WO2016152687A1

WO2016152687A1 - Ceramic material and method for producing same

Info

Publication number: WO2016152687A1
Application number: PCT/JP2016/058376
Authority: WO
Inventors: 崇弘冨田; 研吉永井; 博治小林
Original assignee: 日本碍子株式会社
Priority date: 2015-03-23
Filing date: 2016-03-16
Publication date: 2016-09-29

Abstract

Provided are: a ceramic material that is capable of changing the thermal conductivity thereof in accordance with changes in temperature; and a method for producing same. The ceramic material 1 is configured from nanoparticles 2, has a pore surface area, a pore volume, and an average pore size that satisfy 3.5 < (pore surface area × average pore size/pore volume), has a thermal conductivity that increases monotonically from room temperature to 100 °C, and has a thermal conductivity that changes in accordance with changes in temperature. The nanoparticles 2 of the ceramic material preferably bond and form a three-dimensional mesh skeleton structure.

Description

Ceramic material and manufacturing method thereof

The present invention relates to a ceramic material whose heat transfer performance varies with temperature, and a method for manufacturing the same.

In recent years, effective use of thermal energy has been required due to CO ₂ emission regulations and energy problems. In an apparatus or the like equipped with a heat generation source, heat may be required or heat may be unnecessary. For example, in a battery pack that is mounted on an EV, the resistance increases when the temperature of the battery decreases, so that heat insulation is required at low temperatures. On the other hand, if the temperature is too high, there is concern about ignition due to decomposition of the electrolytic solution, so heat dissipation is required at high temperatures. Therefore, it is thought that the technique of controlling the heat flow at the same location leads to effective use of heat.

As such a technique, an element (Patent Document 1) that switches the thermal conductivity accompanied by an electronic phase transition by applying energy (magnetic field, electric field, light, heat, etc.) to a transition body sandwiched between electrodes. And a switch (Patent Document 2) that switches between a connected state in which the substrate having the carbon nanotube layer contacts and a non-connected state in which the substrate has a carbon nanotube layer are disclosed. In addition, regarding VO ₂ that causes an insulator-metal transition, which is an example of an electronic phase transition, there is a report that the thermal conductivity is increased by 60% around a transition temperature of 70 ° C. (Non-patent Document 1). .

International Publication No. 2004/068604 International Publication No. 2012/140927

However, in Patent Document 1, an electrode, wiring, and the like are necessary to switch the switch by applying energy. In Patent Document 2, an actuator or the like is required to change the connection state of the switch. As described above, the switches described in Patent Document 1 and Patent Document 2 require components in addition to the one whose thermal conductivity changes itself. Therefore, the switch is increased in size and the mounting location is restricted from the viewpoint of heat resistance. Furthermore, it is difficult to manufacture a complicated shape.

Regarding Non-Patent Document 1, the amount of change in thermal conductivity is small in the electronic phase transition (change from 3.5 W / (m · K) to 5.5 W / (m · K) in VO ₂ ), and heat dissipation and heat insulation. It is not possible to obtain characteristics that can be switched.

An object of the present invention is to provide a ceramic material capable of changing the thermal conductivity by itself according to a temperature change, and a method for manufacturing the same.

The present inventors are composed of nanoparticles, satisfying a pore surface area, a pore volume, and an average pore diameter satisfying 3.5 <(pore surface area × average pore diameter / pore volume), and a thermal conductivity from room temperature. It has been found that a ceramic material that monotonously increases over 100 ° C. can solve the above problems. In order to solve the above problems, according to the present invention, the following ceramic material and a method for producing the same are provided.

[1] It is composed of nanoparticles, and the pore surface area, pore volume, and average pore diameter satisfy 3.5 <(pore surface area × average pore diameter / pore volume), and the thermal conductivity is from room temperature to 100 ° C. Monotonically increasing ceramic materials.

[2] The ceramic material according to [1], wherein the nanoparticles are bonded to form a three-dimensional network skeleton structure.

[3] The ceramic material according to [1] or [2], wherein the nanoparticles have a particle size of 10 to 500 nm.

[4] The ceramic material according to any one of [1] to [3], wherein the porosity is 5 to 70%.

[5] The ceramic material according to any one of [1] to [4], wherein the average pore diameter is 10 to 1000 nm.

[6] The ceramic material according to any one of [1] to [5], wherein a neck thickness of a bonding portion of the nanoparticles forming the ceramic material is 5 to 300 nm.

[7] The ceramic material according to any one of [1] to [6], wherein the nanoparticles are any one of SiC, AlN, and Si ₃ N ₄ .

[8] The ceramic material according to any one of [1] to [7], wherein a different material is present on the surface of the nanoparticles.

[9] The ceramic material according to [8], wherein the different material includes at least one selected from the group consisting of O, B, C, N, Al, Si, and Y.

[10] The ceramic material according to any one of [1] to [9], wherein the thermal conductivity at 100 ° C. is 1.5 times or more the thermal conductivity at room temperature.

[11] The ceramic material according to any one of [1] to [10], wherein the thermal conductivity at 200 ° C. is at least twice the thermal conductivity at room temperature.

[12] The method for producing a ceramic material according to any one of [1] to [11], wherein the nanoparticles as a raw material are crushed using an organic solvent, press-molded after drying, and Ar atmosphere Alternatively, a method for producing a ceramic material that is produced in a vacuum under a firing temperature of 1000 to 2000 ° C., a firing pressure of 0 to 80 MPa, and a firing time of 1 to 360 minutes.

The ceramic material of the present invention operates as a thermal switch that has low thermal conductivity at low temperatures to insulate, and has high thermal conductivity at high temperatures to dissipate heat. Therefore, since the thermal conductivity changes due to a change in ambient temperature, it operates as a self-supporting thermal switch. For this reason, the thermal switch using the ceramic material of the present invention does not require parts such as a drive unit, can be miniaturized, and has a high degree of freedom in shape.

It is a schematic diagram which shows an example of a ceramic material. It is a schematic diagram which shows an example of the ceramic material in which a dissimilar material exists on the surface of a nanoparticle. 2 is a photograph of a field emission scanning electron microscope (FE-SEM) of the silicon carbide sintered body produced in Example 1. FIG. 2 is a transmission electron microscope (TEM) photograph of the silicon carbide sintered body produced in Example 1. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

(Ceramic material 1)
FIG. 1 is a schematic view showing an example of a ceramic material 1. FIG. 2 is a schematic diagram illustrating an example of the ceramic material 1 in which the different material 4 exists on the surface of the nanoparticle 2. The ceramic material 1 of the present invention is composed of nanoparticles 2 and has a pore surface area, a pore volume, and an average pore diameter satisfying 3.5 <(pore surface area × average pore diameter / pore volume). Further, the thermal conductivity monotonously increases from room temperature to 100 ° C. Monotonic increase means that if the temperature rises between room temperature and 100 ° C., the thermal conductivity increases or does not change, and there is an area where the thermal conductivity decreases even though the temperature increases. That is not.

FIG. 1 shows a ceramic material 1 of the present invention formed by bonding nanoparticles 2 together.

The ceramic material 1 of the present invention is composed of nanoparticles 2 and has a pore surface area, a pore volume, and an average pore diameter satisfying 3.5 <(pore surface area × average pore diameter / pore volume). For this reason, the shape of the pores is not a shape close to closed pores or a sphere. For example, when the pore shape is a sphere, (pore surface area × average pore diameter / pore volume) = 3. The pores 3 of the ceramic material 1 of the present invention are not spheres, and there are many interfaces between the pores 3 and the nanoparticles 2. The average pore diameter, pore surface area, and pore volume can be measured by mercury porosimetry.

伝導 Phonons and conduction electrons are responsible for heat conduction, but phonons are dominant in ceramic materials. The heat conduction by phonons is also affected by the structure having a length close to the free path of phonons. A phonon having a longer free path than the length of the structure is scattered by the structure and hardly transfers heat, and a short phonon can transfer heat without scattering.

In general, the free path of phonons has a distribution in the range of about 0.1 nm to 1 mm. When the structure is nano-order (in the case of a nano structure), heat conduction due to phonons longer than the length of the structure is suppressed. Therefore, heat can be transferred only about several% to several tens of% of the thermal conductivity that the material originally has at a certain temperature. Therefore, the thermal conductivity is in a low state.

On the other hand, the free path of phonons becomes shorter as the temperature increases. For this reason, at a high temperature, the rate at which heat conduction is suppressed by the nanostructure becomes small. Therefore, the thermal conductivity is a value close to the thermal conductivity that the material originally has at that temperature.

Also, the pore-particle interface is more likely to scatter phonons than the particle-particle interface. As the value of (pore surface area × average pore diameter / pore volume) approaches 3, the shape of the pores becomes closer to a true sphere. When the pore is a true sphere (when the value of the above formula is 3) and when the pore is an ellipsoid (when the value of the above formula is larger than 3), The ellipsoid has a larger surface area. When the surface area of the pores is large, there are many interfaces between the pores and the particles, so that phonons are easily scattered. Therefore, it is desirable that the value of the above formula is larger than 3. However, if the value of the above formula is 3.5 or less, the degree of phonon scattering is still weak, which is not preferable for use as a thermal switch. The ceramic material 1 of the present invention is composed of nanoparticles 2 and has a pore surface area, a pore volume, and an average pore diameter satisfying 3.5 <(pore surface area × average pore diameter / pore volume). There are many interfaces between the pores 3 and the nanoparticles 2, and phonons are easily scattered. For this reason, the thermal conductivity at a low temperature tends to be further lowered, and the rate of change of the thermal conductivity with respect to temperature is improved. The value of (pore surface area × average pore diameter / pore volume) is more preferably 3.6 or more.

As described above, the heat conduction by phonons is also affected by the length of the structure. The length of the structure referred to here is a representative length. The representative length is the interval between the pores 3. Therefore, by appropriately controlling this representative length against the free path of phonons, it is possible to control ceramics that suppresses heat conduction at low temperatures (adiabatic state) and hardly suppresses heat conduction at high temperatures (heat dissipation state). Can be manufactured.

In the present specification, the nanoparticle 2 means a particle having a particle size of 1 nm or more and less than 1000 nm. The particle size of the nanoparticle 2 constituting the ceramic material 1 is preferably 10 to 500 nm, preferably 10 to 300 nm. Is more preferably 10 to 200 nm. If the thickness is smaller than 10 nm, aggregation is likely to occur, and a uniform sintered body may not be obtained. In particular, if it is smaller than 1 nm, the nanoparticles 2 are very likely to condense, so that it is difficult to disperse and it is difficult to obtain a uniform sintered body. On the other hand, if it is larger than 500 nm, long free path phonons are difficult to be scattered.

In the ceramic material 1 of the present invention, it is preferable that the nanoparticles 2 are bonded to form a three-dimensional network skeleton structure. As shown in FIG. 1, it is preferable that the nanoparticles 2 have a structure in which beads are connected. By forming the three-dimensional network skeleton structure, the interface between the nanoparticles 2 and the pores 3 increases.

Such thickness L _A of the skeleton of the ceramic material 1 composed of nanoparticles 2 is preferably 1 to 10 minutes nanoparticles. The thickness L _A of the backbone, is that the thickness of the reticulated skeleton structure. By the thickness L _A of the skeleton is 1 to 10 min nanoparticles, because the greater the surface of the nanoparticle 2 and pores 3, phonons is likely to scatter. Accordingly, it is possible to produce ceramics that suppresses heat conduction at low temperatures (insulated state) and hardly suppresses heat conduction at high temperatures (heat dissipation state). As the thickness L _A of the backbone, using the average value of the thickness of ten skeletal arbitrarily selected.

The skeleton thickness L _A is related to the neck thickness L _B of the bonding portion of the nanoparticles 2. A neck is an interface between the nanoparticles 2. Neck The thickness L _B, the length of the interface nanoparticle 2 and nanoparticles 2, for example, a thickness of the portion shown in FIG. The neck thickness L _B of the bonding part of the nanoparticles 2 forming the ceramic material 1 is preferably 5 to 300 nm. More preferably, it is 5 to 100 nm, and further preferably 5 to 50 nm. By neck thickness L _B is 5nm or more, it is possible to maintain the strength. Further, when the thickness is 300 nm or less, phonons having a long free path are easily scattered. Incidentally, the neck as the thickness L _B, using the average value of the neck thickness of 10 points arbitrarily selected.

The particle diameter, skeleton thickness L _A , and neck thickness L _B of the nanoparticle 2 can be measured from an image obtained by observing the ceramic material 1 (sintered body) with an electron microscope. As the electron microscope, a field emission scanning electron microscope (FE-SEM), a transmission electron microscope (TEM), or the like can be used. In addition, the average particle diameter uses the average value of the particle diameter of 10 places selected arbitrarily.

In addition, the nanoparticle 2 is preferably any one of SiC, AlN, and Si ₃ N ₄ . A material having high thermal conductivity such as SiC, AlN, or Si ₃ N ₄ has a large difference in thermal conductivity between the heat radiation state and the heat insulation state.

Furthermore, the porosity of the ceramic material 1 is preferably 5 to 70%. More preferably, it is 15 to 65%, and further preferably 35 to 65%. When the porosity is 5% or more, the interface between the pores 3 and the particles increases, so that phonons are easily scattered. Further, when the porosity is 70% or less, the strength can be maintained.

The average pore diameter is preferably 10 to 1000 nm. More preferably, it is 10 to 500 nm, and still more preferably 20 to 300 nm. When the average pore diameter is 10 nm or more, the thermal conductivity does not become too small. When the average pore diameter is 1000 nm or less, the strength can be increased.

The ceramic material 1 of the present invention has a monotonous increase in thermal conductivity from room temperature to 100 ° C. Specifically, it is preferable that the thermal conductivity at 100 ° C. is 1.5 times or more the thermal conductivity at room temperature in order to use as a thermal switch. When the thermal conductivity at 100 ° C. is 1.5 times or more the thermal conductivity at room temperature, it is possible to effectively switch between heat dissipation and heat insulation. Furthermore, it is preferable that the thermal conductivity at 200 ° C. is at least twice the thermal conductivity at room temperature. When the thermal conductivity at 200 ° C. is at least twice the thermal conductivity at room temperature, it is possible to more effectively switch between heat dissipation and heat insulation.

FIG. 2 shows a ceramic material 1 in which different materials 4 exist on the surface of the nanoparticles 2 and the nanoparticles 2 are bonded to each other. The ceramic material 1 in FIG. 2 is a composite material in which a different material 4 covers the surface of the nanoparticle 2 (the interface between the nanoparticle 2 and the nanoparticle 2 and the interface between the pore 3 and the nanoparticle 2).

Due to the presence of the heterogeneous material 4, a heterogeneous phase exists at the interface between the nanoparticle 2 and the nanoparticle 2. At the interface where the heterogeneous phase exists, phonons are more easily scattered than at the interface where the heterogeneous phase does not exist. For this reason, the thermal conductivity at low temperatures is lowered, and the rate of change of the thermal conductivity with respect to temperature is improved.

Moreover, it is preferable that the dissimilar material 4 covers the surface of the nanoparticles 2 by 10% or more. If it is covered by 10% or more, it becomes easy to scatter phonons.

The dissimilar material 4 preferably contains at least one selected from the group consisting of O, B, C, N, Al, Si and Y. These dissimilar materials 4 are preferable because the ratio of heat conduction carried by phonons is high.

(Manufacturing method of ceramic material)
The ceramic material 1 of the present invention comprises the above-mentioned nanoparticles 2 as a raw material, pulverized using an organic solvent, press-molded after drying, a firing temperature of 1000 to 2000 ° C. in an Ar atmosphere or vacuum, a firing pressure of 0 to 80 MPa. It is preferable to fabricate under baking conditions of 1 to 360 minutes.

The firing temperature is preferably 1000 to 2000 ° C., more preferably 1000 to 1800 ° C., and further preferably 1200 to 1700 ° C. If it is less than 1000 ° C., the sintering does not proceed sufficiently, the strength of the ceramic material becomes weak, and the thermal conductivity may become too low. Moreover, when the temperature exceeds 2000 ° C., the particle size of the nanoparticles 2 becomes too large, and the thermal conduction of phonons having a long free path may not be suppressed.

The firing pressure is preferably 0 to 80 MPa, more preferably 0 to 60 MPa, and still more preferably 0 to 40 MPa. Since the firing pressure is 0 to 80 MPa, the particle size of the nanoparticles 2 does not become too large, and heat conduction of phonons with a long free path can be suppressed.

The firing time is preferably 1 to 360 minutes, more preferably 1 to 240 minutes, and further preferably 1 to 120 minutes. Since the firing time is 1 minute or longer, a uniform sintered body can be obtained. Further, since the firing time is 360 minutes or less, the cost can be suppressed.

In the case where the different material 4 is present on the surface of the nanoparticle 2, it is preferable that the raw material before molding is mixed with the powder of the different material 4 or a liquid containing the different material 4 and then molded and fired. Alternatively, when firing, it is preferable to place a solid containing the different material 4 on the molded body and perform vacuum firing.

(Thermal switch)
The ceramic material 1 as described above can be used as a thermal switch because the thermal conductivity greatly changes depending on the temperature. For example, the thermal conductivity increases rapidly at a certain temperature above room temperature. A thermal switch is a material that can switch between a low thermal conductivity state (adiabatic state) and a high state (heat transfer state). It can be said that the thermal switch whose thermal conductivity increases when the temperature rises is in an OFF state because the thermal conductivity is low below a certain temperature (first temperature). On the other hand, the thermal switch has a high thermal conductivity above the second temperature higher than the first temperature, and can be said to be in an ON state.

A temperature control structure can be produced by providing a thermal switch using the ceramic material 1 of the present invention around a heat generation source that generates heat. The temperature adjustment structure refers to a structure having a function of adjusting temperature while effectively using heat from a heat generation source. The heat generation source that generates heat refers to the one that generates heat, and is not particularly limited. The temperature adjustment structure changes the heat dissipation state between the first temperature and the second temperature higher or lower than the first temperature. Thereby, the temperature by the heat of a heat generation source can be adjusted and the performance of what was equipped with the temperature adjustment structure can be improved. Specifically, examples of the heat generation source include a battery pack, a motor, a CPU, a control circuit, an engine, a brake, and a gear box. A structure provided with a thermal switch around these is a temperature adjustment structure. When the heat generation source is sunlight, the building material, window, and sash are equipped with a heat switch.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

(Example 1)
Silicon carbide powder having an average particle diameter of 20 nm was dispersed using ethanol containing a dispersant and pulverized by a bead mill. This was dried and press-molded to prepare a disk-shaped molded body having a diameter of 30 mm and a thickness of 6 mm. This molded body was fired at 1400 ° C. for 10 minutes by a discharge plasma sintering method (SPS) to obtain a polycrystalline and porous silicon carbide sintered body. These firing conditions are shown in Table 1.

This sintered body was observed with an electron microscope, and the particle diameter and neck thickness L _B of the silicon carbide constituting the sintered body were measured from the image. FIG. 3 is a photograph of a field emission scanning electron microscope (FE-SEM). FIG. 4 is a photograph of a transmission electron microscope (TEM). The average value of the particle size of 10 silicon carbide particles arbitrarily selected was 29 nm. Further, the neck thickness _{L B} of 10 points arbitrarily selected were 20 nm. Furthermore, it was confirmed that the sintered body obtained from FIGS. 3 and 4 has a three-dimensional network structure.

Moreover, when the pore surface area, pore volume, average pore diameter, and porosity of this sintered body were measured by mercury porosimetry, the pore surface area was 44 m ² / g, the pore volume was 0.32 mL / g, The average pore diameter was 30 nm, and the porosity was 52%. From these measurement results, pore surface area × average pore diameter / pore volume = 4.1. These measurement results for the sintered body are shown in Table 2.

Furthermore, when the thermal conductivity of this sintered body was measured, it was 4.0 W / (m · K) at room temperature (25 ° C.), 6.5 W / (m · K) at 100 ° C., and 9.4 W at 200 ° C. / (M · K). Note that thermal conductivity (W / (m · K)) = thermal diffusivity × specific heat × density. In this equation, “thermal diffusivity” was measured by a laser flash method. The “specific heat” was measured by differential scanning calorimetry. “Density” was measured by Archimedes method. It was confirmed that the thermal conductivity increased from room temperature (25 ° C.) to 100 ° C. Further, the thermal conductivity at 100 ° C. was 1.5 times or more of the thermal conductivity at room temperature, and the thermal conductivity at 200 ° C. was twice or more than the thermal conductivity at room temperature. The results of such thermal conductivity are shown in Table 3. In addition, when the thermal conductivity at 100 ° C. was 1.5 times or more of the thermal conductivity at room temperature, it was set as A (good), and when it was less than 1.5 times, it was set as B (bad). The thermal conductivity at 200 ° C. was A (good) if the thermal conductivity at room temperature was 2 times or more, and B (bad) if it was less than 2 times.

(Examples 2 to 6)
A molded body was prepared in the same manner as in Example 1. The molded body was fired to obtain a polycrystalline and porous silicon carbide sintered body. The firing conditions are shown in Table 1. The sintered body was observed by an electron microscope, from the image, and measured for the particle diameter and the neck thickness L _B of the silicon carbide particles constituting the average particle size of 10 silicon carbide particles arbitrarily selected value was determined neck thickness L _B of 10 points arbitrarily selected. In addition, the pore surface area, pore volume, average pore diameter, and porosity of this sintered body were measured by the mercury intrusion method, and the value of (pore surface area × average pore diameter / pore volume) was determined from the measurement result. Asked. Table 2 shows these results for the sintered body. Furthermore, the thermal conductivity of this sintered body was measured. The results of thermal conductivity are shown in Table 3.

(Example 7)
An aluminum nitride powder having an average particle diameter of 40 nm was press-molded to prepare a disk-shaped molded body having a diameter of 30 mm and a thickness of 6 mm. This molded body was fired at 1400 ° C. for 120 minutes in a nitrogen atmosphere to obtain a porous aluminum nitride sintered body. The firing conditions are shown in Table 1. The sintered body was observed by an electron microscope, from the image, and measured for the particle diameter and the neck thickness L _B of the aluminum nitride particles constituting an average particle size of 10 aluminum nitride particles arbitrarily selected value was determined neck thickness L _B of 10 points arbitrarily selected. In addition, the pore surface area, pore volume, average pore diameter, and porosity of this sintered body were measured by the mercury intrusion method, and the value of (pore surface area × average pore diameter / pore volume) was determined from the measurement result. Asked. Table 2 shows these results for the sintered body. Furthermore, the thermal conductivity of this sintered body was measured. The results of thermal conductivity are shown in Table 3.

(Example 8)
A silicon nitride powder having an average particle size of 25 nm was press-molded to prepare a disk-shaped molded body having a diameter of 30 mm and a thickness of 6 mm. This molded body was fired at 1400 ° C. for 120 minutes in a nitrogen atmosphere to obtain a porous silicon nitride sintered body. The firing conditions are shown in Table 1. The sintered body was observed by an electron microscope, from the image, measures the value of the particle diameter and the neck thickness L _B of the silicon nitride particles constituting the particle of the arbitrarily selected 10 pieces of the silicon nitride particles neck average and optionally 10 locations selected diameter was determined thickness L _B. In addition, the pore surface area, pore volume, average pore diameter, and porosity of this sintered body were measured by the mercury intrusion method, and the value of (pore surface area × average pore diameter / pore volume) was determined from the measurement result. Asked. Table 2 shows these results for the sintered body. Furthermore, the thermal conductivity of this sintered body was measured. The results of thermal conductivity are shown in Table 3.

Example 9
Silicon carbide powder having an average particle diameter of 20 nm was dispersed using ethanol containing a dispersant and pulverized by a bead mill. It was dried, and the TiO ₂ was added 10 wt%. This mixed powder was press-molded to prepare a disk-shaped molded body having a diameter of 30 mm and a thickness of 6 mm. This molded body was fired in vacuum at 1400 ° C. for 120 minutes to obtain a polycrystalline and porous silicon carbide sintered body. The firing conditions are shown in Table 1. The sintered body was observed by an electron microscope, from the image, and measured for the particle diameter and the neck thickness L _B of the silicon carbide particles constituting the average particle size of 10 silicon carbide particles arbitrarily selected value was determined neck thickness L _B of 10 points arbitrarily selected. In addition, the pore surface area, pore volume, average pore diameter, and porosity of this sintered body were measured by the mercury intrusion method, and the value of (pore surface area × average pore diameter / pore volume) was determined from the measurement result. Asked. Table 2 shows these results for the sintered body. Furthermore, the thermal conductivity of this sintered body was measured. The results of thermal conductivity are shown in Table 3.

(Comparative Example 1)
A silicon carbide powder having an average particle diameter of 5 μm was press-molded to prepare a disk-shaped molded body having a diameter of 30 mm and a thickness of 6 mm. This molded body was fired at 2200 ° C. for 120 minutes in an Ar atmosphere to obtain a porous silicon carbide sintered body. The firing conditions are shown in Table 1. The sintered body was observed by an electron microscope, from the image, and measured for the particle diameter and the neck thickness L _B of the silicon carbide particles constituting the average particle size of 10 silicon carbide particles arbitrarily selected value was determined neck thickness L _B of 10 points arbitrarily selected. In addition, the pore surface area, pore volume, average pore diameter, and porosity of this sintered body were measured by the mercury intrusion method, and the value of (pore surface area × average pore diameter / pore volume) was determined from the measurement result. Asked. Table 2 shows these results for the sintered body. Furthermore, the thermal conductivity of this sintered body was measured. The results of thermal conductivity are shown in Table 3.

(Comparative Example 2)
A silicon carbide powder having an average particle size of 0.5 μm was press-molded to prepare a disk-shaped molded body having a diameter of 30 mm and a thickness of 6 mm. This molded body was fired in a vacuum at 1500 ° C. for 120 minutes to obtain a porous silicon carbide sintered body. The firing conditions are shown in Table 1. The sintered body was observed by an electron microscope, from the image, and measured for the particle diameter and the neck thickness L _B of the silicon carbide particles constituting the average particle size of 10 silicon carbide particles arbitrarily selected value was determined neck thickness L _B of 10 points arbitrarily selected. In addition, the pore surface area, pore volume, average pore diameter, and porosity of this sintered body were measured by the mercury intrusion method, and the value of (pore surface area × average pore diameter / pore volume) was determined from the measurement result. Asked. Table 2 shows these results for the sintered body. Furthermore, the thermal conductivity of this sintered body was measured. The results of thermal conductivity are shown in Table 3.

The ceramic materials 1 of Examples 1 to 9 are composed of nanoparticles 2, and the pore surface area, pore volume, and average pore diameter satisfy 3.5 <(pore surface area × average pore diameter / pore volume). The thermal conductivity increases monotonically from room temperature to 100 ° C. Therefore, the ceramic materials 1 of Examples 1 to 9 operate as a thermal switch that has a low thermal conductivity at low temperatures to insulate, and has a high thermal conductivity at high temperatures to dissipate heat. On the other hand, Comparative Example 1 is not composed of nanoparticles 2 and has pore surface area × average pore diameter / pore volume = 3.4, and the thermal conductivity is 33 W / (m · K) at room temperature. It is 25 W / (m · K) at 200 ° C. For this reason, it did not function as a heat switch that switches between a heat insulation state and a heat radiation state. Moreover, although Comparative Example 2 is composed of nanoparticles 2, since the pore surface area × the average pore diameter / pore volume = 3.3, the thermal conductivity does not increase monotonically from room temperature to 100 ° C. . Therefore, it did not function as a thermal switch.

The ceramic material of the present invention and the manufacturing method thereof can be used as a heat switch in which the ease of transferring heat changes depending on the temperature.

1: Ceramic material, 2: Nanoparticle, 3: Pore, 4: Dissimilar material.

Claims

Composed of nanoparticles, pore surface area, pore volume, and average pore diameter satisfy 3.5 <(pore surface area × average pore diameter / pore volume), and thermal conductivity increases monotonically from room temperature to 100 ° C. Ceramic material.
The ceramic material according to claim 1, wherein the nanoparticles are bonded to form a three-dimensional network skeleton structure.
The ceramic material according to claim 1 or 2, wherein the nanoparticles have a particle size of 10 to 500 nm.
The ceramic material according to any one of claims 1 to 3, having a porosity of 5 to 70%.
The ceramic material according to any one of claims 1 to 4, wherein the average pore diameter is 10 to 1000 nm.
The ceramic material according to any one of claims 1 to 5, wherein a neck thickness of a joint portion of the nanoparticles forming the ceramic material is 5 to 300 nm.
The ceramic material according to any one of claims 1 to 6, wherein the nanoparticles are any one of SiC, AlN, and Si 3 N 4 .
The ceramic material according to any one of claims 1 to 7, wherein a different material is present on the surface of the nanoparticle.
The ceramic material according to claim 8, wherein the dissimilar material includes at least one selected from the group consisting of O, B, C, N, Al, Si, and Y.
The ceramic material according to any one of claims 1 to 9, wherein a thermal conductivity at 100 ° C is 1.5 times or more of a thermal conductivity at room temperature.
The ceramic material according to any one of claims 1 to 10, wherein the thermal conductivity at 200 ° C is at least twice that of room temperature.
The method for producing a ceramic material according to any one of claims 1 to 11, wherein the nanoparticles as a raw material are pulverized using an organic solvent, dried and press-molded, and in an Ar atmosphere or a vacuum. A method for producing a ceramic material produced under firing conditions of a firing temperature of 1000 to 2000 ° C., a firing pressure of 0 to 80 MPa, and a firing time of 1 to 360 minutes.