JP2017050325A - Thermoelectric transducer and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoelectric transducer excellent in long-term high-temperature durability and a manufacturing method therefor.SOLUTION: A thermoelectric transducer includes a thermoelectric conversion part and is covered with oxide crystallized glass.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thermoelectric conversion element excellent in high temperature durability and a method for producing the same.

  A thermoelectric conversion element has a function of converting thermal energy into electric energy using a temperature difference, and is formed by using a thermoelectric conversion material as a thermoelectric conversion portion and having electrode portions at both ends thereof. Or what is produced by installing two or more is a thermoelectric conversion module.

  Thermoelectric conversion elements and thermoelectric conversion materials used therefor have been researched and developed for a long time, and for example, bismuth tellurium, lead tellurium, zinc antimonide and the like are known. However, these materials are a hindrance to practical use because they contain harmful elements and rare elements.

  In recent years, silicide-based compounds having excellent characteristics such as high conversion efficiency and low environmental load, particularly polycrystalline magnesium silicide (collectively including those containing and not containing a doping element) have attracted particular attention. (For example, see Patent Document 1 and Patent Document 2)

JP 2011-029632 A International Publication No. 2014/084163

  Thermoelectric conversion elements are required to have various thermoelectric conversion characteristics including dimensionless figure of merit (ZT), but long-term high-temperature durability is required for practical use. For many thermoelectric conversion elements using various thermoelectric conversion materials such as polycrystalline magnesium silicide, the type of dopant to be included is selected to improve the high temperature durability. Since long-term high-temperature durability is insufficient in a high-temperature region of about 0 ° C., improvement in durability is required.

  The object of the present invention is to solve the above problems and to provide a thermoelectric conversion element excellent in long-term high-temperature durability and a method for producing the same.

The inventors of the present invention used polycrystalline magnesium silicide, which is a representative material for the thermoelectric conversion part, as a sample in which the sintered body is doped with 0.5 at% of antimony and heated to about 600 ° C. in an air atmosphere. And observed at each of 10 hours, 100 hours, and 1000 hours. As a result, it was confirmed that the oxygen concentration on the surface of the sintered body was high, and it was found that black grains were formed on the entire surface starting from the grain boundary during sintering, and oxidation progressed. For this reason, it recognized that it was necessary to protect the surface of a thermoelectric conversion part.
In order to solve the above problems, the present inventors have conducted extensive research, and as a result, can develop an oxide crystallized glass that can prevent oxidation even at high temperatures and does not generate voids or cracks. Invented the invention. Specifically, the present invention is as the following (C1) to (C16).

(C1) A thermoelectric conversion element including a thermoelectric conversion part, wherein the thermoelectric conversion part is covered with oxide crystallized glass.
(C2) and the thermal expansion coefficient of the thermoelectric conversion portion, a thermal expansion coefficient of the oxide crystallized glass ^{0.5 × 10 -5 /K~2.0×10 -5 / K} , and the thermoelectric conversion portion The thermoelectric conversion element according to (C1), wherein the difference between the thermal expansion coefficient and the thermal expansion coefficient of the oxide crystallized glass is 0.5 × 10 ⁻⁵ / K or less.
(C3) The oxide crystallized glass contains a glass phase and a crystal phase, and the glass phase contains the following metal oxides (1), (2) and (3) (C1) or (C2) Thermoelectric conversion element.
(1) At least one oxide of an alkali metal element selected from Na and K (2) At least one oxide of an alkaline earth metal element selected from Mg, Ca, Sr and Ba (3) Si Oxide (C4) The thermoelectric conversion element of (C3), wherein the glass phase further contains the following metal oxide of (4).
(4) At least one kind of metal element oxide selected from Al, B and Zn (C5) The oxide crystallized glass has a glass phase of Na ₂ O, K ₂ O, CaO, Al ₂ O ₃ and SiO. _The thermoelectric conversion element of (C3) or (C4) containing the silicate crystal phase containing ₂ and a crystal phase containing an alkali metal oxide and / or an alkaline-earth metal oxide.
(C6) The thermoelectric conversion element according to any one of (C1) to (C6), wherein the thickness of the oxide crystallized glass is 20 to 150 μm.
(C7) The thermoelectric conversion element according to any one of (C1) to (C6), wherein the thermoelectric conversion part contains polycrystalline magnesium silicide.
(C8) A thermoelectric conversion module including the thermoelectric conversion element according to any one of (C1) to (C7).
(C9) A thermoelectric conversion member constituting the thermoelectric conversion element of any one of (C1) to (C7) and covered with a film of oxide crystallized glass.
(C10) a step of immersing the thermoelectric conversion part in a slurry containing oxide glass powder, a step of firing the thermoelectric conversion part coated with the slurry,
The manufacturing method of a thermoelectric conversion element provided with the thermoelectric conversion part coat | covered with the oxide crystallized glass containing.
(C11) The oxide glass powder is at least one oxide of an alkali metal element selected from Na and K, and at least one oxide of an alkaline earth metal element selected from Mg, Ca, Sr and Ba. The manufacturing method of the thermoelectric conversion element of (C10) containing the metal oxide which is an oxide of seed | species and Si.
(C12) The method for producing a thermoelectric conversion element according to (C11), wherein the composition of the metal oxide is the following (1a), (2a), or (3a).
(1a) 10 to 20% of _Na 2 O, 10~20mol% of _K 2 O, 5~15mol% of CaO, 5 to 15 mol% of _Al 2 _{O 3} and 40～70Mol% of SiO ₂
(2a) 15 to 25% of _Na 2 O, _5~15mol% of _K 2 O, _5~15mol% of CaO, 2.5~7.5mol% of _Al 2 _{O 3} and 50～60Mol% of SiO ₂
(3a) 15 to 25% of _Na 2 O, 5~15mol% of _{K 2} O, SiO 2 of 5 to 15 mol% of CaO and 55～65Mol%
(C13) The thermoelectric conversion element according to any one of (C10) to (C12), wherein the concentration of the oxide glass powder in the slurry is 45 to 60% by mass and the average particle diameter of the oxide glass powder is 3 to 15 μm. Production method.
(C14) The method for producing a thermoelectric conversion element according to any one of (C10) to (C13), wherein a speed at which the thermoelectric conversion part immersed in the slurry is pulled up from the slurry is 5 to 25 mm / second.
(C15) In the step of firing the thermoelectric conversion part, the temperature is increased at a rate of 5 to 15 ° C./minute, and after baking at 650 to 750 ° C. for 50 to 70 minutes, the temperature is decreased at a rate of 1 to 5 ° C./minute. The manufacturing method of the thermoelectric conversion element in any one of (C10)-(C14).
(C16) An oxide glass that covers a thermoelectric conversion portion, which includes a metal oxide having the following composition (1a), (2a), or (3a).
(1a) 10 to 20% of _Na 2 O, 10~20mol% of _K 2 O, 5~15mol% of CaO, 5 to 15 mol% of _Al 2 _{O 3} and 40～70Mol% of SiO ₂
(2a) 15 to 25% of _Na 2 O, _5~15mol% of _K 2 O, _5~15mol% of CaO, 2.5~7.5mol% of _Al 2 _{O 3} and 50～60Mol% of SiO ₂
(3a) 15 to 25% of _Na 2 O, 5~15mol% of _{K 2} O, SiO 2 of 5 to 15 mol% of CaO and 55～65Mol%

  ADVANTAGE OF THE INVENTION According to this invention, the thermoelectric conversion element excellent in long-term high temperature durability and its manufacturing method can be provided.

(A) It is the schematic which shows the external appearance of a thermoelectric conversion element, (b) It is the schematic which shows the external appearance of a thermoelectric conversion module. The composition is an X-ray diffraction (XRD) curves after firing of 20 mol% of _Na 2 O, 10mol% of _K 2 O, 10mol% of CaO and 60 mol% of the oxide glass composed of SiO _2. Composition is an XRD curves after firing of 20 mol% of _Na 2 O, 10mol% of _K 2 O, 10mol% of CaO, 5 mol% of _Al 2 _{O 3} and 55 mol% of the oxide glass composed of SiO _2. Composition is an XRD curves after firing of 15 mol% of _Na 2 O, 15mol% of _K 2 O, 10mol% of CaO, 10 mol% of _Al 2 _{O 3} and 50 mol% of the oxide glass composed of SiO _2. It is a figure which shows the XRD measurement result of the coating sample using the oxide glass shown in FIG. 4, and a glass baking sample. It is a figure which shows the thermal expansion curve of the sintered compact of the oxide glass (annealed glass) shown in FIG. 4, a glass baking sample (oxide crystallized glass), and a polycrystalline magnesium silicide.

  Embodiments of the present invention will be described below. In addition, this invention is not limitedly interpreted by the following embodiment.

  This invention is a thermoelectric conversion element provided with the thermoelectric conversion part, Comprising: The thermoelectric conversion part is a thermoelectric conversion element coat | covered with the oxide crystallized glass.

  FIG. 1A is a schematic diagram illustrating an external appearance of a thermoelectric conversion element, and FIG. 1B is a schematic diagram illustrating an external appearance of a thermoelectric conversion module. The thermoelectric conversion element 3 includes a thermoelectric conversion portion 1 and an end portion 2 covered with oxide crystallized glass.

  The thermoelectric conversion material used for the thermoelectric conversion part 1 is not particularly limited, and includes conventionally known bismuth / tellurium, lead / tellurium, zinc / antimonide, magnesium silicide, manganese silicide, iron silicide, barium gallium. Silicide-based materials such as silicide, half-Heusler-based materials, filled skutterudide-based materials, carbon-based materials such as carbon nanotubes, and organic polymer-based materials such as polyaniline and polythiophene are applicable. Among these, polycrystalline magnesium silicide is a particularly preferable material because of its high conversion efficiency and long-term durability provided by coating with oxide crystallized glass.

  The shape of the thermoelectric conversion part is not particularly limited, and for example, it may be a columnar body as shown in FIG. The columnar body includes a prismatic body such as a triangular pillar, a quadrangular pillar, and a hexagonal pillar, a cylinder, an elliptical pillar, and the like.

  The production method of the thermoelectric conversion material used for the thermoelectric conversion part 1 is not specifically limited. For example, in the case of using polycrystalline magnesium silicide, as described in Patent Document 1, approximately stoichiometric proportions of magnesium and silicon can be used, if necessary, a kind of about 0.1 to 2.0 at%. The above dopant elements (for example, Sb, Bi, Al, Zn, Sn, Ta, etc.) are mixed, the mixture is heated and reacted at a temperature at which all raw materials are melted, and then gradually cooled. The ingot B is obtained by subjecting the particles formed by pulverizing the obtained ingot A to spark plasma sintering. The ingot B can be cut into a columnar body of a predetermined size using a wire saw or the like and used as a thermoelectric conversion member of a thermoelectric conversion element. Moreover, when the ingot A is a homogeneous thing with few voids etc., a columnar body can be directly cut out from the ingot A, and it can also be set as a thermoelectric conversion member.

  The end 2 preferably functions as an electrode layer, and may be configured using, for example, metal silicide or a metal material, and is preferably configured of a material having low contact resistance with the thermoelectric conversion unit 1.

  The method of providing the end 2 in the thermoelectric conversion unit 1 is not limited. For example, after the metal particles constituting the end 2 are stacked on both sides of the pulverized particle aggregate of the ingot A accommodated in the sintering apparatus, The ingot C is manufactured by sintering integrally, and is cut into a columnar shape, and can be manufactured as the thermoelectric conversion element 3 provided with the thermoelectric conversion portion 1 and the end portion 2. Moreover, the oxide crystallized glass on the end side of the columnar body coated with oxide crystallized glass is dip-coated in the slurry by a method in which the glass powder film does not adhere to the end side of the columnar body which is the thermoelectric conversion part There are also methods such as removing conductive material and applying a conductive paste thereto, or depositing a conductive material.

  In addition, a thermoelectric conversion element having the thermoelectric conversion portion 1 and the end portion 2 is prepared in advance by the above-described integrated sintering method, and is immersed in an oxide glass powder slurry to be described later, or uniformly applied by spray coating or the like and fired. By doing so, the thermoelectric conversion element 3 having the thermoelectric conversion portion 1 and the end portion 2 which is covered with the oxide crystallized glass can be produced.

The oxide crystallized glass covering the thermoelectric conversion part 1 is excellent in heat resistance, and protects the surface of the thermoelectric conversion part 1 by covering the thermoelectric conversion part 1. The present inventors have focused on crystallized glass having the same thermal expansion coefficient as that of the above-mentioned sintered body, and found that oxidation can be prevented by coating the periphery of the thermoelectric conversion part with the crystallized glass. .
Crystallized glass is obtained by crystallizing glass and consists of a crystal phase and a glass phase. “Oxide” in the oxide crystallized glass means that the glass does not contain a halogen element or a chalcogen element as an anion.

  The thermal expansion coefficient of the material of the thermoelectric conversion part, for example, magnesium silicide, is generally relatively large compared to a highly stable silicate-based oxide glass. On the other hand, when the oxide glass has a composition capable of increasing the thermal expansion coefficient, there is a problem that the softening temperature is lowered and the shape cannot be maintained at a high temperature. Moreover, there exists a problem that chemical durability (especially water resistance) and intensity | strength fall. Furthermore, since glass is a metastable phase, depending on the composition, it may gradually crystallize when used at a high temperature and for a long time, causing cracks and peeling. In addition, when a high-temperature and long-time coating process is required, there is a possibility of adverse effects such as deterioration on thermoelectric element members and electrodes. In order to solve these problems, the present inventors proceeded with softening and sintering (densification) during the heat treatment of the coating, and at the same time produced crystals (high-temperature stable phase) to produce crystallized glass, which was densified. The present inventors have found an oxide crystallized glass capable of simultaneously achieving a thermal expansion coefficient, high-temperature stability (preventing deformation, cracking and peeling due to softening and crystallization), chemical durability, and high strength.

  The film thickness of the oxide crystallized glass is preferably 20 to 150 μm, and more preferably 40 to 100 μm. It is preferable that the oxide crystallized glass film has a thickness of 150 μm or less because peeling hardly occurs.

The thermal expansion coefficient of the oxide crystallized glass, the thermal expansion coefficient of the thermoelectric conversion unit 1, preferably from ^{0.5 × 10 -5 /K~2.0×10 -5 / K} , 1.3 × and more preferably ^{10 -5 /K~1.8×10} -5 / K. The difference between the thermal expansion coefficient of the oxide crystallized glass and the thermal expansion coefficient of the thermoelectric conversion part is preferably as small as possible, preferably 0.5 × 10 ⁻⁵ / K or less, and 0.3 × 10 6. More preferably, it is ⁻⁵ / K or less. Since the difference in thermal expansion coefficient is small, voids and cracks are hardly generated in the crystallized glass, and the long-term durability of the thermoelectric conversion element 3 is further improved.

The oxide crystallized glass is preferably produced as follows so that the thermal expansion coefficient is substantially the same as that of the thermoelectric conversion part 1. That is, the oxide crystallized glass is composed of a crystal phase precipitated by heat treatment from the mother glass and a glass phase due to the remaining components, and the mother glass phase is composed of a plurality of metal oxides selected from the metal oxide group described later. However, since each of the plurality of metal oxides has an individual coefficient factor (αi), the coefficient of thermal expansion of the thermoelectric conversion member is approximately the same value using the following Appen equation (1). Thus, while changing the composition (mol%), the thermal expansion coefficient (α) of the oxide crystallized glass can be estimated to determine the prescription of the oxide glass that is the mother glass.
α = 0.1 × Σαipi Formula (1)
(Αi: coefficient factor, pi: composition (mol%), 0 ≦ pi ≦ 100)

  The main component of the metal oxide used for producing the oxide glass in the present invention is (1) at least one alkali metal element oxide selected from Na and K, (2) Mg, Ca, Sr and At least one oxide of an alkaline earth metal element selected from Ba, and (3) an oxide of Si, and (4) an oxide of a metal element selected from Al, B and Zn as an optional component It is preferable that there is at least one.

In the oxide crystallized glass, the glass phase contains Na ₂ O, K ₂ O, CaO, Al ₂ O ₃ and SiO ₂ , and the crystal phase contains an alkali metal oxide and / or an alkaline earth metal oxide. It is preferable to contain the containing silicate crystal phase. Examples of the silicate crystal phase containing an alkali metal oxide and / or an alkaline earth metal oxide include feldspar containing anorthite and calcilite.

  Based on the prescription determined using Appen's formula (1), the oxide glass is a mixture of metal oxides selected from the groups (1) to (4) described above in a predetermined blending ratio. Oxide glass powder can be produced by pulverizing the rapidly cooled glass after melting the mixture. It is also a preferred embodiment that the rapidly cooled glass is further gradually cooled (the glass obtained by the slow cooling is referred to as gradually cooled glass), and the slowly cooled glass is pulverized to produce an oxide glass powder.

The composition of the oxide glass is preferably any of the following (1a), (2a) or (3a).
(1a) 10 to 20% of _Na 2 O, 10~20mol% of _K 2 O, 5~15mol% of CaO, 5 to 15 mol% of _Al 2 _{O 3} and 40～70Mol% of SiO ₂
(2a) 15 to 25% the _Na 2 O, _5~15mol% for _K 2 O, _5~15mol% for CaO, 2.5~7.5mol% for _Al 2 _{O 3} and 50～60Mol% for SiO ₂
(3a) 15 to 25% of _Na 2 O, _5~15mol% of _K 2 O, _5~15mol% of CaO and 55～65Mol% of SiO ₂

Specific examples of the composition of the oxide glass include the following.
(1a-1) 15 mol% Na ₂ O, 15 mol% K ₂ O, 10 mol% CaO, 10 mol% Al ₂ O ₃ and 50 mol% SiO ₂ (FIG. 4 shows the XRD curve of the glass fired sample. Show).
(2a-1) consisting of 20 mol% Na ₂ O, 10 mol% K ₂ O, 10 mol% CaO, 5 mol% Al ₂ O ₃ and 55 mol% SiO ₂ (FIG. 3 shows the XRD curve of the glass fired sample. Show).
(3a-1) 20 mol% Na ₂ O, 10 mol% K ₂ O, 10 mol% CaO, 60 mol% SiO ₂ (FIG. 2 shows the XRD curve of the glass fired sample).

  Next, after the columnar body that is the thermoelectric conversion member is immersed in the slurry containing the powder, the columnar body that is the object to be coated can be formed on the surface of the columnar body that is the object to be coated. That is, the present invention is coated with an oxide crystallized glass including a step of immersing a thermoelectric conversion unit in a slurry containing oxide glass powder and a step of firing the thermoelectric conversion unit coated with the slurry. It is a manufacturing method of a thermoelectric conversion element provided with a thermoelectric conversion part.

  The oxide glass powder includes at least one oxide of an alkali metal element selected from Na and K, at least one oxide of an alkaline earth metal element selected from Mg, Ca, Sr and Ba, and Si. It is preferable that the metal oxide which is an oxide of this is included.

The slurry to be used is preferably a slurry (glass slurry) in which an oxide glass powder having an average particle size of about 3 to 15 μm is dispersed in ethanol or the like. As will be described later, the concentration of the oxide glass powder in the slurry is determined by the balance with the pulling speed of the columnar body as the thermoelectric conversion unit 1 from the slurry, but is preferably about 45 to 60% by mass, and about 50 to 50% by mass. 55 mass% is more preferable.
If dip coating (dip coating) is performed in a state where the dispersibility of the oxide glass powder in the slurry is good, the glass powder tends to adhere to the surface of the thermoelectric conversion part, and the adhesion becomes uniform and is formed after firing. Since the adhesion of a film made of crystallized glass tends to be improved, it is preferable to improve the dispersion state using ultrasonic waves or the like. Moreover, it is preferable to use it as soon as possible after slurry preparation, and also a dispersing agent can be contained in order to prevent sedimentation of the glass powder.

In order to form a desired oxide crystallized glass film, it is important that the thickness and density of the glass powder adhering to the surface of the thermoelectric conversion part be as uniform as possible, which is the immersion time in the slurry. The pulling speed of the columnar body that is the thermoelectric conversion part from the slurry is greatly affected.
The immersion is preferably performed in a short time of about 1.0 second. This is because if the immersion time is increased, the settling of the glass particles proceeds and the homogeneity is adversely affected. It is important that the pulling speed is constant, 5 to 25 mm / second is preferable, and 15 to 20 mm / second is more preferable. If the pulling speed is 25 mm / second or less, the film made of the adhering glass particles becomes thin, but the crystallized glass film finally formed is hardly cracked, and the crystallized glass film peels off from the thermoelectric conversion part. It tends to be difficult. Further, when the pulling speed is 5 mm / second or more, the film thickness tends to increase or the amount of adhesion tends to increase, and the productivity during mass production tends to increase.

  After pulling up from the slurry, the columnar body as the thermoelectric conversion part is dried in the atmosphere for about 10 minutes, and then fired. Firing is performed at a rate of about 5 to 15 ° C./min in a vacuum of 5 to 20 Pa, and after firing at 650 to 750 ° C. for 50 to 70 minutes, the temperature is lowered at a rate of 1 to 5 ° C./min. Is preferred. At such a temperature lowering rate, residual strain hardly remains, cracks do not easily occur in the crystallized glass film, and the crystallized glass film tends not to peel from the thermoelectric conversion part. Thereby, the columnar body which is a thermoelectric conversion part coat | covered with the oxide crystallized glass used as a thermoelectric conversion element is formed.

Presence of a crystal phase is recognized in the oxide crystallized glass formed by firing. Due to the small difference in coefficient of thermal expansion between the oxide crystallized glass with crystal phase and the slow-cooled glass and the thermoelectric conversion part, the desired high oxidation resistance and high temperature durability are achieved. The present inventors infer that.
Further, even when the columnar body, which is the thermoelectric conversion part coated with the oxide crystallized glass of the present invention, is exposed to a temperature higher than about 600 ° C. in the operating region for a long time, the coating does not crack or peel off and is resistant to oxidation. It is a high temperature durable coating.

  The columnar body which is the thermoelectric conversion part 1 covered with the oxide crystallized glass described above is provided with an end 2 as an electrode layer as shown in FIG. Since current can be taken out also from the side, the thermoelectric conversion part 1 itself that is a columnar body can function as the thermoelectric conversion element 3 without providing the end part 2 that is an electrode part. Therefore, in the present invention, the thermoelectric conversion part 1 itself coated with the oxide crystallized glass can be referred to as a thermoelectric conversion element. However, in order to take out an electric current efficiently, it is preferable to provide the edge part 2 which is an electrode part separately depending on the material of the columnar body which is a thermoelectric conversion part.

  FIG. 1B is a schematic diagram showing the appearance of the thermoelectric conversion module. As shown in FIG. 1B, in the thermoelectric conversion module 5, the thermoelectric conversion element 3 is connected to another thermoelectric conversion element 3 by a connection wiring 4. The thermoelectric conversion module 5 can achieve high output by connecting a plurality of thermoelectric conversion elements 3.

  The thermoelectric conversion module 5 prepares a plurality of thermoelectric conversion elements 3 each having a thermoelectric conversion part 1 and an end 2 in advance, and immerses a structure in which the plurality of thermoelectric conversion elements 3 are sandwiched between electrode plates in a glass powder slurry or sprays them. A thermoelectric conversion module coated with oxide crystallized glass can be produced by uniformly applying and baking by coating or the like.

  Next, the present invention will be described based on examples. In addition, this invention is not limited at all by this Example.

Example 1
<Coefficient of thermal expansion, estimated value and prescription of oxide glass>
Na ₂ O, K ₂ O, CaO, Al ₂ O ₃ , SiO ₂ are selected as the metal oxides constituting the oxide glass to be produced, and the coefficient factors of these metal oxides (Appen's formula described above) Α _i ) in Na ₂ O: 39.5, K ₂ O: 42.0, CaO: 13, Al ₂ O ₃ : -3.0, SiO ₂ : 3.8, the thermal expansion coefficient of the oxide glass When the estimated value was calculated, it was 1.51 × 10 ⁻⁵ / K, which was close to 1.6 × 10 ⁻⁵ / K, which is the thermal expansion coefficient value of polycrystalline magnesium silicide in the thermoelectric conversion part.
Thus obtained, the formulation of the oxide glass is _{15Na 2 O-15K 2 O-} 10CaO-10Al 2 O 3 -50SiO 2 (mol%).

<Preparation of oxide glass powder _{(15Na 2 O-15K 2 O} -10CaO-10Al 2 O 3 -50SiO 2 (mol%))>
Na ₂ CO ₃ (15 mol%), K ₂ CO ₃ (15 mol%), CaCO ₃ (10 mol%), Al ₂ O ₃ (10 mol%) and SiO ₂ (50 mol%) were dry mixed and then 1400 ° C. in the atmosphere. The glass was melted for 60 minutes, rapidly cooled, immediately held at 600 ° C. for 60 minutes, and then gradually cooled to 100 ° C. at a rate of 1 ° C./min to produce a slowly cooled glass.
The slowly cooled glass is pulverized and classified using a sieve through which particles of 45 μm can pass, and then wet-pulverized using an agate planetary ball mill (400 rpm, twice for 60 minutes) to obtain an average particle size of 10 μm. An oxide glass powder was obtained.

Various physical properties of the annealed glass were as follows.
Thermal expansion coefficient (measured with TMA): 1.5 × 10 ⁻⁵ / K (Mg ₂ Si sintered body: 1.6 × 10 ⁻⁵ / K)
Glass transition point (by thermal expansion measurement): 530 ° C
Sag point (by thermal expansion measurement): 584 ° C
Crystallization temperature (according to XRD measurement): 620 ° C.

<Preparation of glass powder and slurry>
The glass powder having an average particle size of 10 μm was dispersed in ethanol to prepare a slurry having a concentration of 48.7 to 50.3% by weight.

<Formation of oxide crystallized glass film by firing glass powder / slurry>
Cut out from a sintered body of magnesium silicide (doped with Sb (0.5 at%) and Zn (0.5 at%)) manufactured by Yasunaga Co., Ltd., 3 mm x 3 mm x 6 mm column for thermoelectric conversion part Prepared the body.
Using a dip coating apparatus equipped with a time control mechanism, the columnar body was immersed in the slurry for 1.0 second, then pulled up at a speed of 20 mm / second, and then dried at room temperature in air for 10 minutes. The temperature was raised to 700 ° C. at a rate of 10 ° C./min under a vacuum of 5 to 20 Pa, baked at 700 ° C. for 60 minutes, and then cooled at a rate of 2 ° C./min, and covered with oxide crystallized glass. A columnar body was prepared.

<Crystal phase formed in crystallized glass by firing>
When the annealed glass powder is fired at 700 ° C., a crystal phase is formed, and the thermal expansion coefficient of the crystallized crystal phase is generally larger than that of the glass phase. Therefore, the thermal expansion coefficient of the crystallized glass is larger than that of the annealed glass.
As described above, the crystallization temperature of the crystallized glass is 620 ° C. However, after heating for 1 hour at each of three points of 620 ° C., 650 ° C. and 700 ° C., as a result of XRD measurement, all of the crystal phases are It was confirmed to be calcilite (KAlSiO ₄ ).

<High-temperature durability test of crystallized glass>
Next, the columnar body covered with the oxide crystallized glass is heated in the air atmosphere at a heating rate of 10 ° C./min, heated at 700 ° C. for 1 hour, 700 ° C. for 100 hours, and 600 ° C. for 500 hours. Three cases were subjected to a high-temperature endurance test to examine crystallization behavior by XRD measurement and scanning electron microscope (SEM) observation, and the presence or absence of mutual diffusion by electron beam macroanalyzer (EPMA) analysis.
Also, as a reference sample, a bulk glass fired sample obtained by molding the above oxide glass powder and firing at 700 ° C. for 1 hour is prepared, and the comparative observation of the crystallization state and the thermal expansion coefficient are used for the measurement. did.

FIG. 5 shows the XRD measurement results. In the bulk glass fired sample, a peak considered to be Ca ₂ SiO ₄ was observed in addition to KAlSiO ₄ as a crystal phase, but in all three cases, the main crystal phase was only KAlSiO ₄ and Ca ₂ SiO ₄ was confirmed. In addition, in all three cases, no change in the crystallization state is observed, and it is assumed that they are almost the same.
Furthermore, according to the SEM observation results, the surface of the coating after the heat endurance test at 700 ° C. increased in surface roughness as the number of cycles increased, but no remarkable cracking or peeling was observed.
Furthermore, when the presence or absence of interdiffusion of elements was examined by EPMA observation, diffusion of constituent elements (Mg, Si, Na, K, Ca and Al) and O of magnesium silicide and oxide crystallized glass was confirmed. There wasn't. This indicates that the thermoelectric conversion part and the crystallized glass film are stable even in a high temperature region, and the oxidation resistance of the thermoelectric conversion part is improved because the glass film becomes a barrier against oxygen in the atmosphere.

FIG. 6 shows the thermal expansion curve of each sample used in the high temperature durability test. The thermal expansion coefficients (× 10 ⁻⁵ / K) of the glass fired sample, the Mg ₂ Si sintered body, and the slowly cooled glass were 1.8, 1.6, and 1.5, respectively.
The coating layer formed on the surface of the thermoelectric conversion member is composed of oxide crystallized glass in which KAlSiO ₄ as a main precipitated crystal phase and a glass phase are combined. The expansion coefficient could not be measured. However, as can be seen from the XRD chart in FIG. 2, many crystal phases (KAlSiO _{4 and} Ca ₂ SiO ₄ ) observed in the glass fired sample are not observed in the coating sample. Therefore, the value of the thermal expansion coefficient of the glass fired sample was assumed to be lower than 1.8, and the value of the coating layer was taken as the value of the coating layer.
Therefore, the difference in thermal expansion coefficient between the coating layer and the Mg ₂ Si sintered body is small, and as a result of a long-term durability test at 700 ° C., as described above, cracks, peeling, etc. do not occur and diffusion Also, the reason for not being observed is that “the difference in thermal expansion coefficient value is small”, and the coating layer functions extremely effectively as an oxidation resistant film.

(Example 2)
In the same manner as in Example 1, an oxide glass (annealed glass) was prepared based on the following composition determined by Appen's formula 1, and the thermoelectric film coated with oxide crystallized glass in the same process according to Example 1 A conversion member was obtained.
20 mol% of _Na 2 O, 10mol% of _K 2 O, 10mol% of CaO, 5 mol% of _Al 2 _{O 3} and 55 mol% of SiO ₂
An XRD measurement chart of the oxide crystallized glass is shown in FIG. About the thermoelectric conversion member coat | covered with the obtained oxide crystallized glass, as a result of performing the same test as an Example, it confirmed that high temperature durability was high.

Example 3
In the same manner as in Example 1, an oxide glass (annealed glass) was prepared based on the following composition determined by Appen's formula 1, and the thermoelectric film coated with oxide crystallized glass in the same process according to Example 1 A conversion member was obtained.
20 mol% of _Na 2 O, 10mol% of _K 2 O, 10mol% of CaO and 60 mol% of SiO _2.
An XRD measurement chart of the oxide crystallized glass is shown in FIG. About the thermoelectric conversion member coat | covered with the obtained oxide crystallized glass, as a result of performing the same test as an Example, it confirmed that high temperature durability was high.

<Function as thermoelectric conversion element>
Although the columnar body manufactured in Examples 1 to 3 and covered with crystallized glass is not provided with an electrode part again, current can be taken out from the end of the columnar body that is the thermoelectric conversion member. It was confirmed that the columnar body itself functions as a thermoelectric conversion element.
Moreover, it confirmed that the thermoelectric conversion module comprised by connecting the thermoelectric conversion element produced in Examples 1-3 also functions.

  DESCRIPTION OF SYMBOLS 1 ... Thermoelectric conversion part coat | covered with oxide crystallized glass, 2 ... End part, 3 ... Thermoelectric conversion element, 4 ... Connection wiring, 5 ... Thermoelectric conversion module.

Claims (16)

A thermoelectric conversion element including a thermoelectric conversion unit,
A thermoelectric conversion element in which the thermoelectric conversion part is covered with oxide crystallized glass. The thermal expansion coefficient of the thermoelectric conversion unit, and the thermal expansion coefficient of the oxide crystallized glass is ^{0.5 × 10 -5 /K~2.0×10 -5 / K} , and the thermoelectric conversion portion The thermoelectric conversion element of Claim 1 whose difference between a thermal expansion coefficient and the thermal expansion coefficient of the said oxide crystallized glass is 0.5 * 10 < ^-5 > / K or less. The thermoelectric conversion according to claim 1 or 2, wherein the oxide crystallized glass contains a glass phase and a crystal phase, and the glass phase contains the following metal oxides (1), (2) and (3). element.
(1) At least one oxide of an alkali metal element selected from Na and K (2) At least one oxide of an alkaline earth metal element selected from Mg, Ca, Sr and Ba (3) Si Oxides of The thermoelectric conversion element according to claim 3, wherein the glass phase further contains the following metal oxide (4).
(4) At least one metal element oxide selected from Al, B and Zn In the oxide crystallized glass, the glass phase contains Na ₂ O, K ₂ O, CaO, Al ₂ O ₃ and SiO ₂ , and the crystal phase is an alkali metal oxide and / or an alkaline earth metal. The thermoelectric conversion element of Claim 3 or 4 containing the silicate crystal phase containing an oxide.   The thermoelectric conversion element as described in any one of Claims 1 thru | or 5 whose film thickness of the said oxide crystallized glass is 20-150 micrometers.   The thermoelectric conversion element according to any one of claims 1 to 6, wherein the thermoelectric conversion portion contains polycrystalline magnesium silicide.   A thermoelectric conversion module provided with the thermoelectric conversion element as described in any one of Claims 1 thru | or 7.   The thermoelectric conversion member which comprises the thermoelectric conversion element as described in any one of Claims 1 thru | or 7, and was coat | covered with the film | membrane of oxide crystallized glass. A step of immersing the thermoelectric converter in a slurry containing oxide glass powder;
Firing the thermoelectric converter coated with the slurry;
The manufacturing method of a thermoelectric conversion element provided with the said thermoelectric conversion part coat | covered with the oxide crystallized glass containing.   The oxide glass powder includes (1) at least one alkali metal element oxide selected from Na and K, and (2) an alkaline earth metal element oxide selected from Mg, Ca, Sr and Ba. The manufacturing method of the thermoelectric conversion element of Claim 10 containing the metal oxide which is at least 1 sort (s) of (3), and the oxide of (3) Si. The manufacturing method of the thermoelectric conversion element of Claim 11 whose composition of the said metal oxide is the following (1a), (2a), or (3a).
(1a) 10 to 20% of _Na 2 O, 10~20mol% of _K 2 O, 5~15mol% of CaO, 5 to 15 mol% of _Al 2 _{O 3} and 40～70Mol% of SiO ₂
(2a) 15 to 25% of _Na 2 O, _5~15mol% of _K 2 O, _5~15mol% of CaO, 2.5~7.5mol% of _Al 2 _{O 3} and 50～60Mol% of SiO ₂
(3a) 15 to 25% of _Na 2 O, 5~15mol% of _{K 2} O, SiO 2 of 5 to 15 mol% of CaO and 55～65Mol%   The thermoelectric conversion according to any one of claims 10 to 12, wherein a concentration of the oxide glass powder in the slurry is 45 to 60% by mass, and an average particle diameter of the oxide glass powder is 3 to 15 µm. Device manufacturing method.   The manufacturing method of the thermoelectric conversion element as described in any one of Claims 10 thru | or 13 whose speed | rate which pulls up the said thermoelectric conversion part immersed in the said slurry from the said slurry is 5-25 mm / sec.   In the step of firing the thermoelectric converter, the temperature is increased at a rate of 5 to 15 ° C / minute, baked at 650 to 750 ° C for 50 to 70 minutes, and then the temperature is decreased at a rate of 1 to 5 ° C / minute. The manufacturing method of the thermoelectric conversion element as described in any one of 10 thru | or 14. The oxide glass which coat | covers the thermoelectric conversion part provided with the metal oxide which has a composition of following (1a) (2a) or (3a).
(1a) 10 to 20% of _Na 2 O, 10~20mol% of _K 2 O, 5~15mol% of CaO, 5 to 15 mol% of _Al 2 _{O 3} and 40～70Mol% of SiO ₂
(2a) 15 to 25% of _Na 2 O, _5~15mol% of _K 2 O, _5~15mol% of CaO, 2.5~7.5mol% of _Al 2 _{O 3} and 50～60Mol% of SiO ₂
(3a) 15 to 25% of _Na 2 O, 5~15mol% of _{K 2} O, SiO 2 of 5 to 15 mol% of CaO and 55～65Mol%

Images