WO2023162844A1

WO2023162844A1 - Silicon alloy, and thermoelectric conversion element and thermoelectric conversion module including same

Info

Publication number: WO2023162844A1
Application number: PCT/JP2023/005377
Authority: WO
Inventors: 幸田陽一朗; 秋池良; 召田雅実
Original assignee: 東ソー株式会社
Priority date: 2022-02-24
Filing date: 2023-02-16
Publication date: 2023-08-31
Also published as: JP2023123385A

Abstract

The present invention provides at least one of: a silver-barium-silicon silicon alloy that has both a large Seebeck coefficient at low temperatures and high density; a thermoelectric material including the silicon alloy; a thermoelectric element including the thermoelectric material; and a thermoelectric module including the thermoelectric element.　The silver-barium-silicon silicon alloy includes at least one group 14 element selected from among germanium, tin, and lead, and the content of the group 14 element is less than 9 at%.

Description

Silicon alloy, thermoelectric conversion element and thermoelectric conversion module containing the silicon alloy

The present disclosure relates to silicon alloys and their uses, as well as silicon alloys suitable as thermoelectric materials and thermoelectric materials using the same.

Thermoelectric materials are incorporated into thermoelectric conversion elements and used as thermoelectric conversion modules. In recent years, the demand for miniaturization of thermoelectric conversion modules has been increasing for the purpose of application to wearable devices. Conventionally, a bismuth-tellurium alloy composed of bismuth (Bi) and tellurium (Te) has been used as a thermoelectric material. However, silicon alloys containing silicon (Si) and elements other than silicon are being studied as thermoelectric materials from the viewpoint of low environmental load and low cost.

Silicon alloys that function as thermoelectric materials include an n-type thermoelectric material in which Mg in Mg ₂ Si is substituted with Al (Patent Document 1), and a p-type thermoelectric material composed of two phases of Mg ₂ Si and CaMgSi (Patent Document 2). ) have been reported. In addition, as a silicon alloy that functions as a p-type thermoelectric material capable of obtaining high thermoelectric conversion performance at room temperature, the present inventors have found a silicon alloy (silicide-based alloy material) has been reported (Patent Document 3).

Japanese Patent Application Laid-Open No. 2002-368291 Japanese Patent Application Laid-Open No. 2008-147261 Japanese Patent Application Laid-Open No. 2021-181397

The Ag-Ba-Si-based silicon alloy disclosed in Patent Document 3 exhibits higher thermoelectric conversion performance at low temperatures (50°C) than the silicon alloys disclosed in Patent Documents 1 and 2. However, an increase in the absolute value of the Seebeck coefficient of the silicon alloy was accompanied by a decrease in density.

The present disclosure provides a silver-barium-silicon-based silicon alloy having a large Seebeck coefficient at low temperatures and high density, a thermoelectric material containing the same, a thermoelectric conversion element containing the thermoelectric material, and the thermoelectric conversion An object of the present invention is to provide at least one thermoelectric conversion module including an element.

The present inventors studied the Seebeck coefficient and densification of silver-barium-silicon-based silicon alloys. As a result, the present inventors have found that by doping the silicon alloy with a specific element, the absolute value of the Seebeck coefficient can be increased without reducing the density of the silver-barium-silicon-based silicon alloy.

That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows.
(1) A silver-barium-silicon based silicon alloy containing at least one Group 14 element selected from germanium, tin and lead, and containing less than 9 at % of the Group 14 element.
(2) When the total atomic weight of the Group 14 elements, silver, barium and silicon contained in the silicon alloy is 100 atomic %, the atomic ratio of the Group 14 elements is 1 atomic % or more and less than 9 atomic %, and the atomic ratio of silver is 9 at % or more and 27 at % or less, the atomic proportion of barium is 20 at % or more and 53 at % or less, and the atomic proportion of silicon is 29 at % or more and 64 at % or less.
(3) The silicon alloy according to (1) or (2) above, which has a relative density of 97% or more.
(4) The silicon alloy according to any one of (1) to (3) above, wherein the Group 14 element is at least one of germanium and tin.
(5) A thermoelectric conversion element containing the silicon alloy according to any one of (1) to (4) above.
(6) A thermoelectric conversion module containing the silicon alloy according to any one of (1) to (4) above.

According to the present disclosure, a silver-barium-silicon-based silicon alloy having a large Seebeck coefficient at low temperatures and high density, a thermoelectric material containing the same, a thermoelectric conversion element containing the thermoelectric material, and the thermoelectric conversion element At least one of the thermoelectric conversion modules can be provided.

Hereinafter, an example of an embodiment of the present disclosure will be described.
[Silicon alloy]
This embodiment is a silver-barium-silicon-based silicon alloy containing at least one Group 14 element selected from germanium, tin and lead, and having a Group 14 element content of less than 9 at%. , is. Such silicon alloys have high thermoelectric conversion performance at low temperatures and have higher densities than conventional silver-barium-silicon based silicon alloys.

In the present embodiment, a "silicon alloy" is a metal composed of silicon (Si) and one or more elements other than silicon. Furthermore, the silicon alloy of the present embodiment is a silver-barium-silicon-based silicon alloy (hereinafter also referred to as "Ag-Ba-Si-based alloy"), which contains silicon and at least silver and barium. It is a metal, especially a metal composed of silicon, silver and barium, and contains silver and barium as elements other than silicon.

The Ag-Ba-Si-based alloy of the present embodiment is at least one Group 14 element selected from germanium (Ge), tin (Sn) and lead (Pb) (hereinafter simply referred to as "group 14 element" .)including. The Group 14 element is preferably at least one of germanium and tin, more preferably tin.

The content of the Group 14 element in the Ag--Ba--Si alloy of the present embodiment is less than 9 at %, preferably 8 at % or less or 7 at % or less. An Ag--Ba--Si alloy with a Group 14 element content higher than this causes an increase in electrical resistance and a significant decrease in density, resulting in a significant decrease in low-temperature thermoelectric conversion performance. The content of the group 14 element is more than 0 atomic %, and may be 0.5 atomic % or more or 1 atomic % or more. A preferred Group 14 element content is more than 0 at % and less than 9 at %, 0.5 at % or more and 8 at % or less, or 1 at % or more and 7 at % or less.

The content of the Group 14 element in this embodiment is the ratio [at %] of the atomic weight of the Group 14 element to the total atomic weight of the Group 14 element, silver, barium and silicon.

Ag-Ba-Si-based alloy of the present embodiment, when the total atomic weight of the Group 14 elements, silver, barium and silicon contained therein is 100 at%, the atomic proportion of Group 14 elements is 1 at% or more. It is preferable that the atomic percentage of silver is 9 at% or more and 27 at% or less, the atomic percentage of barium is 20 at% or more and 53 at% or less, and the atomic percentage of silicon is 29 at% or more and 64 at% or less.

Preferably, when the total atomic weight of the Group 14 element, silver, barium and silicon contained in the Ag-Ba-Si-based alloy of the present embodiment is 100 at%, the preferred atomic ratio of each element is as follows. be.

Group 14 element: 1 at% or more or 3 at% or more, and
8 at% or less, or 5 at% or less Silver: 9 at% or more, or 15 at% or more, and
27 atomic % or less Barium: 20 atomic % or more or 30 atomic % or more, and
53 at% or less or 45 at% or less Silicon: 29 at% or more or 32 at% or more, and
64 at% or less or 52 at% or less When the total atomic weight of the Group 14 elements, silver, barium and silicon contained in the Ag-Ba-Si-based alloy of the present embodiment is 100 at%, the atomic ratio of each element is
Group 14 element: 1 at% or more and 8 at% or less,
Silver: 9 at % or more and 27 at % or less,
Barium: 20 at % or more and 45 at % or less, and
Silicon: more preferably 32 at % or more and 64 at % or less,
Group 14 element: 3 at% or more and 5 at% or less,
Silver: 15 at % or more and 27 at % or less Barium: 30 at % or more and 45 at % or less, and
Silicon: More preferably 32 at % or more and 52 at % or less.

It should be noted that the Ag--Ba--Si-based alloy of the present embodiment may contain unavoidable impurities as long as the effect is exhibited. As inevitable impurities, for example, one or more metal elements selected from the group of tungsten (W), copper (Cu), iron (Fe) and aluminum (Al) or compounds thereof, tungsten, copper, iron and aluminum One or more selected oxides may be mentioned. The Ag-Ba-Si alloy of the present embodiment preferably does not contain metal impurities, for example, the total content of tungsten, copper, iron and aluminum is 100 mass ppm or less, further 10 ppm or less, or even measured It is preferably below the limit.

The composition in this embodiment may be measured by ICP-MS mass spectrometry using a general ICP-MS device (eg Vista-PRO, manufactured by Seiko Instruments).

The relative density of the Ag--Ba--Si alloy of the present embodiment is preferably 97% or higher, more preferably 98% or higher. By having such a relative density, the Seebeck coefficient tends to increase, and the electrical resistivity tends to decrease, and the Ag-Ba-Si alloy of the present embodiment is suitable for use or processing as a thermoelectric conversion material. It becomes easier to have a strong strength. Since the thermal conductivity tends to decrease, the relative density may be 99.5% or less or 99.0% or less. A preferable range of relative density is 97% or more and 99.5% or less, or 98% or more and 99.5% or less.

The relative density in this embodiment is the ratio [%] of the measured density [g/cm ³ ] to the theoretical density [g/cm ³ ]. The theoretical density is a value obtained from the following formula (1) considering the composition change from the theoretical density of AgBa ₂ Si ₃ of 4.78 [g/cm ³ ]. The measured density is a value measured by a method according to JIS R 1634.

Theoretical density [g/cm ³ ] = 4.78 × {M/M _AgBa2Si3 } (1)
In the above formula, M is the amount of Ag—Ba—Si-based alloy whose density was measured [g/mol], and M _AgBa2Si3 is the amount of AgBa ₂ Si ₃ (=466.8 [g/mol]). is. In calculating M, the composition of the Ag—Ba—Si-based alloy may be the composition obtained by ICP-MS mass spectrometry. Ba is 137.3 [g/mol], Si is 28.1 [g/mol], Ge is 72.6 [g/mol], Sn is 118.7 [g/mol], and Pb is 207. 2 [g/mol] may be used.

The shape of the Ag--Ba--Si-based alloy of the present embodiment may be any shape according to the application. and one or more selected from the group of polygonal shapes, and at least one of disc-shaped and columnar-shaped.

The Seebeck coefficient of the Ag—Ba—Si alloy of the present embodiment has an absolute value exceeding 120 μV/K, preferably 130 μV/K or more or 200 μV/K or more, and 500 μV/K or less or 300 μV/K. The following are mentioned. The Seebeck coefficient should be more than 120 μV/K and 500 μV/K or less, 130 μV/K or more and 500 μV/K or less, or 200 μV/K or more and 300 μV/K or less. By having such a Seebeck coefficient and having the above-described relative density, it becomes easier to apply as a small thermoelectric conversion module.

The electrical resistivity of the Ag—Ba—Si alloy of the present embodiment is preferably 1.00×10 ⁻³ Ω·cm or more, and 1.00×10 ⁻¹ Ω·cm or less or 1.00 ×10 ⁻² Ω·cm or less is preferable. A preferable electrical resistivity range is 1.00×10 ⁻³ Ω·cm or more and 1.00×10 ⁻¹ Ω·cm or less, or 1.00×10 ⁻³ Ω·cm or more and 1.00×10 ^{− 2} Ω·cm or less can be exemplified.

The thermal conductivity of the Ag—Ba—Si alloy of the present embodiment is preferably 0.1 W/mK or more or 0.5 W/mK or more, and is preferably 20 W/mK or less or 5 W/mK or less. preferable. A preferable range of thermal conductivity is 0.1 W/mK or more and 20 W/mK or less, or 0.5 W/mK or more and 5 W/mK or less.

The Ag--Ba--Si-based alloy of the present embodiment preferably exhibits high thermoelectric conversion performance that Ag--Ba--Si-based silicon alloys have. The thermoelectric conversion performance in this embodiment can be obtained by the following formula (2).

ZT=S ² T/ρκ (2)
In formula (2), Z is the figure of merit, T is the absolute temperature [K], S is the Seebeck coefficient [V / K], ρ is the electrical resistivity [Ω ・ m] and κ is the thermal conductivity [W / K ・m]. Furthermore, S ² /ρ is the power factor [W/K ² ·m].

The Ag—Ba—Si alloy of the present embodiment preferably has high thermoelectric conversion performance at low temperatures, and the thermoelectric conversion performance (ZT) at T=323 [K] (=50° C.) is 0.04 or more, 0.04 or more. 05 or more or 0.10 or more. The thermoelectric conversion performance (ZT) at T=323 [K] is, for example, 0.30 or less, 0.25 or less, 0.20 or less, or 0.18 or less. The thermoelectric conversion performance (ZT) is more preferably 0.04 or more and 0.30 or less, still more preferably 0.05 or more and 0.25 or less, and even more preferably 0.10 or more and 0.23.

Since the resistance to vibration and heat shock when used as a module is likely to be improved, the Ag—Ba—Si alloy of the present embodiment preferably has high mechanical strength, and more preferably has high Vickers hardness. High hardness and fracture toughness are more preferred.

For example, the Vickers hardness of the bismuth-tellurium alloy used as a thermoelectric material is about 100HV. On the other hand, the Vickers hardness of the Ag--Ba--Si alloy of the present embodiment is preferably 250 HV or higher or 300 HV or higher, which makes it possible to use it as a practical thermoelectric material. Also, Vickers hardness can be exemplified to be 1000 HV or less or 500 HV or less. The Vickers hardness of the Ag--Ba--Si alloy of the present embodiment is preferably 250 HV or more and 1000 HV or less, or 300 HV or more and 500 HV or less.

Further, the fracture toughness value of the Ag—Ba—Si alloy of the present embodiment is preferably 1.0 MPa m ^1/2 or more or 1.2 MPa m ^1/2 or more, and is 3.0 or less or 2.0 or less can be exemplified. The fracture toughness value of the Ag--Ba--Si alloy of the present embodiment may be 1.0 or more and 3.0 or less, or 1.2 or more and 2.0 or less.

Vickers hardness is a value measured by a method according to JIS B7725. A pyramidal indenter is pressed against the alloy material with a force of 1 kgf, the formed indentation is observed with a microscope, and the surface area of the indentation is calculated from the horizontal distance of the diagonal line to calculate the Vickers hardness.

The length of the crack formed at the top of the indentation is measured, and the fracture toughness Kc is calculated using the following formula.

Kc=0.026×E ^1/2 ×P ^1/2 ×C ^−3/2 ×a
E: elastic modulus (measured by the method described in JIS R1602)
P: Pressing load = 1 kgf
C: half the diagonal length of the indentation a: half the length of the crack [manufacturing method of silicon alloy]
The Ag--Ba--Si alloy of the present embodiment can be produced by any method as long as it is a silicon alloy having the above characteristics. As a preferred method for producing the Ag-Ba-Si-based alloy of the present embodiment, a Group 14 element containing one or more elements selected from the group of germanium, tin and lead, silver, barium, and silicon A manufacturing method including a step of treating at 650° C. or higher and 950° C. or lower.

In the manufacturing method of the present embodiment, a melt containing a Group 14 element containing one or more elements selected from the group of germanium, tin and lead, silver, barium, and silicon is treated at 650° C. or higher and 950° C. or lower. It has a step (hereinafter also referred to as a “firing step”). The Ag--Ba--Si alloy of the present embodiment is obtained through the firing process.

For the firing process, a melt (hereinafter also referred to as "raw material melt") containing Group 14 elements containing one or more elements selected from the group of germanium, tin and lead, silver, barium, and silicon is provided.

The raw material melt may have a composition containing the same group 14 elements, silver, barium and silicon as the target Ag-Ba-Si alloy, and the Ag-Ba-Si of the present embodiment described above It suffices if it has a composition similar to that of the system alloy.

The shape of the raw material melt to be subjected to the firing step is arbitrary, and includes at least one of an irregular shape and a powdery shape. A specific example of the shape of the raw material melt is a powdery form with a particle size of 200 μm or less or 150 μm or less. Since the operability (handling property) is improved, the particle diameter of the raw material melt may be 10 μm or more or 50 μm or more. A preferred range of particle size of the raw material melt is 10 μm or more and 200 μm or less, or 50 μm or more and 150 μm or less.

In the firing process, the raw material melt is treated at 650°C or higher and 950°C or lower. The treatment temperature in the firing step is 650° C. or higher, preferably 700° C. or higher, or 750° C. or higher. Below 650° C., densification of the raw material melt does not proceed. Also, the treatment temperature is 950° C. or lower, preferably 900° C. or lower. If the treatment temperature exceeds 950° C., the member of the firing device (for example, hot press mold) to be subjected to the treatment and the raw material melt are fused, and the yield of the Ag—Ba—Si alloy of the present embodiment is significantly reduced. Alternatively, the Ag--Ba--Si alloy of this embodiment cannot be obtained. A preferred treatment temperature is 700° C. or higher and 950° C. or lower, or 750° C. or higher and 900° C. or lower.

The treatment in the sintering step may be any treatment that sinters the raw material melt, preferably pressure sintering, and at least one of hot press treatment, hot isostatic press treatment, and discharge plasma sintering treatment. is more preferred, and discharge plasma firing treatment is even more preferred.

The firing process will be described below by taking discharge plasma firing (hereinafter also referred to as "SPS") treatment as an example.

The SPS process is a process in which the molten raw material is fired by directly energizing the molten raw material while pressurizing it. By firing while pressurizing, it is possible to heat to a high temperature in a short time. As a result, a dense Ag--Ba--Si alloy can be obtained without coarsening the grain size.

The pressure applied to the raw material melt in the SPS treatment is preferably 10 MPa or more or 25 MPa or more, and preferably 100 MPa or less or 75 MPa or less. A preferable range of the applied pressure is 10 MPa or more and 100 MPa or less, or 25 MPa or more and 75 MPa or less.

The atmosphere in the SPS treatment may be a vacuum atmosphere, a vacuum atmosphere with a degree of vacuum of 5.0×10 ⁻³ Pa or less, and a vacuum atmosphere with a degree of vacuum of 1.0×10 ⁻³ Pa or more and 5.0×10 ⁻³ Pa. The following vacuum atmosphere is preferred.

The treatment temperature in the SPS treatment is 650°C or higher, preferably 700°C or higher or 750°C or higher, and preferably 950°C or lower or 900°C or lower. A preferable range of treatment temperature is 650° C. or higher and 950° C. or lower, or 750° C. or higher and 900° C. or lower.

The heating rate to the treatment temperature is arbitrary, but for example, it may be 50°C/min or more and 300°C/min or less.

The holding time at the above treatment temperature may be appropriately adjusted depending on the amount of the raw material melt to be treated and the performance of the SPS furnace used, and is, for example, 15 minutes or less or 12 minutes or less.
In order to uniformly heat even the inside of the raw material melt, the holding time may be 1 minute or longer, or 5 minutes or longer. The retention time may be from 1 minute to 15 minutes, or from 5 minutes to 12 minutes.

The raw material melt to be subjected to the firing step may be produced by any method. Also referred to as a "germanium source" when the Group 14 element is germanium or the like), a step of melting a composition containing a silver source, a barium source, and a silicon source (hereinafter also referred to as a "melting step" It is said.), and a manufacturing method including.

The Group 14 element source may be at least one of germanium, tin, lead, and compounds thereof. The 14th element source preferably has a Group 14 element purity of 3N or higher (99.9% or higher) or 4N or higher (99.99% or higher). The upper limit of the purity of the Group 14 element is 6N or less (99.9999% or less) or 5N or less (99.999% or less). Preferred fourteenth element sources include one or more elements selected from the group consisting of germanium, tin and lead. A preferred germanium source is metallic germanium (pure germanium), a preferred tin source is metallic tin (pure tin), and a preferred lead source is metallic lead (pure lead).

The silver source may be at least one of silver and a silver-containing compound. The silver source preferably has a silver purity of 3N or higher or 4N or higher. The upper limit of purity of silver is 6N or less or 5N or less. Preferred silver sources include metallic silver (pure silver).

The barium source may be at least one of barium and barium-containing compounds. The barium source preferably has a barium purity of 3N or higher or 4N or higher. The upper limit of the purity of barium is 6N or less or 5N or less. Preferred barium sources include metallic barium (pure barium).

The silicon source may be at least one of silicon and a silicon-containing compound. The silicon source preferably has a silicon purity of 3N or higher or 4N or higher. The upper limit of the purity of silicon is 6N or less or 5N or less. Preferred silicon sources include metallic silicon (pure silicon) and amorphous silicon.

The shape of the starting material such as the Group 14 element source is arbitrary, and may be, for example, one or more selected from the group of amorphous, powder, and granules.

The composition to be subjected to the melting step contains a starting material such as a Group 14 source so that the atomic weight ratio of the Group 14 element, silver, barium and silicon of the desired Ag-Ba-Si alloy is obtained. Well, if desired, the starting materials may be mixed by any method.

The mixing method is arbitrary, and at least one of wet mixing and dry mixing can be exemplified.

In the melting step, the composition is melted. A raw material melt is thus obtained. The melting method may be one or more methods selected from the group consisting of arc melting, air melting, high frequency melting, plasma melting, skull melting, zone melting, and electron beam melting. The melting method is preferably arc melting because it can be melted in a short time, the atmosphere can be controlled, and there is little contamination from the crucible (copper mold).

In arc melting, the current value per unit mass of the composition to be processed (hereinafter also simply referred to as "current value") is preferably 30 A/g or more or 50 A/g or more. Thereby, the melting treatment can be performed in a short time. The current value is preferably 150 A/g or less or 120 A/g or less in order to suppress composition fluctuations during arc melting. A preferable current value range is 30 A/g or more and 150 A/g or less, or 50 A/g or more and 120 A/g or less.

The holding time at the above-mentioned current value may be appropriately adjusted according to the amount of the composition to be treated and the performance of the arc melting furnace to be used. and 5 minutes or less or 3 minutes or less. A preferable retention time is 0.5 minutes or more and 5 minutes or less, or 1 minute or more and 3 minutes or less.

In order to efficiently melt the composition, the treatment with the above-described current value and holding time may be performed multiple times, and the treatment may be performed two or more times or three times or more. The treatment need not be performed more than necessary, and may be performed 5 times or less or 4 times or less. The preferable number of treatments is 2 to 5 times, or 3 to 4 times.

The raw material melt after arc melting may be cooled by any method and collected, or may be cooled by quenching. Quenching is a process for instantaneously solidifying a raw material melt in a fluid state (so-called molten state). Thereby, a molten mixture is obtained as a quenched ribbon. A known method can be used for the quenching method, and examples thereof include a cooling method in which the cooling rate is 1×10 ⁵ K/s or more and 1×10 ⁶ K/s or less. As a specific cooling method, it can be exemplified that the raw material melt in a fluid state is brought into contact with a water-cooled roller.

If necessary, the raw material melt may be pulverized or granulated. This allows the raw material melt to be of any shape and size.

Pulverization may be at least one of wet pulverization and dry pulverization, and includes one or more pulverization methods selected from the group of mortar pulverization, ball mill, jet mill and bead mill. Moreover, granulation includes at least one granulation method of spray drying and gas atomization. Pulverization and granulation are preferably carried out by a method that does not cause contamination of oxygen (O ₂ ), and pulverization in an inert atmosphere is preferred. This suppresses the surface oxidation of the melt and, as a result, makes it difficult for the oxygen content to increase.

The manufacturing method of the present embodiment may include a step of processing the Ag—Ba—Si alloy (hereinafter also referred to as “processing step”). In the processing step, the Ag--Ba--Si alloy is processed into a desired shape such as a thermoelectric conversion element. As a working method, a known method applied to alloy working can be applied, and examples thereof include one or more grinding methods selected from the group of surface grinding, rotary grinding and cylindrical grinding.
[Thermoelectric conversion material and thermoelectric conversion element]
The Ag--Ba--Si alloy of the present embodiment can be used as a thermoelectric conversion material containing it, and is preferably used as an n-type thermoelectric conversion material. Furthermore, it can be used as a thermoelectric conversion element comprising the Ag--Ba--Si alloy of this embodiment. In the present embodiment, the “thermoelectric conversion material” is a material that enables direct conversion of thermal energy into electrical energy, and the “thermoelectric conversion element” is a p-type thermoelectric conversion material and an n-type thermoelectric conversion material. It is an element that generates an electromotive force when one thermoelectric conversion material is brought into contact with a high-temperature substance and the other thermoelectric conversion material is brought into contact with a low-temperature substance.

In the thermoelectric conversion element comprising the Ag--Ba--Si-based alloy of the present embodiment, the Ag--Ba--Si-based alloy of the present embodiment and the p-type or n-type thermoelectric conversion material paired therewith do not contact. are installed in parallel, and each thermoelectric conversion material is connected by an electrode.

The thermoelectric conversion element provided with the Ag--Ba--Si alloy of this embodiment can be used as a thermoelectric conversion module in which it is integrated. The thermoelectric conversion module may be any type of module depending on the purpose. For example, one or more selected from the group consisting of a single-stage thermoelectric conversion module, a cascade module, and a segment-type module, and a single-stage thermoelectric conversion module. It is mentioned that it is. A "thermoelectric conversion module" is a module in which two or more thermoelectric conversion elements are integrated.

The present disclosure will now be described with reference to examples. However, the present disclosure is not so limited.
(Average grain size)
Using a Schottky field emission scanning electron microscope (equipment name: JSM-IT800SHL, manufactured by JEOL Ltd.) equipped with backscattered electron diffraction (EBSD), SEM observations of the interior of the alloy samples were obtained under the following conditions.

Accelerating voltage: 15 kV
Observation magnification: 300x or 1000x Sample tilt: 70°
In the obtained SEM observation diagram, the crystal grains were confirmed by considering the portion where the crystal orientation difference at the crystal interface was 5° or more as the crystal grain boundary. The longest diameter of each crystal grain was measured and defined as the crystal grain size. 5000±100 grain sizes were measured, and the average grain size was obtained. Prior to SEM observation, the alloy samples were pretreated by dry polishing and argon ion milling.
(crystal phase)
A general powder X-ray diffractometer (device name: RINT Ultima III, manufactured by RIGAKU) was used to carry out XRD measurement of the alloy sample. The measurement conditions are as follows.

Accelerating current/voltage: 40mA/40kV
Radiation source: CuKα ray (λ = 1.5405 Å)
Measurement mode: Continuous scan Scan conditions: 5°/min Measurement range: 2θ = 20° to 50°
Divergence longitudinal limiting slit: 10mm
Divergence/Entrance Slit: 1°
Light receiving slit: open
Detector: D/teX Ultra
Use of Ni filter The obtained X-ray diffraction pattern is subjected to smoothing processing and background removal of the X-ray diffraction pattern using the analysis program attached to the X-ray diffraction device (software name: PDLX2, manufactured by RIGAKU). The later X-ray diffraction patterns were profile-fitted with a split pseudo-Voigt function. The crystal phase of the alloy sample was identified by comparing the X-ray diffraction pattern after the fitting with the X-ray diffraction pattern of the PDF card (01-086-0810).
(composition)
Using a general ICP-MS device (device name: Vista-PRO, manufactured by Seiko Instruments), the composition of the sample was measured by ICP-MS mass spectrometry. As a pretreatment, the alloy sample was dissolved with hydrofluoric acid and sulfuric acid, and the resulting acid solution was subjected to measurement.
(relative density)
The theoretical density of the alloy sample was obtained from the ratio [%] of the actually measured density [g/cm ³ ] to the theoretical density [g/cm ³ ]. The theoretical density was obtained from the above equation (1) using the composition measured by the method described above. The value of bulk density measured by a method according to JIS R 1634 was used as the actual density. Prior to measuring the density, the alloy sample was pretreated by a vacuum method using kerosene as a solvent.
(Electrical resistance)
Using a specific resistance/Hall measurement system (apparatus name: ResiTest8400, manufactured by Toyo Technica), electrical resistance was measured under the following conditions.

Sample shape: 10 mm diameter x 1 mm thick disc Electrode: Platinum electrode Measurement atmosphere: Vacuum atmosphere Measurement temperature: 50°C
(Seebeck coefficient)
The Seebeck coefficient was measured under the following conditions using a resistivity/Hall measurement system (device name: ResiTest8400, manufactured by Toyo Technica) equipped with a Seebeck coefficient measurement option.

Sample shape: Disk shape with a diameter of 10 mm and a thickness of 1 mm Measurement atmosphere: Vacuum atmosphere Measurement temperature: 50°C
(Thermal conductivity)
Using a laser flash thermal conductivity measuring device (Device name: TC-1200RH, manufactured by Advance Riko), thermal conductivity was measured under the following conditions.

Sample shape: Disk shape with a diameter of 10 mm and a thickness of 1 mm Measurement atmosphere: Vacuum atmosphere Measurement temperature: 50°C
(Vickers hardness test, fracture toughness)
Using a hardness tester (equipment name: HV-115, manufactured by Mitutoyo), a pyramidal indenter is pressed against the alloy material with a force of 1 kgf, and the formed indentation is observed with a microscope. The Vickers hardness was calculated by calculating the surface area of the indentation from the distance. Furthermore, the length of the crack formed at the apex portion of the indentation was measured, and the fracture toughness Kc was calculated using the following formula.

Kc=0.026×E ^1/2 ×P ^1/2 ×C ^−3/2 ×a
E: elastic modulus (measured by the method described in JIS R1602)
P: Pressing load = 1 kgf
C: half the diagonal length of the indentation a: half the length of the crack Example 1
Metallic silicon (amorphous silicon; purity 5N, average size 2 to 5mm, product name: SIE01GB, manufactured by Kojundo Chemical Co., Ltd.), metallic silver (pure silver; purity 3N, average granule diameter 1 to 3mm) so as to have the following composition , Product name: AGE01GB, manufactured by Kojundo Chemical Co., Ltd.), metallic barium (barium; purity 3N, average size 10 mm, manufactured by Furuuchi Chemical Co., Ltd.), and metallic tin (tin granules; purity 4N, average granule diameter 2 to 3 mm, product Name: SNE01GB, manufactured by Kojundo Chemical Co., Ltd.) were weighed so that the atomic weight ratio was Ag:Ba:Si:Sn=1:2:2.9:0.1. After filling the weighed raw material into a water-cooled mold, an arc melting furnace (apparatus name: ACM-S01, manufactured by Daia Vacuum) was used to arc melt under the following conditions to obtain a raw material melt.

Arc melting time: 2 minutes x 4 times Output: 100 A/g
The raw material melt thus obtained was transferred to an agate mortar, and after dry pulverization using the mortar, it was passed through a sieve with an opening of 150 μm to obtain a powder having a particle size of less than 150 μm. Fill 1.00 g of the raw material melt after pulverization into a circular carbon mold with a diameter of 10 mm, use a discharge plasma firing furnace (product name: LABOX-315R-AH, manufactured by Sinterland), and perform SPS treatment under the following conditions. An alloy was obtained and used as the Ag--Ba--Si alloy of the present embodiment. It was measured using a temperature radiation thermometer (product name: IR-AHS, manufactured by Chino Co., Ltd.) in discharge plasma firing.

Heating rate: 150°C/min (~600°C)
100°C/min (600°C to holding temperature)
Degree of vacuum: 5.0×10 ⁻³ Pa
Holding temperature: 800°C
Holding time: 10 minutes Holding pressure: 75 MPa
The resulting Ag--Ba--Si alloy had an average grain size of 11 μm and a relative density of 99.4%.

Examples 2-7
Alloys were obtained in the same manner as in Example 1 except that the compositions were obtained by weighing and mixing metallic silicon, metallic silver, metallic barium and metallic tin so as to have the compositions shown in Table 1. was used as the Ag--Ba--Si alloy of each example.

Example 8
The use of metallic germanium (pure germanium; purity 4N, product name: GE001, manufactured by Kojundo Chemical Co., Ltd.) instead of metallic tin, and metallic silicon, metallic silver, and metallic barium so as to have the compositions shown in Table 1, respectively. and metal germanium were weighed and mixed to obtain a composition, respectively, in the same manner as in Example 1 to obtain alloys, which were used as Ag--Ba--Si alloys of each example.

Comparative Examples 1 to 5
Alloys were obtained in the same manner as in Example 1 except that the compositions were obtained by weighing and mixing metallic silicon, metallic silver and metallic tin so as to have the compositions shown in Table 2, and these were compared with each other. The silicon-based alloy of Example was used.

Comparative example 6
Alloys were obtained in the same manner as in Example 1 except that the compositions were obtained by weighing and mixing metallic silicon, metallic silver, metallic barium and metallic tin so as to have the compositions shown in Table 2. was used as the silicon-based alloy of each comparative example.

Comparative example 7
Alloys were obtained in the same manner as in Example 1, except that the amorphous silicon, silver granules, barium, and germanium powders were weighed and mixed to obtain the compositions shown in Table 2. , which were used as silicon-based alloys of respective comparative examples.

The results of Examples and Comparative Examples are shown in Table 1.

"-" in the table means unmeasured. All of the Ag--Ba--Si alloys of the examples had a relative density exceeding 97% and an absolute value of the Seebeck coefficient exceeding 140 μV/K. The thermoelectric conversion performance (ZT) of any example is 0.05 or more, which can be confirmed to be higher than the thermoelectric conversion performance of the comparative example. In particular, since the silicon-based alloy of Comparative Example 3 has a high electric resistance, it was confirmed that the thermoelectric conversion performance was remarkably lowered, although the Seebeck coefficient was high.

Measurement example (measurement of mechanical strength)
A Vickers hardness test was performed on the silicon-based alloys obtained in Examples 1, 2, 4, and 8 and Comparative Example 5, and the fracture toughness was calculated. The results are shown in the table below.

All of the examples had a Vickers hardness of 250 HV or more, and it was confirmed that the strength was higher than that of the bismuth-tellurium alloy. Moreover, the fracture toughness is 1.1 MPa·m ^1/2 or more, and it can be confirmed that the mechanical strength is higher than that of the comparative example.

This application is based on the Japanese patent application (Japanese Patent Application No. 2022-027208) filed on February 24, 2022 and the Japanese patent application (Japanese Patent Application No. 2022-082511) filed on May 19, 2022, incorporated by reference in its entirety. Also, all references cited herein are incorporated in their entirety.

Claims

A silver-barium-silicon-based silicon alloy containing at least one Group 14 element selected from germanium, tin and lead, and containing less than 9 at% of the Group 14 element.
When the total atomic weight of the Group 14 element, silver, barium and silicon contained in the silicon alloy is 100 at%, the atomic ratio of the Group 14 element is 1 at% or more and less than 9 at%, and the atomic ratio of silver is 9 at%. 27 at % or more, the atomic proportion of barium is 20 at % or more and 53 at % or less, and the atomic proportion of silicon is 29 at % or more and 64 at % or less.
The silicon alloy according to claim 1 or 2, which has a relative density of 97% or more.
The silicon alloy according to any one of claims 1 to 3, wherein the Group 14 element is at least one of germanium and tin.
A thermoelectric conversion element containing the silicon alloy according to any one of claims 1 to 4.
A thermoelectric conversion module containing the silicon alloy according to any one of claims 1 to 4.