Thermoelectric Conversion Element and Thermoelectric Conversion Module

Abstract

A thermoelectric conversion element in which one end of an n-type thermoelectric conversion material and one end of a p-type thermoelectric conversion material are each bonded to a conductive substrate using a bonding agent, the n-type thermoelectric conversion material and the p-type thermoelectric conversion material being specific silicides, the bonding agent being a conductive paste containing conductive metals consisting of silver and at least one noble metal selected from the group consisting of gold, platinum, and palladium, as well as a thermoelectric conversion module comprising a plurality of these thermoelectric conversion elements and having a specific structure, achieve excellent thermoelectric conversion performance in an intermediate temperature range of room temperature to about 700 C., and performance degradation hardly occurs even when electric generation is repeated, making it possible to maintain the excellent performance over a long period of time.

Claims

1. A thermoelectric conversion element wherein one end of an n-type thermoelectric conversion material and one end of a p-type thermoelectric conversion material are each bonded to a conductive substrate using a bonding agent, wherein (1) the n-type thermoelectric conversion material is a silicide of the following item (a) or (b): (a) a silicide represented by the compositional formula: Mn.sub.3-x1M.sup.1.sub.x1Si.sub.y1Al.sub.z1M.sup.2.sub.a1, wherein M.sup.1 is at least one element selected from the group consisting of Ti, V, Cr, Fe, Co, Ni, and Cu, wherein M.sup.2 is at least one element selected from the group consisting of B, P, Ga, Ge, Sn, and Bi, and 0x13.0, 3.5y14.5, 2.0z13.5, and 0a11, the silicide having a negative Seebeck coefficient at a temperature of 25 C.; or higher; or (b) a silicide represented by the compositional formula: Mn.sub.x2M.sup.3.sub.y2Si.sub.m2Al.sub.n2, wherein M.sup.3 is at least one element selected from the group consisting of Ti, V, Cr, Fe, Co, Ni, and Cu, and 2.0x23.5, 0y21.4, 2.5x2+y21.5, 3.5m24.5, and 1.5n22.49, the silicide having a negative Seebeck coefficient at a temperature of 25 C. or higher, (2) the p-type thermoelectric conversion material is a silicide represented by the compositional formula: Mn.sub.m3M.sup.4.sub.n3Si.sub.p3, wherein M.sup.4 is at least one element selected from the group consisting of Ti, V, Cr, Fe, Co, Ni, and Cu, and 0.8m31.2, 0n30.4, and 1.5p32.0, the silicide having a positive Seebeck coefficient at a temperature of 25 C. or higher, and (3) the bonding agent is a conductive paste containing conductive metals consisting of silver and at least one noble metal selected from the group consisting of gold, platinum, and palladium.

2. The thermoelectric conversion element according to claim 1, wherein the conductive paste contains the at least one noble metal selected from the group consisting of gold, platinum, and palladium in a total amount of 0.5 to 95 parts by weight, per 100 parts by weight of silver.

3. The thermoelectric conversion element according to claim 1, wherein the conductive paste further contains a glass powder component, a resin component, and a solvent component.

4. The thermoelectric conversion element according to claim 1, wherein the conductive substrate is a sheet-shaped conductive metal, a conductive ceramics, or an insulating ceramics on which a conductive metal coating is formed.

5. The thermoelectric conversion element according to claim 4, wherein the conductive substrate is a silver sheet having a thickness of 0.05 to 3 mm.

6. A thermoelectric conversion module comprising a plurality of the thermoelectric conversion elements of claim 1, wherein the plurality of the thermoelectric conversion elements are connected in series in such a manner that an unconnected end of the p-type thermoelectric conversion material of one of the plurality of the thermoelectric conversion elements and an unconnected end of the n-type thermoelectric conversion material of another one of the plurality of the thermoelectric conversion elements are bonded to a conductive substrate using a bonding agent, and wherein the bonding agent is a conductive paste containing conductive metals consisting of silver and at least one noble metal selected from the group consisting of gold, platinum, and palladium.

7. The thermoelectric conversion module according to claim 6, wherein the conductive paste contains the at least one noble metal selected from the group consisting of gold, platinum, and palladium in a total amount of 0.5 to 95 parts by weight, per 100 parts by weight of silver.

8. The thermoelectric conversion module according to claim 6, wherein the conductive paste further contains a glass powder component, a resin component, and a solvent component.

9. The thermoelectric conversion module according to claim 6, wherein the conductive substrate is a sheet-shaped conductive metal, a conductive ceramics, or an insulating ceramics on which a conductive metal coating is formed.

10. The thermoelectric conversion module according to claim 9, wherein the conductive substrate is a silver sheet having a thickness of 0.05 to 3 mm.

11. A thermoelectric conversion module comprising an electrically insulating substrate disposed on both sides or one side of the conductive substrates of the thermoelectric conversion module of claim 6.

12. The thermoelectric conversion module according to claim 11, wherein the electrically insulating substrate is an oxide ceramics or a nitride ceramics.

13. A thermoelectric generation method comprising a step of positioning one side of the conductive substrates of the thermoelectric conversion module of claim 6 at a high-temperature section, and the other side of the conductive substrates at a low-temperature section.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0135] FIG. 1 schematically shows an example of a thermoelectric conversion element of the present invention.

[0136] FIG. 2 schematically shows the structure of the (a) side face, (b) front face, and (c) back face of one example of a thermoelectric conversion module of the present invention.

[0137] FIG. 3 schematically shows the structure of the upper and lower faces of one example of a thermoelectric conversion module of the present invention.

[0138] FIG. 4 schematically shows the thermoelectric conversion element obtained in Example 1, in which an electrically insulating substrate is provided at one side.

[0139] FIG. 5(a) is a graph showing the maximum output of the thermoelectric conversion elements of Example 1 and Comparative Example 1, relative to the temperature of a plate-type electric furnace. FIG. 5(b) is a graph showing the internal resistance of the thermoelectric conversion elements of Example 1 and Comparative Example 1, relative to the temperature of a plate-type electric furnace.

[0140] FIG. 6 is a graph showing changes with time of standardized maximum output, in terms of the thermoelectric conversion elements of Example 1 and Comparative Example 1.

[0141] FIG. 7(a) is a graph showing the maximum output of the thermoelectric conversion modules of Example 88 and Comparative Example 2, relative to the temperature of a plate-type electric furnace. FIG. 7(b) is a graph showing the internal resistance of the thermoelectric conversion modules of Example 88 and Comparative Example 2, relative to the temperature of a plate-type electric furnace.

[0142] FIG. 8 is a graph showing changes with time of the standardized maximum output, in terms of the thermoelectric conversion modules of Example 28 and Comparative Example 2.

DESCRIPTION OF EMBODIMENTS

[0143] The present invention is described below in more detail with reference to Examples.

EXAMPLE 1

[0144] Production of p-Type Thermoelectric Conversion Material

[0145] A p-type thermoelectric conversion material represented by the compositional formula: MnSi.sub.1.75 was produced as follows.

[0146] First, small pieces of silicon (Si) and manganese (Mn) were weighed to a ratio of Mn:Si=1:1.75, and placed in a ceramic crucible, followed by melting in a high-frequency melting furnace. The melt was poured into a room-temperature metal crucible, and rapidly cooled for solidification. The obtained molten solidified product was pulverized using a zirconium crucible and a pestle, and sieved to obtain a powder having a particle size of 38 m or less. This powder was pressed into a disk shape having a diameter of 10 cm and a thickness of about 5 mm.

[0147] This disk was put in a carbon mold, and subjected to hot-press sintering at 920 C. for 7 hours under uniaxial pressure of 11 MPa in a vacuum atmosphere. The hot-pressed, sintered body was cut into a prism shape having a cross-section of 3.53.5 mm and a length of 10 mm. The surfaces of this processed product were electroless-plated with NiB. The plating thickness was about 5 m. The surfaces other than the joints were polished with sandpaper to remove the plating, and a p-type thermoelectric conversion material for use in a thermoelectric conversion module was thus obtained.

Production of n-Type Thermoelectric Conversion Material

[0148] Small pieces of manganese (Mn), silicon (Si), and aluminium (Al) were weighed to a ratio of Mn:Si:aluminum (elemental ratio)=3.0:4.0:2.3. Thereafter, the mixture was melted by an arc-melting method under reduced pressure of about 35 kPa in an argon atmosphere. The melt was then sufficiently mixed, and cooled to room temperature to obtain a molten solidified product formed of the above starting components.

[0149] Subsequently, the obtained alloy was pulverized using an agate mortar and a pestle, and sieved to obtain a powder having a particle size of 38 m or less. The resulting powder was pressed into a disk shape having a diameter of 40 mm and a thickness of about 5 mm. The resulting product was put in a carbon mold, heated to 780 C. by applying a pulsed direct current of about 2,700 A (pulse width: 2.5 milliseconds, frequency: 29 Hz), and maintained at that temperature for 15 minutes. After performing electric current sintering, the application of electric current and pressure was stopped, and the resulting product was naturally cooled to obtain a sintered body.

[0150] The sintered body was cut into a prism shape having a cross-section of 3.53.5 mm and a length of 10 mm. The surfaces of this processed product were electroless plated with NiB. The thickness of plating was about 5 m. The surfaces other than the joints were polished with sandpaper to remove the plating, and an n-type thermoelectric conversion material for use in a thermoelectric conversion module was thus obtained.

Preparation of Conductive Paste

[0151] A platinum paste (6 parts by weight) (trade name: TR-7905, produced by Tanaka Kikinzoku Kogyo K.K., platinum content: 85 wt %) per 100 parts by weight of a commercially available silver paste (trade name; MH-108A, produced by Tanaka Kikinzoku Kogyo K.K., silver content; 85 wt %) was weighed, and the silver paste and the platinum paste were sufficiently kneaded to prepare a conductive paste. The silver paste used here consists of 85 wt % of silver powder (particle size: about 0.1 to 5 m), 1 wt % of bismuth borosilicate glass, 5 wt % of ethylcellulose, 4 wt% of terpineol, and 5 wt % of butylcarbitol acetate, while the platinum paste used here consists of 85 wt % of platinum powder (particle size: about 0.1 to 5 m),1 wt % of bismuth borosiiicate glass, 5 wt % of ethylcellulose, 4 wt % of terpineol, and 5 wt % of butylcarbitol acetate.

Production of Thermoelectric Conversion Element

[0152] A silver sheet having a width of 3.5 mm, a length of 7 mm, and a thickness of 0.5 mm was prepared as a conductive substrate, and the conductive paste containing the silver and platinum powders was applied to the NiB plated surfaces (3.5 mm3.5 mm) of the p-type thermoelectric conversion material and n-type thermoelectric conversion material, on the surfaces of which the silver sheet was placed so as to connect the p-type thermoelectric conversion material to the n-type thermoelectric conversion material. Additionally, an electrically insulating aluminum oxide substrate having a width of 5 mm, a length of 8 mm, and a thickness of 0.5 mm was further placed on the silver sheet to cover the entire silver sheet. The paste was applied in such an amount that the thickness before solidification was about 100 m.

[0153] The thermoelectric conversion element above was turned upside down, and the conductive paste was applied in a manner similar to the above to the opposing cross sections of the thermoelectric conversion materials. Two silver sheets were individually placed on each of the n-type thermoelectric material and p-type thermoelectric material; the sheets were used as lead wires for collecting electric current.

[0154] After drying at about 100 C. for about 30 minutes, the resulting product was heated at 350 C. for 5 hours in air to decompose the organic components. The resulting thermoelectric conversion element was then subjected to heat treatment at 600 C. for 7 hours in vacuum in a state in which a uniaxial pressure of 6.5 MPa was perpendicularly applied to the joints. In this manner, the conductive paste was solidified.

[0155] The paste after solidification had a thickness of about 20 m. The aluminum oxide substrate placed on the silver sheet was adhered by heating to the silver sheet during the heat treatment. In this manner, a thermoelectric conversion element having an electrically substrate at one side was obtained. FIG. 4 schematically shows the obtained thermoelectric conversion element.

COMPARATIVE EXAMPLE 1

[0156] A thermoelectric conversion element was produced as in Example 1, except that a commercially available silver paste (trade name: ME-108A, produced by Tanaka Kikinzoku Kogyo K.K., silver content 85 wt %) was used. as the conductive paste.

TEST EXAMPLE 1

[0157] The aluminum oxide substrate side of the thermoelectric conversion elements obtained in Example 1 and Comparative Example 1 was heated at 100 to 600 C. in air using a plate-type electric furnace while the opposing ends were cooled with a copper jacket in which water at 20 C. was circulated, thereby producing a temperature difference.

[0158] The lead wires (silver sheets) provided at the low-temperature side of the p-type thermoelectric conversion material and the n-type thermoelectric conversion material were connected to an electronic load device, and electric current-voltage characteristics were measured while changing external load resistance. In this manner, the internal resistance and output of the module were obtained. In this measurement, the electric current-voltage characteristics are obtained as a straight line, and the absolute values of the slope (negative value) of this straight line serve as the internal resistances of the thermoelectric conversion element. The output is multiplication of electric current and voltage, and forms a quadratic function. The measurement values were regressed to the quadratic function, and the maximum local value of the quadratic curve obtained from the function was considered as the maximum output. When the external load resistance is equal to the internal resistance, a thermoelectric conversion element shows the maximum output. Based on the regression curve as well, the maximum output was obtained at the point in which the external load resistance was equal to the internal resistance.

[0159] FIG. 5(a) is a graph showing the maximum output of the thermoelectric conversion elements of Example 1 and Comparative Example 1, relative to the temperature of a plate-type electric furnace. FIG. 5(b) is a graph showing the internal resistance of the thermoelectric conversion elements of Example 1 and Comparative Example 1, relative to the temperature of a plate-type electric furnace. The thermoelectric conversion element obtained in Example 1 showed lower internal resistance values, resulting in higher maximum output.

[0160] These results clarify the following: in Example 1, the thermoelectric conversion materials were bonded to the silver sheets using the paste containing silver and platinum; in this manner, the silver was prevented from diffusing into the thermoelectric conversion materials at the time of the production of the element and at the time of heating in the test, achieving excellent thermoelectric generation performance. In contrast, in Comparative Example 1, in which a silver paste was used as the bonding agent, the silver diffused into the thermoelectric conversion element at the time of heating, which is presumably why the thermoelectric generation performance was degraded.

[0161] FIG. 6 is a graph showing changes with time of the maximum output when the test was performed for a long period of time with the temperature of a plate-type electric furnace adjusted to 600 C. The vertical axis shows maximum output values standardized by the maximum output measured immediately after the plate-type electric furnace temperature reached 600 C. The maximum output of Comparative Example 1 greatly reduced with time; however, almost no change was observed in Example 1. These results confirm that bonding of the thermoelectric conversion materials to the silver sheets using the paste containing silver and platinum improves the durability in high-temperature air.

EXAMPLES 2 TO 87

[0162] Thermoelectric conversion elements were produced as in Example 1 using the materials shown in Table 1 as the p-type thermoelectric conversion material, n-type thermoelectric conversion material, conductive substrate, and electrically insulating substrate. The method for disposing the insulating substrate at the high-temperature side and the insulating substrate at the low-temperature side is the same as that for disposing the aluminum oxide substrate in Example 1.

[0163] The Noble metal mixture column in Table 1 shows the types of noble metals incorporated in the conductive paste, in addition to silver; the Mixed amount with respect to silver column shows the amount of the noble metals in percent by weight, on the assumption that the silver amount was 100 wt %. The conductive substrates used at the high-temperature and low-temperature sides are respectively shown as a high-temperature-side electrode material and a low-temperature-side electrode material.

[0164] A test was performed for a long period of time as in Test Example 1, with the plate-type electric furnace temperature adjusted to 500 C., and the maximum output after 15 hours was measured. Each table shows the ratio of the maximum output after 15 hours to the initial value. The maximum output and internal resistance of the thermoelectric conversion elements obtained in Examples 2 to 87 vary depending on, for example, the composition of the thermoelectric conversion materials, the materials of the conductive substrate, and the composition of the noble metals in the conductive paste. All of the thermoelectric conversion elements showed a smaller change in the maximum output, compared with the thermoelectric conversion element obtained in Comparative Example 1, and the change was almost the same as that of Example 1. These results confirm that bonding of the thermoelectric conversion materials to the silver sheets using the paste containing silver and platinum improves the durability in high-temperature air.

TABLE-US-00001 TABLE 1 Mixed High- Low- Maximum Composition Composition amount tem- tem- High- Low- output of n-type of p-type with perature- perature- temperature- temperature- (15 hours)/ thermoelectric thermoelectric Noble respect to side side side side Maximum conversion conversion metal silver electrode electrode insulating insulating output Ex. material material mixture (wt %) material material substrate substrate (0 hours) 1 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 1.01 oxide 2 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Gold 6 Silver Silver Aluminum None 1.00 oxide 3 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Palladium 6 Silver Silver Aluminum None 0.998 oxide 4 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Platinum 0.5 Silver Silver Aluminum None 0.980 oxide 5 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Gold 0.5 Silver Silver Aluminum None 0.991 oxide 6 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Palladium 0.5 Silver Silver Aluminum None 0.978 oxide 7 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Platinum 20 Silver Silver Aluminum None 0.993 oxide 8 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Gold 20 Silver Silver Aluminum None 1.01 oxide 9 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Palladium 50 Silver Silver Aluminum None 0.994 oxide 10 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Platinum 95 Silver Silver Aluminum None 0.982 oxide 11 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Gold 95 Silver Silver Aluminum None 0.987 oxide 12 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Palladium 95 Silver Silver Aluminum None 0.977 oxide 13 Mn.sub.2.7Cr.sub.0.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.987 oxide 14 Mn.sub.2.8Co.sub.0.2Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 6 Gold Gold Zirconium Zirconium 0.986 oxide oxide 15 Mn.sub.2.8Fe.sub.0.2Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 20 Platinum Platinum Zirconium Zirconium 0.996 oxide oxide 16 Mn.sub.2.8Ni.sub.0.2Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 0.5 Silver Silver Aluminum Aluminum 1.00 oxide oxide 17 Mn.sub.3Si.sub.4.5Al.sub.3 MnSi.sub.2.0 Platinum 50 Platinum Platinum Aluminum Aluminum 0.989 oxide oxide 18 Mn.sub.3Si.sub.4.2Al.sub.2.8 MnSi.sub.1.75 Gold 6 Silver Silver Aluminum Aluminum 0.981 oxide oxide 19 Mn.sub.3Si.sub.3.8Al.sub.3.2 MnSi.sub.1.5 Palladium 6 Palladium Palladium Titanium Titanium 0.990 oxide oxide 20 Mn.sub.3Si.sub.3.5Al.sub.3 MnSi.sub.1.6 Platinum 10 Silver Silver Aluminum Aluminum 0.990 oxide oxide 21 Mn.sub.3Si.sub.3.9Al.sub.3 MnSi.sub.1.8 Platinum 6 Silver Silver Aluminum Aluminum 1.00 oxide oxide 22 Mn.sub.3Si.sub.3.8Al.sub.3P.sub.0.2 MnSi.sub.1.75 Gold 6 Gold Gold Magnesium Magnesium 0.999 oxide oxide 23 Mn.sub.3Si.sub.4Al.sub.2P MnSi.sub.1.75 Gold 10 Gold Gold Silcon oxide Silicon 1.01 oxide 24 Mn.sub.3Si.sub.3.8Al.sub.3B.sub.0.2 MnSi.sub.1.75 Gold 20 Gold Gold Silcon nitride Silcon 0.992 nitride 25 Mn.sub.3Si.sub.4Al.sub.2B MnSi.sub.1.75 Gold 6 Gold Gold Titanium Titanium 0.979 nitride nitride 26 Mn.sub.3Si.sub.3.8Al.sub.3Ga.sub.0.2 MnSi.sub.1.75 Palladium 10 Palladium Palladium Magnesium Magnesium 0.991 oxide oxide 27 Mn.sub.3Si.sub.4Al.sub.2Ga MnSi.sub.1.75 Palladium 20 Palladium Palladium Silcon oxide Silicon 0.982 oxide 28 Mn.sub.3Si.sub.3.8Al.sub.3Ge.sub.0.2 MnSi.sub.1.75 Palladium 10 Palladium Palladium Silcon nitride Silcon 0.973 nitride 29 Mn.sub.3Si.sub.4Al.sub.2Ge MnSi.sub.1.75 Palladium 20 Palladium Palladium Silcon carbide Silcon 0.973 carbide 30 Mn.sub.3Si.sub.3.8Al.sub.3Sn.sub.0.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.984 oxide 31 Mn.sub.3Si.sub.4Al.sub.2Sn MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.994 oxide 32 Mn.sub.3Si.sub.3.8Al.sub.3Bi.sub.0.2 MnSi.sub.1.75 Platinum 6 Silver Silver None None 0.985 33 Mn.sub.3Si.sub.4Al.sub.2Bi MnSi.sub.1.75 Platinum 6 Silver Silver None None 0.975 34 Mn.sub.3Si.sub.4Al.sub.3Bi.sub.0.02 MnSi.sub.1.75 Platinum 6 Silver Silver None None 0.986 35 Mn.sub.2.9Ti.sub.0.1Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 6 Silver Silver None None 0.996 36 Ti.sub.3Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 6 Gold Titanium Titanium Aluminum 0.978 nitride oxide 37 Mn.sub.2.9V.sub.0.1Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum Aluminum 1.00 oxide oxide 38 V.sub.3Si.sub.4Al.sub.3 MnSi.sub.1.75 Gold 10 Gold Copper Silicon nitride Aluminum 0.971 oxide 39 Mn.sub.2.9Cr.sub.0.1Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum Aluminum 0.962 oxide oxide 40 Cr.sub.3Si.sub.4Al.sub.3 MnSi.sub.1.75 Gold 6 Gold Copper Silicon nitride Aluminum 0.978 oxide 41 Mn.sub.2.9Fe.sub.0.1Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 15 Silver Silver Aluminum Aluminum 0.990 oxide oxide 42 Fe.sub.3Si.sub.4Al.sub.3 MnSi.sub.1.75 Gold 10 Gold Iron Silicon nitride Aluminum 0.970 oxide 43 Mn.sub.2.9Co.sub.0.1Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum Aluminum 0.096 oxide oxide 44 Co.sub.3Si.sub.4Al.sub.3 MnSi.sub.1.75 Gold 10 Gold Copper Silicon nitride Aluminum 0.979 oxide 45 Mn.sub.2.9Ni.sub.0.1Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum Aluminum 0.992 oxide oxide 46 Ni.sub.3Si.sub.4Al.sub.3 MnSi.sub.1.75 Gold 10 Gold Copper Silicon nitride Aluminum 0.983 oxide 47 Mn.sub.2.9Cu.sub.0.1Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.979 oxide 48 Cu.sub.3Si.sub.4Al.sub.3 MnSi.sub.1.75 Gold 10 Gold Copper Aluminum None 0.982 nitride 49 Mn.sub.2.9Cr.sub.0.1Si.sub.4Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.973 oxide 50 Mn.sub.2.7Cr.sub.0.3Si.sub.4Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.992 oxide 51 Mn.sub.2.7Cr.sub.0.3Si.sub.4Al.sub.2 Mn.sub.0.3Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 1.01 oxide 52 Mn.sub.2.6Cr.sub.0.4Si.sub.4Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.992 oxide 53 Mn.sub.2.6Cr.sub.0.4Si.sub.3.5Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.979 oxide 54 Mn.sub.2.6Cr.sub.0.4Si.sub.4.5Al.sub.1.5 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.991 oxide 55 Mn.sub.2.6Cr.sub.0.4Si.sub.3.5Al.sub.2.4 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.982 oxide 56 Mn.sub.2.3Cr.sub.0.7Si.sub.4Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.973 oxide 57 Mn.sub.2.7Ti.sub.0.3Si.sub.4Al.sub.2 Mn.sub.0.9Ti.sub.0.1Si.sub.1.75 Gold 10 Silver Silver Titanium None 0.992 nitride 58 Mn.sub.2.7V.sub.0.3Si.sub.4Al.sub.2 Mn.sub.0.8V.sub.0.1Si.sub.1.75 Gold 10 Silver Silver Titanium None 0.979 nitride 59 Mn.sub.2.7Fe.sub.0.3Si.sub.4Al.sub.2 Mn.sub.0.9Fe.sub.0.1Si.sub.1.75 Gold 10 Silver Silver Aluminum None 0.991 nitride 60 Mn.sub.2.7Co.sub.0.3Si.sub.4Al.sub.2 Mn.sub.0.9Co.sub.0.1Si.sub.1.75 Gold 10 Silver Silver Aluminum None 0.992 nitride 61 Mn.sub.2.7Ni.sub.0.3Si.sub.4Al.sub.2 Mn.sub.0.9Ni.sub.0.1Si.sub.1.75 Gold 10 Silver LaNiO.sub.3 Aluminum None 0.964 nitride 62 Mn.sub.2.7Cu.sub.0.3Si.sub.4Al.sub.2 Mn.sub.0.9Cu.sub.0.1Si.sub.1.75 Gold 10 Silver Silver Aluminum None 0.979 nitride 63 Mn.sub.2.3Ti.sub.0.7Si.sub.4Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 1.00 oxide 64 Mn.sub.2.3V.sub.0.7Si.sub.4Al.sub.3 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.999 oxide 65 Mn.sub.2.3Fe.sub.0.7Si.sub.4Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 1.01 oxide 66 Mn.sub.2.3Co.sub.0.7Si.sub.4Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.992 oxide 67 Mn.sub.2.3Ni.sub.0.7Si.sub.4Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.979 oxide 68 Mn.sub.2.3Cu.sub.0.7Si.sub.4Al.sub.2 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.991 oxide 69 Mn.sub.2.0Cr.sub.0.3Ti.sub.0.2Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.982 oxide 70 Mn.sub.2.0Cr.sub.0.3V.sub.0.2Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.973 oxide 71 Mn.sub.2.0Cr.sub.0.3Fe.sub.0.2Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 1.00 oxide 72 Mn.sub.2.0Cr.sub.0.3Co.sub.0.2Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.999 oxide 73 Mn.sub.2.0Cr.sub.0.3Ni.sub.0.2Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 1.01 oxide 74 Mn.sub.2.0Cr.sub.0.3Cu.sub.0.2Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.992 oxide 75 Mn.sub.2.5Cr.sub.0.3Ti.sub.0.5Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.979 oxide 76 Mn.sub.2.0Cr.sub.0.7Ti.sub.0.7Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.991 oxide 77 Mn.sub.2.0Cr.sub.0.7V.sub.0.7Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.982 oxide 78 Mn.sub.2.0Cr.sub.0.7Cr.sub.0.7Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.973 oxide 79 Mn.sub.2.0Cr.sub.0.7Fe.sub.0.7Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.973 oxide 80 Mn.sub.2.0Cr.sub.0.7Co.sub.0.7Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.984 oxide 81 Mn.sub.2.0Cr.sub.0.7Ni.sub.0.7Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.994 oxide 82 Mn.sub.2.0Cr.sub.0.7Cu.sub.0.7Si.sub.4Al.sub.2 Mn.sub.0.9Cr.sub.0.1Si.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.985 oxide 83 Mn.sub.3.5Si.sub.4Al.sub.2.49 MnSi.sub.1.75 Platinum 6 Silver Silver Aluminum None 0.975 oxide 84 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Plat- 3 Silver Silver Aluminum None 0.986 inum (Plat- oxide Gold inum) 3 (Gold) 85 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Plat- 3 Silver Silver Aluminum None 0.996 inum (Plat- oxide Palla- inum) dium 6 (Palla- dium) 86 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Plat- 6 Silver Silver Aluminum None 0.978 inum (n- (Plat- oxide type) inum) Gold 6 (p-type) (Gold) 87 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 Plati- 6 Silver Silver Aluminum None 0.9865 num (n- (Plat- oxide type) inum) Palla- 6 dium (Palla- (p-type) dium)

EXAMPLE 88

Production of Thermoelectric Conversion Module

[0165] Seven silver sheets having a width of 7 mm, a length of 7 mm, and a thickness of 0.5 mm were placed on an aluminum oxide substrate with a size of 33 cm and a thickness of 0.8 mm at intervals appropriate to allow the thermoelectric conversion materials to be connected.

[0166] As p-type thermoelectric conversion materials and n-type thermoelectric conversion materials, materials in a prism shape having a cross-section of 3.57 mm and a length of 10 mm produced as in Example 1 were used.

[0167] The same conductive paste as used in Example 1 was applied to both of the 3.5 mm7 mm surfaces of each of the thermoelectric conversion materials, and one pair of the p-type thermoelectric conversion material and n-type thermoelectric conversion material was placed on each silver sheet disposed on the aluminum oxide substrate. Altogether, 14 each of the p-type thermoelectric conversion materials and n-type thermoelectric conversion materials were alternately disposed. The paste was applied in such an amount that the thickness before solidification was about 100 m.

[0168] Silver sheets having a width of 7 mm, a length of 7 mm, and a thickness of 0.5 mm were individually placed on the other surfaces of the thermoelectric conversion materials to which the conductive paste was applied, and 14 pairs (28 in total) of the thermoelectric conversion materials were connected in series with the additional use of the silver sheets on the aluminum oxide substrate. Silver sheets having a width of 7 mm, a length of 50 mm, and a thickness of 0.5 mm were individually placed on the surfaces of the p-type thermoelectric conversion material and n-type thermoelectric conversion material at both ends of the series connection, and used as lead wires. In this manner, a thermoelectric conversion module precursor having 14 pairs of thermoelectric conversion elements was produced.

[0169] This precursor was dried at about 100 C. for about 30 minutes, followed by heating at 350 C. for 5 hours in air to thermally decompose the organic components. Next, the conductive paste was solidified by heat treatment at 600 C. for 7 hours in vacuum in a state in which a uniaxial pressure of 6.5 MPa was perpendicularly applied to the joints. The paste layer after solidification had a thickness of about 20 m. The aluminum oxide substrate was adhered by heating to the silver sheets during the heat treatment. In this manner, a thermoelectric conversion module in which 14 pairs of thermoelectric conversion elements were connected in series, and an electrically insulating substrate was disposed at one side was obtained.

EXAMPLE 89

[0170] As p-type thermoelectric conversion materials and n-type thermoelectric conversion materials, materials in a prism shape having a cross-section of 3.57 mm and a length of 10 mm produced as in Example 1 were used. However, a NiB electroless plating layer was not formed on the surfaces of both the p-type thermoelectric conversion materials and the n-type thermoelectric conversion materials.

[0171] A thermoelectric conversion module in which 14 pairs of thermoelectric conversion elements were connected in series, and in which an electrically insulating substrate was disposed at one side was obtained as in Example 88, except that these p-type thermoelectric conversion materials and n-type thermoelectric conversion materials were used.

COMPARATIVE EXAMPLE 2

[0172] A thermoelectric conversion module in which 14, pairs of thermoelectric conversion elements were connected in series, and in which an electrically insulating substrate was disposed at one side was obtained as in Example 88, except that a commercially available silver paste (trade name: MK-108A, produced by Tanaka Kikinzoku Kogyo K.K., silver content: 85 wt %) was used as the conductive paste.

TEST EXAMPLE 2

[0173] The aluminum oxide substrate portion of the thermoelectric conversion modules obtained as above in Example 83, Example 89, and Comparative Example 2 was heated at 100 to 600 C. in air using a plate-type electric furnace while the opposing ends were cooled with a copper jacket in which 20 C. water was circulated, thereby producing a temperature difference.

[0174] The lead wires provided at the low-temperature side of the p-type thermoelectric conversion material and the low-temperature side of the n-type thermoelectric conversion material were connected to an electronic load device, and electric current-voltage characteristics of the module were measured while changing external load resistance. In this manner, the internal resistance and output of the module were obtained. In this measurement, the electric current-voltage characteristics are obtained as a straight line, and the absolute values of the slope (negative value) of this straight line serve as the internal resistances of the thermoelectric conversion module. The output is multiplication of electric current and voltage, and forms a quadratic function. The measurement values were regressed to the quadratic function, and the maximum local value of the quadratic curve obtained from the function was considered as the maximum output. When the external load resistance is equal to the internal resistance, a thermoelectric conversion module shows the maximum output. Based on the regression curve as well, the maximum output was obtained at the point in which the external load resistance was equal to the internal resistance.

[0175] FIG. 7(a) is a graph showing the maximum output of the thermoelectric conversion modules of Example 88, Example 89, and Comparative Example 2, relative to the temperature of a plate-type electric furnace. FIG. 7(b) is a graph showing the internal resistance of the thermoelectric conversion modules of Example 88, Example 89, and Comparative Example 2, relative to the temperature of a plate-type electric furnace.

[0176] The thermoelectric conversion modules obtained in Example 88 and Example 89 showed lower internal resistance values, resulting in higher maximum output. In particular, the thermoelectric conversion module of Example 88, in which a Ni plating layer was formed, had a low internal resistance, and the thermoelectric conversion module of Example 89 also had a sufficiently low internal resistance value. These results clarify the following: in Example 88 and Example 89, the thermoelectric conversion materials were bonded to the silver sheets using the paste containing silver and platinum; in this manner, the silver was prevented from diffusing into the thermoelectric conversion materials at the time of the production of the modules and at the time of heating in the test, achieving excellent thermoelectric generation performance. In contrast, in Comparative Example 2, in which a silver paste was used as the bonding agent, the silver diffused into the thermoelectric conversion element at the time of heating, which is presumably the reason why the thermoelectric generation performance was degraded.

[0177] FIG. 8 shows changes with time of the maximum output when the test was performed for a long period of time with the plate-type electric furnace temperature adjusted to 600 C. The vertical axis shows maximum output values standardized by the maximum output measured immediately after the plate-type electric furnace temperature reached 600 C. The maximum output of Comparative Example 2 greatly reduced with time; however, almost no change was observed in Example 88. Example 89 also showed a smaller reduction in the maximum output, compared to Comparative Example 2. These results confirm that bonding of the thermoelectric conversion materials to the silver sheets using the paste containing silver and platinum improves the durability in high-temperature air.

EXAMPLES 90 TO 98

[0178] Thermoelectric conversion modules were produced as in Example 88 using the materials shown in Table 2 as the p-type thermoelectric conversion material, n-type thermoelectric conversion material, conductive substrate, and electrically insulating substrate. The method for disposing the insulating substrate at the high-temperature side and the insulating substrate at the low-temperature side is the same as that for disposing the aluminum oxide substrate in Example 88.

[0179] The Noble metal mixture column in Table 2 shows the types of noble metals incorporated in the conductive paste, in addition to silver; the Mixed amount with respect to silver column shows the amount of the noble metals in percent by weight, on the assumption that the silver amount was 100 wt %. The conductive substrates used at the high-temperature and low-temperature sides are respectively shown as a high-temperature-side electrode material and a low-temperature-side electrode material.

[0180] A test was performed for a long period of time as in Test Example 2, with the plate-type electric furnace temperature adjusted to 600 C., and the maximum output after 15 hours was measured. Table 2 shows the ratio of the maximum output after 15 hours to the initial value. The maximum output and internal resistance of the thermoelectric conversion modules obtained in Examples 90 to 98 vary depending on, for example, the composition of the thermoelectric conversion materials, the materials of the conductive substrate, and the composition of the noble metals in the conductive paste. However, all of the thermoelectric conversion modules showed a smaller change in the maximum output, compared with the thermoelectric conversion module obtained in Comparative Example 2, and the change was almost the same as that of Example 88. These results confirm that bonding of the thermoelectric conversion materials to the silver sheets using the paste containing silver and platinum improves the durability in high-temperature air.

TABLE-US-00002 TABLE 2 Composition Composition Mixed High- Low- High- Low- Maximum of n-type of p-type amount tem- tem- tem- tem- output (15 thermo- thermo- with perature- perature- perature- perature- hours)/ electric electric Noble respect to side side side side Maximum conversion conversion Number metal silver electrode electrode insulating insulating output (0 Ex. material material of pairs mixture (wt %) material material substrate substrate hours) Plating 88 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 14 Platinum 6 Silver Silver Aluminum None 0.996 Nickel oxide 89 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 14 Platinum 6 Silver Silver Aluminum None 0.979 None oxide 90 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 14 Gold 6 Silver Silver Aluminum None 0.993 Nickel oxide 91 Mn.sub.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 14 Palladium 6 Silver Silver Aluminum None 0.981 Nickel oxide 92 Mn.sub.2.7Cr.sub.0.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 14 Platinum 0.5 Silver Silver Aluminum None 0.975 Nickel oxide 93 Mn.sub.2.7Cr.sub.0.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 14 Platinum 50 Silver Silver Aluminum None 0.973 Nickel oxide 94 Mn.sub.2.7Cr.sub.0.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 14 Platinum 95 Silver Silver Aluminum None 0.984 Nickel oxide 95 Mn.sub.2.7Cr.sub.0.3Si.sub.4Al.sub.2.3 MnSi.sub.1.75 64 Platinum 6 Silver Silver Aluminum None 0.990 Nickel oxide 96 Mn.sub.2.7Cr.sub.0.2Si.sub.4Al.sub.2 MnSi.sub.1.75 64 Platinum 6 Silver Silver Aluminum None 0.981 Nickel oxide 97 Mn.sub.2.7Cr.sub.0.3Si.sub.4Al.sub.2 MnSi.sub.1.75 64 Platinum 6 Silver Silver None None 0.972 Nickel 98 Mn.sub.2.7Cr.sub.0.3Si.sub.4Al.sub.2 MnSi.sub.1.75 64 Platinum 6 Silver Silver Silicon Silicon 0.969 Nickel nitride nitride