JP2009289911A - Method of manufacturing thermoelectric semiconductor material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a thermoelectric semiconductor material by which the thermoelectric semiconductor material with high performance is obtained in high yield. <P>SOLUTION: The method of manufacturing the thermoelectric semiconductor material includes: a plate-shaped pulverized particle producing process S1 of obtaining plate-shaped pulverized particles each having a specified crystal surface of a raw material on a surface; a slurry preparing process S2 of preparing slurry containing ≥30% by volume of plate-shaped pulverized particles by mixing the obtained pulverized particles, a binder, and a dispersion medium; a molding process S3 of molding the obtained slurry into a tape shape to obtain a molding; a degreasing process S4 of heat-treating the obtained molding in an inert atmosphere to obtain a degreased body; a reducing process S5 of subjecting the obtained degreased body to a reduction treatment to obtain a decreased reduced body; a sintering process S6 of sintering the obtained degreased reduced body to obtain a sintered body; and a cutting process S7 of cutting the obtained sintered body to obtain the thermoelectric semiconductor material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a thermoelectric semiconductor material. More specifically, the present invention relates to a method for manufacturing a thermoelectric semiconductor material capable of obtaining a high performance thermoelectric semiconductor material with a high yield.

  The thermoelectric semiconductor material is a material that can be cooled by generating electric power directly from heat or by passing a current through the thermoelectric semiconductor itself. This thermoelectric semiconductor material has a simple structure, is easy to reduce in size and weight, operates silently and without vibration, and does not require maintenance. Application to various fields such as a temperature controller and a power generation device inside a semiconductor device is being studied.

  An example of such a thermoelectric semiconductor material is a sintered material in which bismuth telluride is oriented. As an orientation process of bismuth telluride used for such a thermoelectric semiconductor material, for example, hot plastic working by hot upset forging after sintering bismuth telluride has been proposed (for example, patent document). 1 and 2).

  In addition, a method for producing an oxide thermoelectric semiconductor material is proposed in which a plate-like raw material powder is slurried together with a binder and developed into a sheet shape of a level of 100 μm or less by a doctor blade method or the like where a shearing force is applied. (See Patent Document 3).

JP 2002-151751 A JP 2004-211125 A JP 2003-034576 A

  However, in the conventional method for producing a thermoelectric semiconductor material that performs the above-described hot plastic working, in order to increase the degree of orientation of the resulting thermoelectric semiconductor material, increasing the amount of plastic deformation during processing increases the residual stress, In the subsequent slicing processing and dicing processing, there was a problem that breakage due to cracks and cracks easily occurred. On the other hand, if the amount of plastic deformation at the time of processing is reduced, the degree of orientation is of course lowered, but the uniformity of the degree of orientation of the resulting thermoelectric semiconductor material is lowered, causing a decrease in yield. End up.

  Further, the manufacturing method of Patent Document 3 described above is a method for manufacturing an oxide thermoelectric semiconductor material, and is not suitable for manufacturing a thermoelectric semiconductor material that is vulnerable to oxidation, such as bismuth telluride, for example. In addition, the above-described bismuth telluride has a melting point of about 580 ° C., which is relatively low compared to other thermoelectric semiconductor materials, and is processed at a temperature lower than the melting point. There was a problem that the remaining amount was increased and the performance of the obtained thermoelectric semiconductor material was deteriorated.

  The present invention has been made in view of such problems of the prior art, and the problem is to provide a method for producing a thermoelectric semiconductor material capable of obtaining a high-performance thermoelectric element with a high yield. It is to provide.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have baked a molded body obtained by tape-forming a slurry containing plate-like pulverized particles obtained by pulverizing an ingot made of a raw material of a thermoelectric semiconductor material after a predetermined pretreatment step. The obtained sintered body is cut and processed to produce a thermoelectric semiconductor material, and it is found that the above problems can be achieved, and the present invention has been completed. It was.

  That is, according to the present invention, the following method for producing a thermoelectric semiconductor material is provided.

[1] A plate-like pulverized particle production step of obtaining a plate-like pulverized particle having a specific crystal plane of the raw material by pulverizing an ingot made of a thermoelectric semiconductor raw material and having a specific gravity of 5 or more; A slurry preparation step of mixing the obtained plate-like pulverized particles, a binder, and a dispersion medium to prepare a slurry in which the volume ratio of the plate-like pulverized particles is 30% by volume or more, and the obtained slurry A molding step for obtaining a molded body by molding into a tape shape; a degreasing step for obtaining a degreased body by heat-treating the obtained molded body in an inert atmosphere; and a reduction treatment for the obtained degreased body. A reduction process for obtaining a degreased reductant, a sintering process for obtaining a sintered body by sintering the obtained degreased reductant, and a cutting process for obtaining a thermoelectric semiconductor material by cutting the obtained sintered body And a method for producing a thermoelectric semiconductor material.

[2] The method for producing a thermoelectric semiconductor material according to [1], wherein at least tellurium and bismuth are used as the raw material.

[3] The method for producing a thermoelectric semiconductor material according to [1] or [2], wherein in the sintering step, the degreased reductant is sintered by hot pressing.

[4] The method for producing a thermoelectric semiconductor material according to any one of [1] to [3], wherein the plate-like pulverized particles are particles having a major axis of 20 to 70 μm and an aspect ratio of 3 to 20.

[5] The method for producing a thermoelectric semiconductor material according to any one of [1] to [4], wherein a substance having thermal gelation characteristics or thermosetting characteristics is used as the binder.

[6] In any one of the above [1] to [5], in the molding step, a plurality of the molded bodies molded into a tape shape are produced, and a plurality of the molded bodies are laminated to obtain a laminated body of the molded bodies. The manufacturing method of the thermoelectric-semiconductor material of description.

  According to the method for producing a thermoelectric semiconductor material of the present invention, a high-performance thermoelectric element can be obtained with a high yield. That is, the method for producing a thermoelectric semiconductor material of the present invention makes it possible to produce a thermoelectric semiconductor material having an orientation equivalent to or higher than that of a thermoelectric semiconductor material produced by conventional hot plastic working at a low cost. it can.

  Furthermore, since the thermoelectric semiconductor material manufacturing method of the present invention manufactures a thermoelectric semiconductor material without applying stress such as plastic deformation to the thermoelectric semiconductor material itself, residual stress (residual stress) is present in the obtained thermoelectric semiconductor material. In the subsequent slicing process and dicing process, damage due to cracks and cracks is unlikely to occur.

  Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings. However, the present invention is not limited to the following embodiment and does not depart from the spirit of the present invention. Therefore, it should be understood that design changes, improvements, and the like can be made as appropriate based on ordinary knowledge of those skilled in the art.

[1] Method for producing thermoelectric semiconductor material:
As shown in FIG. 1, the method for producing a thermoelectric semiconductor material of the present invention is a plate-like material comprising a thermoelectric semiconductor raw material, pulverizing an ingot having a specific gravity of 5 or more, and having a specific crystal plane of the raw material on the surface. The plate-like pulverized particle preparation step (S1) for obtaining plate-like pulverized particles, the obtained plate-like pulverized particles, a binder, and a dispersion medium are mixed, and the volume ratio of the plate-like pulverized particles is 30% by volume or more. A slurry preparation step (S2) for preparing a slurry to be formed, a molding step (S3) for forming the obtained slurry into a tape shape to obtain a molded body, and the obtained molded body is heat-treated in an inert atmosphere. A degreasing step (S4) for obtaining a degreased body, a reducing step (S5) for reducing the obtained degreased body to obtain a degreased reduced body, and a sintered body obtained by sintering the obtained degreased reduced body. Sintering step (S6) and cutting the obtained sintered body A cutting step to obtain a material (S7), a method of manufacturing a thermoelectric semiconductor material including.

  Here, FIG. 1 is a flowchart showing an embodiment of a method for producing a thermoelectric semiconductor material of the present invention.

  According to the method for manufacturing a thermoelectric semiconductor material of the present invention, a relatively high concentration (specifically, including plate-like pulverized particles having a specific crystal face of the raw material on the surface, obtained by pulverizing an ingot made of the raw material of the thermoelectric semiconductor material. Is the above-mentioned predetermined pretreatment step (degreasing step (S4)) in which a molded body obtained by molding a slurry having a volume ratio of plate-like pulverized particles of 30% by volume or more into a tape shape (hereinafter sometimes referred to as "tape molding"). ) And after the reduction step (S5)), a sintered body is obtained, and a thermoelectric semiconductor material can be produced by cutting the obtained sintered body. Conventional hot upset forging Thus, a high performance thermoelectric semiconductor material having an orientation comparable to or higher than that of a thermoelectric semiconductor material manufactured by hot plastic working can be obtained with a high yield.

  Furthermore, since the thermoelectric semiconductor material manufacturing method of the present invention manufactures a thermoelectric semiconductor material without applying stress such as plastic deformation to the thermoelectric semiconductor material itself, residual stress (residual stress) is present in the obtained thermoelectric semiconductor material. In the subsequent slicing process and dicing process, damage due to cracks and cracks is unlikely to occur. Moreover, compared with the conventional manufacturing method, a manufacturing facility can be simplified.

  The performance of the thermoelectric semiconductor material is expressed by the following formula (1) using the specific resistance (resistivity) ρ, the thermal conductivity κ, and the Seebeck coefficient α by the figure of merit Z. Note that the Seebeck coefficient takes a positive value in a P-type semiconductor material and takes a negative value in an N-type semiconductor material. As the thermoelectric semiconductor material, a material having a large figure of merit Z is desired.

Z = α ² / ρκ (1)

  The thermoelectric semiconductor material produced by the method for producing a thermoelectric semiconductor material of the present invention is a molded body obtained by tape-forming a slurry containing plate-like pulverized particles, and each plate-like pulverized particle is arranged so that the crystal planes of the raw materials are aligned. In order to form a molded body, a sintered body (thermoelectric semiconductor material) obtained through degreasing, reduction, and sintering becomes highly oriented, and a thermoelectric semiconductor material having an excellent performance index Z can be obtained. .

  In addition, the degreasing step (S4) using an inert atmosphere can appropriately remove the binder contained in the molded body, and furthermore, the oxidation of the crystal grains constituting the plate-like pulverized particles can be removed by the reduction step (S5). Therefore, it is possible to effectively prevent carbon and oxygen from remaining in the obtained thermoelectric semiconductor material, and the performance index Z can be further improved.

  Hereinafter, the steps (S1) to (S7) of the method for producing a thermoelectric semiconductor material of the present invention (hereinafter sometimes simply referred to as “the production method of the present invention”) will be described in more detail.

[1-1] Plate-like pulverized particle production step (S1):
The plate-like pulverized particle preparation step (S1) is a step of obtaining plate-like pulverized particles made of a thermoelectric semiconductor raw material and having a specific crystal face of the raw material on the surface by pulverizing an ingot having a specific gravity of 5 or more. . That is, the specific crystal plane appears on the pulverized surface of the ingot and constitutes the surface of the plate-shaped pulverized particles.

  More specifically, first, as shown in FIG. 1, raw materials for producing an ingot are weighed (S1a). The raw material to be used is not particularly limited as long as it is a material that can be used for manufacturing a thermoelectric semiconductor material and has a specific gravity of 5 or more, and a thermoelectric material for manufacturing a known raw material for a thermoelectric semiconductor material can be used. They can be appropriately weighed so as to have a stoichiometric ratio of the semiconductor material.

In the production method of the present invention, it is preferable to use at least tellurium and bismuth as the raw materials. That is, the production method of the present invention is suitable as a method for producing bismuth telluride as a thermoelectric semiconductor material. For example, as a raw material of a P-type thermoelectric semiconductor material, tellurium (Te), bismuth (Bi), and antimony (Sb) can be weighed so as to be Bi _0.4 Sb _1.6 Te _3. . The specific gravity of bismuth telluride is 6.5 or more.

  Since the above-described bismuth telluride is weak in an oxidizing atmosphere and has a melting point of 580 ° C., which is relatively low compared to other known thermoelectric semiconductor materials, production by molding using slurry has been conventionally performed. In the production method of the present invention, the carbon component in the slurry (mainly in the slurry) is obtained by performing the degreasing step (S4) and the reduction step (S5) after the molding step (S3) using the slurry. The binder) can be removed, and the production of a thermoelectric semiconductor material having an excellent figure of merit Z can be realized.

  Next, in order to produce an ingot from the raw materials thus weighed, the raw materials are mixed and melted (S1b). When the raw material is melted, it is preferably melted in an inert atmosphere so that the dissolved raw material is not oxidized. Specifically, an argon gas atmosphere can be given as a suitable example. Moreover, there is no restriction | limiting in particular about melting temperature, According to the raw material to be used, it can determine suitably.

  Next, the molten raw material is cooled and solidified to produce an ingot (S1c). The melting of raw materials (S1b) and the production of ingots (S1c) can be realized, for example, by the following method.

  The weighed raw materials are introduced into an ampule of a quartz tube, and the internal atmosphere is replaced with an argon atmosphere. Next, the inlet of the ampule is sealed, and the raw material is sealed in the ampule. Next, this ampoule is placed in a furnace heated to the melting temperature to melt the raw material in the ampoule. Next, in order to stir the molten raw material, an ampoule or a furnace is rotated or rocked, and then the molten raw material is cooled to produce an ingot.

  In the manufacturing method of this invention, it is preferable that the crystal | crystallization which consists of the said raw material has a cleavage property. For example, the crystal of bismuth telluride is hexagonal, and in this C plane, the plane bonded by the Te-Te van der Waals force is a cleavage plane. For this reason, plate-like pulverized particles can be obtained satisfactorily when the ingot is pulverized.

  Next, the produced ingot is pulverized to obtain plate-like pulverized particles (S1d). A known pulverizer such as a ball mill, a stamp mill, an impact mill, a jet mill, a ball mill, a tube mill, or a pot mill can be suitably used for pulverizing the ingot.

  The ingot produced as described above becomes plate-like pulverized particles by the pulverization. In the production method of the present invention, the plate-like pulverized particles thus obtained are sieved, and it is preferable to select and use particles having a major axis of 20 to 70 μm and an aspect ratio of 3 to 20. By using such particles, it is possible to improve the orientation in the resulting thermoelectric semiconductor material and reduce the unevenness of the orientation. For example, plate-shaped pulverized particles having a major axis of less than 20 μm may deteriorate the alignment during molding and may deteriorate the orientation, and plate-shaped pulverized particles having a major axis exceeding 70 μm may cause unevenness in location. is there. Further, when the aspect ratio is less than 3, the alignment property at the time of molding may be deteriorated and the orientation may be lowered, and when the aspect ratio exceeds 20, there may be a cause of location unevenness.

  The specific crystal plane in the plate-like pulverized particles refers to the pulverized surface of the plate-like pulverized particles formed when the ingot is pulverized. In particular, the smooth crystal formed by cracking the raw material crystals in a certain direction. It is preferable that the surface be smooth. For example, as described above, when the crystal made of the raw material has a cleavage property, a cleavage plane of the crystal made of the raw material can be mentioned. Such a cleaved surface becomes a surface with high electron conductivity, and therefore, it is possible to improve thermoelectric characteristics in a direction parallel to the oriented surface by orientation.

  Although not particularly limited, it is more preferable that the plate-like pulverized particles have a major axis of 20 to 50 μm and an aspect ratio of 5 to 20, and a major axis of 20 to 40 μm. It is particularly preferable to use particles having a particle size of 10 to 20.

[1-2] Slurry preparation step (S2):
Next, the obtained plate-like pulverized particles, a binder, and a dispersion medium are mixed to prepare a slurry in which the volume ratio of the plate-like pulverized particles is 30% by volume or more (S2).

  When the volume ratio of the plate-like pulverized particles to the whole volume of the slurry is less than 30% by volume, the arrangement of the plate-like pulverized particles becomes non-uniform in the molded product obtained by the subsequent molding step, and the resulting thermoelectric semiconductor The figure of merit Z of the material is significantly reduced.

  In particular, the thermoelectric semiconductor material having a specific gravity of 5 or more, such as bismuth telluride, has a behavior of the plate-like pulverized particles in the slurry unless the volume ratio of the plate-like pulverized particles is within the above range (30% by volume or more) (that is, The orientation of the particles) cannot be controlled, and the plate-like pulverized particles in the molded body are not uniformly arranged, so that a thermoelectric semiconductor material having a good figure of merit Z cannot be obtained. The manufacturing method of the present invention can obtain such a thermoelectric semiconductor material having a specific gravity of 5 or more with a high yield using tape molding.

  The volume ratio of the plate-like pulverized particles to the total volume of the slurry is preferably 30 to 70% by volume in consideration of the moldability in the forming step and the uniformity of the arrangement of the plate-like pulverized particles. More preferably, it is 30-60 volume%, and it is especially preferable that it is 40-50 volume%. For example, when the volume ratio of the plate-like pulverized particles exceeds 70% by volume, the concentration of the plate-like pulverized particles in the slurry becomes too high, and it may be difficult to form the slurry into a tape.

  There is no restriction | limiting in particular about the binder used for preparation of a slurry, For example, the binder contained in the slurry used for the tape shaping | molding of a conventionally well-known ceramic can be used suitably.

  In addition, in the manufacturing method of this invention, it is preferable to use the substance which has a thermogelling characteristic or a thermosetting characteristic as a binder of this slurry. By using such a substance, the prepared slurry has thermal gelation characteristics or thermosetting characteristics, and a molded body of a thermoelectric semiconductor material to which a conventional gel casting method is applied can be formed. Thereby, the drying shrinkage of the molded body becomes extremely small, and the molded body can be prevented from being damaged, and the molding of a thick molded body can be realized in the molding step (S3).

  Examples of the substance having a thermal gelation property or a thermosetting property include a mixture in which an isocyanate and a polyol (these become a urethane resin by a urethane reaction) and a catalyst for promoting the urethane reaction are added in a solvent. .

  Isocyanate is not particularly limited as long as it is a substance having an isocyanate group as a functional group. For example, tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), or modified products thereof can be used. In addition, in the molecule | numerator, reactive functional groups other than an isocyanate group may contain, and also many reactive functional groups may contain like polyisocyanate.

  The polyol is not particularly limited as long as it has a functional group capable of reacting with an isocyanate group, for example, a hydroxyl group, an amino group, etc. For example, ethylene glycol (EG), polyethylene glycol (PEG), propylene glycol (PG). Polypropylene glycol (PPG), polytetramethylene glycol (PTMG), polyhexamethylene glycol (PHMG), polyvinyl butyral (PVB), and the like can be used.

  Although it will not specifically limit as a catalyst if it is a substance which accelerates | stimulates a urethane reaction, For example, a triethylenediamine, hexanediamine, 6-dimethylamino-1-hexanol etc. can be used.

  The addition amount of the binder is preferably 5 to 50 parts by volume, more preferably 10 to 40 parts by volume with respect to 100 parts by volume of the plate-like pulverized particles. By comprising in this way, the failure | damage at the time of drying of a molded object can be prevented effectively.

  As for the dispersion medium used for the preparation of the slurry, for example, a dispersion medium contained in the slurry used for conventionally known ceramic tape molding, for example, an organic solvent can be suitably used. Specifically, toluene, xylene, isopropanol, etc. can be mentioned as a suitable example, for example. In addition, these dispersion media can be used individually by 1 type or in combination of 2 or more types.

  In addition, when constituting the slurry, in addition to the plate-like pulverized particles, the binder, and the dispersion medium described so far, other components contained in the slurry used for tape forming of conventionally known ceramics are further added. May be. Specifically, a plasticizer, a dispersing agent, etc. can be mentioned, for example.

  The plasticizer is an additive for imparting plasticity to the slurry and improving workability. Examples of such a plasticizer include glycerin, polyethylene glycol, dibutyl phthalate, di-2-ethylhexyl phthalate (DOP), diisononyl phthalate (DINP), and the like.

  The addition amount of the plasticizer is preferably 0.5 to 5 parts by mass, and more preferably 1 to 3 parts by mass with respect to 100 parts by mass of the plate-like pulverized particles. If the amount exceeds 5 parts by mass, the molded product may become too soft and easily deformed. On the other hand, if the amount is less than 0.5 parts by mass, the effect of adding a plasticizer hardly appears and the molded product becomes hard. Sometimes.

  The dispersant is an additive for uniformly dispersing the plate-like pulverized particles in the slurry. As such a dispersant, for example, any of an anionic, cationic, nonionic or amphoteric surfactant can be used, and a nonionic surfactant is preferable.

  The addition amount of the dispersant is preferably 0.1 to 5 parts by mass, and more preferably 0.5 to 2 parts by mass with respect to 100 parts by mass of the plate-like pulverized particles. Even if it is added in excess of 5 parts by mass, further improvement in dispersibility of the plate-like pulverized particles cannot be obtained, and conversely, impurities may be increased. On the other hand, if the amount is less than 0.1 parts by mass, the effect of adding the dispersant is hardly exhibited, and cracks may easily occur in the molded body.

  In the slurry preparation step (S2), a plate-like pulverized particle, a binder, a dispersion medium, and various additions as necessary are mixed to prepare a slurry in which the volume ratio of the plate-like pulverized particle is 30% by volume or more. It is. The components may be mixed in advance by adjusting the amount of the dispersion medium so that the volume ratio is as described above. For example, when an excess amount of the dispersion medium is used and the slurry is prepared, Then, the volume ratio of the plate-like pulverized particles may be adjusted to 30% by volume or more by repeating the operation of volatilizing the dispersion medium while stirring under reduced pressure. In this case, the volume ratio of the plate-like pulverized particles can be calculated by subtracting the volatilization amount of the dispersion medium from the charged amount of each component.

[1-3] Molding step (S3):
Next, as shown in FIG. 2A, the obtained slurry is formed into a tape shape to obtain a formed body 12 (S3). There is no restriction | limiting in particular about a shaping | molding method, It can shape | mold in tape shape with common tape forming machines, such as a doctor blade. Here, FIG. 2A is a perspective view for explaining an example of a molding step in one embodiment of the method for producing a thermoelectric semiconductor material of the present invention.

  In the production method of the present invention, since the molded body 12 is molded using a slurry containing 30% by volume or more of the plate-shaped pulverized particles having a specific shape obtained in the plate-shaped pulverized particle production step (S1), the molded body obtained is obtained. The plate-like pulverized particles constituting 12 are arranged so that the orientations of crystal planes in each plate-like pulverized particle are aligned. For this reason, the thermoelectric semiconductor material obtained after sintering has excellent orientation.

  In the production of conventional thermoelectric semiconductor materials, for example, as described in JP-A-2006-040963 and JP-A-10-173110, a slurry containing thermoelectric material particles in a predetermined region on a substrate. (Or paste) printing techniques have been proposed, but the manufacturing methods disclosed therein do not provide sufficient orientation, and only have low properties compared to those produced by hot plastic working. I couldn't. In the production method of the present invention, a thermoelectric semiconductor material is produced using a molded article obtained by tape-molding a slurry containing plate-shaped pulverized particles having a predetermined shape in a specific volume ratio. Therefore, a high-performance thermoelectric semiconductor material can be produced at a high yield. Obtainable.

  The thickness of the molded body 12 is not particularly limited, but is preferably 5 to 500 μm in order to ensure that the orientation of crystal planes in the plate-like pulverized particles is well aligned. It is more preferable to set the thickness to ˜300 μm, and it is particularly preferable to set the thickness to 50 to 200 μm. When the thickness of the molded body exceeds 500 μm, the number of pulverized particles included in the thickness direction of the molded body increases, and the arrangement of the pulverized particles may be disturbed.

  Moreover, in the manufacturing method of this invention, after obtaining a molded object by the above-mentioned shaping | molding process, it is preferable to dry the obtained molded object. The drying method is not particularly limited, and conventionally known drying methods such as hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying and the like can be used.

  In the production method of the present invention, in this molding step (S3), as shown in FIG. 3A, a plurality of molded bodies 22 formed into a tape shape are produced, and the plurality of molded bodies 22 are laminated to form a molded body. Thus, 22 laminated bodies 23 can be obtained. With a single tape molding, there is a limit to the thickness of the molded body to be obtained, but by using the molded body thus obtained as a laminate, it is possible to obtain a molded body with a large thickness. Here, FIG. 3A is a perspective view for explaining another example of the molding step in one embodiment of the method for producing a thermoelectric semiconductor material of the present invention.

  3A shows an example in which four molded bodies 22 are produced and the four molded bodies 22 are laminated to form a laminated body 23, but the number of molded bodies to be laminated is shown. There is no restriction | limiting in particular, According to the thickness of the thermoelectric semiconductor material to manufacture, it can select suitably.

  In addition, when forming a laminated body by laminating a plurality of molded bodies, the laminated bodies of the laminated molded bodies are brought into close contact with each other, and the laminated body is formed in the thickness direction so that the laminated body becomes one thermoelectric semiconductor material. It is preferable to press or heat and integrate.

[1-4] Degreasing step (S4):
Next, the obtained molded body is heat-treated in an inert atmosphere to obtain a degreased body. The degreasing step (S4) is a step in which fats such as binders and additives such as plasticizers and dispersants added as necessary are removed by heat treatment.

  About the heat processing temperature in a degreasing process (S4), although it changes also with kinds of fats, such as a binder and an additive, it is preferable that it is 300-650 degreeC, for example, it is still more preferable that it is 350-600 degreeC, 400 It is particularly preferable that the temperature is ˜550 ° C. By comprising in this way, a fat content can be removed favorably and the residue of carbon in the thermoelectric semiconductor material obtained can be decreased extremely.

[1-5] Reduction step (S5):
Next, the obtained defatted body is reduced to obtain a defatted reduced body (S5). A part of the degreased body or the molded body before degreasing may be oxidized in the production process described so far. When a thermoelectric semiconductor material is manufactured from a degreased body in such a state, a part of crystal grains constituting the thermoelectric semiconductor material is oxidized, the purity of the thermoelectric semiconductor material is lowered, and the performance of the thermoelectric semiconductor material is lowered. Resulting in. In the production method of the present invention, a thermoelectric semiconductor material with little residual oxygen can be produced by reducing the defatted body.

  Examples of the reduction treatment method include a method in which heat treatment is performed at a predetermined temperature in a hydrogen furnace to reduce the defatted body with hydrogen. The temperature of the heat treatment can be appropriately determined according to the type of raw material used, but when producing a temperature lower than the melting point of the raw material, for example, bismuth telluride using tellurium and bismuth as raw materials, The temperature is preferably 250 to 550 ° C, more preferably 300 to 450 ° C, and particularly preferably 300 to 400 ° C. By comprising in this way, a degreased body can be reduced satisfactorily. For example, if the temperature of the reduction treatment is too low, the oxidized crystal grains may not be sufficiently reduced. On the other hand, if the temperature of the reduction treatment is too high, the degreased body is formed before the reduction is performed. May cause sintering of crystal grains.

[1-6] Sintering step (S6):
Next, the obtained degreased reductant is sintered to obtain a sintered body (S6). As a sintering method, a method similar to a method of sintering a conventionally known ceramic sheet compact, for example, a hot press method can be suitably used.

  In addition, it is preferable to perform this sintering process in inert atmosphere, for example, argon gas atmosphere. Moreover, about sintering temperature, it can determine suitably according to the kind of used raw material. For example, when producing bismuth telluride using tellurium and bismuth as raw materials, it is preferably 350 to 580 ° C., more preferably 400 to 550 ° C., and particularly preferably 450 to 550 ° C. preferable.

  Moreover, when sintering a degreasing reductant by hot press, heating and sintering a degreasing reductant, applying a pressure with respect to the thickness direction of a tape-shaped degreasing reductant. Although there is no restriction | limiting in particular about the pressure in a hot press, For example, it is preferable that it is 15-100 MPa, It is more preferable that it is 20-80 MPa, It is especially preferable that it is 30-60 MPa. By comprising in this way, the thermoelectric semiconductor material excellent in the orientation can be obtained favorably.

[1-7] Cutting process (S7):
Next, as shown in FIGS. 2B and 2C, the obtained sintered body 14 is cut into a predetermined shape to obtain a thermoelectric semiconductor material 16. With such a configuration, a high-performance thermoelectric semiconductor material can be obtained with a high yield. In particular, in the manufacturing method of the present invention, since operations such as hot plastic processing are not performed as in the conventional manufacturing method, there is no residual residual stress in the sintered body 14, and in the cutting process, Damage due to cracks and cracks is less likely to occur.

  2B and 2C, the tape-like sintered body 14 obtained by degreasing, reducing, and sintering the tape compact is divided into three equal parts along the longitudinal axis direction, and the longitudinal axis. The example shows a case where a total of 30 rectangular parallelepiped thermoelectric semiconductor materials 16 are manufactured by dividing them into 10 equal parts in a direction perpendicular to the direction, but the cutting method is not particularly limited, It can be determined appropriately according to the shape of the thermoelectric semiconductor material to be manufactured.

  In addition, as shown in FIG. 3A, when a plurality of molded bodies 22 are laminated to produce a molded body made of the laminated body 23, as shown in FIGS. 3B and 3C, the degreasing process described so far ( The thermoelectric semiconductor material 26 is obtained by cutting the sintered body 24 obtained through S4), the reduction step (S5), and the sintering step (S6) into a predetermined shape.

  Here, FIG. 2B and FIG. 2C are perspective views for explaining an example of the cutting process in one embodiment of the method for producing the thermoelectric semiconductor material of the present invention, and FIG. 3B and FIG. 3C are the thermoelectric semiconductor of the present invention. It is a perspective view explaining the other example of the cutting process in one Embodiment of the manufacturing method of material.

  There is no particular limitation on the method for cutting the sintered body, for example, dicing with a dicer, slicing with a slicer, wire sawing with a wire saw, etc. (machining), laser processing with a YAG laser, excimer laser, etc. An electron beam processing etc. can be mentioned as a suitable example.

[2] Thermoelectric semiconductor material:
The thermoelectric semiconductor material produced by the method for producing a thermoelectric semiconductor material of the present invention can be made into a P-type thermoelectric semiconductor material or an N-type thermoelectric semiconductor material by adjusting the composition of the raw material used for producing the ingot.

  Such a thermoelectric semiconductor material can be used as a thermoelectric element of a thermoelectric module used for electronic cooling using the Peltier effect and thermoelectric power generation using the Seebeck effect. Specifically, the thermoelectric module can be used, for example, in a temperature controller, a power generator, a small refrigerator, or the like inside a semiconductor device such as a semiconductor laser.

  For example, as shown in FIG. 4, such a thermoelectric module is configured by sandwiching thermoelectric elements 102p and 102n, which are P-type or N-type thermoelectric semiconductor materials, between a lower substrate 106a and an upper substrate 106b. 100.

  The P-type thermoelectric element 102p and the N-type thermoelectric element 102n are made of raw materials corresponding to the stoichiometric ratio of the thermoelectric semiconductor material to be each thermoelectric element in the thermoelectric semiconductor material manufacturing method of the present invention described so far. It can be manufactured by using. Note that, for example, Ni plating may be performed on the upper and lower surfaces of each thermoelectric element to form an Ni plating layer in order to perform electrical bonding with each substrate 106.

  Further, the lower substrate 106a and the upper substrate 106b are, for example, as shown in FIG. 5, a pair of ceramic substrates 112 (in FIG. 5, a ceramic substrate constituting the lower substrate of the pair of ceramic substrates is shown). And the electrode 114 is formed on the thermoelectric element mounting portion on the ceramic substrate 112, and the Ni plating layer 116 is formed on the formed electrode 114. In addition, the said electrode 114 can be formed by well-known methods, such as copper metallization, for example.

  Here, FIG. 5 is a schematic cross-sectional view schematically showing a cross-sectional configuration of a substrate used in the thermoelectric module.

  When the electronic module 100 as shown in FIG. 4 is manufactured, first, P-type thermoelectric elements 102p and N-type thermoelectric elements 102n are alternately placed on the electrodes of the lower substrate 106a, and the P-type is placed. The Ni plating layer forming surface of the thermoelectric element 102p and the N-type thermoelectric element 102n (that is, the lower surface of the thermoelectric element) and the electrode of the lower substrate 106a are electrically joined.

  Next, the upper substrate 106b is placed on the other surface (that is, the upper surface of the thermoelectric element) on which the Ni plating layer of the P-type thermoelectric element 102p and the N-type thermoelectric element 102n is formed. The electrode and the Ni plating layer forming surface (upper surface) of the P-type thermoelectric element 102p and the N-type thermoelectric element 102n are electrically joined. In this way, the electronic module 100 as shown in FIG. 4 can be manufactured. Note that the electrical connection between the electrode and the thermoelectric element can be performed by, for example, soldering.

  In such a thermoelectric module 100, for example, when a current is passed through the P-type thermoelectric element 102p and the N-type thermoelectric element 102n connected by the electrodes of the lower substrate 106a and the upper substrate 106b, the current is below the N-type thermoelectric element 102n. From the upper substrate 106b to the lower side of the P-type thermoelectric element 102p. On the other hand, energy moves in the same direction as the current in the P-type thermoelectric element 102p, and in the opposite direction to the current in the N-type thermoelectric element 102n. Therefore, the energy is insufficient on the electrode side of the upper substrate 106b, and the temperature decreases. On the electrode side of the substrate 106a, energy is released and the temperature rises.

  Since the thermoelectric semiconductor material manufactured by the manufacturing method of the thermoelectric semiconductor material of the present invention described so far is excellent in the figure of merit Z, it causes a good temperature difference between the upper surface and the lower surface of the thermoelectric module. Can do.

  Note that the thermoelectric module is not limited to a one-stage thermoelectric module as shown in FIG. 4, that is, a one-stage module in which thermoelectric elements are arranged on a single plane. A multi-stage module in which modules are stacked in stages or more may be used.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples. Moreover, the evaluation method of the various characteristics of the thermoelectric semiconductor material (thermoelectric element) manufactured by each Example and the comparative example is shown below.

<Measurement of figure of merit Z>
For the thermoelectric semiconductor material (thermoelectric element) manufactured by each example and comparative example, the Seebeck coefficient α (μV / K), the thermal conductivity κ (W / mK), and the specific resistance ρ (× 10 ⁻⁵ Ωm) are measured. And the figure of merit Z was computed from the above-mentioned formula (1). The larger the figure of merit Z is, the better the thermoelectric semiconductor material is.

<Measurement of yield>
According to each example and comparative example, 10 rectangular parallelepiped thermoelectric semiconductor materials having a length of 6 mm and a cross section perpendicular to the major axis were produced, and among the obtained thermoelectric semiconductor materials, the number of cracks and chips generated. Was measured. In addition, as a crack and a chip | tip, it was set as the damage or defect | deletion part of 0.3 mm or more confirmed with a stereomicroscope.

(Example 1)
First, bismuth (Bi), tellurium (Te), and antimony (Sb) powders were weighed so that the stoichiometric ratio was Bi _0.4 Sb _1.6 Te ₃ as a raw material of the P-type thermoelectric element. Next, the weighed raw materials were melted in an Ar atmosphere at 700 ° C. and then solidified to produce an ingot. The specific gravity of the obtained bismuth telluride ingot was 7.

  Next, the obtained ingot was coarsely pulverized with a mortar and a ball mill and passed through a 100-mesh sieve so that the particle size was 150 μm or less. Then, it grind | pulverized so that it might become plate-shaped particle | grains with the single nozzle type jet mill apparatus (brand name: Starburst, Sugino machine company make). The obtained crushed pieces were passed through a 500 mesh sieve as a fine particle removing step, and particles that did not pass through the mesh (about 20 μm or more) were selected to obtain plate-like crushed particles (plate-like pulverized particle production step (S1)). .

  In addition, the obtained plate-like pulverized particles had a major axis in the range of 20 to 70 μm and an aspect ratio in the range of 3 to 20.

  Next, a slurry for tape molding was prepared using the plate-like pulverized particles (slurry preparation step (S2)). Specifically, a mixture of equal amounts of toluene and isopropanol as a dispersion medium, and the above plate-like pulverized particles and poly (n-butyl methacrylate) as a binder (trade name: Hyperl M-6003, manufactured by Negami Kogyo Co., Ltd.) A slurry was prepared by mixing a plasticizer (di-2-ethylhexyl phthalate (DOP), manufactured by Kurokin Kasei Co., Ltd.) and a dispersant (trade name: SP-O30, manufactured by Kao Corporation).

  The formulation of each component was 50 parts by mass of the dispersion medium, 4 parts by mass of the binder, 2 parts by mass of the plasticizer, and 1 part by mass of the dispersant with respect to 100 parts by mass of the plate-like pulverized particles. When preparing the slurry, after boiling the mixture mixed at the above ratio at 80 ° C., the process of volatilizing the dispersion medium while stirring under reduced pressure is repeated, so that the volume concentration of the plate-like pulverized particles becomes 35% by volume. A slurry was prepared as follows. The volume concentration of the plate-like pulverized particles was calculated by subtracting the volatilization amount of the dispersion medium from the charged amount of each component.

  Next, the obtained slurry was molded into a tape shape on a PET film by a doctor blade method to produce a molded body (molding step (S3)). The obtained molded body had a thickness of 30 μm after drying.

  Next, 100 layers of the obtained tape-shaped molded product punched out to a diameter of 30 mm were laminated and thermocompression bonded to produce a pellet (multi-layer molded product).

  Next, the obtained pellet was degreased by heating at 450 ° C. for 5 hours in an Ar atmosphere (degreasing step (S4)). Next, the degreased degreased body was heat-treated at 350 ° C. for 10 hours in a hydrogen furnace to reduce the hydrogen (reduction step (S5)).

  Next, the obtained degreased reductant was sintered at 450 ° C. for 1 hour in an Ar atmosphere by a hot press apparatus to obtain a sintered body (sintering step (S6)).

  Next, the surfaces (upper and lower surfaces) parallel to the laminated surface of the obtained sintered body were polished to a thickness of 2 mm. Thereafter, a thermoelectric semiconductor material (thermoelectric element) was produced by cutting into a rectangular parallelepiped having a length of 6 mm and a cross section perpendicular to the major axis of 2 mm in length and breadth with a dicer (cutting step (S7)).

  The figure of merit Z of the obtained thermoelectric semiconductor material was measured. Moreover, ten thermoelectric semiconductor materials were manufactured, and the above-described yield measurement was performed. Table 1 shows the performance index Z of the thermoelectric semiconductor material and the measurement results of the yield.

(Example 2)
In the slurry preparation step (S2), a thermoelectric semiconductor material was produced in the same manner as in Example 1 except that the slurry was prepared so that the volume concentration of the plate-like pulverized particles was 30% by volume.

(Example 3)
In the slurry preparation step (S2), a thermoelectric semiconductor material was produced by the same method as in Example 1 except that the slurry was prepared so that the volume concentration of the plate-like pulverized particles was 40% by volume.

Example 4
100 parts by mass of plate-like pulverized particles prepared in the same manner as in Example 1, 20 parts by mass of a mixture of triacetin and organic dibasic acid ester as a dispersion medium (mixing ratio 1: 9), and polycarboxylic acid as a dispersant 3 parts by mass of an acid copolymer was mixed for 3 hours using a ball mill to prepare a slurry precursor.

  Next, the slurry precursor is produced from an isocyanate and a polyol as a binder, and the functional group ratio of the polyol to the isocyanate (that is, the molar ratio of the hydroxyl group to the isocyanate group) is 2 / 11.5, and further repeated. 7 parts by mass of a urethane resin having a unit molecular weight of 290, an isocyanate and a polyol were mixed.

  As the isocyanate, 4,4′-diphenylmethane diisocyanate was used, and as the polyol, a solution obtained by dissolving 10% by mass of polyvinyl butyral in a mixture of triacetin and organic dibasic acid ester (a solvent having a mixing ratio of 1: 9) was used. It was.

  Furthermore, 0.05 parts by mass of 6-dimethylamino-1-hexanol as a catalyst was mixed with the precursor of the slurry, and the mixture was vacuum degassed to prepare a slurry. The concentration of the plate-like pulverized particles in the slurry calculated from the amount of the prepared slurry charged was 40% by volume.

  The obtained slurry was formed into a sheet on a PET film by the doctor blade method, and solidified and dried at 40 ° C. for 2 hours by heating in a sheet forming machine. Thereafter, it was further solidified and dried in a room at room temperature for 12 hours to obtain a molded body having a thickness of 60 μm.

  Next, 50 layers of the obtained tape-shaped molded product punched out to a diameter of 30 mm were laminated and thermocompression bonded to produce a pellet (multi-layer molded product).

  The obtained pellet (multi-layered molded product) was degreased, reduced, sintered and cut in the same manner as in Example 1 to obtain a rectangular parallelepiped having a length of 6 mm and a cross section perpendicular to the major axis of 2 mm in length and width. The thermoelectric semiconductor material (thermoelectric element) was manufactured by cutting.

(Comparative Example 1)
In the slurry preparation step (S2), a thermoelectric semiconductor material was produced by the same method as in Example 1 except that the slurry was prepared so that the volume concentration of the plate-like pulverized particles was 20% by volume.

(Comparative Example 2)
In Comparative Example 2, a thermoelectric semiconductor material was manufactured by hot plastic working (hot extrusion) by conventional hot upset forging. First, plate-like pulverized particles produced in the same manner as in Example 1 were subjected to reduction treatment, and the plate-like pulverized particles were uniaxially formed on pellets, and then hot pressed under conditions of 500 ° C. and 40 MPa in an Ar atmosphere.

  After the hot pressing, the uniaxially formed compact was hot extruded. The mold used for the hot extrusion has a cylindrical shape with a diameter of 30 mm on the sintered body input side and a cylindrical shape with a diameter of 6 mm on the extrusion side, and a taper angle of 45 degrees therebetween. In the hot extrusion, the mold was kept at 450 ° C. and extruded in an Ar atmosphere.

  The obtained sintered extrudate was cut so as to have a length of 6 mm in the extrusion direction, and further cut with a dicer so that the cross section perpendicular to the extrusion direction was a square of 2 mm in length and breadth to produce a thermoelectric semiconductor material.

  The figure of merit Z was measured for each of the thermoelectric semiconductor materials of Examples 2 to 4 and Comparative Examples 1 and 2. In each example and comparative example, ten thermoelectric semiconductor materials were manufactured, and the above-described yield measurement was performed. Table 1 shows the performance index Z of the thermoelectric semiconductor material and the measurement results of the yield.

(result)
Thermoelectric semiconductor material manufactured by tape molding a slurry containing predetermined plate-like pulverized particles at a specific volume ratio, and obtained through degreasing, reduction, firing, and cutting steps (Examples 1 to 4) The performance index Z is comparable to that of the conventional manufacturing method using hot extrusion (Comparative Example 2), and the generation of cracks in the thermoelectric semiconductor material was suppressed. In particular, the thermoelectric semiconductor material obtained in Example 4 using a substance having a thermal gelation property or a thermosetting property as a binder was excellent in the figure of merit Z, and cracks and chips were not confirmed (yield improvement) ).

  In Comparative Example 1, the performance index Z of the thermoelectric semiconductor material was low because the volume ratio of the plate-like pulverized particles was less than 30% by volume (specifically, 20% by volume). Further, in Comparative Example 2, since a molded body was formed by hot extrusion, stress during extrusion remained in the thermoelectric semiconductor material, and many cracks and chips were generated.

  The method for producing a thermoelectric semiconductor material of the present invention can be used as a method for producing a thermoelectric semiconductor material having high performance. The thermoelectric semiconductor material obtained by the method for producing a thermoelectric semiconductor material of the present invention can be used for, for example, a temperature controller inside a semiconductor device such as a small refrigerator or a semiconductor laser, a power generator, and the like.

It is a flowchart which shows one Embodiment of the manufacturing method of the thermoelectric-semiconductor material of this invention. It is a perspective view explaining an example of the shaping | molding process in one Embodiment of the manufacturing method of the thermoelectric-semiconductor material of this invention. It is a perspective view explaining an example of the cutting process in one Embodiment of the manufacturing method of the thermoelectric-semiconductor material of this invention. It is a perspective view explaining an example of the cutting process in one Embodiment of the manufacturing method of the thermoelectric-semiconductor material of this invention. It is a perspective view explaining the other example of the formation process in one Embodiment of the manufacturing method of the thermoelectric-semiconductor material of this invention. It is a perspective view explaining the other example of the cutting process in one Embodiment of the manufacturing method of the thermoelectric-semiconductor material of this invention. It is a perspective view explaining the other example of the cutting process in one Embodiment of the manufacturing method of the thermoelectric-semiconductor material of this invention. It is a perspective view showing typically a thermoelectric module using a thermoelectric semiconductor material. It is a schematic sectional drawing which shows typically the structure of the cross section of the board | substrate used for a thermoelectric module.

Explanation of symbols

12: Molded body, 14: Sintered body, 16: Thermoelectric semiconductor material, 22: Molded body, 23: Laminated body, 24: Sintered body, 26: Thermoelectric semiconductor material, 100: Thermoelectric module, 102n: Thermoelectric element (N Type thermoelectric element), 102p: thermoelectric element (P type thermoelectric element), 106: substrate, 106a: lower substrate, 106b: upper substrate, 112: ceramic substrate, 114: electrode, 116: Ni plating layer.

Claims (6)

A plate-like pulverized particle production step of obtaining a plate-like pulverized particle having a specific crystal face of the raw material by pulverizing an ingot having a specific gravity of 5 or more, comprising a raw material of a thermoelectric semiconductor;
A slurry preparation step of mixing the obtained plate-like pulverized particles, a binder, and a dispersion medium to prepare a slurry in which the volume ratio of the plate-like pulverized particles is 30% by volume or more,
A molding step of molding the obtained slurry into a tape shape to obtain a molded body; and
A degreasing step of heat-treating the obtained molded body in an inert atmosphere to obtain a degreased body;
A reduction step of reducing the obtained defatted body to obtain a defatted reduced body;
Sintering the obtained degreased reductant to obtain a sintered body;
A cutting process step of cutting the obtained sintered body to obtain a thermoelectric semiconductor material. A method for producing a thermoelectric semiconductor material.   The method for producing a thermoelectric semiconductor material according to claim 1, wherein at least tellurium and bismuth are used as the raw material.   The method for producing a thermoelectric semiconductor material according to claim 1 or 2, wherein in the sintering step, the degreased reductant is sintered by hot pressing.   The method for producing a thermoelectric semiconductor material according to any one of claims 1 to 3, wherein the plate-like pulverized particles are particles having a major axis of 20 to 70 µm and an aspect ratio of 3 to 20.   The manufacturing method of the thermoelectric-semiconductor material as described in any one of Claims 1-4 which uses the substance which has a thermogelling characteristic or a thermosetting characteristic as the said binder.   The thermoelectric device according to any one of claims 1 to 5, wherein in the molding step, a plurality of the molded bodies molded into a tape shape are produced, and the plurality of molded bodies are laminated to obtain a laminate of the molded bodies. Manufacturing method of semiconductor material.

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