CN111463341A - Low-contact-resistivity half-heusler alloy thermoelectric device and preparation method thereof - Google Patents
Low-contact-resistivity half-heusler alloy thermoelectric device and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a half heusler alloy thermoelectric device with low contact resistivity and a preparation method thereof, wherein the half heusler alloy thermoelectric device comprises a half heusler alloy thermoelectric element, and the half heusler alloy thermoelectric element comprises a half heusler alloy thermoelectric material and an electrode layer integrally formed at least one end of the half heusler alloy thermoelectric material; the melting point temperature of the material of the electrode layer is above 1000 ℃, preferably above 2000 ℃, and more preferably, the material of the electrode layer is at least one of a chromium simple substance, a molybdenum simple substance, a tungsten simple substance, an alloy mainly containing three metals of the chromium simple substance, the molybdenum simple substance and the tungsten simple substance, or a pseudo alloy mainly containing three metals of the chromium simple substance, the molybdenum simple substance and the tungsten simple substance.
Description
Technical Field
The invention relates to a half-heusler alloy thermoelectric device and a preparation method thereof, in particular to a thermoelectric device integrated electrode design with low contact resistivity, and belongs to the technical field of thermoelectric conversion.
Background
The thermoelectric material is a semiconductor functional material which realizes the direct conversion of heat energy and electric energy by utilizing Seebeck effect and Peltier effect. The thermoelectric device has a solid structure, does not generate noise and gas pollution, and is suitable for micro equipment.
half-Heusler (HH) material is a thermoelectric material suitable for medium-high temperature and has a space group of
The number of valence electrons is typically 8 or 18. In recent years, with the development of preparation technology and theoretical research, the optimal thermoelectric figure of merit (ZT) of both N type and P type of the half heusler alloy thermoelectric material has broken through 1. Wherein the thermoelectric figure of merit of the N-type HH material ZrNiSn-based thermoelectric material reaches 1.2(Phys Chem Phys 2013,15(6),1868-1872) at 830K, and the thermoelectric figure of merit of the P-type NbFeSb-based material reaches 1.5(Naturecommunications,2015,6:8144.) at 1200K. The half-heusler alloy material is a material with great commercial application potential due to cheap raw materials, excellent mechanical property and thermal stability and more excellent thermoelectric property.
Among the factors affecting the service performance of thermoelectric devices, the interface stability between the thermoelectric base material and the electrode layer is one of the important determining factors of the service life of the whole device.
At present, aiming at the problem of unstable interface between the thermoelectric material and the electrode, such as interface diffusion or interface chemical reaction, diffusion and reaction between the matrix material and the electrode material can be inhibited by introducing a diffusion barrier layer. For example, the Shanghai silicate research institute of Chinese academy of sciences introduces Ti-Al mixture as diffusion barrier layer (Journal of Alloys and Compounds 610(2014) 665-2The stability of the interface and the service life of the device are effectively improved, but the introduction of the diffusion barrier layer can also improve the stability of the interface and the service life of the deviceThe difficulty of process connection is improved.
Semi-heusler alloy thermoelectric devices are typically used at higher temperatures (> 700K), and interface studies are more important because the interface diffusion or reaction between the electrodes and the thermoelectric material is more pronounced at high temperatures. The university of Denmark science and technology studied Ag/Incusil/HH solder and Ag/HH thermocompression bonding (Journal of Electronic Materials,2016,45(1):594-601.), but the diffusion layer was thicker, and the interfacial contact resistivity at room temperature was also greater than 50 μ Ω cm2. Joshi (journal of Electronic Materials,2016,45(12):1-5.) achieves a one-step connection of Ti and HH Materials with an interfacial resistance of about 1 μ Ω cm2However, this experiment is not verified by aging, and at the same time, Ti is one of the main elements of the N-type HH material, and during long-term aging, Ti enters the base material in a solid solution manner, and the barrier layer is rapidly consumed, so that it is difficult to obtain a long-term stable interface structure. Currently, Shenzhen university makes related research work aiming at HH material barrier layer selection by using a step-by-step sintering method (research on material of Fe/Ni/Ti-based electrode barrier layer of high-temperature thermoelectric device in Half-Heusler [ D]Shenzhen university, 2017). They use Fe/Ni/Ti and their mixture as diffusion barrier layer, and the contact resistivity of P-type material is about 16-18 mu omega cm2Contact resistivity of N-type material 13 mu omega cm2(Chinese publication No. CN 107665943A). But the thickness of the interface diffusion layer is increased rapidly during aging, and the chemical reaction of the interface is complex after aging. Moreover, the electrode material or solder layer material selected by the current HH device is generally Sn, In, Cu, Ag and the like, the melting point is low, and the Cu and Ag are softened seriously In the optimal performance temperature zone (1200K) of the current P-type HH material, so that the use requirement is difficult to meet. In summary, the half heusler alloy thermoelectric device currently lacks an electrode material with low contact resistivity and long-term stability and reliability.
Disclosure of Invention
The invention aims to solve the problems that a half heusler alloy thermoelectric material and an electrode connecting interface in a half heusler alloy thermoelectric device are unstable and the process is complex, and provides a half heusler alloy thermoelectric device with extremely low contact resistivity and a connecting method for integrating electrode materials of the half heusler alloy thermoelectric device.
In a first aspect, the present invention provides a half heusler alloy thermoelectric device comprising a half heusler alloy thermoelectric element comprising a half heusler alloy thermoelectric material, and an electrode layer integrally formed on at least one end of the half heusler alloy thermoelectric material; the melting point temperature of the material of the electrode layer is above 1000 ℃, preferably above 2000 ℃, and more preferably, the material of the electrode layer is at least one of a chromium simple substance, a molybdenum simple substance, a tungsten simple substance, an alloy mainly containing three metals of the chromium simple substance, the molybdenum simple substance and the tungsten simple substance, or a pseudo alloy mainly containing three metals of the chromium simple substance, the molybdenum simple substance and the tungsten simple substance.
In the invention, the melting point temperature of the selected electrode materials is over 1000 ℃, and the melting point of the selected electrode materials is preferably over 2000 ℃ (for example, the melting point temperature of the selected electrode materials is chromium simple substance, molybdenum simple substance, tungsten simple substance, alloy taking three metals of chromium simple substance, molybdenum simple substance and tungsten simple substance as main bodies, or pseudo alloy taking three metals of chromium simple substance, molybdenum simple substance and tungsten simple substance as main bodies, etc.), and the electrode materials can meet the use requirements of high-temperature HH material devices. The electrode material used in the invention has the functions of a conductive electrode and a diffusion barrier layer, so that the functions of blocking diffusion, reaction and flow guide between the base material and the electrode can be realized through a single metal layer or a metal mixture or a metal alloy layer, an additional barrier layer is not required to be added in the device integration process, the process cost and the process complexity are reduced, and the stability of the device is improved. Moreover, the selected electrode material enables the semi-heusler alloy thermoelectric material and the electrode layer to have extremely low contact resistivity, and the semi-heusler alloy thermoelectric material is difficult to enter a matrix material in a solid solution mode or a doping mode in the long-term aging service process of the HH thermoelectric device, so that the thermoelectric device has long-term high-temperature stability.
Preferably, the thickness of the electrode layer is 0.001 μm to 2mm, preferably 100 μm.
Preferably, the general formula of the half heusler alloy thermoelectric material is ABX, wherein A is at least one of Sc, Y, Ti, Zr, Hf, V, Nb and Ta, B is at least one of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt, and X is at least one of Sn, Sb and Bi; preferably, the half heusler alloy thermoelectric material is at least one of ZrNiSn, ZrCoSb, a solid solution and doped ZrNiSn-based half heusler alloy, and a solid solution and doped ZrCoSb-based half heusler alloy.
In a second aspect, the present invention provides a method for connecting the above half heusler alloy thermoelectric device in one step, wherein the one-step connecting method for the half heusler alloy thermoelectric material and the electrode layer in the half heusler alloy thermoelectric element comprises:
firstly, laying the powder of the half-heusler thermoelectric alloy material in a mould and compacting the powder, and then laying the powder or the slice consisting of the material of the electrode layer on the surface of the powder of the half-heusler thermoelectric alloy material and compacting the powder;
and finally, placing the die in a protective atmosphere, and realizing one-step connection of the semi-heusler alloy thermoelectric material and the electrode layer by adopting discharge plasma sintering, laser sintering, hot-pressing sintering or microwave sintering.
The invention adopts the sintering connection process, the selected connection method does not need to use solder, and the problems of diffusion between interfaces and unstable chemical properties caused by complex element composition in the solder are avoided. The invention adopts a one-step sintering process to ensure that the electrode layer metal material with high melting point can be directly connected with the HH substrate material, thereby solving the problem that the high melting point metal is difficult to be directly connected with the substrate material through step-by-step sintering.
In a third aspect, the present invention provides a method for step-by-step connection of the above-mentioned half heusler alloy thermoelectric device, wherein the step-by-step connection method of the half heusler alloy thermoelectric material and the electrode layer in the half heusler alloy thermoelectric element includes:
spreading powder or thin slices composed of the material of the electrode layer on the surface of the obtained semi-heusler thermoelectric alloy material ingot and compacting;
and then placing the die in a protective atmosphere, and realizing the connection of the semi-heusler alloy thermoelectric material and the electrode layer by adopting discharge plasma sintering, laser sintering, hot-pressing sintering or microwave sintering. In the disclosure, on the premise of excluding the doping elements and the solid solution elements for a specific material system, a specific high-melting-point material with a blocking function is selected, and an appropriate connection method is used for the specific material system, so that an extremely low contact resistance value is obtained.
Preferably, the semi-heusler thermoelectric alloy material powder is spread in a mold and compacted, and is placed in a protective atmosphere, and the semi-heusler thermoelectric alloy material ingot is prepared by adopting spark plasma sintering, hot-pressing sintering or microwave sintering.
Preferably, the sintering temperature of the discharge plasma is 600-1200 ℃, the heat preservation time is 1-60 minutes, and the sintering pressure is 20-120 MPa; the hot-pressing sintering temperature is 800-1400 ℃, the heat preservation time is 1-120 minutes, and the sintering pressure is 20-120 MPa; the parameters of the microwave sintering comprise: 0.5-10 kilowatts are continuously adjustable, and the working frequency is as follows: 2.45 gigahertz, the sintering time is 10 to 60 minutes, and the pressure can be 10 to 80 Mpa; the parameters of the laser sintering include: laser frequency: 10-40 Hz, pulse width: 2-5 milliseconds, a moving speed of 1-1000 millimeters per minute, a sintering current of 80-150 amperes, and an applied pressure of 10-60 MPa.
Preferably, the heating rate of the spark plasma sintering and the hot-pressing sintering is 20-200 ℃/min; and after sintering, the cooling rate of the discharge plasma sintering and the hot-pressing sintering is 5-100 ℃/min.
Preferably, the protective atmosphere is a vacuum atmosphere, a nitrogen atmosphere, or an inert atmosphere; the inert atmosphere is argon or/and helium, and the vacuum degree of the vacuum atmosphere is less than 10 Pa.
In a fourth aspect, the present invention provides a method for step-by-step connection of the above-described half heusler alloy thermoelectric device, wherein the step-by-step connection method of the half heusler alloy thermoelectric material and the electrode layer in the half heusler alloy thermoelectric element includes: and preparing an electrode layer on the surface of the half-heusler thermoelectric alloy material ingot by adopting an electroplating method, a magnetron sputtering method, an ion plating method, a pulse laser deposition method or an evaporation method, so as to realize the connection between the half-heusler alloy thermoelectric material and the electrode layer.
Compared with the prior art, the invention has the beneficial effects that:
the electrode material of the integrated thermoelectric device with the blocking function provided by the invention is pure metal, metal mixture or metal alloy, has better conductivity and is a better electrode material. The connection between the semi-heusler alloy thermoelectric material and the electrode layer is carried out by a one-step sintering method such as hot-pressing sintering and spark plasma sintering or a step-by-step connection method such as sputtering, deposition and evaporation. The interface connected with the electrode in the half heusler alloy thermoelectric element prepared by the method has the characteristics of small contact resistance, less diffusion and good thermal stability. In addition, the invention does not need a solder layer, and realizes integrated sintering, so that the service performance of the device is better.
Drawings
FIG. 1 is a schematic diagram of a conventional thermoelectric device employing a barrier-electrode thermoelectric device structure and an integrated electrode with barrier function provided by the present invention;
FIG. 2 is a microstructure plan view of an N-type HH material and a chromium layer;
FIG. 3 is a line scan at the microscopic interface of an N-type HH material and a chromium layer;
FIG. 4 shows the resistance change of an unaged N-type HH material and a chromium layer obtained by a self-built four-probe resistance test platform;
FIG. 5 shows the resistance change of the N-type HH material and the chromium layer aged at 800 deg.C for 3 days, which is obtained by a self-built four-probe resistance testing platform;
FIG. 6 is a microscopic backscattering plot of a P-type HH material and a chromium layer;
FIG. 7 shows the resistance change of an unaged P-type HH material and Cr layer obtained by a self-built four-probe resistance test platform;
FIG. 8 is a microscopic backscattering plot of N-type HH material and molybdenum layer;
FIG. 9 shows the resistance change of an unaged N-type HH material and Mo layer obtained by a self-built four-probe resistance test platform;
FIG. 10 is a microscopic backscattering plot of N-type HH material and tungsten layer;
FIG. 11 shows the resistance change of an unaged N-type HH material and W layer obtained by a self-built four-probe resistance test platform;
FIG. 12 is a graph showing the change in interfacial resistance of a chromium layer coupled N-type HH material in accordance with the present invention after aging at 850 deg.C for 480 hours, while using a TiNi alloy when a barrier layer coupled N-type HH material is aged at 600 deg.C for 96 hours as a control;
FIG. 13 is a microscopic backscattering plot of a ZrCoSb based HH material and Cr layer prepared in example 5;
FIG. 14 is a line scan at the microscopic interface of ZrCoSb based HH and Cr layers prepared in example 5;
FIG. 15 is a test chart of the interfacial resistance of ZrCoSb based HH and Cr layers prepared in example 5.
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.
In the present disclosure, the half heusler alloy-based thermoelectric element employs an integrated electrode layer structure having a function of blocking interface diffusion, and realizes extremely low interface contact resistivity while simplifying the electrode layer structure. The electrode layer with the barrier function is composed of one or more of chromium, molybdenum and tungsten elementary metals, or an alloy and a pseudo alloy which are prepared by taking the chromium, the molybdenum and the tungsten elementary metals as main bodies, or a mixture of the chromium, the molybdenum and the tungsten elementary metals.
In an alternative embodiment, the half heusler alloy thermoelectric material has a general formula ABX, where a is the most electropositive transition metal element, typically one or a mixture of Sc, Y, Ti, Zr, Hf, V, Nb, Ta; b is transition metal element with slightly weaker electropositivity, and one or a mixture of more of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt; x is a main group element with stronger electronegativity, and is usually one or a mixture of several elements of Sn, Sb and Bi. In alternative embodiments, the electrode layer may have a thickness of 0.001 μm to 2mm, preferably a thickness of 100 μm.
In the disclosure, the integrated electrode of the half heusler alloy thermoelectric device with the blocking function simplifies the structure of the thermoelectric device, the preparation process is simple, good ohmic contact can be formed between interfaces, the thermal stability is high, the long-term service performance is stable, the cost is low, and the integrated electrode is suitable for large-scale preparation and use. The following exemplarily illustrates a method for manufacturing a half heusler alloy thermoelectric device of low contact resistivity.
In one embodiment of the present invention, a one-step connection method between a half heusler alloy and an electrode layer of low contact resistance in a half heusler alloy thermoelectric device includes: the semi-heusler alloy and the electrode layer are sintered in one step by adopting methods such as spark plasma sintering, hot-pressing sintering, laser sintering, microwave sintering and the like so as to complete the connection of the semi-heusler thermoelectric material and the electrode layer material, and the thickness of a plating layer can be accurately controlled.
Firstly, half-heusler thermoelectric alloy material powder is paved in a mould and compacted, and then powder or thin slices composed of the material of the electrode layer are paved on the surface of the half-heusler thermoelectric alloy material powder and compacted. And finally, placing the die in a protective atmosphere, and realizing one-step connection of the semi-heusler alloy thermoelectric material and the electrode layer by adopting discharge plasma sintering, laser sintering, hot-pressing sintering or microwave sintering.
As an example of a one-step connection method between a half heusler alloy and an electrode layer of low contact resistivity, there is included: (1) firstly, spreading powder of the HH material in a graphite mold, and compacting; (2) spreading the powder or flake electrode material on the HH material by a spreading system or manually, and compacting; (3) the mixed powder raw material is directly sintered in one step by the processes of hot pressing, spark plasma sintering, laser sintering, microwave sintering and the like. The electrode layer material can be chromium, molybdenum, tungsten powder, mixed powder thereof, mixed powder mainly containing chromium, molybdenum and tungsten powder, or alloy powder thereof, the form of the electrode layer material can be powder or flake, and the electrode layer material not only can be directly used as an electrode of a half heusler alloy thermoelectric element, but also can be used for preparing a barrier layer of the half heusler alloy thermoelectric element by using the material.
In one embodiment of the present invention, a method for step-by-step connection between a half heusler alloy and an electrode layer of low contact resistivity in a half heusler alloy thermoelectric device includes: the connection between the semi-heusler thermoelectric material ingot and the electrode layer material is completed on the compact semi-heusler thermoelectric material ingot (HH material ingot) by adopting methods such as spark plasma sintering, hot-pressing sintering, laser sintering, microwave sintering and the like, and the thickness of the coating can be accurately controlled. In an alternative embodiment, a method of making a half heusler thermoelectric material ingot comprises: spark plasma sintering, hot-press sintering, laser sintering, microwave sintering, and the like.
In alternative embodiments, the atmosphere of the hot-pressing sintering, spark plasma sintering, laser sintering, microwave sintering, and other methods may be vacuum, nitrogen atmosphere, or inert atmosphere. Wherein the vacuum condition is less than 10Pa, and the inert atmosphere is argon or helium.
In an optional embodiment, the sintering temperature of the discharge plasma can be 600-1200 ℃, the heat preservation time is 1-60 minutes, and the sintering pressure is 20-120 MPa. Preferably, the pressure of the discharge plasma sintering is 45-120 Mpa, and the heat preservation time is 2-45 min. The hot-pressing sintering temperature can be 800-1400 ℃, the heat preservation time is 1-120 minutes (preferably 2-60 minutes), and the sintering pressure is 20-120 MPa (preferably 45-120 MPa). The parameters of the microwave sintering comprise: 0.5-10 kilowatts are continuously adjustable, and the working frequency is as follows: 2.45 gigahertz, the sintering time is 10 to 60 minutes, and the pressure can be 10 to 80 Mpa. The parameters of laser sintering include: laser frequency: 10-40 Hz, pulse width: 2-5 milliseconds, a moving speed of 1-1000 millimeters per minute, a sintering current of 80-150 amperes, and an applied pressure of 10-60 MPa. Further preferably, the heating rate of the electric plasma sintering and the hot-pressing sintering can be 20-200 ℃/min; after sintering, the cooling rate of the discharge plasma sintering and the hot-pressing sintering can be 5-100 ℃/min.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
Example 1
The embodiment is a preparation method of an electrode with a blocking and guiding integrated function, wherein a chromium layer is used as an N-HH material of a ZrNiSn group, and the preparation method mainly comprises the following steps:
1) ZrNiSn based powder of an HH material of N type (here ZrNiSn)0.99Sb0.01) Laying in a mould, laying flat, here 5mm thick, slightly compacted;
2) spreading metal chromium powder or flaky chromium in a mold, spreading the chromium powder or flaky chromium with the thickness of 300 mu m, and compacting;
3) placing the mould paved with the powder in the step 2 into sintering equipment, wherein the sintering equipment can be spark plasma sintering and hot-pressing sintering, sintering is started under 10Pa, the heating rate is 100K/min, the sintering temperature is 900 ℃, the sintering pressure is 65Mpa, the heat preservation time is 20min, and the cooling rate is 10K/min to room temperature;
4) taking out the obtained block sample, cutting the block sample into a required shape by using wire electrical discharge machining or diamond cutting, testing the interface resistance, observing the diffusion structure of the interface and testing the interface resistance condition of the interface, and analyzing the test result as follows:
from the surface scanning diagram of fig. 2, it can be seen that the interface bonding between the Cr layer and the N-type HH thermoelectric material is good, no obvious diffusion layer exists on a macroscopic scale, and the elements are uniformly distributed;
from the line scanning of the interface between the ZrNiSn based N-HH matrix material layer and the chromium layer in FIG. 3 and FIG. 2, it can be seen that the abrupt change of the elements at the interface connection is sharper on the microscopic scale of the interface between the ZrNiSn based N-HH matrix material layer and the chromium layer, the left side of the interface connection is basically compounded by Ni atoms, Zr atoms and Zn atoms, the right side is basically Cr atoms, no obvious second phase or impurity phase exists, and no obvious interdiffusion zone exists, which indicates that no new intermediate compound is generated by the combination at the interface;
it can be seen from fig. 4 that the interface between the cr layer and the ZrNiSn-based N-HH matrix is a perfect ohmic contact, and there is no obvious abrupt change in resistance, so the interface resistance at this point is negligible, and the influence on the output performance of the device is very small, which indicates that cr is an excellent material with blocking and guiding functions for the N-type HH material.
Fig. 5 shows the change of the interface resistance of the group of samples after aging for 3 days at 800 ℃, and it can be seen that the bonding interface between the chromium layer and the N-HH matrix material is still perfect ohmic contact, which indicates that the electrode material with the integrated blocking and guiding function provided by the invention has good stability at high temperature.
Fig. 12 is a comparison of the change of the contact resistivity of the sample after aging for 0, 24, 72, 120, 240 and 480 hours at a constant temperature of 800 ℃ (thermoelectric device electrode and preparation method thereof, publication number: CN 107665943A). the change of the contact resistivity after 0, 24, 48 and 96 hours at 600 ℃ (using TiNi alloy as the N-type HH device barrier layer) can be seen, the electrode structure provided by the invention shows more excellent contact resistivity at higher temperature and has small change along with the aging time, and the integrated electrode provided by the invention has extremely low contact resistivity, extremely small diffusion thickness and long-term high-temperature stability by combining fig. 4.
Example 2
1) Mixing powders of P-type HH material (here FeNb)0.86Hf0.14Sb) was laid in a mould, laid flat, here 5mm thick, slightly compacted;
2) spreading metal chromium powder or flaky chromium in a mold, spreading the chromium powder or flaky chromium with the thickness of 300 mu m, and compacting;
3) placing the mould spread with the powder in the step 2 into sintering equipment, wherein the sintering equipment can be spark plasma sintering and hot-pressing sintering, sintering is started under 10Pa, the heating rate is 100K/min, the sintering temperature is 850 ℃, the sintering pressure is 65Mpa, the heat preservation time is 10min, and the cooling rate is 25K/min to room temperature;
4) taking out the obtained block sample, cutting the block sample into a required shape by using electric sparks or diamond wire cutting, testing the interface resistance, observing the diffusion structure of the interface and testing the interface resistance condition of the interface, and analyzing the test result as follows:
it can be seen from FIG. 6 that the interface is well bonded, no crack microcracks exist, and there is a thin transition zone at the interface, here NbSb2And CrSb2A mixing region of (a);
as can be seen from the interface resistance measured in FIG. 7, the interface resistance at the interface connection is about 1-2 μ Ω. cm2The interface resistance of the order of magnitude can well meet the design requirements of devices.
Example 3
The embodiment is a preparation method of an electrode with a blocking and guiding integrated function, wherein a metal molybdenum layer is used as a ZrNiSn-based N-HH material, and the preparation method mainly comprises the following steps:
1) powder of an N-type HH material (here ZrNiSn)0.99Sb0.01) Laying in a mould, laying flat, here 5mm thick, slightly compacted;
2) spreading molybdenum powder or flaky molybdenum in a mold, spreading the molybdenum powder or flaky molybdenum with the thickness of 200 mu m, and compacting;
3) placing the mould paved with the powder in the step 2 into sintering equipment, wherein the sintering equipment can be spark plasma sintering and hot-pressing sintering, sintering is started under 10Pa, the heating rate is 100K/min, the sintering temperature is 900 ℃, the sintering pressure is 65Mpa, the heat preservation time is 20min, and the cooling rate is 10K/min to room temperature;
4) taking out the obtained block sample, cutting the block sample into a required shape by using electric sparks or diamond wire cutting, testing the interface resistance, observing the diffusion structure of the interface and testing the interface resistance condition of the interface, and analyzing the test result as follows:
FIG. 8 shows that the molybdenum and ZrNiSn based N-type HH material has good combination, a cleaner interface and no obvious transition layer;
fig. 9 shows that the interface between the molybdenum layer and the ZrNiSn-based N-HH matrix material is a substantially perfect ohmic contact without any obvious abrupt change in resistance, so that the interface resistance at this position is substantially negligible, and the influence on the output performance of the device is very small, which indicates that molybdenum is also an electrode material having both barrier and current-guiding functions for the N-type HH material.
Example 4
The embodiment is a preparation method of an electrode with a blocking and guiding integrated function, which selects metal tungsten as a ZrNiSn-based N-type HH material, and mainly comprises the following steps:
1) ZrNiSn based powder of an HH material of N type (here ZrNiSn)0.99Sb0.01) Laying in a mould, laying flat, here 5mm thick, slightly compacted;
2) spreading tungsten powder or tungsten flakes in a mold, spreading the tungsten powder or tungsten flakes with the thickness of 200 mu m, and compacting;
3) placing the mould paved with the powder in the step 2 into sintering equipment, wherein the sintering equipment can be spark plasma sintering and hot-pressing sintering, sintering is started under 10Pa, the heating rate is 100K/min, the sintering temperature is 900 ℃, the sintering pressure is 65Mpa, the heat preservation time is 30min, and the cooling rate is 10K/min to room temperature;
4) taking out the obtained block sample, cutting the block sample into a required shape by using electric sparks or diamond wire cutting, testing the interface resistance, observing the diffusion structure of the interface and testing the interface resistance condition of the interface, and analyzing the test result as follows:
FIG. 10 shows that the tungsten and ZrNiSn based N-type HH material are well combined, although the tungsten does not achieve high compactness, the interface is still relatively clean, and no obvious transition layer or second phase appears;
fig. 11 shows that the interface between the tungsten layer and the ZrNiSn-based N-type HH matrix is substantially perfect ohmic contact, and there is no significant abrupt change in resistance, so the interface resistance at this point is substantially negligible, and the impact on the device output performance is minimal. It is explained that tungsten is also an electrode material having both barrier and current-guiding functions for an N-type HH material.
Example 5
The embodiment is a preparation method of an electrode with a blocking and guiding integrated function, which selects chromium metal as an HH material of a ZrCoSb group HH material, and mainly comprises the following steps:
1) laying a powder of a ZrCoSb-based HH material (ZrCoSb in this case) in a mould, laying flat, here 5mm thick, slightly compacted;
2) spreading Cr powder or flaky Cr in a mold, spreading the Cr powder or flaky Cr with the thickness of 200 mu m, and compacting;
3) placing the mould spread with the powder in the step 2 into sintering equipment, wherein the sintering equipment can be spark plasma sintering and hot-pressing sintering, sintering is started under 10Pa, the heating rate is 100K/min, the sintering temperature is 1150 ℃, the sintering pressure is 60Mpa, the heat preservation time is 20min, and the cooling rate is 30K/min to room temperature;
4) taking out the obtained block sample, cutting the block sample into a required shape by using electric sparks or diamond wires, testing the interface resistance, observing the diffusion structure of the interface and testing the interface resistance condition of the interface, and analyzing the test result as follows;
FIG. 13 is a microscopic backscattering pattern of the ZrCoSb based HH material and the Cr layer prepared in example 5, from which it can be seen that the ZrCoSb based HH material and the Cr layer are tightly connected, the interfacial bonding condition is good, and no obvious diffusion and chemical reaction phenomena occur;
FIG. 14 is a line scan of the microscopic interface between the ZrCoSb based HH material prepared in example 5 and the Cr layer, which shows that the element mutation at the interface junction is sharper on the microscopic scale of the interface between N-HH and the Cr layer, the HH matrix is basically the Sb atom, the Cr atom and the Co atom in a composite manner at the left side of the interface junction, the Cr atom is basically at the right side of the interface junction, no obvious second phase or impurity phase exists, and no obvious mutual diffusion phenomenon is observed, indicating that no new intermediate compound is generated by the combination at the interface;
the result of the interfacial resistance test in fig. 15 shows that the interface between the ZrCoSb-based HH material prepared in example 5 and the Cr layer is substantially perfect ohmic contact, and there is no obvious abrupt resistance change, so the interfacial resistance at this position is substantially negligible, and the influence on the output performance of the device is very small. It is explained that Cr is also an electrode material having both barrier and current-guiding functions for an N-type HH material.
Claims (9)
1. A half heusler alloy thermoelectric device, comprising a half heusler alloy thermoelectric element including a half heusler alloy thermoelectric material, and an electrode layer integrally formed on at least one end of the half heusler alloy thermoelectric material; the melting point temperature of the material of the electrode layer is above 1000 ℃, preferably above 2000 ℃, and more preferably, the material of the electrode layer is at least one of a chromium simple substance, a molybdenum simple substance, a tungsten simple substance, an alloy mainly containing three metals of the chromium simple substance, the molybdenum simple substance and the tungsten simple substance, or a pseudo alloy mainly containing three metals of the chromium simple substance, the molybdenum simple substance and the tungsten simple substance.
2. The half heusler alloy thermoelectric device according to claim 1, wherein the thickness of the electrode layer is 0.001 μm to 2mm, preferably 100 μm.
3. The half heusler alloy thermoelectric device according to claim 1 or 2, wherein the half heusler alloy thermoelectric material has a general formula of ABX, where a is at least one of Sc, Y, Ti, Zr, Hf, V, Nb, Ta, B is at least one of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, and X is at least one of Sn, Sb, Bi; preferably, the half heusler alloy thermoelectric material is at least one of ZrNiSn, ZrCoSb, a solid solution and doped ZrNiSn-based half heusler alloy, and a solid solution and doped ZrCoSb-based half heusler alloy.
4. A method of one-step joining of the half heusler alloy thermoelectric device according to any one of claims 1 to 3, wherein the one-step joining method of the half heusler alloy thermoelectric material and the electrode layer in the half heusler alloy thermoelectric element comprises:
firstly, laying the powder of the half-heusler thermoelectric alloy material in a mould and compacting the powder, and then laying the powder or the slice consisting of the material of the electrode layer on the surface of the powder of the half-heusler thermoelectric alloy material and compacting the powder;
and finally, placing the die in a protective atmosphere, and realizing one-step connection of the semi-heusler alloy thermoelectric material and the electrode layer by adopting discharge plasma sintering, laser sintering, hot-pressing sintering or microwave sintering.
5. A method of step-connecting the half heusler alloy thermoelectric device according to any one of claims 1 to 3, wherein the step-connecting method of the half heusler alloy thermoelectric material and the electrode layer in the half heusler alloy thermoelectric element includes:
spreading powder or thin slices composed of the material of the electrode layer on the surface of the obtained semi-heusler thermoelectric alloy material ingot and compacting;
and then placing the die in a protective atmosphere, and realizing the connection of the semi-heusler alloy thermoelectric material and the electrode layer by adopting discharge plasma sintering, laser sintering, hot-pressing sintering or microwave sintering.
6. The method according to claim 5, wherein the semi-heusler thermoelectric alloy material powder is laid in a mold, compacted, placed in a protective atmosphere, and subjected to spark plasma sintering, laser sintering, hot-pressing sintering or microwave sintering to prepare the semi-heusler thermoelectric alloy material ingot.
7. The method according to any one of claims 4 to 6, wherein the temperature of the spark plasma sintering is 600 to 1200 ℃, the holding time is 1 to 60 minutes, and the sintering pressure is 20 to 120 MPa; the hot-pressing sintering temperature is 800-1400 ℃, the heat preservation time is 1-120 minutes, and the sintering pressure is 20-120 MPa; the parameters of the microwave sintering comprise: the power is 0.5-10 kilowatts and can be continuously adjusted, the working frequency is 2.45 gigahertz, the sintering time is 10-60 minutes, and the applicable pressure is 10-80 Mpa; the parameters of the laser sintering include: the laser frequency is 10-40 Hz, the pulse width is 2-5 milliseconds, the moving speed is 1-1000 millimeters per minute, the sintering current is 80-150 amperes, and the applied pressure is 10-60 MPa.
8. The method according to claim 7, wherein the temperature rise rate of the spark plasma sintering and the hot press sintering is 20-200 ℃/min; and after sintering, the cooling rate of the discharge plasma sintering and the hot-pressing sintering is 5-100 ℃/min.
9. The method according to any one of claims 4 to 8, wherein the protective atmosphere is a vacuum atmosphere, a nitrogen atmosphere, or an inert atmosphere; the inert atmosphere is argon or/and helium, and the vacuum degree of the vacuum atmosphere is less than 10 Pa.
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