycomb structure 2 includes the electric resistor 1. An electrically heated catalyst device 3 has the honeycomb structure 2.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, electric resistors are used for energization heating in various fields. For example, in the vehicle field, an electrically heated catalyst device is known in which a catalyst is supported on a honeycomb structure composed of an electrical resistor containing aluminosilicate, silicon and the like, and heat is generated by energization heating.

  In addition, in prior patent document 1, an electrical resistance containing 5 to 60% by weight of Si or FeSi as a conductive material in 45 to 95% by weight of a heat-resistant insulating material mainly composed of an aluminosilicate and a glass component. Techniques for applying the body to a honeycomb structure are described.

Japanese Patent Laid-Open No. 2-144874

  The electrical resistor used for energization heating is repeatedly heated and cooled. Therefore, cracks are generated in the electric resistor due to the expansion / contraction associated therewith, and the breakdown is likely to occur. In particular, the honeycomb structure of an electrically heated catalyst device used in an exhaust gas purification device for an internal combustion engine is disposed at the rear of the internal combustion engine and is exposed to a very severe heating / cooling environment. It is.

  The present invention has been made in view of such problems, and an electric resistor capable of improving thermal shock resistance, a honeycomb structure using the electric resistor, and an electric heating type using the honeycomb structure A catalytic device is to be provided.

One aspect of the present invention provides a borosilicate (10),
Si-containing particles (11);
At least one (12) of β-spodumene solid solution and β-quartz solid solution,
In the electrical resistor (1).

  Another aspect of the present invention resides in a honeycomb structure (2) configured to include the electric resistor.

  Yet another embodiment of the present invention resides in an electrically heated catalyst device (3) having the above honeycomb structure.

  The electric resistor has the above configuration. Therefore, the electrical resistor can reduce the thermal expansion coefficient. Therefore, according to the electric resistor, the thermal shock resistance can be improved.

  The honeycomb structure includes the electric resistor. For this reason, the honeycomb structure can suppress expansion and contraction associated therewith even when heating and cooling due to current heating or use in a thermal environment are repeated. Therefore, according to the honeycomb structure, the structural reliability can be improved.

  The electrically heated catalyst device has the honeycomb structure. For this reason, in the above electrically heated catalyst device, the honeycomb structure is hardly broken even when heating and cooling are repeated, and the reliability can be improved.

  In addition, the code | symbol in the parenthesis described in the means to solve a claim and a subject shows the correspondence with the specific means as described in embodiment mentioned later, and limits the technical scope of this invention. It is not a thing.

FIG. 3 is an explanatory diagram schematically showing a microstructure of the electric resistor according to the first embodiment. 6 is an explanatory view schematically showing a honeycomb structure of Embodiment 2. FIG. It is explanatory drawing which showed typically the electric heating type catalyst apparatus of Embodiment 3. FIG. It is a crystal structure analysis result about the electrical resistor of sample 1 in an experimental example. It is the graph which showed the relationship between the displacement (%) by the temperature of the electrical resistor of the sample 1, and the electrical resistor of the sample 1C in an experiment example, and expansion. It is the graph which showed the relationship between the temperature of the electrical resistor of the sample 1, and the electrical resistor of the sample 1C, and an electrical resistivity in an experiment example.

(Embodiment 1)
The electrical resistor according to Embodiment 1 will be described with reference to FIG. As illustrated in FIG. 1, the electrical resistor 1 according to the present embodiment includes at least one of a borosilicate 10, a Si-containing particle 11, a β-spodumene solid solution, and a β-quartz solid solution 12. , Including.

  The borosilicate 10 may be amorphous or crystalline. The borosilicate 10 can contain, for example, Al (aluminum) atoms in addition to atoms such as B (boron), Si (silicon), and O (oxygen). In this case, the borosilicate 10 is an aluminoborosilicate. According to this configuration, it is possible to ensure the electrical resistor 1 in which the thermal shock resistance is improved by reducing the thermal expansion coefficient. In addition, the borosilicate 10 may contain alkali metal atoms such as Na (sodium) and K (potassium), and alkaline earth metal atoms such as Mg (magnesium) and Ca (calcium). One or more of these may be contained. In FIG. 1, the borosilicate 10 is in the form of particles.

  Since the electrical resistor 1 contains the borosilicate 10, it contains B. B content in the borosilicate 10 can be 0.1 mass% or more and 5 mass% or less. According to this configuration, the temperature dependence of the electrical resistivity can be easily reduced.

The B content is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and still more preferably 0%, from the viewpoint of easily reducing the electrical resistance of the electrical resistor 1. 0.5% by mass or more, still more preferably 0.6% by mass or more, still more preferably 0.8% by mass or more, and even more preferably, the temperature dependence of the electrical resistivity is small, and the electrical resistance From the viewpoint of easily exhibiting PTC characteristics (characteristics in which electrical resistivity increases as temperature increases), the ratio can be set to 1% by mass or more. In addition, the B content is limited in the amount of doping to the silicate, and if not doped, it is unevenly distributed in the material as B ₂ O ₃ which is an insulator and causes a decrease in conductivity. Preferably, it is 4 mass% or less, More preferably, it is 3.5 mass% or less, More preferably, it can be 3 mass% or less. The B content is measured using an inductively coupled plasma (ICP) analyzer. However, according to the ICP analysis, since the B content in the entire electrical resistor 1 is measured, the obtained measurement result is converted into the B content in the borosilicate 10.

The Si-containing particles 11 are electron conductive particles containing Si atoms. Accordingly, the Si-containing particles 11 do not include SiO ₂ particles. Specifically, the Si-containing particles include Si particles, Si—Fe based particles (FeSi particles, FeSi ₂ particles, etc.), Si—Ti based particles (TiSi ₂ particles, etc.), Si—Ta based particles (TaSi ₂ particles, etc.). Etc.), Si-Cr based particles (CrSi ₂ particles etc.), Si-V based particles (VSi ₂ particles etc.), Si-Mo based particles (MoSi ₂ particles etc.), Si-W based particles (WSi ₂ particles etc.) And Si—C-based particles (SiC particles and the like). One or more of these may be contained. According to this configuration, there is an advantage that the Si-containing particles that are electron conductive particles can easily bridge the borosilicate 10 electrically.

Of these Si-containing particles 11, from the viewpoint of a relatively low melting point and difficulty of the plague phenomenon, Si—Fe-based particles, Si—Ti-based particles, Si—Ta-based particles, and Si—Cr-based particles are preferable. And Si-V-based particles. The plague phenomenon is a phenomenon in which a polycrystalline body is pulverized by oxidation at a relatively low temperature of about 500 ° C. observed with MoSi ₂ or WSi ₂ . The Si-containing particles 11 are more preferably TiSi ₂ particles, TaSi ₂ particles, CrSi from the viewpoint that the volume expansion in the temperature range of 300 ° C. to 800 ° C. is small and the structural strength of the electrical resistor 1 is easily secured. ₂ particles, and may be composed of at least one selected from the group consisting of VSi ₂ particles.

The electrical resistor 1 can include either a β-spodumene solid solution or a β-quartz solid solution, or both a β-spodumene solid solution and a β-quartz solid solution. Specifically, the β-spodumene solid solution can be represented by Li ₂ O—Al ₂ O ₃ —nSiO ₂ (8 ≧ n ≧ 4). In the present specification, the β-spodumene solid solution includes β-spodumene (Li ₂ O—Al ₂ O ₃ -4SiO ₂ ). On the other hand, the β-quartz solid solution can be specifically represented by Li ₂ O—Al ₂ O ₃ —nSiO ₂ (4> n ≧ 2). The electrical resistor 1 can include two or more types of β-spodumene solid solutions having different n numbers, and can include two or more types of β-quartz solid solutions having different n numbers.

  The electrical resistor 1 contains Li (lithium) because it contains at least one of a β-spodumene solid solution and a β-quartz solid solution. Li content in the electrical resistor 1 can be 0.1 mass% or more and 4 mass% or less. According to this configuration, it is possible to reliably reduce expansion and contraction by securing a β-spodumene solid solution or a β-quartz solid solution.

  The Li content in the electrical resistor 1 is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and further preferably 1% by mass from the viewpoint of securing a β-spodumene solid solution or the like. This can be done. In addition, the Li content in the electrical resistor 1 is preferably 3% by mass or less, more preferably 2% from the viewpoint that, when a large amount of β-spodumene solid solution is contained, the electric conductivity tends to decrease. It can be set to not more than mass%, more preferably not more than 1.5 mass%. In addition, content of Li contained in the electrical resistor 1 can be measured using an ICP analyzer similarly to B content mentioned above.

  In addition to the above, the electrical resistor 1 may be, for example, a filler, a material that lowers the coefficient of thermal expansion, a material that increases the thermal conductivity, a material that improves the strength, kaolin, or the like, if necessary. Can be included.

  Moreover, the electrical resistor 1 can be comprised by the porous containing the pore 13, as illustrated in FIG. According to this configuration, the bulk density and the heat capacity are reduced as compared with an electric resistor in which pores 13 formed between borosilicate 10, Si-containing particles 11, β-spodumene solid solution 12 and the like are closed with glass. can do. Moreover, according to this structure, since the unevenness | corrugation is formed in the surface of the electrical resistor 1 by the pore 13, the carrying | support property of catalysts, such as an exhaust gas purification catalyst, can be improved.

The electrical resistor 1 has an electrical resistivity of 0.0001 Ω · m to 1 Ω · m and an electrical resistance increase rate of 0 / K to 5.0 × 10 ^{−4 in} a temperature range of 25 ° C. to 500 ° C. / K or less. According to this configuration, since the temperature dependency of the electrical resistor 1 is small, it is difficult to generate a temperature distribution in the interior during energization heating, and it is possible to obtain the electrical resistor 1 that is less susceptible to cracking due to thermal expansion and contraction. Further, according to the above configuration, the material of the honeycomb structure that is required to be warmed early for early activation of the catalyst because the electric resistor 1 can be heated earlier at a lower temperature during energization heating. Useful as.

  The electrical resistivity of the electrical resistor 1 varies depending on the required specifications of the system using the electrical resistor 1, but from the viewpoint of reducing the electrical resistance of the electrical resistor 1, for example, preferably 0.5 Ω · m In the following, it is more preferably 0.1 Ω · m or less, and still more preferably 0.05 Ω · m or less. The electrical resistivity of the electrical resistor 1 is preferably 0.0002 Ω · m or more, more preferably 0.0005 Ω · m or more, and still more preferably 0.001 Ω from the viewpoint of increasing the amount of heat generated during energization heating. -It can be set to m or more.

The rate of increase in electrical resistance of the electrical resistor 1 is preferably 0.001 × 10 ⁻⁶ / K or more, more preferably 0.01 × 10 ⁶ from the viewpoint of facilitating suppression of temperature distribution due to current heating. ⁻⁶ / K or more, and more preferably 0.1 × 10 ⁻⁶ / K or more. The electrical resistance increase rate of the electrical resistor 1 is ideal from the viewpoint that there is an optimal electrical resistance value for energization heating in the electrical circuit, and it is ideal that the electrical resistance increase rate does not change. ⁻⁶ / K or less, more preferably 10 × 10 ⁻⁶ / K or less, and even more preferably 1 × 10 ⁻⁶ / K or less.

  In addition, the electrical resistivity of the electrical resistor 1 is an average value of measured values (n = 3) measured by the four probe method. Moreover, the electrical resistance increase rate of the electrical resistor 1 can be calculated by the following calculation method after measuring the electrical resistivity of the electrical resistor 1 by the above method. First, the electrical resistivity is measured at three points of 50 ° C., 200 ° C., and 400 ° C. The value obtained by subtracting the electrical resistivity at 50 ° C. from the electrical resistivity at 400 ° C. is divided by a temperature difference of 350 ° C. between 400 ° C. and 50 ° C. to calculate the electrical resistance increase rate.

  The coefficient of thermal expansion of the electrical resistor 1 is preferably 0.5 ppm / K or more and 3 ppm / K or less. According to this configuration, it is possible to reliably improve the thermal shock resistance of the electrical resistor 1. Also, according to this configuration, when used as a material for a honeycomb structure of an electrically heated catalyst device used in an exhaust gas purification apparatus for an internal combustion engine, cracks are hardly generated in the honeycomb structure due to repeated heating and cooling.

  The thermal expansion coefficient of the electrical resistor 1 is preferably 0.6 ppm / K or more, more preferably 0.7 ppm / K or more, and still more preferably 0.8 ppm / K or more from the viewpoint of ensuring conductivity. can do. The thermal expansion coefficient of the electrical resistor 1 is preferably 2.9 ppm / K or less, more preferably 2.8 ppm / K or less, and still more preferably 2.7 ppm / K from the viewpoint of improving thermal shock resistance. K or less.

  The thermal expansion coefficient of the electrical resistor 1 is such that when the test piece (5 mm × 5 mm × 10 mm) is heated in the temperature range from room temperature to 400 ° C., the test piece expands when the temperature rises by 1 Kelvin. It can be measured by determining the length (displacement).

  The electrical resistor 1 of the present embodiment includes borosilicate 10, Si-containing particles 11, a β-spodumene solid solution, and at least one 12 of β-quartz solid solution. Therefore, the electrical resistor 1 of this embodiment can reduce a thermal expansion coefficient. Therefore, according to the electrical resistor 1 of the present embodiment, the thermal shock resistance can be improved.

(Embodiment 2)
The honeycomb structure of Embodiment 2 will be described with reference to FIG. Of the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the above-described embodiments represent the same components as those in the above-described embodiments unless otherwise indicated.

  As illustrated in FIG. 2, the honeycomb structure 2 of the present embodiment includes the electric resistor 1 of the first embodiment. In the present embodiment, specifically, the honeycomb structure 2 is constituted by the electric resistor 1 of the first embodiment. In FIG. 2, specifically, in a honeycomb cross-sectional view 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 cell 20, and an outer peripheral portion of the cell wall 21. The structure which has the outer peripheral wall 22 which is provided and hold | maintains the cell wall 21 integrally is illustrated. In addition, a well-known structure can be applied to the honeycomb structure 2, and it is not limited to the structure of FIG. FIG. 2 shows an example in which the cell 20 has a quadrangular cross section, but the cell 20 may have a hexagonal cross section.

  The honeycomb structure 2 of the present embodiment is configured to include the electrical resistor 1 of the first embodiment. Therefore, the honeycomb structure 2 of the present embodiment can suppress the expansion and contraction associated therewith even when heating and cooling due to current heating or use in a thermal environment are repeated. Therefore, according to the honeycomb structure 2 of the present embodiment, the structural reliability can be improved.

(Embodiment 3)
The electrically heated catalyst device of Embodiment 3 will be described with reference to FIG. As illustrated in FIG. 3, the electrically heated catalyst device 3 of the present embodiment includes the honeycomb structure 2 of the third embodiment. In the present embodiment, specifically, the electrically heated catalyst device 3 includes a honeycomb structure 2, an exhaust gas purification catalyst (not shown) supported on the cell walls 21 of the honeycomb structure 2, and the honeycomb structure 2. A pair of electrodes 31, 32 disposed opposite to the outer peripheral wall 22, and a voltage application unit 33 that applies a voltage to the electrodes 31, 32 are provided. In addition, a well-known structure can be applied to the electrically heated catalyst device 3, and is not limited to the structure of FIG.

  The electrically heated catalyst device 3 of the present embodiment has the honeycomb structure 2 of the second embodiment. Therefore, the electrically heated catalyst device 3 of the present embodiment is applied to an exhaust gas purification device of an internal combustion engine, for example, and the honeycomb structure 2 is not easily broken even when heating and cooling are repeated, thereby improving reliability. Can do.

<Experimental example>
(Sample preparation)
-Sample 1-
Petalite, spodumene (prepared in β-type at the raw material stage, omitted below), boric acid (ground product, omitted below) and silicon particles were mixed at a mass ratio of 26.5: 26.5: 6: 41. . Both petalite and spodumene are lithium-containing minerals. As other lithium-containing minerals, eucryptite or the like can also be used. Next, 2% by mass of methylcellulose as a binder was added to the mixture, and water was added and kneaded. Next, the obtained mixture was formed into pellets by an extrusion molding machine and subjected to primary firing. The primary firing conditions were a firing temperature of 700 ° C., a heating time of 100 ° C./hour, a holding time of 1 hour, an atmospheric atmosphere and a normal pressure. Next, the fired body subjected to primary firing was subjected to secondary firing. The conditions for the secondary firing were an N ₂ gas atmosphere and normal pressure, a firing temperature of 1250 ° C., a firing time of 30 minutes, and a heating rate of 200 ° C./hour. As a result, an electric resistor of Sample 1 having a shape of 5 mm × 5 mm × 18 mm was obtained.

-Sample 2-
An electric resistor of Sample 2 was obtained in the same manner as Sample 1 except that a mixture of petalite, boric acid, and silicon particles mixed at a mass ratio of 53: 6: 41 was used.

-Sample 3-
The electrical resistor of sample 3 is the same as sample 1 except that a mixture of kaolin, spodumene, boric acid and silicon particles mixed at a mass ratio of 26.5: 26.5: 6: 41 is used. Obtained.

-Sample 4-
An electrical resistor of Sample 4 was obtained in the same manner as Sample 1 except that a mixture of spodumene, boric acid and silicon particles mixed at a mass ratio of 53: 6: 41 was used.

-Sample 1C-
An electric resistor of Sample 1C was obtained in the same manner as Sample 1, except that a mixture in which kaolin, boric acid, and silicon particles were mixed at a mass ratio of 53: 6: 41 was used. In addition, the electrical resistor of sample 1C is a comparative sample using kaolin which is not lithium-containing mineral without using petalite and spodumene which are lithium-containing minerals.

(Crystal structure analysis)
With respect to the electric resistor of Sample 1, a crystal structure analysis by XRD was performed. The result is shown in FIG. As shown in FIG. 4, it was confirmed that a β-spodumene solid solution was generated in the electric resistor of sample 1. In addition, the β-spodumene solid solution was similarly generated for the electrical resistors of Samples 2 to 4.

(Measurement of B content and Li content)
An ICP analyzer (manufactured by Hitachi High-Tech Science Co., Ltd., “SPS-3520UV”) was used to measure the B content and Li content of the electrical resistor of Sample 1. As a result, the electrical resistor of Sample 1 had a B content of 0.68% in the borosilicate. Further, the Li content in the electric resistor of Sample 1 was 1.3%.

(Measurement of thermal expansion coefficient)
Regarding the electric resistor of sample 1 and the electric resistor of sample 1C, the thermal expansion coefficient was measured by the method described above. For the measurement of the coefficient of thermal expansion, “TMA4000” manufactured by NETZSCH was used. The results are shown in FIG. As shown in FIG. 5 and Table 1, the electrical resistance of sample 1C had a coefficient of thermal expansion of 3.4 ppm / K, whereas the electrical resistance of sample 1 had a coefficient of thermal expansion of 1.4 ppm. / K. From this result, it was confirmed that the thermal expansion coefficient can be reduced by including the β-spodumene solid solution in the electric resistor. Table 1 also shows the coefficient of thermal expansion of the electrical resistors of Samples 2 to 4. Similarly to the electrical resistor of sample 1, the thermal resistance of samples 2 to 4 was also reduced as compared with the electrical resistor of sample 1C.

(Measurement of electrical resistivity)
The electrical resistivity of the electrical resistor of sample 1 and the electrical resistor of sample 1C was measured. In addition, the electrical resistivity was measured by a four-terminal method using a thermoelectric property evaluation apparatus (“ZEM-2” manufactured by ULVAC-RIKO, Inc.) for a prism sample of 5 mm × 5 mm × 18 mm. The result is shown in FIG. As shown in FIG. 6, it can be seen that the electrical resistor of sample 1 has a small temperature dependency of the electrical resistivity and maintains the PTC characteristics, like the electrical resistor of sample 1C. Moreover, the electrical resistance of sample 1 is smaller in the temperature range from 25 ° C. to 500 ° C. than the electrical resistance of sample 1C, and the electrical resistivity is 0.0001Ω · m or more and 1Ω · m or less. there were. Moreover, it was confirmed that the electrical resistance body of the sample 1 has an electrical resistance increase rate of 5.0 × 10 ⁻⁴ / K or less by the above-described calculation method. Table 1 shows the electrical resistivity of the electrical resistors of Samples 1 to 4 at room temperature (25 ° C.). In addition, the electrical resistors of Samples 2 to 4 also have an electrical resistivity of 0.0001 Ω · m to 1 Ω · m in the temperature range from 25 ° C. to 500 ° C., similar to the electrical resistor of Sample 1, and The rate of increase in electrical resistance was 5.0 × 10 ⁻⁴ / K or less.

  The present invention is not limited to the above-described embodiments and experimental examples, and various modifications can be made without departing from the scope of the invention. Moreover, each structure shown by each embodiment and each experiment example can be combined arbitrarily, respectively.

10 Borosilicate 11 Si-containing particle 12 β-spodumene solid solution and β-quartz solid solution, at least one kind 2 Honeycomb structure 3 Electric heating type catalyst device

Claims (9)

Borosilicate (10),
Si-containing particles (11);
At least one (12) of β-spodumene solid solution and β-quartz solid solution,
An electrical resistor (1) comprising:   The electrical resistor according to claim 1, wherein the borosilicate is an aluminoborosilicate. In a temperature range from 25 ° C. to 500 ° C., the electrical resistivity is 0.0001 Ω · m to 1 Ω · m and the electrical resistance increase rate is 0 / K to 5.0 × 10 ⁻⁴ / K, The electrical resistor according to claim 1 or 2.   The electrical resistor according to any one of claims 1 to 3, wherein the Li content in the electrical resistor is 0.1 mass% or more and 4 mass% or less.   The electrical resistor according to any one of claims 1 to 4, wherein the coefficient of thermal expansion is 0.5 ppm / K or more and 3 ppm / K or less.   The electrical resistor according to any one of claims 1 to 5, wherein a B content in the borosilicate is 0.1 mass% or more and 5 mass% or less.   The electrical resistor according to claim 1, wherein the electrical resistor is configured to be used for a honeycomb structure in an electrically heated catalyst device.   A honeycomb structure (2) configured to include the electrical resistor according to any one of claims 1 to 6.   An electrically heated catalyst device (3) comprising the honeycomb structure according to claim 8.

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