Patent Application
20150380624
(1) Field of the Invention
This disclosure relates to a method of manufacturing a thermoelectric conversion material utilized for thermoelectric power generation and thermoelectric cooling.
(2) Description of Related Art
The thermoelectric power generation is a technology of converting thermal energy directly into electric energy by utilizing the Seebeck effect i.e., thermoelectromotive force generated between both ends of a substance by a temperature difference made between the both ends of the substance in proportion to the temperature difference. This technology is practically used as a power source for a remote place, a power source for space use, a power source for military use, etc. in some cases.
The thermoelectric cooling is a technology using the Peltier effect, i.e., a phenomenon of transferring heat through electrons carried by an electric current. Specifically, the thermoelectric cooling is a technology of absorbing heat of a joint part by utilizing a fact that when an electric current is applied to two substances different in polarity of electric conduction carriers connected thermally in parallel and electrically in series, the difference in polarity of the electric conduction carriers (carriers) is reflected on a difference in direction of a heat flow. For example, the two substances different in polarity of electric conduction carriers used in this case are a p-type semiconductor having the electric conduction carriers (carrier) that are holes and an n-type semiconductor having the electric conduction carriers (carriers) that are electrons. Such an element configuration is of a so-called π type and is a most common configuration.
The energy conversion efficiency between heat and electricity in thermoelectric power generation and thermoelectric cooling is determined by a figure of merit ZT of material used. The figure of merit ZT is expressed by using a Seebeck coefficient S, an electric resistivity p, and a thermal conductivity κ of the material and an absolute temperature T of evaluation environment as ZT=S2T/ρκ. The energy conversion efficiency becomes higher when the figure of merit ZT is higher. Therefore, a semiconductor with a high absolute value of Seebeck coefficient S, a low electric resistivity ρ, and a low thermal conductivity κ is a necessary condition for achieving the high figure of merit ZT.
A sample formed by a conventional manufacturing method has a low Seebeck coefficient S and cannot form uniform crystals. Therefore, a highly reliable manufacturing method must be established for extracting the thermoelectric conversion characteristics specific to a thermoelectric conversion material X3Ni3Sb4 (X=Zr, Hf).
One non-limiting and exemplary embodiment provides a highly reliable method of manufacturing the thermoelectric conversion material X3Ni3Sb4 (X=Zr, Hf).
In one general aspect, the techniques disclosed here feature: a method of manufacturing a thermoelectric conversion material expressed by a chemical formula X3T3Z4 (X is composed of one or more elements selected from Zr, Hf, Y, La, Nb, and Ta, while including at least Zr or Hf; T is composed of one or more elements selected from Ni, Co, Cu, Rh, Pd, Ir, and Pt, while including at least Ni; Z is composed of one or more elements selected from Sb, Ge, and Sn, while including at least Sb), the method includes:
preparing materials containing elements, which are one or more elements selected from Zr, Hf, Y, La, Nb, and Ta, while including at least Zr or Hf, one or more elements selected from Ni, Co, Cu, Rh, Pd, Ir, and Pt, while including at least Ni, and one or more elements selected from Sb, Ge, and Sn, while including at least Sb;
forming an alloy A by melting the materials containing desired elements selected from Zr, Hf, Y, La, Nb, Ta, Ni, Co, Cu, Rh, Pd, Ir, Pt, Ge, and Sn; and
forming an alloy B by melting the alloy A and the material containing Sb.
The method of manufacturing a thermoelectric conversion material according to this disclosure can provide an intermetallic compound X3T3Z4 (X is composed of one or more elements selected from Zr, Hf, Y, La, Nb, and Ta, while including at least Zr or Hf; T is composed of one or more elements selected from Ni, Co, Cu, Rh, Pd, Ir, and Pt, while including at least Ni; Z is composed of one or more elements selected from Sb, Ge, and Sn, while including at least Sb) having a high Seebeck coefficient.
The method of manufacturing a thermoelectric conversion material according to this disclosure enables production of a thermoelectric conversion material exhibiting a high Seebeck coefficient S in the thermoelectric conversion material Zr3-xHfxNi3Sb4 and an element-substituted material system of Zr3-xHfxNi3Sb4.
Additional benefits and advantages of the disclosed embodiments will be apparent from the specification and figures. The benefits and/or advantages may be individually provided by the various embodiments and features of the specification and drawings disclosure, and need not all be provided in order to obtain one or more of the same.
The present disclosure will become readily understood from the following description of non-limiting and exemplary embodiments thereof made with reference to the accompanying drawings, in which like parts are designated by like reference numeral and in which:
According to a first aspect, a method of manufacturing a thermoelectric conversion material expressed by a chemical formula X3T3Z4 (X is composed of one or more elements selected from Zr, Hf, Y, La, Nb, and Ta, while including at least Zr or Hf; T is composed of one or more elements selected from Ni, Co, Cu, Rh, Pd, Ir, and Pt, while including at least Ni; Z is composed of one or more elements selected from Sb, Ge, and Sn, while including at least Sb), the method includes:
preparing materials containing elements, which are one or more elements selected from Zr, Hf, Y, La, Nb, and Ta, while including at least Zr or Hf, one or more elements selected from Ni, Co, Cu, Rh, Pd, Ir, and Pt, while including at least Ni, and one or more elements selected from Sb, Ge, and Sn, while including at least Sb;
forming an alloy A by melting the materials containing desired elements selected from Zr, Hf, Y, La, Nb, Ta, Ni, Co, Cu, Rh, Pd, Ir, Pt, Ge, and Sn; and
forming an alloy B by melting the alloy A and the material containing Sb.
Further, as a method of manufacturing a thermoelectric conversion material of a second aspect, in the first aspect, the step of forming the alloy A may be performed by any one of an arc melting method, an electromagnetic induction heating method, and a heating method using a resistance heating element.
Further, as a method of manufacturing a thermoelectric conversion material of a third aspect, in the first aspect, in the step of forming the alloy A, the alloy A may be formed by melting the materials containing the elements except the material containing Sb at 2000° C. or higher.
Further, as a method of manufacturing a thermoelectric conversion material of a fourth aspect, in the first aspect, in the step of forming the alloy B, the alloy B may be formed by melting the alloy A and the material containing Sb at 1500° C. or lower.
Further, as a method of manufacturing a thermoelectric conversion material of a fifth aspect, in the first aspect, the method may further include a step of forming a sintered body having a density higher than the alloy B by using the alloy B after the step of forming the alloy B.
Further, as a method of manufacturing a thermoelectric conversion material of a sixth aspect, in the fifth aspect, the step of forming a sintered body having a density higher than the alloy B by using the alloy B may be performed by either a hot press method or a spark plasma sintering method (SPS method).
Further, as a method of manufacturing a thermoelectric conversion material of a seventh aspect, in the first aspect, X may be composed of one or more elements selected from Zr and Hf; T may be composed of one or more elements selected from Ni, Co, Cu, Pd, and Pt, while including at least Ni; Z may be composed of one or more elements selected from Sb and Sn, while including at least Sb.
The method of manufacturing a thermoelectric conversion material according to an embodiment of this disclosure will now be described with reference to the drawings.
Description will be made of a method of manufacturing the thermoelectric conversion material X3T3Z4 (X is composed of one or more elements selected from Zr, Hf, Y, La, Nb, and Ta, while including at least Zr or Hf; T is composed of one or more elements selected from Ni, Co, Cu, Rh, Pd, Ir, and Pt, while including at least Ni; Z is composed of one or more elements selected from Sb, Ge, and Sn, while including at least Sb) according to a first embodiment of this disclosure. The compound X3T3Z4 is a thermoelectric conversion material and has symmetry of a cubic crystal belonging to a space group I-43d.
(1) First, ingredients containing necessary elements selected from Zr, Hf, Y, La, Nb, Ta, Ni, Co, Cu, Rh, Pd, Ir, Pt, Sn, Ge, and Sb are weighed to a stoichiometric ratio of (Zr+Hf+Y+La+Nb+Ta):(Ni+Co+Cu+Rh+Pd+Ir+Pt):(Sb+Ge+Sn)=3:3:4 (process P1).
(2) Among the weighed ingredients, the ingredients containing desired elements selected from Zr, Hf, Y, La, Nb, Ta, Ni, Co, Cu, Rh, Pd, Ir, Pt, Ge, and Sn are alloyed to acquire an alloy A (first alloy) (process P2). The alloy A may be formed by melting ingredients containing a substance other than Zr, Hf, Y, La, Nb, Ta, Ni, Co, Cu, Rh, Pd, Ir, Pt, Ge, and Sn at an impurity level. The “impurity level” in this case refers to less than 1% relative to the weight ratio of the ingredients containing desired elements selected from Zr, Hf, Y, La, Nb, Ta, Ni, Co, Cu, Rh, Pd, Ir, Pt, Ge, and Sn. In the process P2, all the weighed ingredients except Sb may be alloyed to acquire the alloy A. The method of alloying is not particularly limited and the specific methods include, for example, an arc melting method, an electromagnetic induction heating method, and a heating method using a resistance heating element.
(3) The acquired alloy A and Sb are alloyed to acquire an alloy B (second alloy) (process P3). As is the case with the process P2, the method of alloying in the process P3 is not particularly limited.
If a sintered body with a density higher than the alloy B is formed by using the alloy B acquired in the process P3, a process P4 of sintering may further be provided. The method of sintering may be a hot press method, a spark plasma sintering method (SPS method), etc. If the SPS method is used, after the alloy acquired in the process P3 is ground on a mortar etc., a pulsed current is applied while the alloy is pressurized to 50 MPa, so as to increase temperature to 800 to 900° C., and the temperature is then retained for 5 minutes, thereby acquiring a sintered body of the compound X3T3Z4.
A sintered body was formed by the manufacturing method described in the first embodiment from the compound X3T3Z4 (X is composed of one or more elements selected from Zr, Hf, Y, La, Nb, and Ta, while including at least Zr or Hf; T is composed of one or more elements selected from Ni, Co, Cu, Rh, Pd, Ir, and Pt, while including at least Ni; Z is composed of one or more elements selected from Sb, Ge, and Sn, while including at least Sb).
A specific manufacturing method will first be described.
(a) Zr, Hf, Y, La, Nb, Ta, Ni, Co, Cu, Rh, Pd, Ir, Pt, Sn, Ge, and Sb used as ingredients were weighed to a stoichiometric ratio of Zr+Hf+Y+La+Nb+Ta:Ni+Co+Cu+Rh+Pd+Ir+Pt:Ge+Sn+Sb=3:3:4 (process P1). A composition ratio estimated from the weighed ingredients is referred to as preparation composition.
(b) Among the weighed ingredients, the ingredients except Sb (materials containing desired elements selected from Zr, Hf, Y, La, Nb, Ta, Ni, Co, Cu, Rh, Pd, Ir, Pt, Ge, and Sn) were alloyed by the arc melting method (process P2).
The arc melting method was performed by the following procedure.
(i) First, the ingredients Zr, Hf, Y, La, Nb, Ta, Ni, Co, Cu, Rh, Pd, Ir, Pt, Ge, and Sn were placed on a copper hearth liner and the atmosphere is filled with Ar.
(ii) The ingredients on the hearth liner were melted at a high temperature of 2000° C. or higher by applying arc discharge. The copper hearth liner was cooled by cooling water to quench a sample, thereby acquiring the alloy A.
(iii) An operation of reversing the alloy A and performing the arc discharge again was further repeated three times to acquire the more uniform alloy A.
(c) The acquired alloy A and Sb are alloyed by using the arc melting method (process P3). The arc discharge in this case was performed by using discharge of weak power as compared to the process P2 to the extent that the alloy was at 1500° C. or lower.
(d) To form a denser sample, a sintered body was formed by a discharge plasma sintering method. The discharge plasma sintering method is a sintering method using pressurization and pulse energization at the same time.
(i) The alloy B acquired in the process P3 is finely ground by using a mortar and a pestle in a glove box under an Ar atmosphere so as to avoid oxidization.
(ii) The acquired powder was filled in a cylindrical graphite die having an outer diameter of 50 mm and an inner diameter of 10 mm and was pressurized by graphite punches from above and below the cylinder.
(iii) A pulsed current was applied to this die in a vacuum of 1 Pa or less to increase temperature to about 800 to 900° C. at a rate of about 100° C./min.
(iv) After the temperature of 800 to 900° C. was retained for 5 minutes, slow cooling was performed to acquire a sintered body.
The sintered body was cut into a rectangular parallelepiped of about 2 mm*2 mm*8 mm to acquire a sample for evaluating the Seebeck coefficient S.
The Seebeck coefficient of the cut sample at room temperature was evaluated by a four-terminal method to confirm the superiority of the effect of the manufacturing method of this disclosure. The measurement of the Seebeck coefficient S by the four-terminal method was performed by using the measurement device ZEM-3 manufactured by ULVAC-RIKO in the environment of a helium atmosphere at 0.1 atm. While a temperature difference was generated in the sample longitudinal direction by heating one end in the longitudinal direction, probe electrodes were brought into contact with two points interposed between the both ends in the longitudinal direction to detect a potential difference ΔV and a temperature difference ΔT between the probes. The Seebeck coefficient S was obtained from the generated voltage difference ΔV and temperature difference ΔT by a definitional equation S=−ΔV/ΔT.
Lastly, the actual composition of the sintered body acquired by the manufacturing process was analyzed by using the energy dispersive X-ray spectroscopy (EDX). The EDX method is a method of measuring a ratio of an element near a sample surface from energy distribution of characteristic X-rays generated when an electron beam is applied to a sample. Even in a conventional example, composition analysis is performed by using an electron probe microanalyzer (EPMA), which is an equivalent technique. In this measurement, the composition analysis was performed at four different points on a sample surface by the EDX method to obtain the composition from the average of the four points. In this description, the overall composition is represented by adjusting the abundance of Ni atoms to three in accordance with the Nonpatent Literature 1. In a system having substitution for an Ni atom, the overall composition ratio is represented such that the total number of atoms of Ni, Co, Cu, Rh, Pd, Ir, and Pt including a substituted element is set to three. The sum of the amounts of Sb, Ge, and Sn represented in this way less than four is defined as a state of insufficient Sb.
Table 1 describes the sintered body compositions and the Seebeck coefficients at room temperature of examples 1 to 4 of sintered bodies of ZrxHf3-xNi3Sb4 (0≦x≦3) formed under the conditions of X=Zr, Hf and T=Ni and Z=Sb, comparison examples 1, 2 of sintered bodies from a different manufacturing method, and conventional examples 1 to 4 reported in Nonpatent Literature 1 described above. In the conventional examples 2 and 4, the sintered body composition slightly contains Hf although the preparation composition does not contain Hf. In the conventional example 3, the sintered body composition slightly contains Zr although the preparation composition does not contain Zr. It is considered this is because Zr or Hf used as ingredients in Nonpatent Literature 1 contained Hf or Zr as an impurity at about 1%.
The measurement results of the examples 1 to 4 indicate a high Seebeck coefficient exceeding 200 μV/K regardless of a ratio of Zr and Hf.
The conventional examples 1 to 4 indicate the Seebeck coefficients S at room temperature of samples acquired through the process of melting all the ingredients at a time as in the comparison examples 1, 2. The respective Seebeck coefficients at room temperature of the conventional examples are reported for the conventional examples 1, 3 acquired through annealing treatment and a sintering process of an alloy acquired by batch melting and the conventional examples 2, 4 acquired by sintering following the mixing of Sb corresponding to a reduced amount after annealing. A high Seebeck coefficient as in the examples 1 to 4 is not acquired in the conventional examples.
The superiority of the manufacturing method of this disclosure could be confirmed not only in ZrxHf3-xNi3Sb4 but also in the case of substituting Y, La, Nb, or Ta for a portion of Zr or Hf of ZrxHf3-xNi3Sb4, in the case of substituting Co, Cu, Rh, Pd, Ir, or Pt for a portion of Ni, or in the case of substituting Ge or Sn for a portion of Sb. In the case of substituting Co, Rh, or Ir for Ni, or in the case of substituting Sn for Sb, a reduction in the number of electrons in crystals provides a hole-doped p-type semiconductor and the Seebeck coefficient S takes a positive value (S>0). In the case of substituting Nb or Ta for Zr or Hf, or in the case of substituting Cu for Ni, an electron-doped n-type semiconductor is provided and the Seebeck coefficient S takes a negative value (S<0). For the element-substituted alloys, the Seebeck coefficient S at room temperature is described below for the samples (examples and comparison examples) formed by using the respective manufacturing methods of
When a preparation composition was Zr3Ni2.9Co0.1Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.7Co0.3Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.5Co0.5Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.3Co0.7Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.9Cu0.1Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.7Cu0.3Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.5Cu0.5Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni3Sb3.9Sn0.1, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni3Sb3.7Sn0.3, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.7Pd0.3Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.6Pd0.3Coa1Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.7Pt0.3Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.6Pt0.3Co0.1Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.9Rh0.1Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni2.9Ir0.1Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr2.9Y0.1Ni3Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr2.9La0.1Ni3Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr3Ni3Sb3.9Ge0.1, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr2.9Nb0.1Ni3Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
When a preparation composition was Zr2.9Ta0.1Ni3Sb4, a sintered body was manufactured by the manufacturing method according to this disclosure of
Tables 2-21 show the Seebeck coefficient of the examples and comparative examples of the thermoelectric conversion material expressed in the chemical formula X3Ni3Sb4 (X is Zr or Hf), when X is partially replaced with Y, La, Nb, Ta; Ni is partially replaced with Co, Cu, Rh, Pd, Ir, Pt; Sb is partially replaced with Ge, Sn. It is noted that it is hardly to define the actual composition of the example with three-digits accuracy by using the energy dispersive X-ray spectroscopy (EDX). Referring to Tables 2-21 in whole, each example employing the manufacturing method of
As described above, the thermoelectric conversion material created by the manufacturing method of this disclosure reduced a loss of Sb as compared to conventional cases and had excellent thermoelectric conversion performance.
The method of manufacturing a thermoelectric conversion material according to this disclosure can be used for forming a thermoelectric conversion material performing thermoelectric power generation or thermoelectric cooling.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-082363 | Apr 2013 | JP | national |
This is a continuation application of International Application No. PCT/JP2014/001883, with an international filing date of Mar. 31, 2014, which claims priority of Japanese Patent Application No. 2013-82363 filed on Apr. 10, 2013, the contents of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2014/001883 | Mar 2014 | US |
| Child | 14847362 | US |
