JP2022050680A - Thermoelectric conversion material and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material consisting of a sintered body with magnesium silicide as a main component, having excellent durability when used under high-temperature conditions, and a manufacturing method of the same.

SOLUTION: A thermoelectric material is a sintered material mainly composed of magnesium silicide and contains aluminum within the range of 0.3 mass% or more and 1.0% or less and titanium oxide within the range of 1.5 mass% or more and 9.5 mass% or less.

SELECTED DRAWING: None

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a thermoelectric conversion material made of a sintered body containing magnesium silicide as a main component, and a method for producing the thermoelectric conversion material.

A thermoelectric conversion element made of a thermoelectric conversion material is an electronic element capable of mutually converting heat and electricity, such as the Seebeck effect and the Peltier effect. The Zeebeck effect is an effect of converting thermal energy into electrical energy, and is a phenomenon in which an electromotive force is generated when a temperature difference is generated at both ends of a thermoelectric conversion material. Such electromotive force is determined by the characteristics of the thermoelectric conversion material. In recent years, the development of thermoelectric power generation utilizing this effect has been active.
The above-mentioned thermoelectric conversion element has a structure in which electrodes are bonded to one end side and the other end side of the thermoelectric conversion material via a metallized layer, respectively.

As an index showing the characteristics of such a thermoelectric conversion element (thermoelectric conversion material), for example, the power factor (PF) represented by the following equation (1) or the dimensionless performance index represented by the following equation (2) (ZT) is used. In the thermoelectric conversion material, it is necessary to maintain a temperature difference between the one-sided side and the other-sided side, so that it is preferable that the thermal conductivity is low.
PF = S ² σ ・ ・ ・ (1)
However, S: Seebeck coefficient (V / K), σ: electrical conductivity (S / m)
ZT = S ² σT / κ ... (2)
However, T = absolute temperature (K), κ = thermal conductivity (W / (m × K))

Here, as the above-mentioned thermoelectric conversion material, for example, as shown in Patent Document 1, a material in which various dopants are added to magnesium silicide has been proposed. The thermoelectric conversion material made of magnesium silicide shown in Patent Document 1 is manufactured by sintering a raw material powder adjusted to a predetermined composition.

Japanese Unexamined Patent Publication No. 2013-179322

Here, in a thermoelectric conversion material containing magnesium silicide as a main component, when used under high temperature conditions, a part of magnesium silicide may be decomposed to form magnesium oxide and discoloration may occur. Further, when the decomposition further progresses and magnesium oxide is formed, there arises a problem that the thermoelectric conversion material itself is damaged due to the difference in thermal expansion between magnesium silicide and magnesium oxide, or the thermoelectric conversion material is peeled off from the electrode. It ends up. Therefore, the thermoelectric conversion material is required to have durability when used under high temperature conditions.

The present invention has been made in view of the above-mentioned circumstances, and is a thermoelectric conversion material which is composed of a sintered body containing magnesium silicide as a main component and has excellent durability when used under high temperature conditions, and this thermoelectric conversion material. It is an object of the present invention to provide a method for manufacturing a conversion material.

In order to solve the above problems, the thermoelectric conversion material of the present invention is a thermoelectric conversion material made of a sintered body containing magnesium silicide as a main component, and aluminum is in the range of 0.3 mass% or more and 1.0 mass% or less. It is characterized in that it contains titanium oxide in the range of 1.5 mass% or more and 9.5 mass% or less.

According to the thermoelectric conversion material having this configuration, aluminum is contained in the range of 0.3 mass% or more and 1.0 mass% or less, and titanium oxide is contained in the range of 1.5 mass% or more and 9.5 mass% or less. Therefore, aluminum and titanium oxide can suppress oxygen in the atmosphere from entering the inside of magnesium silicide, thereby suppressing decomposition of magnesium silicide and improving durability when used under high temperature conditions. It is thought that it can be made to.

Here, in the thermoelectric conversion material of the present invention, as a dopant, one selected from Li, Na, K, B, Al, Ga, In, N, P, As, Sb, Bi, Ag, Cu, and Y. Alternatively, it may contain two or more kinds.
In this case, the thermoelectric conversion material can be a specific semiconductor type, that is, an n-type thermoelectric conversion material or a p-type thermoelectric conversion material.

The method for producing a thermoelectric conversion material of the present invention is a method for producing a thermoelectric conversion material composed of a sintered body containing magnesium silicide as a main component, in which 0.3 mass% or more of aluminum powder is added to the raw material powder containing Mg and Si. A step of forming a sintered raw material powder to obtain a sintered raw material powder by mixing titanium oxide powder within a range of 1.0 mass% or less and within a range of 1.5 mass% or more and 9.5 mass% or less. It includes a sintering step of heating the sintered raw material powder while pressurizing it to form a sintered body, and the average particle size of the raw material powder containing Mg and Si is within the range of 0.5 μm or more and 100 μm or less. The sintering temperature in the sintering step is in the range of 800 ° C. or higher and 1020 ° C. or lower.

According to the method for producing a thermoelectric conversion material having this configuration, sintering contains aluminum powder in the range of 0.3 mass% or more and 1.0 mass% or less, and titanium oxide powder in the range of 1 mass% or more and 10 mass% or less. Since the raw material powder is sintered by heating under pressure, Al and Ti generated by the decomposition of some titanium oxides are dispersed in the sintered magnesium silicide grains, and aluminum and aluminum are dispersed in the grain boundaries. A sintered body in which titanium oxide is unevenly distributed can be obtained.

According to the present invention, it is possible to provide a thermoelectric conversion material which is composed of a sintered body containing magnesium silicide as a main component and has excellent durability when used under high temperature conditions, and a method for producing the thermoelectric conversion material. Will be.

It is sectional drawing which shows the thermoelectric conversion material which is one Embodiment of this invention, and the thermoelectric conversion element using this. It is a flow chart of the manufacturing method of the thermoelectric conversion material which is one Embodiment of this invention. It is sectional drawing which shows an example of the sintering apparatus used in the manufacturing method of the thermoelectric conversion material which is one Embodiment of this invention.

Hereinafter, a thermoelectric conversion material according to an embodiment of the present invention and a method for manufacturing the thermoelectric conversion material will be described with reference to the attached drawings. It should be noted that each of the embodiments shown below is specifically described in order to better understand the gist of the invention, and is not limited to the present invention unless otherwise specified. In addition, the drawings used in the following description may be shown by enlarging the main parts for convenience in order to make the features of the present invention easy to understand, and the dimensional ratios of each component are the same as the actual ones. It is not always the case.

FIG. 1 shows a thermoelectric conversion material 11 according to an embodiment of the present invention and a thermoelectric conversion element 10 using the thermoelectric conversion material 11.
The thermoelectric conversion element 10 includes the thermoelectric conversion material 11 of the present embodiment, metallized layers 18a and 18b formed on one surface 11a of the thermoelectric conversion material 11 and the other surface 11b facing the same, and the metallizing. It includes electrodes 19a and 19b laminated on the layers 18a and 18b.

Nickel, silver, cobalt, tungsten, molybdenum or the like is used for the metallized layers 18a and 18b. The metallized layers 18a and 18b can be formed by current-carrying sintering, plating, electrodeposition and the like.
The electrodes 19a and 19b are formed of a metal material having excellent conductivity, for example, a plate material such as copper or aluminum. In this embodiment, a rolled aluminum plate is used. Further, the thermoelectric conversion material 11 (metallized layers 18a and 18b) and the electrodes 19a and 19b can be joined by Ag wax, Ag plating or the like.

The thermoelectric conversion material 11 is a sintered body containing magnesium silicide as a main component, and in the present embodiment, antimony (Sb) is added as a dopant to magnesium silicide (Mg ₂ Si). .. For example, the thermoelectric conversion material 11 of the present embodiment has a composition in which antimony is contained in Mg ₂ Si in the range of 0.1 at% or more and 2.0 at% or less. In the thermoelectric conversion material 11 of the present embodiment, an n-type thermoelectric conversion material having a high carrier density is obtained by adding antimony, which is a pentavalent donor.

As the material constituting the thermoelectric conversion material 11, compounds in which other elements are added to magnesium silicide, such as Mg ₂ Si _X Ge _1-X and Mg ₂ Si _X Sn _1-x , can also be used in the same manner.
Further, as a donor for using the thermoelectric conversion material 11 as an n-type thermoelectric conversion element, bismuth, aluminum, phosphorus, arsenic and the like can be used in addition to antimony.
Further, the thermoelectric conversion material 11 may be a p-type thermoelectric conversion element, and in this case, it can be obtained by adding a dopant such as lithium or silver as an acceptor.

The thermoelectric conversion material 11 of the present embodiment contains aluminum in the range of 0.3 mass% or more and 3 mass% or less, and titanium oxide in the range of 1 mass% or more and 10 mass% or less. ..
As for the content of titanium oxide in the thermoelectric conversion material 11, a measurement sample was taken from the thermoelectric conversion material 11 and the Al amount and the Ti amount _were obtained by a fluorescent X-ray analysis method. It is calculated by converting on the assumption that it is ₂ .

As described above, the thermoelectric conversion material 11 of the present embodiment contains aluminum and titanium oxide, and is made of aluminum and titanium oxide dispersed in a sintered body containing magnesium silicide as a main component. It is suppressed that oxygen in the atmosphere penetrates into the thermoelectric conversion material, and the decomposition of magnesium silicide is suppressed.

Here, when the content of aluminum is less than 0.3 mass%, oxygen in the atmosphere may not be sufficiently suppressed from entering the inside of magnesium silicide. On the other hand, if the aluminum content exceeds 3 mass%, the thermal conductivity may increase and the Seebeck coefficient may decrease.
From the above, in the present embodiment, the aluminum content is defined within the range of 0.3 mass% or more and 3 mass% or less.
In order to surely suppress the invasion of oxygen in the atmosphere into the magnesium silicide, the lower limit of the aluminum content is preferably 0.3 mass% or more, and 0.5 mass% or more. More preferred.
Further, in order to further suppress the increase in thermal conductivity, the upper limit of the aluminum content is preferably 3 mass% or less, and more preferably 2 mass% or less.

Further, when the content of the titanium oxide is less than 1 mass%, it may not be possible to sufficiently suppress the invasion of oxygen in the atmosphere into the inside of the magnesium silicide. On the other hand, since titanium oxide is a semiconductor having a large bandgap, when the content of titanium oxide exceeds 10 mass%, the electric resistance becomes high, and the power factor (PF) and the dimensionless performance index (ZT) are reversed. It may decrease.
From the above, in the present embodiment, the content of titanium oxide is defined within the range of 1 mass% or more and 10 mass% or less.
In order to surely suppress the invasion of oxygen in the atmosphere into the magnesium silicide, the lower limit of the titanium oxide content is preferably 1 mass% or more, and more preferably 3 mass% or more. ..
Further, in order to further suppress the increase in electrical resistance, the upper limit of the titanium oxide is preferably 10 mass% or less, and more preferably 7 mass% or less.

Hereinafter, a method for manufacturing the thermoelectric conversion material 11 according to the present embodiment will be described with reference to FIGS. 2 and 3.

(Magnesium silicide powder preparation step S01)
First, a powder of magnesium silicide (Mg ₂ Si), which is the parent phase of the sintered body which is the thermoelectric conversion material 11, is produced.
In the present embodiment, the magnesium silicide powder preparation step S01 comprises a lumpy magnesium silicide forming step S11 for obtaining a lumpy magnesium silicide and a crushing step S12 for crushing the lumpy magnesium silicide (Mg ₂ Si) into a powder. I have.

In the massive magnesium silicide forming step S11, the silicon powder, the magnesium powder, and the dopant are weighed and mixed. For example, when forming an n-type thermoelectric conversion material, a pentavalent material such as antimony or bismuth or aluminum is used as a dopant, and when forming a p-type thermoelectric conversion material, lithium is used as a dopant. Mix materials such as silver and silver. In this embodiment, antimony is used as a dopant in order to obtain an n-type thermoelectric conversion material, and the amount of antimony added is in the range of 0.1 at% or more and 2.0 at% or less.

Then, this mixed powder is introduced into, for example, an alumina crucible, heated to a range of 800 ° C. or higher and 1150 ° C. or lower, cooled and solidified. As a result, for example, a lumpy magnesium silicide is obtained.
Since a small amount of magnesium sublimates during heating, it is preferable to add a large amount of magnesium, for example, about 5 at% with respect to the stoichiometric composition of Mg: Si = 2: 1 when weighing the raw material.

In the pulverization step S12, the obtained lumpy magnesium silicide is pulverized by a pulverizer to form magnesium silicide powder (crushing step S12).
Here, it is preferable that the average particle size of the magnesium silicide powder is in the range of 0.5 μm or more and 100 μm or less.

When a commercially available magnesium silicide powder or magnesium silicide powder to which a dopant is added is used, the lumpy magnesium silicide forming step S11 and the pulverizing step S12 can be omitted.

(Sintered raw material powder forming step S02)
Next, aluminum powder and titanium oxide powder were mixed with the obtained magnesium silicide powder, and the content of the aluminum powder was within the range of 0.3 mass% or more and 3 mass% or less, and the content of the titanium oxide powder was high. A sintered raw material powder having a range of 1 mass% or more and 10 mass% or less is obtained.
The average particle size of the aluminum powder and the titanium oxide powder is preferably smaller than the average particle size of the magnesium silicide powder. Specifically, the average crystal grain size of the aluminum powder is preferably in the range of 0.5 μm or more and 30 μm or less. The average particle size of the titanium oxide powder is preferably in the range of 0.5 μm or more and 30 μm or less.
As the titanium oxide powder, TiO, Ti ₂ O ₃ and the like can be used in addition to TiO ₂ (anatase, rutile) powder.

(Sintering step S03)
Next, the sintered raw material powder obtained as described above is heated while pressurizing to obtain a sintered body.
In the present embodiment, in the sintering step S03, the sintering device (current-carrying sintering device 100) shown in FIG. 3 is used.

The sintering device (current current sintering device 100) shown in FIG. 3 includes, for example, a pressure resistant housing 101, a vacuum pump 102 for depressurizing the inside of the pressure resistant housing 101, and a hollow cylinder arranged inside the pressure resistant housing 101. A voltage is applied between the carbon mold 103 of the shape, a pair of electrode portions 105a and 105b for applying a current while pressurizing the sintered raw material powder Q filled in the carbon mold 103, and the pair of electrode portions 105a and 105b. The power supply device 106 is provided. Further, a carbon plate 107 and a carbon sheet 108 are arranged between the electrode portions 105a and 105b and the sintered raw material powder Q, respectively. In addition to this, it has a thermometer, a displacement meter, etc. that are not shown.
Further, in the present embodiment, the heater 109 is arranged on the outer peripheral side of the carbon mold 103. The heaters 109 are arranged on four side surfaces so as to cover the entire outer peripheral side of the carbon mold 103. As the heater 109, a carbon heater, a nichrome wire heater, a molybdenum heater, a cantal wire heater, a high frequency heater and the like can be used.

In the sintering step S03, first, the sintering raw material powder Q is filled in the carbon mold 103 of the energization sintering device 100 shown in FIG. The inside of the carbon mold 103 is, for example, covered with a graphite sheet or a carbon sheet. Then, using the power supply device 106, a direct current is passed between the pair of electrode portions 105a and 105b, and a current is passed through the sintered raw material powder Q to raise the temperature by self-heating. Further, of the pair of electrode portions 105a and 105b, the movable side electrode portion 105a is moved toward the sintered raw material powder Q, and the sintered raw material powder Q is moved between the fixed side electrode portions 105b and the sintered raw material powder Q at a predetermined pressure. Pressurize. It also heats the heater 109.
As a result, the sintered raw material powder Q is sintered by the self-heating of the sintered raw material powder Q, the heat from the heater 109, and the pressurization.

In the present embodiment, the sintering conditions in the sintering step S03 are such that the sintering temperature of the sintering raw material powder Q is within the range of 800 ° C. or higher and 1020 ° C. or lower, and the holding time at this sintering temperature is 0.15 minutes or longer. It is said to be within the range of 5 minutes or less. Further, the pressurized load is within the range of 20 MPa or more and 50 MPa or less.
Further, the atmosphere inside the pressure-resistant housing 101 may be an inert atmosphere such as an argon atmosphere or a vacuum atmosphere. In the case of a vacuum atmosphere, the pressure should be 5 Pa or less.

Here, when the sintering temperature of the sintered raw material powder Q is less than 800 ° C., the oxide film formed on the surface of each powder of the sintered raw material powder Q cannot be sufficiently removed, and the crystal grain boundaries cannot be sufficiently removed. The oxide film remains in the sinter, and the density of the sintered body becomes low. Therefore, the resistance of the obtained thermoelectric conversion material may increase.
On the other hand, when the sintering temperature of the sintering raw material powder Q exceeds 1020 ° C., the decomposition of magnesium silicide proceeds in a short time, the composition shifts, the resistance increases, and the Seebeck coefficient decreases. There is a risk.
Therefore, in the present embodiment, the sintering temperature in the sintering step S03 is set to 800 ° C. or higher and 1020.
It is set within the range of ℃ or less.
The lower limit of the sintering temperature in the sintering step S03 is preferably 850 ° C. or higher, and more preferably 900 ° C. or higher. On the other hand, the upper limit of the sintering temperature in the sintering step S03 is preferably 1000 ° C. or lower, and more preferably 980 ° C. or lower.

Further, if the holding time at the sintering temperature is less than 0.15 minutes, the sintering may be insufficient and the resistance of the obtained thermoelectric conversion material may increase.
On the other hand, if the holding time at the sintering temperature exceeds 5 minutes, the decomposition of magnesium silicide progresses, the composition shifts, the resistance increases, and the Seebeck coefficient may decrease.
Therefore, in the present embodiment, the holding time at the sintering temperature in the sintering step S03 is set within the range of 0.15 minutes or more and 5 minutes or less.
The lower limit of the holding time at the sintering temperature in the sintering step S03 is preferably 0.15 minutes or more, and more preferably 0.5 minutes or more. On the other hand, the upper limit of the holding time at the sintering temperature in the sintering step S03 is preferably 5 minutes or less, and more preferably 3 minutes or less.

Further, when the pressurizing load in the sintering step S03 is less than 20 MPa, the density does not increase and the resistance of the thermoelectric conversion material may increase.
On the other hand, if the pressurized load in the sintering step S03 exceeds 50 MPa, the life of the carbon mold used for producing the sintered body may be shortened, or the carbon mold may be damaged in some cases.
Therefore, in the present embodiment, the pressurizing load in the sintering step S03 is set within the range of 20 MPa or more and 50 MPa or less.
The lower limit of the pressurizing load in the sintering step S03 is preferably 20 MPa or more, and more preferably 25 MPa or more. On the other hand, the upper limit of the pressurizing load in the sintering step S03 is preferably 50 MPa or less, and more preferably 40 MPa or less.

The thermoelectric conversion material 11 according to the present embodiment is manufactured by the above steps.

According to the thermoelectric conversion material 11 of the present embodiment having the above configuration, aluminum is contained in the range of 0.3 mass% or more and 3 mass% or less, and titanium oxide is contained in the range of 1 mass% or more and 10 mass% or less. Since it is contained within the range, aluminum and titanium oxide can suppress the invasion of oxygen in the atmosphere into the inside of magnesium silicide, thereby suppressing the decomposition of magnesium silicide and when used under high temperature conditions. I think we were able to improve the durability of. Further, it is considered that Al dispersed in magnesium silicide and Ti generated by decomposition of a part of titanium oxide are preferentially oxidized on the surface in contact with the outside air to prevent the progress of oxidation.

Further, according to the thermoelectric conversion material 11 of the present embodiment, the composition contains a dopant, specifically, Mg ₂ Si contains antimony in the range of 0.1 at% or more and 2.0 at% or less. Therefore, it can be suitably used as an n-type thermoelectric conversion material having a high carrier density.

Further, according to the method for producing a thermoelectric conversion material according to the present embodiment, aluminum powder and titanium oxide powder are mixed with magnesium silicide powder, and the content of aluminum powder is in the range of 0.3 mass% or more and 3 mass% or less. Since the sintered raw material powder forming step S02 for obtaining the sintered raw material powder having the titanium oxide powder content in the range of 1 mass% or more and 10 mass% or less is provided, the sintered magnesium is provided. It is possible to obtain a sintered body in which Al and Ti generated by decomposition of a part of titanium oxide are dispersed in the grains of silicide, and aluminum and titanium oxide are unevenly distributed at the grain boundaries.

Although the embodiments of the present invention have been described above, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the invention.
For example, in the present embodiment, it has been described as constituting a thermoelectric conversion element having a structure as shown in FIG. 1, but the present invention is not limited to this, and if the thermoelectric conversion material of the present invention is used, the metallized layer is used. There are no particular restrictions on the structure and arrangement of the electrodes.

Further, in the present embodiment, the sintering is performed using the sintering device (electric current sintering device 100) shown in FIG. 3, but the present invention is not limited to this, and the sintering raw material is indirectly used. A method of pressurizing and sintering while heating, for example, hot pressing, HIP, or the like may be used.

Further, in the present embodiment, the powder of magnesium silicide to which antimony (Sb) is added as a dopant is described as being used as a sintering raw material, but the present invention is not limited to this, and for example, Li, Na, K, B. , Al, Ga, In, N, P, As, Bi, Ag, Cu, Y may contain one or more selected as a dopant, or these elements in addition to Sb. May include.

Further, in addition to the magnesium silicide powder, a silicon oxide powder may be mixed. As the silicon oxide, SiOx (x = 1 to 2) such as amorphous SiO ₂ , cristobalite, quartz, tridymite, coesite, stationobite, tridymite, and shocked quartz can be used. The mixing amount of the silicon oxide is in the range of 0.5 mol% or more and 13.0 mol% or less. More preferably, it is 0.7 mol% or more and 7 mol% or less. The silicon oxide may be in the form of a powder having a particle size of 0.5 μm or more and 100 μm or less.

Hereinafter, the results of experiments carried out to confirm the effects of the present invention will be described.

Mg with a purity of 99.9% (particle size 180 μm: manufactured by High Purity Chemical Laboratory Co., Ltd.), Si with a purity of 99.99% (particle size 300 μm: manufactured by High Purity Chemical Laboratory Co., Ltd.), purity 99.9% Sb (particle size 300 μm: manufactured by High Purity Chemical Laboratory Co., Ltd.) was weighed. These powders were mixed well in a mortar, placed in an alumina crucible and heated at 850 ° C. for ₂ hours in Ar-5% H2. Considering the deviation from the stoichiometric composition of Mg: Si = 2: 1 due to the sublimation of Mg, Mg was mixed in an amount of 5 at% more. As a result, massive magnesium silicide (Mg ₂ Si) containing 1 at% of the dopant Sb was obtained.
Next, this massive magnesium silicide (Mg ₂ Si) was finely crushed in a milk pot and classified to obtain magnesium silicide powder (Mg ₂ Si powder) having an average particle size of 30 μm.

Further, magnesium silicide powder, aluminum powder (Al powder manufactured by High Purity Chemical Co., Ltd., average particle size 3 μm) and titanium oxide powder (TiO ₂ , manufactured by High Purity Chemical Co., Ltd., average particle size 2 μm) are mixed and sintered raw material powder. Got

The obtained sintered raw material powder was filled in a carbon mold whose inside was covered with a carbon sheet. Then, the sintering device (energized sintering device 100) shown in FIG. 3 was used for current-carrying sintering under the conditions shown in Table 1.

The obtained thermoelectric conversion material was evaluated for aluminum content, titanium oxide content, durability when used under high temperature conditions, and thermoelectric conversion characteristics by the following procedure.

(Aluminum and titanium oxide content)
A measurement sample was taken from the obtained thermoelectric conversion material, and the amount of Al was measured by a fluorescent X-ray analysis method (scanning type fluorescent X-ray analyzer ZSX PrimusII manufactured by Rigaku Corporation).
In addition, the amount of Ti was measured by a fluorescent X-ray analysis method. The titanium oxide content was calculated assuming that the total amount of Ti measured was TiO ₂ . The measurement results are shown in Table 1.

(Durability when used under high temperature conditions)
A sample was cut out from the sintered thermoelectric conversion material so as to have a size of 3 mm × 3 mm × 2 mmt with a diamond band saw, and one side of 3 mm × 3 mm was mirror-polished using abrasive paper (# 1000, # 2000). The thermoelectric conversion material was charged into the furnace, the pressure was reduced to 1.3 kPa or less, and then Ar gas was introduced so as to be 11.3 kPa. Under this atmosphere (11.3 kPa), the temperature rising and falling from room temperature to 550 ° C. was repeated twice.
The thermoelectric conversion material taken out from the furnace was evaluated for the film thickness of MgO formed on the surface layer by XPS analysis (PHI5000 VersaProbe II manufactured by ULVAC-PHI). The film thickness of MgO was calculated from the sputtering time until the oxygen intensity became 1/2 of the outermost surface. The evaluation results are shown in Table 1.

(Thermoelectric characteristics)
For the thermoelectric characteristics, a 4 mm × 4 mm × 15 mm rectangular parallelepiped is cut out from the sintered thermoelectric conversion material, and the power factor (PF) of each sample at 550 ° C is determined using a thermoelectric characteristic evaluation device (ZEM-3 manufactured by Advanced Riko). I asked.

In Comparative Example 1 in which aluminum and titanium oxide were not added, Comparative Example 2 in which the amount of aluminum added was less than the range of the present invention, and Comparative Example 4 in which the amount of titanium oxide added was less than the range of the present invention. The thickness of the oxide film after the temperature rise and fall became relatively thick, and the durability when used under high temperature conditions was insufficient.
In Comparative Example 3 in which the amount of aluminum added was larger than the range of the present invention and Comparative Example 5 in which the amount of titanium oxide added was larger than the range of the present invention, the PF was low and the thermoelectric characteristics were insufficient. ..

On the other hand, in Examples 1-3, 6, 8-10 of the present invention in which the amount of aluminum added and the amount of titanium oxide added were within the range of the present invention, the thickness of the oxide film after the temperature was raised and lowered. It was thin and had sufficient durability when used under high temperature conditions. In addition, the PF was high and the thermoelectric characteristics were excellent.

From the above, it was confirmed that according to the example of the present invention, it is possible to provide a thermoelectric conversion material having excellent durability when used under high temperature conditions.

Claims (3)

It is a thermoelectric conversion material composed of a sintered body containing magnesium silicide as a main component.
A thermoelectric conversion material containing aluminum in the range of 0.3 mass% or more and 1.0 mass% or less, and titanium oxide in the range of 1.5 mass% or more and 9.5 mass% or less. .. Claims comprising, as a dopant, one or more selected from Li, Na, K, B, Al, Ga, In, N, P, As, Sb, Bi, Ag, Cu, Y. Item 1. The thermoelectric conversion material according to Item 1. It is a method for manufacturing a thermoelectric conversion material composed of a sintered body containing magnesium silicide as a main component.
In the raw material powder containing Mg and Si, the aluminum powder should be in the range of 0.3 mass% or more and 1.0 mass% or less, and the titanium oxide powder should be in the range of 1.5 mass% or more and 9.5 mass% or less. Sintered raw material powder forming process to obtain sintered raw material powder by mixing,
It is provided with a sintering step of forming a sintered body by heating while pressurizing the sintered raw material powder.
The average particle size of the raw material powder containing Mg and Si is within the range of 0.5 μm or more and 100 μm or less.
A method for producing a thermoelectric conversion material, wherein the sintering temperature in the sintering step is in the range of 800 ° C. or higher and 1020 ° C. or lower.

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