Method for manufacturing thermoelectric conversion element

Abstract

Provided is a method for manufacturing a thermoelectric conversion element. If upsizing is performed for mass production, the pressure during pressure sintering is likely to be insufficient, and the relative density of the thermoelectric conversion element is likely to be insufficient, due to insufficient load and the like resulting from upsizing of the area of the pressure surface. As a solution, a method for manufacturing a thermoelectric conversion element is characterized by comprising: a step of mixing a powder of a skutterudite-type thermoelectric conversion material containing Sb and a sintering aid containing a compound composed of Mn and Sb to obtain a mixture; and a step of sintering the mixture.

Description

TECHNICAL FIELD

[0001] The present application relates to a thermoelectric conversion element that directly converts thermal energy into electric energy. BACKGROUND

[0002] In recent years, in order to reduce energy consumption, waste heat from heat sources such as boilers, incinerators, and automobiles has been studied as power recovery. In particular, a thermoelectric conversion module that uses a thermoelectric conversion element capable of directly converting thermal energy into electric energy using the Seebeck effect and is capable of efficiently recovering electric energy has attracted attention. As a material that has made the most progress in practical use, a Bi2Te3-based compound can be cited, which is mainly used in a temperature range of normal temperature to about 200°C, however, aiming at the next popular material, materials that exhibit high thermoelectric properties in various temperature ranges are being actively explored. In particular, silicide-based, Pb-Te-based, skutterudite-based, Si-Ge-based, and Heusler-based inorganic materials exhibit high thermoelectric properties in a temperature range of 300°C or higher, and research is being actively conducted.

[0003] A thermoelectric conversion module of a well-known inorganic material arranges an N-type element that uses electrons as carriers and a P-type element that uses holes as carriers, and connects one end by an electrode to become a π-type. The element used in the π-type module is a rectangular parallelepiped or a cube of several mm to about 1 cm, and therefore a technology that efficiently produces an element block material of several mm is also required. As a method thereof, a method that is generally performed is a method in which a material that is melted from a raw material to become a desired composition is formed into a powder shape by crushing or the like, and then the powder is pressure-sintered. Pressure-sintering is a method that simultaneously performs sintering and molding by performing compression in heating, and uses a hot-pressing method or HIP (Hot Isostatic Pressing), and a spark plasma sintering method (SPS method) that simultaneously performs mechanical pressurization and pulse current heating, or the like.

[0004] For example, in Patent Literature 1, a thermoelectric conversion element using a skutterudite-based compound Ce 0.2 Co 3.95 Mn 0.05 Sb 12 and a manufacturing method thereof are disclosed, in which a metal raw material containing Ce, Co, Mn, and Sb is put in a quartz tube, sealed in a vacuum, melted at 1100°C for 12 hours, then quenched in water, the obtained ingot is heat-treated at 800°C for 120 hours, and the obtained powder is subjected to SPS sintering at 600°C for 5 minutes at a pressure of 50 MPa.

[0005] Further, in Patent Literature 2, a thermoelectric conversion material whose average particle diameter of crystals is 50 nm or less and whose relative density is 85% or more, and a manufacturing method thereof are disclosed, in which the manufacturing method includes preparing a finely pulverized powder, and performing sintering or solidification under a pressure of 0.5 GPa or more and 10 GPa or less.

[0006] Patent Literature 1: International Publication No. 2013 / 009430

[0007] Patent Literature 2: International Publication No. 2004 / 049464

[0008] In the method of Patent Literature 1, if upsizing for mass production, there is a problem that the relative density of the thermoelectric conversion element easily becomes insufficient due to insufficient pressure or the like. On the other hand, in the case where a finely pulverized powder is obtained as in Patent Literature 2, since the specific surface area becomes large, oxidation is easily promoted in the pre-sintering stage, and in the case where a thermoelectric conversion element is obtained using this finely pulverized powder, there is a problem that the thermoelectric properties of the thermoelectric conversion element easily decrease. SUMMARY

[0009] An object of the present application is to provide a manufacturing method of a thermoelectric conversion element which is excellent in mass productivity and suitable for high densification while maintaining thermoelectric properties.

[0010] The manufacturing method of a thermoelectric conversion element of the present application is characterized by including a step of mixing a thermoelectric conversion material powder of a skutterudite type containing Sb and a sintering aid containing a compound composed of Mn and Sb to obtain a mixture, and a step of sintering the mixture.

[0011] Further, it is preferable that the compound composed of Mn and Sb be observed by XRD to have a peak of a crystal structure of at least any one of Sb and Mn2Sb. 1.1 Sb and Mn2Sb.

[0012] Further, it is preferable that the sintering aid be 10% by mass or less relative to the total amount of the thermoelectric conversion material and the sintering aid in the mixture.

[0013] Further, it is preferable that the thermoelectric conversion material powder contain Yb and Co.

[0014] Further, it is preferable that the thermoelectric conversion material powder contain Ce and Fe.

[0015] According to the present application, it is possible to provide a manufacturing method of a thermoelectric conversion element which is excellent in mass productivity and suitable for high densification while maintaining thermoelectric properties. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1is a flowchart showing a manufacturing method of a thermoelectric conversion element.

[0017] Figure 2 is a flowchart showing a process of preparing a thermoelectric conversion material powder.

[0018] Figure 3 is a flowchart showing a process of mixing the thermoelectric conversion material powder with a sintering aid and a process incidental thereto.

[0019] Figure 4 is a flowchart showing a sintering process.

[0020] Figure 5 is a graph showing a comparison of (a) resistance, (b) Seebeck coefficient, and (c) power factor of Example 1 and Comparative Example 1.

[0021] Figure 6 is a photograph of an SEM observation of a cross section of Example 1 at (a) 500 times and (b) 2000 times.

[0022] Figure 7 is a photograph of an SEM observation of a cross section of Comparative Example 1 at (a) 500 times and (b) 2000 times.

[0023] Figure 8 is a photograph of an SEM observation of a cross section of (a) Example 3 at 2000 times and (b) Comparative Example 3 at 2000 times.

[0024] Figure 9 is a graph showing a relationship between density of a thermoelectric conversion element and sintering pressure.

[0025] Figure 10 is a graph of results of HAADF-STEM-EDX line analysis of a grain boundary of a thermoelectric conversion element.

[0026] Figure 11 is a graph of correlation of pressurized sintering pressure and density of Example 10 and Comparative Example 4.

[0027] Figure 12 is a graph of correlation of pressurized sintering pressure and density of Example 11, Example 12, and Comparative Example 5.

[0028] Figure 13 is a graph of correlation of pressurized sintering pressure and density of Example 14 and Comparative Example 7. DETAILED DESCRIPTION

[0029] The following describes an embodiment of a manufacturing method of a thermoelectric conversion element of the present application. As Figure 1The manufacturing method of the thermoelectric conversion element of the present embodiment includes: a process of preparing a thermoelectric conversion material powder of skutterudite type containing Sb (S1: thermoelectric conversion material powder preparation process); a process of mixing the thermoelectric conversion material powder with a sintering aid containing a compound composed of Mn and Sb to obtain a mixture (S2: sintering aid mixing process); and a process of sintering the mixture (S3: sintering process). In addition, the thermoelectric conversion material powder of skutterudite type containing Sb can be purchased, for example, and the process of preparing the thermoelectric conversion material powder of skutterudite type containing Sb (S1: thermoelectric conversion material powder preparation process) can be omitted.

[0030] First, the following describes Figure 2 The process of preparing the thermoelectric conversion material powder is shown. In the present application, the thermoelectric conversion material contains Sb, and the crystal structure has skutterudite type. For example, materials of Yb-containing CoSb3 type, CoSb3 type, Ce-containing CoSb3 type, Ce-containing FeSb3 type, and the like can be listed. For example, CoSb3 type containing Yb 0.3 Co4Sb 12 The metal raw material of the desired composition formula of the thermoelectric conversion material is weighed (S1-1: raw material weighing process). At this time, since the vapor pressure of antimony (Sb) is high, a slight evaporation at the time of heating is taken into consideration, and a few amounts, for example, 1 to 3 mass% can be weighed at the time of weighing. In addition, the raw material that is easily oxidized, for example, cerium (Ce), and the like is preferably weighed in a non-active atmosphere.

[0031] The weighed metal raw material is melted and solidified in a non-oxidizing atmosphere using an electric furnace or a high-frequency furnace (S1-2: melting and solidification step). As the non-oxidizing atmosphere, it is sufficient to use a non-active gas (argon, nitrogen N2, etc.), or vacuum sealing in a quartz tube, etc., and liquid quenching solidification can also be used in the melting and solidification. The melting and liquid quenching solidification can be continuously performed in the same furnace, or the raw material mixed ingot can be melted and produced once, and then the ingot is heated and melted again and subjected to liquid quenching solidification. For example, in the case of high-frequency melting, it is confirmed that the entire body becomes a liquid phase and the molten liquid is stirred by high-frequency stirring, and after being maintained for several tens of seconds to several minutes or so, it is flowed into a mold to become an ingot. In the liquid quenching solidification, a method in which a roller of about 100°C or less (it can also be room temperature, water cooling, etc.) is rotated and the molten liquid is flowed thereon, and a method in which the molten liquid is sprayed from a spout in a crucible with a spout by air pressure, etc. can also be applied. The sample obtained by the liquid quenching solidification is a band, and the thickness thereof is preferably in the range of 1 μm or more and 1 mm or less. The band-shaped sample after the quenching solidification is in a mixed state of skutterudite crystals, amorphous mixtures, intermetallic compounds other than skutterudite, etc. In order to increase the skutterudite crystals, heat treatment can also be performed at a predetermined temperature in a non-oxidizing atmosphere (S1-3: heat treatment step). As for the thermoelectric conversion material, whether the skutterudite type is the main phase can be confirmed by XRD (X-ray Diffraction).

[0032] The skutterudite material obtained by heat treating the band-shaped sample can also be pulverized in a non-active atmosphere (S1-4: pulverization step). The pulverization method can be, for example, a method using a hammer mill, a jet mill, a ball mill, a crusher provided with a mortar, etc. The average particle diameter is sufficient to be able to be used for wet-type laser diffraction, etc., and for example, it is desired that D50 be 0.5 μm or more and 100 μm or less, it is preferably 1 μm or more and 80 μm or less, and it is more preferably 2 μm or more and 50 μm or less. After the pulverization, a method of classifying fine powder and coarse powder by a sieve, etc. can also be appropriately used.

[0033] Next, the Figure 3The process of mixing the thermoelectric conversion material powder with the sintering aid containing a compound composed of Mn and Sb to obtain a mixture is shown (S2-4: mixing process of mixing the thermoelectric conversion material powder with the sintering aid). As long as the powder of the thermoelectric conversion material and the sintering aid are sufficiently mixed and dispersed in a manner to promote densification in the sintering process, for example, as long as milling using a medium, mortar mixing, rotational mixing using a V-type mixer, or the like is performed. The sintering aid used is described below. The sintering aid in the present embodiment contains a compound composed of Mn and Sb, and by mixing the above sintering aid with the thermoelectric conversion material powder and sintering, an effect of easy sintering is obtained. Here, the compound composed of Mn and Sb is, for example, a target compound obtained by weighing pure manganese and pure antimony (S2-1: sintering aid weighing process) in an atomic ratio Mn / Sb = 0.2 to 3 and melting (S2-2: melting and solidification process). The aid component thus obtained is, for example, a mixture of MnSb and Sb in the case of an atomic ratio Mn / Sb of 1 or less, MnSb in the vicinity of an atomic ratio Mn / Sb = 1, and a mixture of MnSb and Mn2Sb in the case of an atomic ratio Mn / Sb > 1.2. In the case of Mn / Sb > 2, it is in a state where excess Mn is mixed in Mn2Sb. That is, it can be said that the compound composed of Mn and Sb contains a compound in which Mn is approximately 1 with respect to Sb (hereinafter sometimes referred to as MnSb), or a compound in which Mn is approximately 2 with respect to Sb (hereinafter sometimes referred to as Mn2Sb). Whether or not the compound composed of Mn and Sb is contained can be confirmed by XRD, and according to the alloy phase diagram of Mn and Sb, MnSb and Mn2Sb are both stable alloys, so a compound containing them is used. That is, regarding the sintering aid, as long as the compound composed of Mn and Sb can be observed by XRD to have a crystal structure peak of at least either one of MnSb and Mn2Sb. 1.1 Sb), or a compound in which Mn is approximately 2 with respect to Sb (hereinafter sometimes referred to as Mn2Sb). Whether or not the compound composed of Mn and Sb is contained can be confirmed by XRD, and according to the alloy phase diagram of Mn and Sb, MnSb and Mn2Sb are both stable alloys, so a compound containing them is used. That is, regarding the sintering aid, as long as the compound composed of Mn and Sb can be observed by XRD to have a crystal structure peak of at least either one of MnSb and Mn2Sb. 1.1 Sb), or a compound in which Mn is approximately 2 with respect to Sb (hereinafter sometimes referred to as Mn2Sb). Whether or not the compound composed of Mn and Sb is contained can be confirmed by XRD, and according to the alloy phase diagram of Mn and Sb, MnSb and Mn2Sb are both stable alloys, so a compound containing them is used. That is, regarding the sintering aid, as long as the compound composed of Mn and Sb can be observed by XRD to have a crystal structure peak of at least either one of MnSb and Mn2Sb. 1.1 Sb), or a compound in which Mn is approximately 2 with respect to Sb (hereinafter sometimes referred to as Mn2Sb). Whether or not the compound composed of Mn and Sb is contained can be confirmed by XRD, and according to the alloy phase diagram of Mn and Sb, MnSb and Mn2Sb are both stable alloys, so a compound containing them is used. That is, regarding the sintering aid, as long as the compound composed of Mn and Sb can be observed by XRD to have a crystal structure peak of at least either one of MnSb and Mn2Sb.

[0034] In addition, in the melting process (S2-2: Melting and solidification process) in the pre-process of the mixing process, either an electric furnace or a high-frequency furnace can be used. Further, a liquid quenching and solidification method can be used, and a melting process can be performed using a liquid quenching and solidification device provided with a metal roller, so that the molten liquid flows on the rotating roller to be quenched and solidified to obtain a strip-shaped sample, thereby making the subsequent pulverization process easy. Subsequently, the ingot-shaped material obtained by the melting and solidification can be pulverized into powder (S2-3: Pulverization process). The powder functions as a sintering aid by being well dispersed and coordinated on the surface of the thermoelectric conversion material. Whether the thermoelectric conversion material and the sintering aid are uniformly dispersed can be determined, for example, by observing the distribution of Mn in the aid and Co, Fe, and the like in the thermoelectric conversion material using SEM-EDX (Scanning Electron Microscope Energy Dispersive X-ray Spectroscopy). The amount of the sintering aid to be added is preferably such that the thermoelectric conversion material does not be relatively significantly reduced from the total amount, and for example, is preferably 10% by mass or less, and more preferably 0.01% by mass or more and 2% by mass or less, with respect to the total amount of the thermoelectric conversion material and the sintering aid.

[0035] Next, the sintering process shown in FIG. 2 will be described. Figure 4

[0036] To become a dense block by a solid phase reaction, the mixture is put into a mold for pressure sintering and subjected to pressure heat treatment (S3-2: Sintering process), or a material shaped into a green body (S3-1: Preliminary shaping) by uniaxial pressing or CIP (Cold Isostatic Pressing) or the like is subjected to heat treatment (S3-2: Sintering process) to be sintered, thereby obtaining a skutterudite thermoelectric conversion element. By using a sintering aid, pressure sintering of 45 MPa or less can be achieved in a case where the mold is made large using the same device as that of the pressure capacity, that is, the force applied to the surface is constant and the area is large so that the force per unit area is small, and the like, and further, high densification under sintering without pressure can be achieved. As a result, in the case of using the density of a sintered body obtained by pressure heat treatment of 50 MPa or more as a reference, even in the case of sintering without pressure, the relative density is 90% or more, and if it is pressure heat treatment of about 10 MPa, the relative density is 97% or more. For example, high densification can be achieved at a pressure of 35 MPa or less, 15 MPa or less, and further, 10 MPa or less. At this time, with respect to the power factor, for example, for Yb 0.3 Co4Sb 12 ​If 0.05 to 2 mass% of a sintering aid is added and heat treatment is performed under pressure of about 10 MPa, the thermal conductivity at 500°C is 5 mW-m -1 ·K -2 The above enables the desired values to be obtained. The temperature at the time of sintering is preferably in the range of 550°C or higher and 860°C or lower. If it is 550°C or higher, sintering is easily promoted, and if it is 860°C or lower, decomposition of skutterudite is easily suppressed. As for the atmosphere, it is preferably non-oxidizing, and a non-active gas (argon Ar, nitrogen N2, etc.), vacuum, etc. can be used. Furthermore, hydrogen, which is reducing, can also be used. In the following examples, the sintered body obtained is processed into an evaluation size using a chipper, etc. and used for evaluation.

[0037] Example

[0038] [Example 1]

[0039] Manganese (high purity chemical, 3N, particle size 300 μm or less) and antimony (Japan concentrate, 4N, granular) were weighed so as to become atomic ratio (Mn / Sb) = 1, assuming that MnSb is a sintering aid. The weighed raw materials were put into a carbon crucible, and heating and melting were performed using a high-frequency melting furnace in an argon atmosphere. After confirming that the melt had been stirred by high frequency, the melt was caused to flow into a mold. The ingot that had solidified in the mold was placed in a liquid quenching and solidification device, and was again melted in an argon atmosphere. The temperature of the melt was measured using a radiation thermometer, and after becoming 1100°C, the melt was sprayed onto a rotating copper roll to perform quenching and solidification, and a strip-shaped material was obtained. The strip-shaped material was finely pulverized using a pulverizer (bladed mill), and a sintering aid (MnSb fine powder) was obtained. When this sintering aid powder was measured by XRD, a peak of a single phase of MnSb was obtained with respect to the compound composed of Mn and Sb. 1.1 Sb.

[0040] A thermoelectric conversion material Yb 0.3 Co4Sb 12The composition of pure metals Yb, Co, and Sb was weighed. The weighed pure metal raw materials were placed in a carbon crucible and heated and melted in a high-frequency melting furnace under an inert gas atmosphere. After confirming that the melt was stirred at high frequency, the melt was allowed to flow into a mold. The ingot solidified in the mold was placed in a liquid quenching device and melted again under an inert atmosphere. The temperature of the melt was measured using a radiation thermometer, and after reaching 1150°C, quenching was performed by spraying the melt onto a rotating copper roller. The quenched material was then heat-treated at 700°C for 24 hours under an inert atmosphere and then pulverized using a hammer mill. This yielded a powder of thermoelectric conversion material (cobaltite powder). MnSb micro powder was added to the cobaltite powder at a mass percentage relative to the total amount, and the mixture was rotated 1500 times using a mixing rotor. 20g of the mixed powder was placed in a carbon mold with an inner diameter of Φ30mm and held at 700°C and a pressure of 15MPa for 1 hour under an argon atmosphere. That is, the mixture is placed in a mold for pressure sintering and sintered under pressure. This yields an apparent density of 7.74 Mg / m³. 3 A dense sintered body. Furthermore, the apparent density was determined using Archimedes' method. When performing SEM observations on the interior of the sintered body, such as... Figure 6 As shown, it becomes a dense block.

[0041] The sintered body is machined for measurement purposes. Figure 5 This indicates the results of thermoelectric properties measured using the ADVANCE RIKO ZEM-3. According to... Figure 5 At 300℃, the Seebeck coefficient is -158 μV / K, the resistivity is 4.69 μΩm, and the power factor is 5.29 mW·m. -1 ·K -2 At 400℃, the Seebeck coefficient is -168 μV / K, the resistivity is 5.09 μΩm, and the power factor is 5.55 mW·m. -1 ·K -2 At 500℃, the Seebeck coefficient is -175 μV / K, the resistivity is 5.48 μΩm, and the power factor is 5.60 mW·m. -1 ·K -2 Compared to Comparative Example 1 described later, it shows low resistance and high power factor.

[0042] [Comparative Example 1]

[0043] Except for the absence of sintering aids, a sintered body was prepared and evaluated in the same manner as in Example 1. The apparent density of this sintered body based on the Archimedes method was 7.45 Mg / m³. 3 When observing the cross-section of the sintered body using SEM, such as... Figure 7 As shown, voids exist throughout the material.

[0044] The obtained sintered body was subjected to cutting processing for measurement, Figure 5 The results of measurement of thermoelectric properties using ADVANCE RIKO ZEM-3 are shown. According to Figure 5 At 300°C, the Seebeck coefficient was -154 μV / K, the resistivity was 7.19 μΩm, and the power factor was 3.29 mW-m -1 ·K -2 At 400°C, the Seebeck coefficient was -165 μV / K, the resistivity was 7.84 μΩm, and the power factor was 3.46 mW-m -1 ·K -2 At 500°C, the Seebeck coefficient was -176 μV / K, the resistivity was 8.49 μΩm, and the power factor was 3.63 mW-m -1 ·K -2 .

[0045] [Example 2]

[0046] MnSb fine powder as a sintering aid and a thermoelectric conversion material Yb 0.3 Co4Sb 12 powder were prepared and mixed. Sintering was performed in the same manner as in Example 1 except that the pressure was maintained at 10 MPa for 1 hour. The apparent density of the sintered body based on the Archimedes method was 7.70 Mg / m 3 When the inside of the sintered body was observed by SEM, a dense bulk was obtained.

[0047] The obtained sintered body was subjected to cutting processing for measurement, and the thermoelectric properties were measured using ADVANCE RIKO ZEM-3, and the results were that at 300°C, the Seebeck coefficient was -158 μV / K, the resistivity was 5.31 μΩm, and the power factor was 4.68 mW-m -1 ·K -2 At 400°C, the Seebeck coefficient was -168 μV / K, the resistivity was 5.76 μΩm, and the power factor was 4.92 mW-m -1 ·K -2 At 500°C, the Seebeck coefficient was -176 μV / K, the resistivity was 6.06 μΩm, and the power factor was 5.11 mW-m -1 ·K -2 Compared with Comparative Example 1, a low resistance and a high power factor were shown.

[0048] [Example 3]

[0049] As to the sintering aid, manganese and antimony were weighed in a manner that the atomic ratio Mn / Sb = 1.8, and the powder of the sintering aid was produced in the same manner as in Example 1. When the sintering aid was measured by XRD, it was found to be a mixture of Mn 1.1 Sb and Mn2Sb. The Yb 0.3 Co4Sb 12 skutterudite powder was produced in the same manner as in the example. When the sintering aid was measured by XRD, it was found to be a mixture of Mn

[0050] In the Yb 0.3 Co4Sb 12 skutterudite powder, 1 mass% of MnSb fine powder was added, and the mixture was mixed using a mortar. The mixed powder 2 g was placed in a mold with an inner diameter of Φ 10 mm, and was press-formed at room temperature using uniaxial pressing at 15 kN. The formed body was placed in a vacuum-compatible furnace, and was subjected to heat treatment at a vacuum degree of less than 10 Pa, with the temperature being raised at 35°C / min and then held at 730°C for 1 hour. That is, the mixture was placed in a mold for press-forming, and was subjected to sintering in a vacuum without pressure after being press-formed. The formed body before sintering was and was sintered to become The apparent density based on the Archimedes method was 7.52 Mg / m 3 When SEM observation was performed, as shown in (a) of FIG. 6, it was found that sintering was promoted. Figure 8

[0051] As is clear from the above example, even without pressure, a density of 7.50 Mg / m 3 above was obtained at a pressure of 15 MPa or less. 3 above.

[0052] [Comparative Example 2]

[0053] The same batch of skutterudite powder as used in Example 3 was used, and the skutterudite powder 2 g was placed in a mold with an inner diameter of Φ 10 mm, and was press-formed at room temperature using uniaxial pressing at 15 kN. The formed body was placed in a vacuum-compatible furnace, and was subjected to heat treatment at a vacuum degree of less than 10 Pa, with the temperature being raised at 35°C / min and then held at 730°C for 1 hour. The diameter of the sample after heat treatment was also Φ 10 mm as before heat treatment. When the structure was observed using SEM, as shown in (b) of FIG. 7, it was found that the skutterudite powder remained as it was and was not sintered. Figure 8

[0054] [Example 4]

[0055] The skutterudite powder and the MnSb fine powder were prepared in the same manner as in Example 1 and Example 2, Figure 9 ​​The density change of the sintered body when the pressure at the time of sintering is changed in the range of 10 MPa or more and 68 MPa or less is shown. The pressure sintering at 68 MPa is taken as a reference example. As a result, in the range of low pressure of 5 MPa or more and 35 MPa or less, the density is higher than that of the comparative example (no sintering aid is added), and the apparent density at the time of 68 MPa pressure sintering is 7.77 Mg / m 3 If the sintered body sintered at 68 MPa is taken as a reference, the relative density is 99% or more even if the pressure is reduced to 10 MPa. As a result, it is known that densification is easily achieved even by pressure sintering at low pressure, and the mass productivity is high.

[0056] [Example 5]

[0057] The sintering aid was 0.1 mass% under each condition of Example 2. The density at this time was 7.71 Mg / m 3 (the relative density is 99% if the sintered body sintered at 68 MPa of the reference example is taken as a reference). Figure 9 The results are shown. As a result, the density is higher than that of Comparative Example 2, and it is known that densification is easily achieved even by pressure sintering at low pressure, for example, in the case where the amount of sintering aid is small, and the mass productivity is high.

[0058] In Figure 10 Example 3, HAADF-STEM-EDX (High-angle Annular Dark Field Scanning TEM Energy dispersive X-ray spectroscopy) was used to perform 70 nm line analysis in a manner that crosses the grain boundary. As a result, it was known that the concentration of Mn at the grain boundary has a tendency to be 3 times higher than that in the vicinity of the grain boundary.

[0059] [Example 6]

[0060] The skutterudite powder and the MnSb fine powder were prepared in the same manner as in Example 1, and a mixed powder in which the MnSb addition amount was 0.05 mass% was mixed, and sintering was performed at a pressure of 10 MPa at the time of sintering. The density of the sintered body was 7.70 Mg / m 3 If the sintered body sintered at 68 MPa without adding a sintering aid as shown in Example 4 or Figure 9 the relative density is 99%, and the same density as that of the 10 MPa pressure sintered body of Example 4 in which 1 mass% of the sintering aid was added is shown, and it is known that even in the case where the addition amount is 0.05 mass%, it is not inferior to the case where 1 mass% is added, and has a densification effect.

[0061] When the thermal-electric properties of the sintered body thus obtained were measured in the same manner as in Example 1 and Comparative Example 1, the Seebeck coefficient was -160 μV / K, the resistivity was 4.93 μΩm, and the power factor was 5.16 mW-m -1 ·K -2 at 400°C. The Seebeck coefficient was -171 μV / K, the resistivity was 5.39 μΩm, and the power factor was 5.39 mW-m -1 ·K -2 at 500°C. The Seebeck coefficient was -179 μV / K, the resistivity was 5.76 μΩm, and the power factor was 5.59 mW-m -1 ·K -2 A low resistivity and a high power factor were shown as compared with Comparative Example 1.

[0062] [Example 7]

[0063] A skutterudite powder and MnSb micro powder as a sintering aid were prepared in the same manner as in Example 1, a mixed powder in which the MnSb addition amount was 1.5 mass% was mixed, and sintering was performed at a pressure of 5 MPa. The density of the sintered body was 7.54 Mg / m 3 It was found that a higher density than that of Comparative Example 3 was obtained, and the high density was achieved by the addition of the MnSb micro powder.

[0064] [Comparative Example 3]

[0065] A sintered body at a sintering pressure of 5 MPa was produced in the same manner as in Example 7 except that no sintering aid was added, and the density was measured, and the result was 7.08 Mg / m 3 .

[0066] [Example 8]

[0067] A sintered body was produced in the same manner as in Example 7 except that the sintering pressure was 3 MPa, and the density was measured, and the result was 7.36 Mg / m 3 Although the sintering pressure was lower as compared with Comparative Example 3, the density was high, and it was found that the high density was achieved by the addition of the sintering aid.

[0068] [Example 9]

[0069] As to the sintering aid, manganese and antimony were weighed so as to become the atomic ratio Mn / Sb = 0.606, and the powder of the sintering aid was produced in the same manner as in Example 1 thereafter. If the sintering aid was measured by XRD, it was found to be a mixture of Mn 1.1 Sb and Sb. A Yb 0.3 Co4Sb 12Skutterudite powder. As in Example 7, a mixed powder was prepared by mixing with the addition amount of sintering aid powder being 1.5 mass%, and sintering was performed with the pressure at sintering being 5 MPa. The density of the sintered body was 7.57 Mg / m 3 . A higher density than that of Comparative Example 3 was obtained, and it was found that high density was achieved by the addition of a sintering aid of a mixture of Sb 1.1 and Sb.

[0070] [Example 10]

[0071] A skutterudite powder was prepared in the same manner as in Example 1, with the composition formula of the thermoelectric conversion material Ce 0.2 (Co 3.95 Mn 0.05 )Sb 12 . Pure metals of Ce, Co, Mn, and Sb were weighed, and thereafter, a skutterudite powder was prepared in the same manner as in Example 1. The preparation of a sintering aid of MnSb fine powder (showing a peak of a single phase of Mn 1.1 Sb by XRD) and the mixing of the skutterudite powder and the MnSb fine powder were performed in the same manner as in Example 1.

[0072] The density of the sintered body when the pressure at sintering was changed in the range of 8.5 MPa or more and 45 MPa or less using this mixed powder was 7.67 Mg / m 3 at 45 MPa, 7.64 Mg / m 3 at 30 MPa, and 7.58 Mg / m 3 at 8.5 MPa. Figure 11 The change in the pressure at pressurized sintering and the density is shown. The pressurized sintering at 70 MPa without the addition of a sintering aid was taken as a reference example. As a result, in the range of low pressure of 8.5 MPa or more and 45 MPa or less, the density was higher than that of the sintered body without the addition of a sintering aid, and was 7.66 Mg / m 3 , which was the density of the sintered body of the pressurized sintering at 70 MPa as the reference example. Even if the sintering pressure was lowered to 8.5 MPa, the relative density of the sintered body in which the sintering aid of MnSb fine powder was mixed was 99%, and was high density. As a result, in the range of 45 MPa or less, a density of 7.50 Mg / m 3 or more was obtained.

[0073] [Comparative Example 4]

[0074] Except that a sintering aid was not added, the pressure at sintering was changed in the range of 8.5 MPa or more and 45 MPa or less in the same manner as in Example 10, Figure 11 The results of the pressurized sintering are shown. The density of the sintered body was 7.64 Mg / m 3 at 45 MPa, 7.58 Mg / m 37.50 Mg / m3 at 15 MPa 3 7.39 Mg / m3 at 8.5 MPa 3 The density of Example 10 was high at any sintering pressure, and the sintering promoting effect by the sintering aid was confirmed.

[0075] [Example 11]

[0076] Pure metals of Co and Sb were weighed according to the composition formula of thermoelectric conversion material CoSb3, and thereafter, skutterudite powder was produced in the same process as Example 1. The production of MnSb fine powder (showing a single phase of MnSb by XRD) as a sintering aid and the mixing of the skutterudite powder and the MnSb fine powder (1 mass% of MnSb fine powder) were performed in the same process as Example 1. 1.1 Sb single phase) as a sintering aid and the mixing of the skutterudite powder and the MnSb fine powder (1 mass% of MnSb fine powder) were performed in the same process as Example 1.

[0077] The mixed powder was subjected to pressure sintering at a pressurizing pressure of 10 MPa, and was performed in the same conditions as Example 1 except for this. The apparent density of the sintered body based on the Archimedes method was 7.56 Mg / m 3 The density of the sintered body was 7.60 Mg / m 3 at 68 MPa without adding a sintering aid. Thus, even at a low pressure of 10 MPa, by adding a sintering aid, the relative density was 99% if based on the sintered body at 68 MPa, and became high density. Further, it became high density compared to the sintered body at 10 MPa in Comparative Example 5 (without adding a sintering aid) described later. Figure 12 The results thereof are shown.

[0078] [Comparative Example 5]

[0079] The same as Example 11 except that a sintering pressure was changed in the range of 5 MPa or more and 45 MPa or less at the time of sintering, and a sintering aid was not added, Figure 12 The results of pressure sintering are shown. The density was 7.57 Mg / m 3 at 45 MPa, 7.45 Mg / m 3 at 30 MPa, 7.33 Mg / m 3 at 15 MPa, and 7.23 Mg / m 3 at 10 MPa, and 7.16 MPa at 5 MPa. The sintering at 45 MPa was the same as Example 11, and the density of Example 11 was high at a sintering pressure of 30 MPa or less, and the sintering promoting effect by the sintering aid was confirmed.

[0080] [Example 12]

[0081] Sintering was performed at 5 MPa with the addition of the sintering aid fine powder prepared by compounding Mn / Sb = 2 in atomic ratio to the CoSb3 skutterudite powder, compared with the 5 MPa pressure sintering of Comparative Example 5 (without the addition of the sintering aid). The sintering aid fine powder was prepared in the same manner as in Example 1, and mixed with the skutterudite powder in such a manner that the sintering aid fine powder became 1.5 mass%. The density of the sintered body was 7.40 Mg / m 3 A high density was obtained compared with the 5 MPa pressure sintered body of Comparative Example 5.

[0082] [Example 13]

[0083] The mixed powder prepared in the same manner as in Example 11 (the thermoelectric material CoSb3 skutterudite powder mixed with the MnSb fine powder in such a manner that the MnSb fine powder became 1 mass%) was subjected to pressure sintering at 600°C and a pressure of 68 MPa. The conditions were the same as in Example 11 except for the temperature and the pressure. The density of the sintered body was 7.57 Mg / m 3 A sintered body with a high density was obtained compared with Comparative Example 6, i.e., the result of not adding the MnSb sintering aid. Further, a high density with a relative density of 100% was obtained even though the sintering temperature was lowered from 700°C to 600°C compared with the sintering at 700°C and 68 MPa described in Example 11.

[0084] [Comparative Example 6]

[0085] A sintered body was prepared in the same manner as in Example 13 except that the sintering aid was not added, and the density measurement resulted in 7.40 Mg / m 3 A low density was obtained compared with the sample to which the sintering aid was added.

[0086] [Example 14]

[0087] A MnSb fine powder was prepared as a sintering aid in the same manner as in Example 1. Next, pure metals Ce, Fe, Mn, and Sb were weighed in accordance with the composition formula of the thermoelectric conversion material Ce1(Fe0.5Mn0.5)Sb1.5. The weighed pure metal raw materials were put into a carbon crucible, and subjected to heating and melting using a high-frequency melting furnace in a non-active gas atmosphere. After confirming that the molten liquid was stirred by high frequency, the molten liquid was caused to flow into a mold. The ingot solidified in the mold was placed in a liquid quenching and solidification device, and subjected to melting again in a non-active atmosphere. The temperature of the molten liquid was measured using a radiation thermometer, and after becoming 1100°C, quenching and solidification were performed by spraying the molten liquid onto a rotating copper roll. After heat treatment of the material after quenching and solidification at 660°C for 24 hours in a non-active atmosphere, pulverization was performed using a hammer mill. A powder of the thermoelectric conversion material (skutterudite powder) was thereby obtained. 1.1 3.925 0.075 12 Sb fine powder. Next, pure metals Ce, Fe, Mn, and Sb were weighed in accordance with the composition formula of the thermoelectric conversion material Ce1(Fe0.5Mn0.5)Sb1.5. The weighed pure metal raw materials were put into a carbon crucible, and subjected to heating and melting using a high-frequency melting furnace in a non-active gas atmosphere. After confirming that the molten liquid was stirred by high frequency, the molten liquid was caused to flow into a mold. The ingot solidified in the mold was placed in a liquid quenching and solidification device, and subjected to melting again in a non-active atmosphere. The temperature of the molten liquid was measured using a radiation thermometer, and after becoming 1100°C, quenching and solidification were performed by spraying the molten liquid onto a rotating copper roll. After heat treatment of the material after quenching and solidification at 660°C for 24 hours in a non-active atmosphere, pulverization was performed using a hammer mill. A powder of the thermoelectric conversion material (skutterudite powder) was thereby obtained.​​​

[0088] Mn was added to and mixed in the skutterudite powder at 0.8 mass% relative to the total amount 1.1 Sb fine powder. Pressure sintering was performed at a sintering temperature of 660°C under five conditions of a pressurizing pressure of 3 MPa, 5 MPa, 7.5 MPa, 10 MPa, and 15 MPa, and sintered bodies were produced. The other sintering conditions were the same as in Example 1. The density of the sintered body was 7.67 Mg / m 3 under a pressurizing pressure of 3 MPa, 7.83 Mg / m 3 under a pressurizing pressure of 5 MPa, 7.84 Mg / m 3 under a pressurizing pressure of 7.5 MPa, 7.84 Mg / m 3 under a pressurizing pressure of 10 MPa, and 7.85 Mg / m 3 under a pressurizing pressure of 15 MPa. As a reference example, it was 7.86 Mg / m 3 under a pressurizing pressure of 68 MPa without adding a sintering aid. Thus, if the sintered body under a pressurizing pressure of 68 MPa is taken as a reference, the relative density was 98% in sintering at 3 MPa and 100% in sintering at 5 MPa, and a density equivalent to that in high-pressure sintering was obtained even at a low pressure. In addition, compared with Comparative Example 7 (without adding a sintering aid), the side with the added sintering aid became high-density in low-pressure sintering at 7.5 MPa or less.

[0089] The 3 MPa pressure-sintered body was subjected to cutting processing for measurement, and the thermoelectric properties were measured using ADVANCE RIKO ZEM-3, and the results were a Seebeck coefficient of 140 μV / K, an electrical resistivity of 6.67 μΩm, and a power factor of 2.92 mW·m -1 ·K -2 at 300°C, a Seebeck coefficient of 152 μV / K, an electrical resistivity of 7.18 μΩm, and a power factor of 3.23 mW·m -1 ·K -2 at 400°C, and a Seebeck coefficient of 162 μV / K, an electrical resistivity of 7.64 μΩm, and a power factor of 3.43 mW·m -1 ·K -2 at 500°C. Compared with Comparative Example 7 described later, a low electrical resistivity and a high power factor were shown.

[0090] [Comparative Example 7]

[0091] A sintered body was produced and evaluated in the same manner as in Example 14 except that no sintering aid was added and the pressurizing pressure at the time of sintering. The density of the sintered body was 7.57 Mg / m 37.76 Mg / m2 at a pressurizing pressure of 5 MPa 3 7.81 Mg / m2 at a pressurizing pressure of 7.5 MPa 3 7.85 Mg / m2 at a pressurizing pressure of 10 MPa 3 7.85 Mg / m2 at a pressurizing pressure of 15 MPa 3 .

[0092] The 3 MPa pressurized sintered body was subjected to cutting processing for use in measurement, and the thermoelectric properties were measured using ADVANCE RIKO ZEM-3, and as a result, in the sample produced at a pressurizing pressure of 3 MPa, at 300°C, the Seebeck coefficient was 137 μV / K, the resistivity was 7.83 μΩm, and the power factor was 2.39 mW·m -1 ·K -2 At 400°C, the Seebeck coefficient was 149 μV / K, the resistivity was 8.44 μΩm, and the power factor was 2.64 mW·m -1 ·K -2 At 500°C, the Seebeck coefficient was 157 μV / K, the resistivity was 8.93 μΩm, and the power factor was 2.76 mW·m -1 ·K -2 .

Claims

1. A method for manufacturing a thermoelectric conversion element, characterized in that, include: The process of mixing Sb-containing cobaltite-type thermoelectric conversion material powder with a sintering aid containing a compound composed of Mn and Sb to obtain a mixture. as well as The process of sintering the mixture.

2. The method for manufacturing the thermoelectric conversion element according to claim 1, characterized in that, The compound composed of Mn and Sb can be observed to contain Mn by XRD. 1.1 Peaks in the crystal structure of at least one of Sb and Mn2Sb.

3. The method for manufacturing the thermoelectric conversion element according to claim 1, characterized in that, In the mixture, the sintering aid is less than 10% by mass relative to the total amount of thermoelectric conversion material and sintering aid.

4. The method for manufacturing the thermoelectric conversion element according to claim 2, characterized in that, In the mixture, the sintering aid is less than 10% by mass relative to the total amount of thermoelectric conversion material and sintering aid.

5. A method for manufacturing a thermoelectric conversion element according to any one of claims 1 to 4, characterized in that, The thermoelectric conversion material powder contains Yb and Co.

6. A method for manufacturing a thermoelectric conversion element according to any one of claims 1 to 4, characterized in that, The thermoelectric conversion material powder contains Ce and Fe.

7. The method for manufacturing the thermoelectric conversion element according to claim 1, characterized in that, In the process of sintering the mixture, the mixture is pressure sintered at a pressure below 45 MPa.

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