JP2009170438A - Manufacturing method of thermoelectric conversion unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an efficient manufacturing method of a thermoelectric conversion unit as an assembly of a number of thermoelectric conversion devices, capable of collecting power in practical manner. <P>SOLUTION: The manufacturing method of a thermoelectric conversion unit includes a raw material filling process for alternately filling a p-type semiconductor raw material and an n-type semiconductor raw material into each through-hole of a honeycomb, made of a non-metal inorganic material; a semiconductor formation process for forming a p-type semiconductor and an n-type semiconductor in each through-hole of the honeycomb by sintering the p-type semiconductor raw material and the n-type semiconductor raw material filled into the honeycomb; and an electrode junction process for jointing the p-type semiconductor to the n-type semiconductor, formed in the through-hole of the honeycomb by an electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method for manufacturing a thermoelectric conversion device as a power generation device.

  When one end of the p-type semiconductor and one end of the n-type semiconductor are joined by an electrode, and this junction is heated to a high temperature and the other ends of the p-type semiconductor and the n-type semiconductor are cooled, the temperature difference between the high-temperature portion and the low-temperature portion is increased. Accordingly, an electromotive force is generated between the end portions of the p-type semiconductor and the n-type semiconductor. An electromotive force generated between the end portions of the p-type semiconductor and the n-type semiconductor is called a thermoelectromotive force, and such an effect is called a Seebeck effect. Note that when one end of a p-type semiconductor and one end of an n-type semiconductor are joined by an electrode, and a current is passed from the other end of the p-type semiconductor and the n-type semiconductor, a temperature difference occurs at both ends of the semiconductor. It is said that the elements having these effects are collectively referred to as a thermoelectric conversion element. The Seebeck effect reverses the direction of the current by increasing or decreasing the temperature of the junction of the thermoelectric conversion element. It is also known that a larger electromotive force can be obtained as the temperature difference increases.

  Although the electromotive force of each thermoelectric conversion element is not so large, a thermoelectric conversion module that combines many such thermoelectric conversion elements has no moving parts that generate vibration, noise, wear, etc., and has a simple structure and high reliability. It is a static thermoelectric conversion device that has the characteristics of being high, long-life and easy to maintain. Such a thermoelectric conversion module has a plurality of thermoelectric conversion elements, usually several tens or more, and each thermoelectric conversion element is electrically connected in series and thermally arranged in parallel. Yes. The thermoelectric conversion module having such a configuration depends on a thermoelectric power generation device using the Seebeck effect that extracts the starting force depending on the temperature difference set at both ends of the thermoelectric conversion element, or on the voltage applied to both ends of the thermoelectric conversion module. Therefore, it is also used as a thermoelectric temperature control device using the Peltier effect that cools or heats one end by generating a temperature difference.

  Thermoelectric conversion materials are materials that can directly convert heat into electricity by the Seebeck effect, and conversely, can use electricity for heat (heating / cooling) by the Peltier effect. A known thermocouple material for temperature measurement may be a combination of an alloy or metal such as alumel / chromel, platinum / platinum rhodium. However, a combination of a p-type semiconductor and an n-type semiconductor is used when a small size and a large electromotive force or heat output are required. Thermoelectric conversion modules using semiconductors have advantages such as precise temperature control, local cooling, quietness, no chlorofluorocarbon regulations, long life, high reliability, and no maintenance required. It has been used for temperature control of laser diodes.

On the other hand, in recent years, as a global warming problem, there has been a demand for significant suppression of CO ₂ emissions. However, effective use of unused thermal energy in the industrial, consumer, and transportation fields greatly contributes to energy saving and CO ₂ reduction. In order to contribute, thermoelectric power generation modules that can directly convert thermal energy into electrical energy have been developed. For example, an automobile engine uses only about 30% of combustion energy as power, and most of the remainder is discharged together with exhaust gas. If an efficient thermoelectric conversion device is developed in such a field, a significant energy saving effect and a CO ₂ emission suppressing effect can be expected. As a thermoelectric conversion device for an automobile, it is required to have strength, vibration resistance, shape flexibility, durability, wide operating temperature range, maintenance-free, and low environmental load as well as being small and light. In particular, vibration resistance and shape flexibility are required performances different from those of other applications.

  For example, FIG. 3 shows a cross-sectional view of two coupled thermoelectric conversion elements. A p-type semiconductor 12 and an n-type semiconductor 13 are coupled by an upper electrode 14, and an electrode 18 is coupled at the lower part on the opposite side. Are connected. The electrode 14 and the electrode 18 do not couple the same semiconductors, but, for example, the p-type semiconductor 12 and the n-type semiconductor 13 are coupled to each other in series from the left side to the top so that the p-type semiconductor 12 and the n-type semiconductor 13 are coupled in series. The current is flown from the upper left to the lower right by sequentially coupling to the n-type semiconductor 13, then from the n-type semiconductor 13 to the p-type semiconductor 12 at the lower part, and further from the p-type semiconductor 13 to the n-type semiconductor 12 at the upper part. It has become. A plan view of the thermoelectric conversion module 11 in which 144 thermoelectric conversion elements are modularized in this manner is shown in FIG. In FIG. 2, for example, a p-type semiconductor 12 and an n-type semiconductor 13 are combined by electrodes 14 to form a set of thermoelectric conversion elements, but the opposite side of the thermoelectric conversion elements (not shown in the figure) On the lower side, the p-type semiconductor 12 and the n-type semiconductor 13 of the adjacent thermoelectric conversion elements are coupled together by electrodes to form a set of thermoelectric conversion elements. That is, the p-type semiconductor 12 and the n-type semiconductor 13 are alternately coupled in series by the electrodes. If a temperature difference is given to both sides of the thermoelectric conversion module 11 (upper and lower in FIG. 3), the performance of the individual thermoelectric conversion elements, the performance of the thermoelectric conversion elements connected to the ends of the semiconductors at both ends are provided. The predetermined electromotive force is generated due to the temperature difference applied to both sides of the thermoelectric conversion module 11.

Semiconductors for thermoelectric conversion elements include Bi / Te, Se / Te, Cs / Bi / Te, Pb / Te, Pb / Se / Te, Zn / Sb, Co / Sb, Ce / Semiconductors such as Fe / Co / Sb and Si / Ge are known. For example, as a thermoelectric conversion material used in a low temperature range from room temperature to about 200 ° C., a BiTe-based thermoelectric conversion material discovered by Goldsmid of GE Corporation in the United States in 1954 is generally known. In general, many thermoelectric conversion materials have a narrow application temperature range. Therefore, in the case of a BiTe-based thermoelectric conversion material, a single-layer module is sufficient in a low temperature range of 200 ° C. or lower, but in a medium / high temperature range exceeding 200 ° C., a combination of thermoelectric conversion materials having different application temperature ranges can be combined. Research has been conducted to obtain a highly efficient thermoelectric module as three layers. In addition, materials that exhibit excellent performance in the middle and high temperature range have been developed. One of them is a Zn ₄ Sb ₃ material, which is a p-type semiconductor thermoelectric material exhibiting high thermoelectric conversion performance in a medium temperature range of 200 to 400 ° C. On the other hand, a thermoelectric conversion material based on CoSb can also be a p-type semiconductor and an n-type semiconductor having high performance in a medium to high temperature range of 300 to 700 ° C.

However, many of these semiconductors contain harmful metals, and care must be taken in manufacturing and use. Recently, metal oxide-based semiconductors have attracted attention as thermoelectric conversion materials that can easily solve environmental problems. For example, semiconductor thermoelectric conversion materials such as InO ₂ —SnO ₂ , (Ca, Bi) MnO ₃ , (Zn, Al) O, Na (Co, Cu) O ₄ , and NaCo ₂ O ₄ are developed. It is practical.

  In general, a thermoelectric conversion module is composed of several tens or more, sometimes hundreds or more, of minute semiconductor elements, but the semiconductors are separated from each other and have a skeleton structure. However, as shown in FIG. 2, accurately arranging fine semiconductor elements in accordance with a desired arrangement pattern and forming electrodes on both ends is complicated in manufacturing. Another problem is that the completed module has low mechanical strength. Several reports have been made on the structure of a thermoelectric conversion module or a manufacturing method for solving these problems.

  For example, the p-type and n-type semiconductor elements are accommodated in a thermoelectric conversion module (Patent Document 1) in which a p-type semiconductor element and an n-type semiconductor element are arranged in a heat-resistant porous insulator or a molded substrate in which element accommodation holes are formed. There is a thermoelectric conversion module (Patent Document 2). The thermoelectric conversion module having such a configuration does not use a jig for disposing the p-type and n-type semiconductor elements, and disposes the semiconductor elements on the insulator in which the through holes are formed. Characteristics are improved, the insulation between the semiconductor elements is improved, and the mechanical strength of the thermoelectric conversion module is increased.

In addition, a thermoelectric conversion module having a configuration in which a gap between semiconductor elements is filled with an insulating material has been proposed. Specifically, a thermoelectric conversion module (Patent Document 3) having a configuration in which a pair of p-type semiconductor elements and n-type semiconductor element pairs installed in a desired arrangement are embedded with an insulating material, or a plurality of p-type semiconductor layers In addition, there is a thermoelectric conversion module (Patent Document 4) configured to stack an n-type semiconductor layer, leave a pn junction, form a void, and fill the void with glassy material. In addition, there is a thermoelectric conversion module (Patent Document 5) configured by a semiconductor thermoelectric element inserted into an insulating honeycomb structure through an insulating filler made of an alkali metal silicate-based inorganic adhesive or sol-gel glass. Furthermore, a cordierite mold is used as a mold for the thermoelectric conversion module, and the thermal conductivity is adjusted by adjusting the porosity of the cordierite, thereby obtaining a highly reliable thermoelectric conversion module (Patent Document 6). . These thermoelectric conversion modules are characterized in that the mechanical strength of the thermoelectric conversion module is improved and the oxidation resistance and corrosion resistance of the semiconductor element are improved because the gap between the semiconductor elements is filled with an insulating material. In addition, as a form of a thermoelectric conversion module, as shown in Patent Document 7, a low melting point glass of B ₂ O ₃ —PbO is used, and as shown in Patent Document 8, calcium silicate is used. Are used by machining, and as disclosed in Patent Document 9, quartz glass is assembled in a cross-beam shape.

  As conventional methods for producing a thermoelectric conversion element, there are known a crystal growth method, a hot pressure sintering method such as a normal pressure powder sintering method using a cold press and a hot press method. In general, it is said that the crystal growth method is better than the powder sintering method by cold pressing or the hot pressing method as the performance of the thermoelectric conversion element. However, the crystal growth method has a drawback in that it takes a long time to manufacture, has crystal anisotropy, and has cleavage properties, so that the mechanical strength is low and the device yield is low, so that the manufacturing cost is high. The powder sintering method by cold pressing is a method in which raw material powder is put into a mold and press-molded, and then heat treatment is performed, and the mechanical strength of the element is increased and the yield is improved. It is necessary to granulate the prepared raw material again to an appropriate size or to remove fine powder. Moreover, the characteristics of the thermoelectric conversion element are liable to deteriorate due to impurities, and it is necessary to remove these, and management of raw materials becomes important. The hot press method can sinter in one step as compared with the powder sintering method by cold pressing, but since the raw powder is sintered by directly pressing and heating at the same time, it is very difficult to increase the sintering density. High pressure and high temperature conditions are required, and long sintering times cannot be shortened much. In addition, appropriate purity control of the raw material powder is necessary.

  Recently, a sintering method called a discharge plasma sintering method has been developed. In this discharge plasma sintering method, the raw material powder is sintered under pressure in the same way as the hot press method. However, instead of using normal external heating, a high voltage is applied to both ends of the raw material powder to form the raw material powder. In the meantime, discharge plasma is generated, and the raw material powder is sintered using the heat. This sintering method is characterized in that the sintering temperature can be lowered and the sintering time can be shortened.

  Patent documents 10 and 11 are mentioned as a manufacturing method of a thermoelectric conversion element using a discharge plasma sintering method. In Patent Document 10, a semiconductor thermoelectric conversion element and an electrode are simultaneously formed by a discharge plasma sintering method. Since sintering at a low temperature is possible, it is characterized by being able to sinter while dissimilar materials are suitably joined. In Patent Document 11, p-type and n-type oxide semiconductor materials are arranged in layers, and p-type and n-type oxide semiconductor materials are joined at once by a discharge plasma sintering method. The device is manufactured.

On the other hand, metal materials such as Al and Cu are used as the electrode material used for the thermoelectric conversion module. These electrode materials are joined to the thermoelectric conversion element by a thermal spraying method or a brazing method. In particular, when an electrode is formed by a thermal spraying method, the thermoelectric conversion element needs to be sprayed after being inserted into a mold material. This is because the p-type semiconductor element and the n-type semiconductor element cannot be joined without a formwork, and a thermal spray material is attached to the side surface of the thermoelectric conversion element, so that the electric and thermal surfaces of the thermoelectric conversion element are electrically and thermally This is because the power generation characteristics are deteriorated.
Japanese Patent Laid-Open No. 5-283753 JP-A-7-162039 JP-A-8-18109 JP 61-263176 A Japanese Patent Laid-Open No. 10-321921 JP 2005-129765 A JP-A-8-153899 JP 11-340526 A JP 2003-234516 A Japanese Unexamined Patent Publication No. 5-55640 JP 2002-118300 A

  As described above, various thermoelectric conversion devices have been reported, but they can be used from room temperature to about 1000 ° C., are resistant to vibration, have a certain level of strength, and are suitable for the environment, as are thermoelectric conversion devices mounted on automobiles. As a thermoelectric conversion device for recovering electric power that has a small influence and is easy to manufacture, a thermoelectric conversion device in which an oxide-based semiconductor is placed in a mold made of a ceramic material can be considered. However, although there are reports on individual element technologies such as semiconductors as thermoelectric conversion elements, molds for arranging multiple thermoelectric conversion elements, and electrodes to connect thermoelectric conversion elements, the overall performance of the device is well balanced. A method for efficiently mass-producing a thermoelectric conversion device as a set of a large number of thermoelectric conversion elements capable of practically recovering electric power while having it has not been reported yet. Even in the method for manufacturing thermoelectric conversion elements described in Patent Documents 10 and 11, individual thermoelectric conversion elements must be manufactured and a predetermined number of them must be arranged to form a practical thermoelectric conversion device.

  In view of the above-described problems, an object of the present invention is to provide an efficient manufacturing method of a thermoelectric conversion device as a set of a large number of thermoelectric conversion elements that can practically recover electric power.

Means for solving the problems of the present invention will be described below.
The present invention includes a raw material filling step of alternately filling a p-type semiconductor raw material and an n-type semiconductor raw material into each through-hole of a honeycomb made of a nonmetallic inorganic material,
A semiconductor forming step of sintering the p-type semiconductor raw material and the n-type semiconductor raw material filled in the honeycomb to form a p-type semiconductor and an n-type semiconductor in each through-hole of the honeycomb;
A method for manufacturing a thermoelectric conversion device, comprising: an electrode bonding step of bonding a p-type semiconductor and an n-type semiconductor formed in the through-hole of the honeycomb with electrodes.

  Preferably, the present invention is characterized in that the semiconductor forming step generates a discharge plasma by applying voltage while applying pressure to the p-type semiconductor material and the n-type semiconductor material filled in the honeycomb, and then sinters. A method for manufacturing a thermoelectric conversion device is included.

  In a preferred aspect of the present invention, the non-metallic inorganic material is a ceramic precursor, and the honeycomb, the p-type semiconductor raw material, and the n-type semiconductor raw material are sintered in the semiconductor forming step. including.

  In a preferred embodiment of the present invention, the non-metallic inorganic material is ceramic, and only the p-type semiconductor material and the n-type semiconductor material are sintered in the semiconductor formation step.

  In the present invention, at least one of the p-type semiconductor raw material and the n-type semiconductor raw material is filled in the through hole as powder, or filled in the through hole as slurry or paste and dried, and then sintered. The manufacturing method of the said thermoelectric conversion apparatus characterized by doing is included.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method suitable for mass production of the thermoelectric conversion apparatus for electric power collection | recovery can be provided.

  In the method for manufacturing a thermoelectric conversion device of the present invention, the configuration of a thermoelectric conversion device for power generation that is suitably manufactured will be briefly described. Usually, a thermoelectric conversion device for power generation requires a temperature difference of about 300 ° C. in order to obtain a large electromotive force. Therefore, even if the low temperature side of the thermoelectric conversion element is set to normal temperature, the high temperature side is exposed to a high temperature of 300 ° C. or higher. Under such circumstances, a heat-resistant material is required, and a ceramic honeycomb is used as a mold, and each through-hole of the honeycomb (each through-hole of the honeycomb is also referred to as a cell) is a p-type semiconductor or An n-type semiconductor is preferably disposed. Adjacent p-type semiconductor end portions and n-type semiconductor end portions are electrically coupled so as to be connected in series or in parallel, respectively. For this reason, each semiconductor element is connected with the edge part of a different semiconductor element in the high temperature side edge part and the low temperature side edge part. That is, the end of the p-type semiconductor 12 and the end of the n-type semiconductor 13 are connected to the high-temperature side electrode 14 as in the example of the cross-sectional view in which two thermoelectric conversion elements schematically shown in FIG. The low temperature side electrodes 18 are alternately connected.

  FIG. 2 is a plan view showing an example of a thermoelectric conversion device for power generation. In the thermoelectric conversion device 11 of this embodiment, the p-type semiconductors 12 and the n-type semiconductors 13 are alternately arranged in the cells formed between the honeycomb partition walls 15 of the ceramic honeycomb. The thermoelectric conversion device 11 is formed by combining the mold semiconductor 13 with the electrode 14. In the honeycomb, each cell may have a desired cross-sectional shape and cross-sectional area. In FIG. 2, a p-type semiconductor 12 is formed with an octagonal shape close to a square, and a n-type semiconductor 13 is formed with a square cell. In the thermoelectric conversion device 11 of this embodiment, the honeycomb has 289 cells (17 × 17). And 144 thermoelectric conversion elements (8.5 horizontal × 17 vertical 17 = 144.5) are arranged. Usually, several tens to several hundreds of thermoelectric conversion elements that combine such p-type semiconductor 12 and n-type semiconductor 13 are arranged to form a thermoelectric conversion device for power generation.

  The manufacturing method of the thermoelectric conversion device of the present invention will be described on the premise of a practical thermoelectric conversion device for power generation as described above. First, a method for manufacturing a honeycomb having a large number of cells will be described. The combination of cell cross-sectional shapes corresponds to the combination of two types of semiconductors for p-type semiconductors and n-type semiconductors, and is suitable for the production of ceramic honeycombs, and other than the part where the semiconductor is arranged and functions effectively It is desirable that the ratio of the honeycomb partition walls between the cells is small. In consideration of the strength of the whole honeycomb and the electrical insulation between cells, the thickness of the honeycomb partition wall 15 cannot be extremely thin. To satisfy such a condition, the strength and the electrical insulation are maintained. It is desirable to make the partition walls substantially constant with the smallest possible thickness. If the thickness of the honeycomb partition walls 15 is not uniform, the ratio of the partition walls as a whole is increased, and the ratio of the cell portions that are through holes is decreased. That is, the ratio of the part which can arrange | position a semiconductor element becomes small, and the part which can be utilized effectively as a thermoelectric conversion apparatus decreases.

  The honeycomb for thermoelectric conversion devices in the present invention may be any insulating non-metallic inorganic material. The honeycomb may be made of glass, inorganic crystal material, amorphous material or the like, but is preferably made of ceramics. In addition, as a honeycomb before finally becoming a thermoelectric conversion device, a ceramic precursor described later may be used. The ceramic material may be a material having strength, insulating properties, and heat resistance, such as oxide ceramics, silicon nitride, aluminum nitride, silicon carbide, or a composite material made of or containing these ceramics. Of these ceramic materials, oxide ceramics are particularly preferable. Oxide ceramics are suitable materials in terms of heat resistance, insulation, strength, thermal conductivity, thermal expansion, and the like. The thermal conductivity and thermal expansibility are preferably close to those of a semiconductor material that is a thermoelectric element material to be described later, rather than being particularly large or small. If the thermal expansion value of the honeycomb material is close to the value of the thermoelectric element material, the temperature in the internal cross section parallel to the surface of the thermoelectric conversion device becomes uniform when the thermoelectric conversion device is placed in an environment with a large temperature difference. It is easy to reduce distortion due to thermal expansion. Preferred oxide ceramics include alumina, silica, magnesia, mullite, cordierite, aluminum titanate, titania, ceria and the like. Among these, alumina and cordierite are particularly suitable honeycomb materials with a good balance of strength, insulation and heat resistance.

  Such honeycomb structure ceramics may be manufactured by a conventionally known method. For example, the ceramic powder precursor having a honeycomb structure may be manufactured by adjusting the particle size of the raw material powder to form a slurry, followed by molding, drying, degreasing, etc., and sintering this. At the time of molding, it is convenient to produce a honeycomb structure by extrusion molding, cut it into an appropriate length, and dry and degrease it. Alternatively, the honeycomb structure may be produced by pressure molding while being powdered and sintered. Furthermore, the honeycomb structure can be formed and sintered in one step by hot pressing. The resulting ceramic honeycomb may have a size corresponding to the size of each thermoelectric conversion device before sintering, but in general, the size of the thermoelectric conversion device for power generation is several millimeters to several tens of centimeters square. Since it has a plate shape of 5 mm to several mm, it is fired as an integral multiple of a size corresponding to the size of a predetermined thermoelectric conversion device, and after sintering or after forming a semiconductor element in each cell described later, the thermoelectric You may cut | disconnect to the magnitude | size of a converter.

A manufacturing method of cordierite will be described as an example of the ceramic honeycomb in the thermoelectric conversion device of the present invention. The cordierite raw material powder is mainly composed of oxides of Al, Si, and Mg. When Al, Si, and Mg are converted into oxides to make a total of 100%, Al ₂ O ₃ is 10 to 30%, It contains 40 to 60% of SiO ₂ and 10 to 30% of MgO. _{Further, CaO: 0~0.05%, Na 2} O: 0~0.05%, K 2 O: 0~0.05%, TiO 2: 0~1%, Fe 2 O 3: 0~1% , PbO: 0 to 1%, P ₂ O ₅ : 0 to 0.2%, etc. may be contained. Components inevitably mixed such as CaO, Na ₂ O, K ₂ O, TiO ₂ , Fe ₂ O ₃ , PbO, P ₂ O ₅ are preferably 2.5% or less as a whole. Most of the honeycomb after firing becomes cordierite, but it may contain mullite, spinel and the like.

  The above-mentioned raw materials are introduced into a medium such as water or alcohol together with a molding aid, sufficiently mixed and pulverized by a ball mill or the like, and then formed into a slurry, and a columnar honeycomb structure is formed by an extrusion molding method. This honeycomb structure may be the same size as the thermoelectric conversion device, but it is usually convenient to use the honeycomb structure with a cross-sectional area and a length larger than those of the thermoelectric conversion device while cutting in the manufacturing process of the thermoelectric conversion device. is there. In addition, as for the shape of each cell of the honeycomb structure, the cross-sectional shape of the cell is usually a square, a regular hexagon, a circle, a rectangle close to a square, an octagon, or the like. The cross-sectional area ratio between the p-type semiconductor and the n-type semiconductor may be determined in accordance with the cross-sectional area of each semiconductor planned from the performance of the p-type semiconductor and the n-type semiconductor of the desired thermoelectric conversion module. For example, the cross-sectional area ratio between the p-type semiconductor and the n-type semiconductor may be 1: 3 to 3: 1. The honeycomb structure is dried and degreased. The degreased honeycomb structure may be cut into a thickness corresponding to the thickness of the fired thermoelectric conversion device to form a thin plate-like honeycomb. Firing is completed at 1200 to 1450 ° C. for several hours to several tens of hours. The finished cordierite honeycomb may be cut into a thin plate-shaped honeycomb. Note that the cutting can be performed after inserting a semiconductor material, which will be described later, or after firing the semiconductor material.

  Next, a semiconductor raw material filling process for filling a semiconductor raw material in a honeycomb and a semiconductor forming process for forming a p-type semiconductor and an n-type semiconductor in a honeycomb cell will be described. A predetermined semiconductor material is inserted into each cell of the plate-shaped honeycomb manufactured as described above. The semiconductor material may have any shape such as powder, slurry, paste, and the like. In the case of slurry or paste, drying is performed again to remove the solvent, and a plate-like honeycomb in which a semiconductor material is inserted is fired to obtain a cordierite honeycomb in which a semiconductor is inserted into each cell. Firing may be performed at 900 to 1400 ° C. according to the sintering temperature of the semiconductor, similarly to the ordinary cordierite firing conditions. When a semiconductor is sintered, there is an advantage that sintering under pressure is easy to form a semiconductor that is dense and has low electric resistance and good thermoelectric conversion performance. The surface of the resulting semiconductor-formed honeycomb is polished to smooth the fired semiconductor surface and the honeycomb surface. When the honeycomb is larger than the desired thermoelectric conversion device, the honeycomb for cutting the thermoelectric conversion device is cut out. For example, if each of the vertical and horizontal directions of the honeycomb is three times that of the thermoelectric conversion device, a total of nine honeycombs for the thermoelectric conversion device are manufactured by cutting each of the vertical and horizontal directions by 1/3. If the thickness of the honeycomb is 10 times that of the honeycomb for the thermoelectric conversion device, the honeycomb is cut into 10 pieces to produce the honeycomb for the thermoelectric conversion device.

  As a modified example of semiconductor formation, a semiconductor material may be inserted into a honeycomb in a state of a formed shape before sintering as described above, and the honeycomb and the semiconductor material may be sintered simultaneously.

  The semiconductor material for the thermoelectric conversion element in the method for manufacturing a thermoelectric conversion device of the present invention may be any material as long as it has a thermoelectric conversion function after sintering. The thermoelectric conversion function after sintering of the semiconductor material is such that the p-type semiconductor and the n-type semiconductor generate positive and negative electromotive forces due to the same temperature difference, so that the end portion of the p-type semiconductor on one side of the thermoelectric conversion device And the end portion of the n-type semiconductor are coupled by an electrode, so that the electromotive force of the p-type semiconductor and the electromotive force of the n-type semiconductor are between the end portion of the p-type semiconductor and the end portion of the n-type semiconductor on the opposite surface. The total electromotive force with the electric power is obtained. Usually, the electromotive force is increased by combining the terminal on the opposite side with the terminal of the adjacent thermoelectric conversion element. At this time, serial coupling and parallel coupling are conceivable as coupling methods of adjacent thermoelectric elements. If only the theoretical electromotive force is considered, the same electromotive force can be obtained in either case, and the difference is whether it is recovered with high voltage and small current power or with low voltage and large current power. However, in practice, a semiconductor material is not a good conductor, and thus generates an internal resistance when a current flows. In order to reduce this effect, it is better to reduce the current flowing inside the semiconductor. In order to do this, it is preferable to connect individual thermoelectric conversion elements in the thermoelectric conversion device in series. In this way, an electromotive force with a high voltage and a small current is generated.

Specific p-type semiconductor and n-type semiconductor materials include Bi / Te, Se / Te, Cs / Bi / Te, Pb / Te, Pb / Se / Te, Zn / Sb, Co / Examples include Sb, Ce / Fe / Co / Sb, and Si / Ge systems. Further, preferable semiconductor materials include InO ₂ —SnO ₂ system, (Ca, Bi) MnO ₃ system, (Zn, Al) O system, Na (Co, Cu) O ₄ system, and NaCo ₂ O ₄ system. Can be mentioned. Particularly preferred combinations of p-type and n-type semiconductors are NaCoO ₂ and ZnO, NaCoO ₂ and (Ca _0.9 Bi _0.1 ) MnO ₃ , Ca ₃ Co ₄ O ₉ and ZnO, and Ca ₃ Co ₄ O. ₉ and a combination of (Ca _0.9 Bi _0.1 ) MnO _{3 and} the like. In addition, although Bi / Te system or ZnO is described as a semiconductor material here, these are all semiconductors, and not only pure metals and metal compounds but also p-type doped with other elements. Or an n-type semiconductor. For example, ZnO is an n-type semiconductor doped with Al.

  Next, an electrode joining process for joining the p-type semiconductor and the n-type semiconductor in the honeycomb with an electrode such as copper will be described with reference to a cross-sectional view of the thermoelectric conversion element shown in FIG. An electrode is connected to a honeycomb in which a semiconductor is formed in a cell whose shape as a thermoelectric converter is arranged. In the upper part of the figure, which is the high-temperature side coupling of the thermoelectric conversion element 17, the p-type semiconductor 12 and the n-type semiconductor 13 are coupled by a copper high-temperature side electrode 14. At this time, the high temperature side electrode 14 and the p-type semiconductor 12 and the n-type semiconductor 13 are brought into close contact with each other by a conductive adhesive member. This adhesive member not only improves the adhesion between the high temperature side electrode 14 and the p-type semiconductor 12 and the n-type semiconductor 13, but also prevents atoms from diffusing with each other. This is because thermoelectric conversion performance may be deteriorated when atoms move into and diffuse from the semiconductor. As a raw material for the adhesive member, a material such as platinum, hafnium, silver, or the like that has little diffusion of atoms into the semiconductor and less atoms from the semiconductor is preferable. The electrodes may be connected by any method such as thermal spraying, transfer, coating, and adhesion. In addition, it is preferable that the electrode surface of the thermoelectric conversion element is coat | covered with the insulator. In this way, the generated power is prevented from leaking to the outside, and at the same time, the semiconductor material and the electrode material are protected from oxidative deterioration due to a high temperature atmosphere on the high temperature electrode side.

  In the connection at the lower part of the thermoelectric element, which is the low-temperature side coupling of the thermoelectric conversion element, the p-type semiconductor 12 and the n-type semiconductor 13 are joined by a copper low-temperature side electrode 18. At this time, the low-temperature side electrode 18 is bonded to the p-type semiconductor 12 and the n-type semiconductor 13 by a conductive adhesive member similarly to the high-temperature side electrode 14, but the temperature during use is low. In addition, atoms are hardly transferred and diffused from the semiconductor into the electrode material.

  As a preferred embodiment of the present invention, a method for manufacturing a thermoelectric conversion device using a discharge plasma sintering method in a semiconductor formation step will be described. The method for manufacturing a thermoelectric conversion device using this discharge plasma sintering method can significantly reduce the sintering time in forming a semiconductor and lower the sintering temperature than the above-described method for manufacturing a thermoelectric conversion device.

The discharge plasma sintering method is a method in which an oxide semiconductor raw material powder having conductivity is sintered in a one-step process at a low temperature and in a short time directly by discharge plasma in vacuum under pressure. Usually, the sintering time is a few minutes. The starting material is the same as that used in atmospheric pressure sintering, hot press sintering, etc., and raw material powder obtained after mixing and reaction by a ball mill, such as alkali metals and transition metals having p-type semiconductor characteristics As a conductive metal oxide compound containing Na, NaCo ₂ O ₄ , Na, Li solid solution type tetragonal crystal, a wurtzite type zinc oxide having a trace amount of Al added so as to have n-type semiconductor characteristics, and the like are used. .

  The particle size of the powder is preferably a fine powder of 0.1 μm to 100 μm. These starting powder materials are filled into honeycomb cells, placed in a discharge plasma sintering apparatus, evacuated so that discharge plasma can be generated, and a DC pulse is applied while pressing from both sides of the cell. Sintering is performed using heat generated by the discharge plasma generated between the raw material powder particles. The raw material powder filled in the cells of the honeycomb may be filled in the cell as it is, but if it is difficult to fill due to the fine powder, it is filled into the cell as a slurry or paste and dried. Sintering may be performed. In this discharge plasma sintering method, the applied pressure is 10 MPa to 47 MPa, the time is 1 to 5 minutes, the applied current voltage is 1 to 3 KA, 1 to 10 V, and the temperature is controlled to 600 ° C. to 900 ° C. It is preferable.

  In spark plasma sintering, the semiconductor raw materials filled in the cells may be sintered one by one, but all the cells in one honeycomb are filled with the semiconductor raw materials, and the semiconductor raw materials in each cell It is advantageous from the viewpoint of shortening the sintering time that the discharge plasma sintering is simultaneously performed. When the sintering conditions of the p-type semiconductor raw material and the n-type semiconductor raw material are significantly different, the p-type semiconductor raw material and the n-type semiconductor raw material may be classified and sintered. Also in this case, it is preferable that the p-type semiconductor raw material and the n-type semiconductor raw material are respectively sintered together.

  Further, there is a method in which a honeycomb filled with a semiconductor material is not a ceramic honeycomb but a ceramic precursor honeycomb before sintering, and the entire honeycomb filled with the semiconductor material is pressed and sintered. In spark plasma sintering, sintering can be performed at a relatively low temperature and in a short time, so there is less movement and diffusion of elements between different materials, so this ceramic honeycomb manufacturing process and semiconductor manufacturing process are performed simultaneously. Easy to do.

  Further, the raw material of the close contact member between the semiconductor element and the electrode in the joining step for joining the semiconductor element and the electrode can be pulverized and subjected to discharge plasma sintering simultaneously with the semiconductor raw material. As a raw material of the adhesion member, a material such as platinum, hafnium, silver, or the like that diffuses atoms into a semiconductor and has little diffusion of atoms from the semiconductor is preferable.

  A specific example of spark plasma sintering will be described with reference to FIG. FIG. 1 is a view in which a semiconductor raw material filled in one cell of a ceramic honeycomb is sintered by a discharge plasma sintering apparatus. 1 is a discharge plasma sintering apparatus, and 10 is a raw material powder of a semiconductor material filled in a cell of a ceramic honeycomb 9. The semiconductor material 10 is placed in a sintered space 7 partitioned by a sintering vessel 6 and in a vacuum state to the extent that plasma is generated between the raw material powders. The semiconductor material 10 is pressurized from above and below by the pressure members 4 and 5 under vacuum, and the raw material powder is densely filled. The tips of the pressure members 4 and 5 are electrodes 2 and 3 that can apply a high voltage to the semiconductor material 10. The semiconductor material 10 is applied with a pulsed high voltage in a vacuum environment and a pressurized environment. Then, discharge plasma is generated between the fine powders of the semiconductor material 10. At this time, high temperature is generated around the plasma and the fine powders are sintered together. Since only the vicinity of the fine powder receives the heat generated by the plasma, the entire powder can be sintered without much influence. For this reason, the semiconductor material 10 as a whole can be sintered even if it does not reach a high temperature.

  The advantages of spark plasma sintering are as follows: (1) Sintering can be performed in a short time. (2) It can be sintered at a relatively low temperature. (3) A highly conductive semiconductor can be obtained, and the internal resistance as a thermoelectric conversion element can be reduced. (4) Since sintering is performed under pressure, a dense sintered body is likely to be generated. (5) Carrier concentration can be controlled by atmosphere control. (6) Since the grain growth does not progress and the grain interface increases, the thermal conductivity of the polycrystal decreases. (7) Different materials can be sintered simultaneously.

  In general, a thermoelectric conversion device requires a large number of thermoelectric conversion elements in order to generate a large electromotive force. On the other hand, in order to efficiently generate an electromotive force in the thermoelectric conversion element, it is necessary to make the length of the thermoelectric conversion element in the temperature difference direction, that is, the thickness of the thermoelectric conversion device as thin as possible. In order to satisfy both of these requirements, a thin plate-like thermoelectric conversion device is required. However, when such a shape is used, the change due to thermal expansion is large and it is easy to break. Further, if the thermoelectric conversion device is thin and has a large area, it is easily broken by external stress such as bending stress. Therefore, in the thermoelectric conversion device of the present invention, it is preferable to manufacture a thermoelectric conversion device that generates a desired electromotive force by connecting a plurality of thermoelectric conversion modules having a predetermined size or less as a unit of thermoelectric conversion. Each thermoelectric conversion module may be a predetermined size according to each application. If the thermoelectric conversion module is a predetermined size or less, the thermal strain due to the difference in thermal expansion on both sides of the thermoelectric conversion module is small, and it is difficult to be damaged by thermal shock, mechanical shock, and vibration. Furthermore, sufficient strength is obtained even when ceramics, which is a brittle material, is used as a mold. In the case of such modularization, ceramics is convenient as a mold because it has heat resistance and electrical insulation.

  As for the specific size of this thermoelectric conversion module, the maximum length in a cross section perpendicular to the through-holes of the honeycomb is desirably 10 cm or less, and more desirably 5 cm or less. The maximum length of the cross section is the side length in the case of a square or rectangle, the distance between opposing sides in the case of a hexagon or octagon, and the diameter in the case of a circle. Usually, the shape of the cross section perpendicular to the through-holes of the honeycomb is preferably a square or a rectangle or octagon close to a square in terms of strength and arrangement efficiency of the thermoelectric conversion module. The lower limit of the maximum length of the cross-section is not particularly limited, but considering the size of the semiconductor element and the number of each cell of the ceramic honeycomb, it is preferably 5 mm or more, particularly 10 mm or more, more preferably 20 mm or more. It is more desirable to do. In general, a ceramic honeycomb structure having a thickness of about 0.7 to 2.0 mm has a high risk of brittle fracture against bending stress when the maximum cross-sectional length is 50 mm or more, particularly 100 mm or more. Further, the weight increases in proportion to the size, and stress is easily applied to an impact, increasing the risk of breakage.

  The number of cells that can be formed is 100 (100) when the width of each cell is 0.8 mm and the thickness of the partition wall between cells is 0.2 mm on the basis of the above-mentioned honeycomb 10 cm square. × 100), and the number of cells is preferably smaller than this. Usually, it is preferably 100 to 2,000.

  As the honeycomb having the same cross-sectional shape for the p-type semiconductor and n-type semiconductor cells, a square or regular hexagonal cell structure is known. These honeycombs are regularly arranged with cells divided by the same partition wall thickness. As a honeycomb having different cross-sectional shapes for cells for p-type semiconductor and n-type semiconductor, for example, the combination of cells is cut out at four corners of a square as shown in FIG. 2 and a larger square. It is preferable to use a combination of octagons. Further, a combination of a square and a rectangle in which the length of the short side of the rectangle is the same as the length of the side of the square may be used. With such a honeycomb structure, the area ratio of the two types of cells can be arbitrarily changed, the partition walls between the cells can be made constant at the minimum necessary thickness, and the partition wall portions not involved in power generation It is possible to suppress waste and is suitable as a specific combination of two types of cells.

  It is preferable that the thermoelectric conversion apparatus which connected the some thermoelectric conversion module is connected so that a mutual change is possible. If the thermoelectric conversion modules are coupled so as to be able to change relative to each other, even if the thermoelectric conversion device is subjected to mechanical or thermal stress, the thermoelectric conversion modules can move relative to each other. Can relieve stress. Or the coupling member which couple | bonds the thermoelectric conversion module so that a fluctuation | variation absorbs stress, and it becomes difficult to apply a deformation stress to a thermoelectric conversion module.

  A thermoelectric conversion device in which thermoelectric conversion modules are connected to each other so as to be variable is also effective in handling and installation in a desired part. For example, the thermoelectric conversion device can be arranged while being deformed according to the shape of the installation place. For example, when a thermoelectric conversion device is installed in an exhaust pipe of an automobile engine, the thermoelectric conversion device can be cylindrical.

  As a method of connecting the thermoelectric conversion modules so that they can be varied, for example, the thermoelectric conversion modules may be arranged on a flexible substrate. The substrate and the thermoelectric conversion module may be connected by any method, for example, by bolting, fixing with a hook protruding from the substrate, or bonding with an adhesive. The material of the substrate and the joining jig and the joining method are selected in consideration of the usage environment of the thermoelectric conversion module. For example, when the substrate is disposed on the high temperature side of the thermoelectric conversion module, it is preferable to use a metal material that can withstand the use temperature. When the substrate is disposed on the low temperature side of the thermoelectric conversion module, it can be made of a plastic or rubber material that can withstand the use temperature. Moreover, as a connection method, it is not necessary to use a board | substrate and you may connect a thermoelectric conversion module with a flexible tape or a string-like connection member. Or you may couple | bond thermoelectric conversion modules with a flexible adhesive agent. Moreover, the conducting wire and connection terminal for electrically connecting a thermoelectric conversion module can also be utilized as a flexible connection member.

  The above-described thermoelectric conversion device can be suitably used for in-vehicle use utilizing automobile waste heat. Electric power can be generated by arranging the thermoelectric conversion device of the present invention around an exhaust pipe of an automobile. For example, in an in-vehicle thermoelectric conversion device, a thermoelectric conversion device is disposed in an exhaust pipe, and a cooling water circulation type or air cooling type cooling device is provided on a low temperature side. The thermoelectric conversion device fixes a square plate-like thermoelectric conversion module having a thickness of about 1 mm and a side length of about 3 cm with a thin metal plate. Since the metal plate is flexible, it absorbs automatic vibrations and shocks to prevent a large mechanical stress from being applied to the thermoelectric conversion module. Further, since the thermoelectric conversion module has a square plate shape of about 3 cm square, thermal stress does not increase. Since this thermoelectric conversion module is formed integrally with a small ceramic honeycomb, it is excellent in strength, vibration resistance, durability and the like, and is suitable for in-vehicle use.

  According to the method for manufacturing a thermoelectric conversion device of the present invention, it is possible to easily provide a thermoelectric conversion device that can take out a large amount of power from a heat source from a relatively low temperature to a high temperature of 1000 ° C. or more and can be used as a power generation device. . In particular, it is possible to provide a thermoelectric conversion device that has high heat utilization efficiency and can effectively extract electric power from an automobile exhaust gas as an in-vehicle power generation device and can be used as a power source for power or auxiliary equipment.

It is the schematic of a semiconductor sintering apparatus. It is a top view of a thermoelectric converter. It is a schematic sectional drawing of a part of thermoelectric conversion apparatus.

Explanation of symbols

1: Semiconductor sintering device 2: Electrode 3: Electrode 4: Pressurizing member 5: Pressurizing member 6: Sintering vessel 7: Sintering space 8: Power supply device 9: Honeycomb partition wall 10: Semiconductor raw material 11: Thermoelectric converter 12 : P-type semiconductor 13: n-type semiconductor 14: high temperature side electrode 15: honeycomb partition 16: terminal 17: thermoelectric conversion element 18: low temperature side electrode

Claims (5)

A raw material filling step of alternately filling a p-type semiconductor raw material and an n-type semiconductor raw material into each through-hole of a honeycomb made of a nonmetallic inorganic material;
A semiconductor forming step of sintering the p-type semiconductor raw material and the n-type semiconductor raw material filled in the honeycomb to form a p-type semiconductor and an n-type semiconductor in each through-hole of the honeycomb;
A method of manufacturing a thermoelectric conversion device, comprising: an electrode bonding step of bonding a p-type semiconductor and an n-type semiconductor formed in the through-hole of the honeycomb with electrodes.   The said semiconductor formation process applies a voltage, pressurizes the p-type semiconductor raw material and n-type semiconductor raw material with which the honeycomb was filled, generates discharge plasma, and sinters it. A method for manufacturing a thermoelectric converter.   The thermoelectric conversion device according to claim 1 or 2, wherein the non-metallic inorganic material is a ceramic precursor, and the honeycomb, the p-type semiconductor raw material, and the n-type semiconductor raw material are sintered in the semiconductor forming step. Manufacturing method.   The method for manufacturing a thermoelectric conversion device according to claim 1, wherein the non-metallic inorganic material is ceramic, and only the p-type semiconductor material and the n-type semiconductor material are sintered in the semiconductor forming step.   It is characterized in that at least one of a p-type semiconductor raw material and an n-type semiconductor raw material is filled into a through-hole as a powder, or filled into a through-hole as a slurry or a paste and dried, and then sintered. The manufacturing method of the thermoelectric conversion apparatus as described in any one of Claims 1-4.

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