U.S. patent application number 13/434774 was filed with the patent office on 2013-06-27 for methods of manufacturing multi-element thermoelectric alloys.
This patent application is currently assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. The applicant listed for this patent is Ya-Wen Chou, Chia-Hung Kuo, Chien-Hsuan Yeh. Invention is credited to Ya-Wen Chou, Chia-Hung Kuo, Chien-Hsuan Yeh.
Application Number | 20130164165 13/434774 |
Document ID | / |
Family ID | 48654748 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130164165 |
Kind Code |
A1 |
Yeh; Chien-Hsuan ; et
al. |
June 27, 2013 |
METHODS OF MANUFACTURING MULTI-ELEMENT THERMOELECTRIC ALLOYS
Abstract
Disclosed is a method of forming a multi-element thermoelectric
alloy. A plurality of binary alloys and milling balls are put in a
milling pot to perform a ball-milling process to obtain a
multi-element thermoelectric alloy powders. The milling balls have
a diameter of 1 mm to 10 mm. The milling balls and the binary
alloys have a weight ratio of 1:1 to 50:1. The rotation rate of the
ball-milling process is of 200 rpm to 1000 rpm. The ball-milling
process is processed for 4 hours to 12 hours.
Inventors: |
Yeh; Chien-Hsuan; (Miaoli
County, TW) ; Chou; Ya-Wen; (Hsinchu County, TW)
; Kuo; Chia-Hung; (Tainan City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yeh; Chien-Hsuan
Chou; Ya-Wen
Kuo; Chia-Hung |
Miaoli County
Hsinchu County
Tainan City |
|
TW
TW
TW |
|
|
Assignee: |
INDUSTRIAL TECHNOLOGY RESEARCH
INSTITUTE
Hsinchu
TW
|
Family ID: |
48654748 |
Appl. No.: |
13/434774 |
Filed: |
March 29, 2012 |
Current U.S.
Class: |
419/32 ;
75/352 |
Current CPC
Class: |
C01P 2006/40 20130101;
C04B 2235/666 20130101; H01L 35/16 20130101; C04B 2235/6562
20130101; C01B 19/002 20130101; C01B 19/007 20130101; C04B 35/645
20130101; C04B 2235/6567 20130101; C01P 2002/50 20130101; C04B
35/547 20130101; C01P 2002/72 20130101; C04B 35/62615 20130101 |
Class at
Publication: |
419/32 ;
75/352 |
International
Class: |
B22F 1/00 20060101
B22F001/00; B22F 3/12 20060101 B22F003/12; B22F 9/04 20060101
B22F009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2011 |
TW |
TW100148813 |
Claims
1. A method of manufacturing a multi-element thermoelectric alloy,
comprising: providing a plurality of binary alloys and milling
balls in a milling pot to perform a ball-milling process to obtain
a multi-element thermoelectric alloy powder, wherein the milling
balls have a diameter of 1 mm to 10 mm, the milling balls and the
binary alloys have a weight ratio of 1:1 to 50:1, the ball-milling
process has a rotation rate of 200 rpm to 1000 rpm, and the
ball-milling process is processed for 4 hours to 12 hours.
2. The method as claimed in claim 1, wherein the binary alloys
comprise a combination of Bi.sub.2Te.sub.3 and Sb.sub.2Te.sub.3,
and the multi-element thermoelectric alloy powder is
Bi.sub.xSb.sub.2-xTe.sub.3, wherein x is a value of 0.1 to 0.8.
3. The method as claimed in claim 1, wherein the binary alloys
comprise a combination of Bi.sub.2Te.sub.3 and Bi.sub.2Se.sub.3,
and the multi-element thermoelectric alloy powder is
Bi.sub.2Se.sub.yTe.sub.3-y, wherein y is a value of 0.1 to 0.8.
4. The method as claimed in claim 1, wherein the binary alloys
comprise a combination of PbTe and SnTe, and the multi-element
thermoelectric alloy powder is Pb.sub.zSn.sub.1-zTe, wherein z is a
value of 0.1 to 0.9.
5. The method as claimed in claim 1, wherein the binary alloys
comprise a combination of PbTe and AgSb, a combination of PbAg and
Sb.sub.2Te.sub.3, or a combination of PbSb and AgTe, and the
multi-element thermoelectric alloy powder is
Ag.sub.mPb.sub.nTe.sub.pSb, wherein m is a value of 0.1 to 1, n is
a value of 15 to 25, and p is a value of 15 to 25.
6. The method as claimed in claim 5, further adding a metal
compound into the milling pot, wherein the metal compound comprises
PbI.sub.2, TeI.sub.4, SbI.sub.2, or AgI.
7. The method as claimed in claim 1, further adding a metal
compound into the milling pot, wherein the metal compound comprises
PbI.sub.2, TeI.sub.4, SbI.sub.2, or AgI.
8. The method as claimed in claim 7, wherein the binary alloys and
the metal compound comprise a combination of PbAg, PbSb, and
TeI.sub.4, a combination of PbAg, PbTe, and SbI.sub.2, a
combination of PbTe, PbSb, and AgI, or a combination of AgTe, AgSb,
and PbI.sub.2, and the multi-element thermoelectric alloy powder is
Ag.sub.mPb.sub.nTe.sub.pSbI.sub.q, wherein m is a value of 0.1 to
1, n is a value of 15 to 25, p is a value of 15 to 25, and q is a
value of 0.1 to 1.
9. The method as claimed in claim 1, further comprising sintering
and compressing the multi-element thermoelectric alloy powder in
argon or vacuum by a spark plasma sintering process, thereby
forming a multi-element thermoelectric bulk alloy, wherein the
spark plasma sintering process is performed at a temperature of
300.degree. C. to 600.degree. C. for a period of 3 minutes to 30
minutes.
10. The method as claimed in claim 9, wherein the spark plasma
sintering process has a heating rate of 25.degree. C./minute to
100.degree. C./minute, and the multi-element thermoelectric alloy
powder is compressed by a pressure of 25 MPa to 100 MPa.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application claims priority of Taiwan Patent
Application No. 100148813, filed on Dec. 27, 2011, the entirety of
which is incorporated by reference herein.
TECHNICAL FIELD
[0002] The disclosure relates to thermoelectric materials, and in
particular relates to methods for manufacturing the same.
BACKGROUND
[0003] A thermoelectric material can be controlled to move the
internal carriers thereof, thereby directly transferring heat to
electricity (or electricity to heat) without a mechanical moving
part. The thermoelectric material is applied to temperature
differential power generation, waste heat recovery, electronic
component cooling, air condition system, and the likes. The
electricity/heat conversion efficiency of the thermoelectric
material is usually represented as the thermoelectric figure of
merit (ZT value). ZT=S.sup.2.sigma.T/.kappa., wherein S is the
Seebeck coefficient, .sigma. is the electrical conductivity, T is
the absolute temperature, and .kappa. is thermal conductivity. The
ZT value is positively correlated to high electricity/heat
conversion efficiency. The ZT value of the thermoelectric material
can be increased by increasing the electrical conductivity
(.sigma.), increasing the Seebeck coefficient (S), or decreasing
the thermal conductivity (.kappa.) of the thermoelectric
material.
[0004] The multi-element thermoelectric alloy powders can be
prepared from an alloy rod or element powders. In a process of
manufacturing the alloy rod, the element ratio of alloy rod will
not match a predetermined element ratio due to the melting of the
raw materials at a high temperature, in which some elements may
evaporate. In the thermoelectric alloy researches, the powders from
the alloy rods result in the interactions of the defects during
ball-milling, such that the thermoelectric property of the product
is reduced. For example, a p-type BiSbTe alloy will be milled to
produce too much electrons due to the interaction of anti-site
defects and vacancies during ball-milling, thereby reducing the
thermoelectric property of a product. To avoid the above problems
of the alloy rod, the element powders may be directly mechanically
ball-milled for a long period to manufacture a multi-element
thermoelectric alloy. However, the ball-milling for alloying the
element powders takes up much time, e.g. dozens of hours. In
addition, it is difficult to get the sufficiently uniform alloy
powders by this method, and therefore the application value of the
method utilizing the element powders is reduced.
[0005] Accordingly, novel methods of manufacturing multi-element
thermoelectric alloy powders and thermoelectric materials are
called-for.
SUMMARY
[0006] One embodiment of the disclosure provides a method of
manufacturing a multi-element thermoelectric alloy, comprising:
providing a plurality of binary alloys and milling balls in a
milling pot to perform a ball-milling process to obtain the
multi-element thermoelectric alloy powders, wherein the milling
balls have a diameter of 1 mm to 10 mm, the milling balls and the
binary alloys have a weight ratio of 1:1 to 50:1, the ball-milling
process has a rotation rate of 200 rpm to 1000 rpm, and the
ball-milling process is processed for 4 hours to 12 hours.
[0007] A detailed description is given in the following embodiments
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The disclosure can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0009] FIG. 1 shows X-ray diffraction spectra of multi-element
thermoelectric alloy powders in Examples and Comparative Examples
of the disclosure;
[0010] FIG. 2 shows the ZT value to temperature curves of
thermoelectric bulk materials in Examples and Comparative Examples
of the disclosure;
[0011] FIG. 3A shows X-ray diffraction spectra of a multi-element
thermoelectric alloy powder and a thermoelectric bulk material in
Comparative Examples of the disclosure;
[0012] FIG. 3B shows a partial enlarged diagram of FIG. 3A;
[0013] FIG. 4 shows the ZT value to temperature curves of
thermoelectric bulk materials in Comparative Examples of the
disclosure;
[0014] FIG. 5A shows X-ray diffraction spectra of thermoelectric
bulk materials in Examples and Comparative Examples of the
disclosure; and
[0015] FIG. 5B shows a partial enlarged diagram of FIG. 5A.
DETAILED DESCRIPTION
[0016] Below, exemplary embodiments will be described in detail
with reference to accompanying drawings so as to be easily realized
by a person having ordinary knowledge in the art. The inventive
concept may be embodied in various forms without being limited to
the exemplary embodiments set forth herein. Descriptions of
well-known parts are omitted for clarity, and like reference
numerals refer to like elements throughout.
[0017] In one embodiment, different compound powders such as binary
alloys are adopted to prepare multi-element alloys. For example, a
combination of binary alloys Bi.sub.2Te.sub.3 and Sb.sub.2Te.sub.3
can be ball-milled with high energy to form a ternary alloy powder,
Bi.sub.xSb.sub.2-xTe.sub.3, wherein x is a value of 0.1 to 0.8. In
one embodiment, x is a value of 0.3 to 0.6. A combination of binary
alloys Bi.sub.2Te.sub.3 and Bi.sub.2Se.sub.3 can be ball-milled
with high energy to form a ternary alloy powder,
Bi.sub.2Se.sub.yTe.sub.3-y, wherein y is a value of 0.1 to 0.8. A
combination of binary alloys PbTe and SnTe can be ball-milled with
high energy to form a ternary alloy powder, Pb.sub.zSn.sub.1-zTe,
wherein z is a value of 0.1 to 0.9. In one embodiment, z is a value
of 0.6 to 0.9.
[0018] In other embodiments, a combination of binary alloys PbTe
and AgSb, a combination of binary alloys PbAg and Sb.sub.2Te.sub.3,
or a combination of binary alloys PbSb and AgTe can be ball-milled
with high energy to form a quaternary alloy powder,
Ag.sub.mPb.sub.nTe.sub.pSb, wherein m is a value of 0.1 to 1, n is
a value of 15 to 25, and p is a value of 15 to 25. Still in this
embodiment, other metal compounds such as PbI.sub.2, TeI.sub.4,
SbI.sub.2, or AgI can be added a little to modify the Pb, Te, Sb or
Ag element ratio of the quaternary alloy
Ag.sub.mPb.sub.nTe.sub.pSb. A combination of binary alloys PbAg and
PbSb and a metal compound TeI.sub.4, a combination of binary alloys
PbAg and PbTe and a metal compound SbI.sub.2, a combination of
binary alloys PbTe and PbSb and a metal compound AgI, or a
combination of binary alloys AgTe and AgSb and a metal compound
PbI.sub.2 can be ball-milled with high energy to form a quinary
alloy powder, Ag.sub.mPb.sub.nTe.sub.pSbI.sub.q, wherein m is a
value of 0.1 to 1, n is a value of 15 to 25, p is a value of 15 to
25, and q is a value of 0.1 to 1.
[0019] The ball-milling process is a critical point of the
disclosure. A suitable ball-milling energy is beneficial for
forming a stable and uniform multi-element thermoelectric alloy
powder. The ball-milling process can be performed by rotation,
stirring, attrition, and/or vibration. In one embodiment, a
plurality of binary alloy and milling balls are put into a milling
pot, and then ball-milled in argon to obtain a multi-element
thermoelectric alloy powder. The milling balls can be stainless,
and have a diameter of 1 mm to 10 mm. Overly small milling balls
will not provide enough impact energy during the ball-milling
process, thereby forming multi-element thermoelectric alloy powder
with a poor alloying degree. Overly large milling balls will limit
the refinement degree of the ball-milling process. The milling
balls and the binary alloys have a weight ratio of 1:1 to 50:1. An
overly high weight ratio of the milling balls will cause an overly
low milling energy due to an overly short motion path of the
milling balls. An overly low weight ratio of the milling balls will
also cause an overly low milling energy due to overly few
collisions between the milling balls. The ball-milling process has
a rotation rate of 200 rpm to 1000 rpm, or of about 300 rpm to 600
rpm. An overly high rotation rate will cause an overly high
ball-milling energy, such that the content loss of ball-milled
powders increases. An overly low rotation rate will cause the low
alloying degree of ball-milled powders. The ball-milling process is
processed for 4 hours to 12 hours, or of about 5 hours to 10 hours.
The overly short ball-milling period will cause raw binary alloys
residue without further alloying due to incomplete alloying. An
overly long ball-milling period will produce too much reverse
carriers due to the overly long period of the defect
interaction.
[0020] Subsequently, the mentioned multi-element thermoelectric
alloy powders can be sintered by spark plasma sintering (SPS) to
form a disorder nano-structure thermoelectric bulk alloy, which
would have the internal phonon scattering, low thermal
conductivity, and high electrical conductivity. The alloying
process may obtain the thermoelectric alloy powders with high
alloying degree in a short period. The spark plasma sintering is a
fast powder sintering process. Therefore, this manufacturing
process of multi-element thermoelectric bulk alloys has the
potential to be applied in mass production. Different compound
powders can be collocated with the above alloying processes to
prepare a multi-element thermoelectric alloy with a high ZT value,
flexibility of modifying the content of a product, and alloy
content stability.
[0021] The spark plasma sintering (SPS) is a critical point of the
disclosure. In one embodiment, the multi-element thermoelectric
alloy powder formed by the ball-milling is sintered and compressed
by the SPS in argon or vacuum to obtain a thermoelectric bulk
material. The spark plasma sintering process is performed at a
temperature of 300.degree. C. to 600.degree. C. An overly high SPS
temperature will cause the powders to be easily melted to result in
content loss. An overly low SPS temperature will not sinter the
sintered powder densely due to too many void defects existing in
the microstructure. The spark plasma sintering process is performed
for a period of 3 minutes to 30 minutes. An overly long SPS period
will cause the nano grains to disappear due to the increase of the
grain size in the sintered bulk material. An overly short SPS
period will not completely dense the sintered bulk due to many void
defects existing. The SPS has a heating rate of 25.degree.
C./minute to 100.degree. C./minute from room temperature to a
processing temperature. An overly slow heating rate of the SPS will
cause the nano grains to disappear due to the grain growth during
sintering. In the SPS process, the multi-element thermoelectric
alloy powders are compressed by a pressure of 25 MPa to 100 MPa. An
overly low compressing pressure will lower the powder sintering
density. An overly high compressing pressure will make the grain
structure in the sintered alloy to have the obvious orientations,
thereby influencing the alloy properties according to the grain
orientations.
[0022] After the ball-milling and SPS processes, a thermoelectric
bulk material is obtained. The described processes have advantages
as below:
[0023] (1) High alloying degree and uniformity: binary alloys and
other metal compounds (high stability and no defect/void/impurity)
can be ball-milled for a period of less than 10 hours to obtain a
multi-element thermoelectric alloy powders with high alloying
degree and uniformity.
[0024] (2) Reducing the interaction of defects: in high energy
ball-milling process, it may reduce internal defects, voids, defect
interaction, and reverse carriers of the alloy product by milling
the binary alloys and other metal compounds. As such, the
electrical conductivity of the alloy product will be not reduced by
the reverse carriers.
[0025] (3) Nano-structure effect: the high energy mechanical
ball-milling process not only alloys different compound powders,
but also manufactures the alloy powders with nano grains. The
powders can be rapidly sintered by an electrical current, in which
a pulse current passes through the powder interfaces to form high
energy plasma. The rapid sintering may remove oxides on the powder
surface to form a complete interface between the grains and keep
the nano grain structure. A nano inclusion will be precipitated to
grain boundaries and the inside of grains by a sintering current
effect. The nano-inclusion can cause the quantum effect and enhance
Seebeck coefficient. Simultaneously, the phonons should have the
scattering effect due to the nano grains and nano grain boundaries
in the microstructure, thereby efficiently reducing the thermal
conductivity to enhance thermoelectric conversion efficiency.
[0026] (4) Process stability and energy saving: the compound
powders serving as starting materials have the excellent chemical
stability. It will be difficult to result in content loss during
the ball-milling and sintering processes at high temperatures. As
such, the content ratio of the product is easily controlled, and
the process stability is enhanced. The compound powders adopted to
prepare the multi-element thermoelectric alloy powders can be
ball-milled for a short period to obtain the powders with high
alloying degree. The alloyed powders can be rapidly sintered by the
temperature lower than that of a conventional alloy melting and the
heat-pressing method. In addition, the alloyed powders can be
rapidly sintered for several minutes. Accordingly, the rapid
sintering process of the disclosure may largely decrease the
process period to save energy.
EXAMPLES
Comparative Example 1
Bi.sub.0.4Sb.sub.1.6Te.sub.3 Alloy Rod
[0027] A Bi.sub.0.4Sb.sub.1.6Te.sub.3 alloy rod prepared by the
alloy melting method was crushed and then put into a ball-milling
pot to perform a ball-milling process in argon to obtain the
multi-element thermoelectric alloy powders. An X-ray diffraction
spectrum of the multi-element thermoelectric alloy powders is shown
in FIG. 1. The milling balls were stainless balls having a diameter
of 3 mm. The milling balls and the Bi.sub.0.4Sb.sub.1.6Te.sub.3
alloy had a weight ratio of 20:1. The rotation rate of the
ball-milling process was 600 rpm. The ball-milling process was
performed for 9 hours.
[0028] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0029] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 400.degree. C. for 10 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The thermoelectric bulk material had the ZT value to
temperature curve as shown in FIG. 2.
Example 1
[0030] 4 molar parts of Sb.sub.2Te.sub.3 (commercially available
from Alfa Aesar) and 1 molar part of Bi.sub.2Te.sub.3 (commercially
available from Alfa Aesar) were put into a ball-milling pot to
perform a ball-milling process in argon to obtain the multi-element
thermoelectric alloy powders Bi.sub.0.4Sb.sub.1.6Te.sub.3. An X-ray
diffraction spectrum of the multi-element thermoelectric alloy
powders Bi.sub.0.4Sb.sub.1.6Te.sub.3 is shown in FIG. 1. The
milling balls were stainless balls having a diameter of 3 mm. The
milling balls and the binary alloys (Sb.sub.2Te.sub.3 and
Bi.sub.2Te.sub.3) had a weight ratio of 20:1. The rotation rate of
the ball-milling process was 600 rpm. The ball-milling process was
performed for 9 hours.
[0031] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0032] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 400.degree. C. for 10 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The thermoelectric bulk material had the ZT value to
temperature curve as shown in FIG. 2.
Example 2
[0033] 4 molar parts of Sb.sub.2Te.sub.3 (commercially available
from Alfa Aesar) and 1 molar part of Bi.sub.2Te.sub.3 (commercially
available from Alfa Aesar) were put into a ball-milling pot to
perform a ball-milling process in argon to obtain the multi-element
thermoelectric alloy powders Bi.sub.0.4Sb.sub.1.6Te.sub.3. An X-ray
diffraction spectrum of the multi-element thermoelectric alloy
powders Bi.sub.0.4Sb.sub.1.6Te.sub.3 is shown in FIG. 1. The
milling balls were stainless balls having a diameter of 3 mm. The
milling balls and the binary alloys (Sb.sub.2Te.sub.3 and
Bi.sub.2Te.sub.3) had a weight ratio of 30:1. The rotation rate of
the ball-milling process was 600 rpm. The ball-milling process was
performed for 9 hours.
[0034] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0035] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 400.degree. C. for 10 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The thermoelectric bulk material had the ZT value to
temperature curve as shown in FIG. 2.
[0036] As shown in FIG. 1, the binary alloys Bi.sub.2Te.sub.3 and
Sb.sub.2Te.sub.3 were ball-milled and alloyed to form the
multi-element alloy powders having a similar crystallization
structure as the Bi.sub.0.4Sb.sub.1.6Te.sub.3 alloy rod. In
addition, the multi-element alloy powders formed by ball-milling
had an excellent alloying degree.
Example 3
[0037] 4 molar parts of Sb.sub.2Te.sub.3 (commercially available
from Alfa Aesar) and 1 molar part of Bi.sub.2Te.sub.3 (commercially
available from Alfa Aesar) were put into a ball-milling pot to
perform a ball-milling process in argon to obtain the multi-element
thermoelectric alloy powders Bi.sub.0.4Sb.sub.1.6Te.sub.3. An X-ray
diffraction spectrum of the multi-element thermoelectric alloy
powders Bi.sub.0.4Sb.sub.1.6Te.sub.3 is shown in FIG. 1. The
milling balls were stainless balls having a diameter of 3 mm. The
milling balls and the binary alloys (Sb.sub.2Te.sub.3 and
Bi.sub.2Te.sub.3) had a weight ratio of 30:1. The rotation rate of
the ball-milling process was 600 rpm. The ball-milling process was
performed for 9 hours.
[0038] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0039] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 400.degree. C. for 5 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 50
MPa. The thermoelectric bulk material had the ZT value to
temperature curve as shown in FIG. 2.
[0040] As shown in FIG. 2, the thermoelectric bulk material in the
Examples had a better ZT value than that of the thermoelectric bulk
material in the Comparative Example 1.
Comparative Example 2
[0041] 3 molar parts of Sb.sub.2Te.sub.3 (commercially available
from Alfa Aesar) and 1 molar part of Bi.sub.2Te.sub.3 (commercially
available from Alfa Aesar) were put into a ball-milling pot to
perform a ball-milling process in argon to obtain the multi-element
thermoelectric alloy powders Bi.sub.0.5Sb.sub.1.5Te.sub.3. An X-ray
diffraction spectrum of the multi-element thermoelectric alloy
powders Bi.sub.0.5Sb.sub.1.5Te.sub.3 is shown in FIG. 3A. The
milling balls were stainless balls having a diameter of 3 mm. The
milling balls and the binary alloys (Sb.sub.2Te.sub.3 and
Bi.sub.2Te.sub.3) had a weight ratio of 20:1. The rotation rate of
the ball-milling process was 300 rpm. The ball-milling process was
performed for 3 hours.
[0042] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0043] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 350.degree. C. for 5 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The X-ray diffraction spectrum of the thermoelectric bulk
material is shown in FIG. 3A, and the ZT value to temperature curve
is shown in FIG. 4.
Comparative Example 3
[0044] 3 molar parts of Sb.sub.2Te.sub.3 (commercially available
from Alfa Aesar) and 1 molar part of Bi.sub.2Te.sub.3 (commercially
available from Alfa Aesar) were put into a ball-milling pot to
perform a ball-milling process in argon to obtain the multi-element
thermoelectric alloy powders Bi.sub.0.5Sb.sub.1.5Te.sub.3. The
milling balls were stainless balls having a diameter of 3 mm. The
milling balls and the binary alloys (Sb.sub.2Te.sub.3 and
Bi.sub.2Te.sub.3) had a weight ratio of 20:1. The rotation rate of
the ball-milling process was 300 rpm. The ball-milling process was
performed for 3 hours.
[0045] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0046] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 400.degree. C. for 5 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The X-ray diffraction spectrum of the thermoelectric bulk
material is shown in FIG. 3A. As shown in FIG. 3B, an enlarged
diagram of a dotted circle 41 in FIG. 3A, two diffraction peaks
mean that the sintered thermoelectric bulk material had an
insufficient alloying degree due to the low energy ball-milling
process.
Comparative Example 4
[0047] 3 molar parts of Sb.sub.2Te.sub.3 (commercially available
from Alfa Aesar) and 1 molar part of Bi.sub.2Te.sub.3 (commercially
available from Alfa Aesar) were put into a ball-milling pot to
perform a ball-milling process in argon to obtain the multi-element
thermoelectric alloy powders Bi.sub.0.5Sb.sub.1.5Te.sub.3. The
milling balls were stainless balls having a diameter of 3 mm. The
milling balls and the binary alloys (Sb.sub.2Te.sub.3 and
Bi.sub.2Te.sub.3) had a weight ratio of 20:1. The rotation rate of
the ball-milling process was 300 rpm. The ball-milling process was
performed for 3 hours.
[0048] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0049] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 300.degree. C. for 5 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The thermoelectric bulk material had the ZT value to
temperature curve as shown in FIG. 4. As shown in FIG. 4, the
thermoelectric bulk material formed by the low energy ball-milling
process and the SPS process had a ZT value of a little higher than
0.4, which was obviously less than the ZT value of the
thermoelectric bulk material in the Examples.
Comparative Example 5
[0050] 3 molar parts of PbTe (commercially available from Aldrich)
and 1 molar part of SnTe (commercially available from Alfa Aesar)
were put into a ball-milling pot to perform a ball-milling process
in argon to obtain the multi-element thermoelectric alloy powders.
The milling balls were stainless balls having a diameter of 3 mm.
The milling balls and the binary alloys (PbTe and SnTe) had a
weight ratio of 20:1. The rotation rate of the ball-milling process
was 300 rpm. The ball-milling process was performed for 1 hour.
[0051] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0052] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 300.degree. C. for 5 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The X-ray diffraction spectrum of the thermoelectric bulk
material is shown in FIG. 5A.
Comparative Example 6
[0053] 3 molar parts of PbTe (commercially available from Aldrich)
and 1 molar part of SnTe (commercially available from Alfa Aesar)
were put into a ball-milling pot to perform a ball-milling process
in argon to obtain the multi-element thermoelectric alloy powders.
The milling balls were stainless balls having a diameter of 3 mm.
The milling balls and the binary alloys (PbTe and SnTe) had a
weight ratio of 20:1. The rotation rate of the ball-milling process
was 300 rpm. The ball-milling process was performed for 1 hour.
[0054] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0055] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 400.degree. C. for 5 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The X-ray diffraction spectrum of the thermoelectric bulk
material is shown in FIG. 5A.
Comparative Example 7
[0056] 3 molar parts of PbTe (commercially available from Aldrich)
and 1 molar part of SnTe (commercially available from Alfa Aesar)
were put into a ball-milling pot to perform a ball-milling process
in argon to obtain the multi-element thermoelectric alloy powders.
The milling balls were stainless balls having a diameter of 3 mm.
The milling balls and the binary alloys (PbTe and SnTe) had a
weight ratio of 20:1. The rotation rate of the ball-milling process
was 300 rpm. The ball-milling process was performed for 3
hours.
[0057] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0058] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 300.degree. C. for 5 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The X-ray diffraction spectrum of the thermoelectric bulk
material is shown in FIG. 5A.
Example 4
[0059] 3 molar parts of PbTe (commercially available from Aldrich)
and 1 molar part of SnTe (commercially available from Alfa Aesar)
were put into a ball-milling pot to perform a ball-milling process
in argon to obtain the multi-element thermoelectric alloy powders.
The milling balls were stainless balls having a diameter of 3 mm.
The milling balls and the binary alloys (PbTe and SnTe) had a
weight ratio of 20:1. The rotation rate of the ball-milling process
was 300 rpm. The ball-milling process was performed for 6
hours.
[0060] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0061] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 300.degree. C. for 5 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The X-ray diffraction spectrum of the thermoelectric bulk
material is shown in FIG. 5A. FIG. 5B shows a partial enlarged
diagram of FIG. 5A.
Example 5
[0062] 3 molar parts of PbTe (commercially available from Aldrich)
and 1 molar part of SnTe (commercially available from Alfa Aesar)
were put into a ball-milling pot to perform a ball-milling process
in argon to obtain the multi-element thermoelectric alloy powders.
The milling balls were stainless balls having a diameter of 3 mm.
The milling balls and the binary alloys (PbTe and SnTe) had a
weight ratio of 20:1. The rotation rate of the ball-milling process
was 300 rpm. The ball-milling process was performed for 6
hours.
[0063] The multi-element thermoelectric alloy powders were put into
a sintering mold, and the sintering mold was cold compressed to be
molded by a clamping machine.
[0064] The molded multi-element thermoelectric alloy powders were
then put into a spark plasma sintering equipment (SPS, SYNTEX INC.,
DR.SINTER Model: SPS-511S) to perform a sintering process in argon
at a temperature of 400.degree. C. for 5 minutes to obtain a
thermoelectric bulk material, wherein the heating rate from room
temperature to the processing temperature was 100.degree.
C./minute. During the sintering process, the molded multi-element
thermoelectric alloy powders were compressed by a pressure of 100
MPa. The X-ray diffraction spectrum of the thermoelectric bulk
material is shown in FIG. 5A. FIG. 5B shows a partial enlarged
diagram of FIG. 5A.
[0065] Different compound powders (e.g. binary alloys) were
directly alloyed to form the multi-element thermoelectric alloy in
the Examples. Because the compound powders were more stable than
pure element powders, the compound powders were ball-milled with
high energy to form the multi-element thermoelectric alloy powders
with little content variation. In other words, the ball-milling
problem such as content loss or defect interaction can be avoided
by utilizing the compound powders. The parameters of the high
energy ball-milling process can be controlled to increase the
stability and uniformity of the processes for manufacturing the
multi-element thermoelectric alloy powders, which is good for
controlling of the alloy content, reducing the process period, and
increasing the alloying degree of products. The thermoelectric bulk
materials of the Examples had several advantages such as a maximum
ZT value which was greater than 0.4 and a short ball-milling
period. Furthermore, the thermoelectric alloy powders had a high
alloying degree.
[0066] It will be apparent to those skilled in the art that various
modifications and variations can be made to the disclosed
embodiments. It is intended that the specification and examples be
considered as exemplary only, with a true scope of the disclosure
being indicated by the following claims and their equivalents.
* * * * *