JP2024041693A - Co-Mn-Ga ALLOY POWDER, CONDUCTIVE MOLDING, MANUFACTURING METHOD THEREOF, AND THERMOELECTRIC CONVERSION ELEMENT - Google Patents

Abstract

To provide a technology that utilizes the anomalous Nernst effect and is suitable for manufacturing thermoelectric conversion elements capable of obtaining high Nernst coefficient with good productivity.SOLUTION: There is provided Co-Mn-Ga alloy powder that is powder containing an intermetallic compound Co2MnGa as a main component. The powder has a cumulative 50% particle size D50 of 1 to 150 μm and a cumulative 90% particle size D90 of 250 μm or less in a volume-based particle size distribution according to a laser diffraction/scattering method. An average circularity of particles that constitute the powder is 0.80 or more, where the average circularity corresponds to an arithmetic mean for a circularity of each particle determined from a SEM (scanning electron microscope) image by the following formula: circularity=4πS/L2. In the formula, S represents an area (μm2) of the particle on an image, and L represents a perimeter (μm) of the particle on an image.SELECTED DRAWING: Figure 2

Description

The present invention relates to a Co--Mn--Ga based alloy powder useful as a material for thermoelectric conversion elements, and a method for producing the same. The present invention also relates to a conductive molded body of Co--Mn--Ga based alloy powder, a method for manufacturing the same, and a thermoelectric conversion element using the conductive molded body.

In recent years, research on thermoelectric conversion elements that utilize the anomalous Nernst effect has been progressing. The anomalous Nernst effect is a phenomenon in which when a spontaneously magnetized magnetic material is subjected to a heat flow in a direction perpendicular to the magnetization, an electromotive force is generated in a direction perpendicular to both the magnetization and the heat flow. Using the anomalous Nernst effect allows current to be extracted in a direction perpendicular to the heat flow, which has the advantage of being able to construct thin thermoelectric conversion devices, unlike when using the Seebeck effect.

The ferromagnetic intermetallic compound Co ₂ MnGa is known as a material that exhibits a large anomalous Nernst effect at room temperature.

Patent Document 1 describes an experimental example in which a Co ₂ MnGa single crystal was prepared by the Czochralski method and the abnormal Nernst coefficient was measured. The Nernst coefficient of a Co ₂ MnGa single crystal at room temperature (300K) is a high value of about 6 μV/K even when the direction of magnetic field application is parallel to the [100], [110], or [111] directions of the crystal. (Paragraph 0021, Figure 4).

Patent Document 2 describes the use of an abnormal Nernst material film in the heat flow sensor in a composite sensor having a heat flow sensor and a temperature sensor. Several substances are listed as abnormal Nernst materials, one of which is Co ₂ MnGa (paragraph 0026). A sputtering method is indicated as a method for forming the abnormal Nernst material film (paragraph 0030).

International Publication No. 2019/009308 JP2020-153668A

Main applications of thermoelectric conversion elements include thermoelectric power generation devices and heat flow sensors.

A thermoelectric conversion element for realizing a thermoelectric power generation device is preferably a bulk body with a thickness of several millimeters. By using a single crystal body using the Czochralski method, it is possible to produce a bulk body of the size described above. However, single crystal manufacturing techniques such as the Czochralski method are expensive and have low productivity, so they are not practical for industrial production of materials for thermoelectric power generation devices. On the other hand, it is difficult to apply film formation techniques such as sputtering to the industrial production of bulk materials for thermoelectric power generation devices.

Considering that a thermoelectric conversion element for realizing a heat flow sensor is used by being incorporated into a part of a minute circuit pattern, it is desired that the thermoelectric conversion element be a small-sized element. Cutting out a large number of small-sized elements from a single crystal obtained by the Czochralski method or the like is difficult to put into practical use industrially due to cost considerations. Furthermore, it is difficult to directly form small-sized elements with a predetermined shape using the Czochralski method. On the other hand, according to film forming techniques such as sputtering, it is possible to directly form small-sized elements according to a predetermined circuit pattern on an insulating substrate. However, such a film forming method has low productivity and increases the manufacturing cost of the heat flow sensor.

The present applicant has developed an alloy lump containing the intermetallic compound Co ₂ MnGa as a main component by solidifying a molten Co-Mn-Ga alloy as a method for synthesizing Co ₂ MnGa crystals in place of the Czochralski method or sputtering method. Japanese Patent Application No. 2021-103682 discloses a technique for obtaining Co--Mn--Ga based alloy powder with a predetermined particle size distribution by adopting a method of melting and pulverizing and classifying the alloy ingot. It was confirmed that the Co--Mn--Ga based alloy powder obtained by this technique can be processed into conductive molded bodies of various shapes, and that the conductive molded bodies exhibit a high Nernst coefficient at room temperature. However, this technique requires a pulverization process to powderize the alloy ingot, and a classification process is essential in order to obtain a powder product with a predetermined particle size distribution. In the crushing process, if mass production is intended, equipment for crushing a large amount of large alloy ingots is required, which increases the manufacturing load. Furthermore, when it is pulverized into powder, angular shaped particles are produced. Therefore, a powder composed of particles pulverized by pulverization is disadvantageous from the viewpoint of producing a highly homogeneous conductive molded body with good productivity with little local variation in the filling properties of the particles.

The present invention is a technology suitable for manufacturing thermoelectric conversion elements with high productivity that utilizes the anomalous Nernst effect and can obtain a high Nernst coefficient, and is particularly applicable to a wide range of manufacturing of elements of various shapes and sizes. The purpose of the present invention is to provide a technology that is advantageous in obtaining highly homogeneous devices with good productivity. Another object of the present invention is to provide a thermoelectric conversion element with a high Nernst coefficient obtained using the technique.

In order to achieve the above object, the following invention is disclosed in this specification.

[1] Powder mainly composed of intermetallic compound Co ₂ MnGa, which has a cumulative 50% particle diameter D50 of 1 to 150 μm and a cumulative 90% particle diameter D90 in volume-based particle size distribution determined by laser diffraction/scattering method. is 250 μm or less, and the average circularity of the particles constituting the powder is 0.80 or more.
Here, the average circularity corresponds to the arithmetic mean of the circularity of each particle determined from the following equation (1) from a SEM (scanning electron microscope) image.
Circularity = 4πS/L ² ...(1)
However, S is the area (μm ² ) of the particle on the image, and L is the circumference length (μm) of the particle on the image.
[2] The intermetallic compound Co is produced by a gas atomization method in which particles of the molten metal are rapidly solidified by spraying a stream of inert gas onto the molten metal of Co-Mn-Ga based alloy in a gas phase space with an inert gas atmosphere. _2. Metal particle synthesis step of synthesizing metal particles containing MnGa as a main component,
The method for producing a Co--Mn--Ga based alloy powder according to [1] above.
[3] The intermetallic compound Co is produced by a gas atomization method in which particles of the molten metal are rapidly solidified by spraying a stream of inert gas onto the molten metal of a Co-Mn-Ga alloy in a gas phase space in an inert gas atmosphere. _2. Metal particle synthesis step of synthesizing metal particles containing MnGa as a main component,
a classification step of adjusting the particle size distribution by removing some particles from the powder made of the metal particles;
The method for producing a Co--Mn--Ga based alloy powder according to [1] above.
[4] The molten metal of the Co-Mn-Ga-based alloy is formed using a Co-Mn-Ga-based master alloy obtained by melting Co, Mn, and Ga, alloying them, and then solidifying them. The method for producing a Co--Mn--Ga based alloy powder according to [2] or [3] above.
[5] A conductive molded body of Co--Mn--Ga alloy powder according to [1] above.
[6] A conductive molded body made of a sintered body of the Co--Mn--Ga alloy powder described in [1] above.
[7] The conductive molded article according to [5] or [6] above, which exhibits a Nernst coefficient of 5.5 μV/K or more at a temperature of 300K.
[8] A method for producing a conductive molded body, comprising a sintering step of obtaining a conductive molded body by sintering the Co-Mn-Ga alloy powder described in [1] above.
[9] A thermoelectric conversion element using the conductive molded body according to [5] or [6] above.
[10] A thermoelectric conversion element using the conductive molded body according to [7] above.

According to the present invention, a thermoelectric conversion element with a high Nernst coefficient can be obtained. Since the material used for the thermoelectric conversion element is powder, the technology of the present invention can be widely applied to elements of various shapes and sizes. Since the powder is composed of spherical particles, it is advantageous in manufacturing highly homogeneous devices with good productivity. Furthermore, the technique of the present invention is superior in terms of cost and productivity compared to conventional techniques using single crystals or thin films formed by sputtering.

X-ray diffraction pattern of the powder obtained in Example 1. SEM photograph of the powder obtained in Example 1. The figure which schematically showed the attachment position of the terminal for power measurement, the probe for temperature measurement, heat flow, and the application direction of a magnetic field about the Nernst effect measurement sample used in the Example. 2 is a graph showing the measurement results of the Nernst coefficient of the powder conductive molded body obtained in Example 1. SEM photograph of the powder obtained in Example 2.

[Co-Mn-Ga alloy powder]
The present invention targets Co--Mn--Ga based alloy powder containing the intermetallic compound Co ₂ MnGa as a main component as a material suitable for thermoelectric conversion elements. Co ₂ MnGa is a type of Heusler alloy having an L2 ₁ crystal structure. This intermetallic compound is a Weyl ferromagnetic material, and is known to have a Nernst coefficient of about 6 μV/K near room temperature, and is a substance that exhibits a large anomalous Nernst effect.

In a certain composition range where the composition ratio of Co, Mn, and Ga is close to the stoichiometric composition of Co ₂ MnGa, an intermetallic compound having a Co ₂ MnGa type crystal structure can stably exist as a single phase. It is thought that a Co--Mn--Ga based alloy containing an intermetallic compound phase having a Co ₂ MnGa type crystal structure and a different phase is obtained around this composition range. In this specification, an intermetallic compound phase having a Co ₂ MnGa type (i.e. L2 ₁ ) crystal structure in a Co-Mn-Ga ternary alloy is referred to as an "intermetallic compound Co ₂ MnGa" or simply a "Co ₂ MnGa phase". ” is called. Even if the intermetallic compound has a composition ratio slightly different from the stoichiometric composition of Co ₂ MnGa, those having a Co ₂ MnGa type crystal structure are included in the "intermetallic compound Co ₂ MnGa" referred to in this specification. .

"Containing the intermetallic compound Co ₂ MnGa as a main component" means that among the metal phases contained in the powder, the metal phase having the largest mass proportion is the Co ₂ MnGa phase. In a thermoelectric conversion element using Co--Mn--Ga based alloy powder, even if a different phase other than the Co ₂ MnGa phase is contained, a thermoelectric conversion effect occurs due to the abnormal Nernst effect of the Co ₂ MnGa phase. However, in order to realize efficient thermoelectric conversion characteristics, it is desirable that the amount of foreign phases that do not exhibit the anomalous Nernst effect be small. For example, the proportion of the Co ₂ MnGa phase in the powder is preferably 50% by mass or more, more preferably 90% by mass or more. Particularly preferred is a powder made of the intermetallic compound Co ₂ MnGa, ie, a powder in which components other than the intermetallic compound Co ₂ MnGa are unavoidable impurities.

The particle size distribution of the particles constituting the Co-Mn-Ga alloy powder of the present invention is determined by the volume-based particle size distribution by laser diffraction/scattering method, with a cumulative 50% particle diameter D50 of 1 to 150 μm and a cumulative 90% particle diameter. D90 is in the range of 250 μm or less. If the cumulative 50% particle diameter D50 is too large, the average particle diameter becomes large, leading to a decrease in coercive force. If the cumulative 90% particle diameter D90 is too large, the proportion of coarse particles present increases, which also leads to a decrease in coercive force. From the viewpoint of ensuring coercive force, the cumulative 50% particle diameter D50 is preferably 100 μm or less, more preferably 60 μm or less.

The Co--Mn--Ga based alloy powder of the present invention is composed of spherical particles. Specifically, the target is a Co--Mn--Ga based alloy powder in which the average circularity of the particles constituting the powder is 0.80 or more. By applying a powder with such a high average circularity, loading workability when loading the powder into a mold in the process of manufacturing a conductive molded body, which will be described later, is improved by using a powder consisting of angularly shaped particles. It is greatly improved compared to . Moreover, it is advantageous in obtaining a highly homogeneous conductive molded body with small local variations in packing density. Improving the homogeneity of a conductive molded body is extremely effective in constructing a device that exhibits stable and desired performance with little variation among products in terms of element characteristics represented by the Nernst coefficient. Furthermore, when creating coating liquids (including pastes) that use powder as a filler, using powder with a high average circularity is effective in improving the dispersibility of particles in the medium. It is. More preferably, the average circularity is 0.85 or more. A Co--Mn--Ga based alloy powder with a high average circularity can be realized by employing a metal particle synthesis process using a gas atomization method. The average circularity can be determined as follows.

(How to find average circularity)
The powder to be measured is observed using a scanning electron microscope (SEM), and all particles whose entire contours can be grasped in the SEM image of a randomly selected field of view are defined as particles to be measured. For each particle to be measured, the degree of circularity is determined using the following equation (1).
Circularity = 4πS/L ² ...(1)
Here, S is the area (μm ² ) of the particle on the image, and L is the circumference length (μm) of the particle on the image.
The circularity is measured using SEM images of one or more randomly selected fields of view such that the total number of particles to be measured is 50 or more, and the sum of the circularity of each particle is measured. The value divided by the total number of target particles is defined as the average circularity of the particles constituting the powder. Note that the circularity value determined by the above equation (1) has a maximum value of 1 when it is a perfect circle.

The metal particles constituting the Co--Mn--Ga based alloy powder of the present invention can be obtained by a "metal particle synthesis step" using a gas atomization method. The gas atomization method can be carried out, for example, as follows. The raw metal is melted in a melting furnace to form a molten Co-Mn-Ga alloy, and the molten metal is temporarily stored in a tundish placed in a non-oxidizing atmosphere as necessary, and then placed in an orifice, for example. The hot water is discharged from a tap nozzle equipped with a hot water into a gas phase space having an atmosphere of an inert gas such as Ar or _N2 . Discharging into the gas phase space can be performed using gravity or extrusion force by pressurized gas. The discharge flow of the molten metal is usually made to flow down in the form of droplets or strings. An inert gas such as Ar or N ₂ is blown at high pressure onto the molten metal flowing down into the gas phase space to turn the molten metal into particles. The particles of the molten metal are rapidly solidified in the gas phase to become spherical particles containing the intermetallic compound Co ₂ MnGa as a main component. The average particle diameter of the metal particles obtained can be controlled by the shape of the tapping nozzle, the flow rate per unit time of the molten metal discharged into the gas phase space, the flow rate of the gas to be blown, and the like.

As the raw material metal used in the gas atomization method, it is preferable to use, for example, a Co--Mn--Ga based mother alloy prepared in advance by melting Co, Mn, and Ga, alloying them, and then solidifying them. Thereby, the chemical composition of the powder obtained by the gas atomization method can be controlled more accurately. To produce a Co-Mn-Ga-based master alloy, Co, Mn, and Ga raw material metals weighed to a predetermined composition are placed in a crucible, heated and melted in a non-oxidizing atmosphere, and the resulting molten metal is placed in the crucible. This can be done by cooling and solidifying in a mold or by casting into a mold and solidifying.

The metal particle synthesis process using the gas atomization method can directly produce Co-Mn-Ga alloy powder having the above-mentioned particle size distribution and average circularity, but after the metal particle synthesis process, a "classification process" may be carried out once or multiple times using a sieve or the like to further adjust the particle size distribution.

[Conductive molded body]
In this specification, an object that is molded into a predetermined shape using powder as a material and has a fixed shape that can maintain its shape in a usage environment is referred to as a "powder molded object." In particular, a molded body of powder having conductivity is called a "conductive molded body of powder". A conductive molded body of powder containing the intermetallic compound Co ₂ MnGa as a main component, using the above Co--Mn--Ga alloy powder as a material, is useful as a thermoelectric conversion element.

Typical forms of conductive powder compacts include pressed powder and sintered compacts. Even pressed powder can be used as a thermoelectric conversion element by incorporating it into a device in a way that allows it to maintain its shape in the usage environment. Sintered compacts are preferred to ensure stable shape.

Examples of forms of the conductive molded body of powder other than green compacts and sintered bodies include molded bodies obtained by solidifying powder into a predetermined shape with a binder component such as a resin. When using a non-conductive binder component, it is necessary to solidify the powder particles in a state where they are in contact with each other. When using a binder component having conductivity, contact between powder particles is not essential.

When applying a sintered body as a conductive molded body of powder containing the intermetallic compound Co ₂ MnGa as the main component, a known "sintering process" is used to form the intermetallic compound Co ₂ MnGa as the main component. A sintered body of powder can be produced. When using part or all of a circuit pattern formed on an insulating substrate as a conductive molded body of powder containing intermetallic compound Co ₂ MnGa as a main component, the insulating substrate is coated with a paint containing the powder as a filler. An applicable method is to form a coating film with a circuit pattern thereon and then heat and sinter the coating film.

In order to use it as a thermoelectric conversion element, it is preferable to construct a powder conductive molded body exhibiting a Nernst coefficient of 5.5 μV/K or more, more preferably 5.8 μV/K or more at a temperature of 300K. By using the Co-Mn-Ga based alloy powder obtained by the metal particle synthesis process using the gas atomization method described above, it is possible to produce powder exhibiting a high Nernst coefficient as described above without performing a special classification process. It is possible to obtain a conductive molded body.

[Example 1]
(Preparation of Co-Mn-Ga-based mother alloy)
The raw materials, metallic Co (made by Rare Metallic Co., Ltd., purity 3N), metallic Mn (made by Rare Metallic Co., Ltd., purity 3N), and metallic Ga (made by Rare Metallic Co., Ltd., purity 6N), were weighed to have an atomic ratio of Co:Mn:Ga = 50:25:25 and placed in an alumina crucible. The crucible was placed in a vertical electric furnace (manufactured by Siliconit Co., Ltd., high-temperature vertical tubular furnace UVHT631K), and in an Ar gas atmosphere, the molten metal of the Co-Mn-Ga alloy was solidified in the crucible by the following heat pattern: heating from room temperature to 1000°C over 4 hours, heating from 1000°C to 1250°C over 2 hours, holding at 1250°C for 12 hours, and then cooling in the furnace for 5 hours. Thus, a Co-Mn-Ga mother alloy was obtained.

(Synthesis of Metal Particles)
The above-mentioned Co-Mn-Ga-based mother alloy was crushed to a predetermined size, then charged into the melting furnace of a gas atomizer and melted under an Ar gas atmosphere to obtain a molten metal. The molten metal was placed in a tundish under an Ar gas atmosphere, and then discharged from a discharge nozzle equipped with an orifice having a diameter of 1.2 mm into a gas phase space of an Ar gas atmosphere. Ar gas was blown onto the molten metal discharged into the gas phase space with a pressure of 8 MPa, and the molten metal was granulated and solidified in the gas phase space. In this way, a Co-Mn-Ga-based alloy powder was obtained. This Co-Mn-Ga-based alloy powder is called the "test powder". This test powder was subjected to the following tests.

(Measurement of X-ray diffraction pattern)
The X-ray diffraction pattern of the above sample powder using Cu-Kα rays was measured using an X-ray diffraction device (XRD-6100 LabX, manufactured by Shimadzu Corporation).
FIG. 1 illustrates the X-ray diffraction pattern. It was confirmed that the sample powder had a Co ₂ MnGa type crystal structure. Since no phase other than the Co ₂ MnGa phase was observed, this sample powder corresponds to "powder whose main component is the intermetallic compound Co ₂ MnGa."

(Measurement of particle size distribution)
The above sample powder was subjected to laser diffraction using a dry laser diffraction particle size distribution analyzer (manufactured by Sympatec, HELOS/KR & RODOS) at a dispersion pressure of 1.7 bar (0.17 MPa) and a lens with a focal length of 200 mm. - Volume-based particle size distribution was measured using a scattering method. The cumulative 10% particle diameter D10 calculated based on the obtained particle size distribution was 5.9 μm, the cumulative 50% particle diameter D50 was 22.1 μm, and the cumulative 90% particle diameter D90 was 54.3 μm.

(Measurement of average circularity)
The average circularity was measured based on the SEM (scanning electron microscope) image of the sample powder according to the above-mentioned "How to determine average circularity". As a result, the average circularity of the sample powder was 0.88.
FIG. 2 illustrates an SEM (scanning electron microscope) photograph of the sample powder. The photographing conditions were a magnification of 500 times and an accelerating voltage of 15 kV. The length of the white scale bar displayed at the bottom of the photo corresponds to 10 μm. The SEM used was FE-SEM JSM-7200F manufactured by JEOL Ltd.

(Composition analysis of powder by EDX)
The composition of the above sample powder was analyzed using an EDX (energy dispersive X-ray analysis) device (manufactured by Oxford Instruments, X-Max20) attached to the SEM, and the atomic ratio was Co:Mn:Ga = 49. It was 2:27.9:22.9.

(Preparation of conductive molded body)
A sintered body using the above sample powder was produced as follows. Approximately 5.9 g of the sample powder was subjected to discharge plasma sintering in a vacuum atmosphere of approximately 1 Pa with a pressure of 90 MPa (7.065 kN) applied by upper and lower pistons in a cylinder of a cylindrical graphite cell with an inner diameter of 10 mm. By heating with an apparatus, a cylindrical sintered body with a diameter of 10 mm and a height of about 8 mm was obtained. The heat pattern was to raise the temperature to 650°C, hold at 650°C for 10 minutes, raise the temperature to 750°C, hold at 750°C for 10 minutes, and let it cool.

(Measurement of the anomalous Nernst effect)
A rectangular parallelepiped sample with a length ( _L1 ) of 8.269 mm, a width (W) of 1.460 mm, and a thickness (H) of 0.624 mm was cut out from the conductive compact (sintered body). Figure 3 shows the positions of the terminals for measuring electromotive force and the probes for measuring temperature, as well as the directions of heat flow and magnetic field application. Terminals 2a and 2b for measuring electromotive force were attached to the center of the opposing sides of the Nernst effect measurement sample 1 with conductive epoxy adhesive, so that the voltage (V) generated between the two terminals could be measured with a voltmeter. This voltage is generated by the anomalous Nernst effect, and is therefore indicated as V _ANE . Temperature measuring probes were attached with conductive epoxy adhesive at two points (positions indicated by reference numerals 31 and 32) on the top surface of the sample 1 at an interval (L ₂ ) of 5.0 mm so that the temperature difference ΔT between them could be monitored. A magnetic field was applied in the thickness direction of the sample while a heat flow was generated in the longitudinal direction of the sample in a physical property measurement system PPMS device manufactured by Quantum Design, and the electromotive force generated between both ends in the width direction of the sample was measured at room temperature (300 K). The black arrow (reference numeral 4) in FIG. 3 indicates the direction of the heat flow in the sample. After the temperatures T ₁ and T ₂ were stabilized, a magnetic field was applied to the sample and the voltage V _ANE (V) was measured. The white arrow (reference numeral 5) in FIG. 3 indicates the direction of the magnetic field. The magnetic field was swept between 3T to -3T and -3T to 3T.
The Nernst coefficient S _ANE (μV/K) was calculated using the following formula (2).
_SANE (μV/K)= _VANE (V)/W/ΔT(K)/ _L2 ... (2)
here,
V _ANE : Electromotive force (V) generated at both ends of the sample in the width direction,
W: width of sample (mm),
ΔT: temperature difference between the two temperature probe mounting positions (K),
_L2 : Distance in the longitudinal direction of the sample between the two temperature probe attachment positions (mm),
It is.

FIG. 4 shows the measurement results of the Nernst coefficient. The Nernst coefficient reached at a temperature of 300K was 5.99 μV/K. This Nernst coefficient is almost comparable to that of single crystal Co ₂ MnGa.
The above results are shown in Table 1.

[Example 2]
The Co--Mn--Ga based alloy powder obtained in Example 1 was classified using a sieve with a nominal opening of 9 μm. The powder obtained under the sieve in this classification step was used as the test powder of this example.
When the particle size distribution of this sample powder was measured using the same method as in Example 1, the cumulative 10% particle diameter D10 was 3.0 μm, the cumulative 50% particle diameter D50 was 5.4 μm, and the cumulative 90% particle diameter D90 was It was 8.8 μm.
FIG. 5 illustrates an SEM (scanning electron microscope) photograph of the sample powder of this example. The photographing conditions are the same as those in FIG. 2 described above.

Furthermore, the average circularity, compositional analysis, and abnormal Nernst effect were measured in the same manner as in Example 1 for the sample powder of this example. As a result, the average circularity was 0.87, the composition was Co:Mn:Ga=49.1:28.3:22.6 in atomic ratio, and the Nernst coefficient reached at a temperature of 300K was 5.95 μV/K.
These results are shown in Table 1.

1 Sample for Nernst effect measurement 2a, 2b Electromotive force measurement terminals 31, 32 Temperature measurement position 4 Direction of heat flow in the sample 5 Direction of magnetic field

Claims (10)

A powder whose main component is the intermetallic compound Co ₂ MnGa, with a cumulative 50% particle diameter D50 of 1 to 150 μm and a cumulative 90% particle diameter D90 of 250 μm or less in a volume-based particle size distribution determined by laser diffraction/scattering method. Co--Mn--Ga based alloy powder, wherein the average circularity of the particles constituting the powder is 0.80 or more.
Here, the average circularity corresponds to the arithmetic mean of the circularity of each particle determined from the following equation (1) from a SEM (scanning electron microscope) image.
Circularity = 4πS/L ² ...(1)
However, S is the area (μm ² ) of the particle on the image, and L is the circumference length (μm) of the particle on the image. The intermetallic compound Co ₂ MnGa is produced by a gas atomization method in which particles of the molten metal are rapidly solidified by blowing an inert gas stream onto the molten metal of Co-Mn-Ga based alloy in a gas phase space with an inert gas atmosphere. A metal particle synthesis step of synthesizing metal particles as the main component;
The method for producing a Co--Mn--Ga based alloy powder according to claim 1. The intermetallic compound Co ₂ MnGa is produced by a gas atomization method in which particles of the molten metal are rapidly solidified by blowing an inert gas stream onto the molten metal of Co-Mn-Ga based alloy in a gas phase space with an inert gas atmosphere. A metal particle synthesis step of synthesizing metal particles as the main component;
a classification step of adjusting the particle size distribution by removing some particles from the powder made of the metal particles;
The method for producing a Co--Mn--Ga based alloy powder according to claim 1. The molten metal of the Co-Mn-Ga-based alloy is formed using a Co-Mn-Ga-based master alloy obtained by melting Co, Mn, and Ga, alloying them, and then solidifying them. The method for producing a Co--Mn--Ga based alloy powder according to claim 2 or 3. A conductive molded body of the Co--Mn--Ga based alloy powder according to claim 1. A conductive molded body comprising a sintered body of the Co--Mn--Ga based alloy powder according to claim 1. The conductive molded article according to claim 5 or 6, which exhibits a Nernst coefficient of 5.5 μV/K or more at a temperature of 300K. A method for producing a conductive molded body, comprising a sintering step of obtaining a conductive molded body by sintering the Co-Mn-Ga based alloy powder according to claim 1. A thermoelectric conversion element using the conductive molded body according to claim 5 or 6. A thermoelectric conversion element using the conductive molded body according to claim 7.

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