CN114497335A - A kind of skutterudite thermoelectric material electrode and connection method of skutterudite thermoelectric material and electrode - Google Patents

Abstract

The invention discloses a skutterudite thermoelectric material electrode and a connection method of the skutterudite thermoelectric material and the electrode. The electrode raw materials are aluminum powder, alumina powder and ammonium chloride powder. In the invention, the skutterudite thermoelectric material is embedded in the mixed powder of the raw material, and the reaction and diffusion occur at a certain temperature, so as to realize the connection between the electrode and the _CoSb3 thermoelectric material. The method has the advantages of short production cycle, small equipment investment, simple operation, etc., greatly improves the efficiency of connecting the thermoelectric material and the electrode, and is suitable for large-scale production.

Description

A kind of skutterudite thermoelectric material electrode and connection method of skutterudite thermoelectric material and electrode

technical field

The invention relates to a skutterudite thermoelectric material electrode, and also relates to a connection method of a skutterudite thermoelectric material and an electrode, belonging to the technical field of thermoelectric power generation.

Background technique

Thermoelectric power generation technology is a technology that directly converts thermal energy into electrical energy through the Seebeck effect. Thermoelectric power generation devices have gained important applications in deep space exploration power supplies and special military power supplies due to their small size, no moving parts, no noise, no pollution, maintenance-free, and long life. At the same time, in the fields of industrial waste heat and automobile exhaust waste heat recovery, thermoelectric power generation devices also have broad application prospects and potential social and economic benefits.

Since most thermoelectric power generation devices usually work under harsh environmental conditions, such as high temperature, large temperature difference, broadband vibration, and extremely long working time, the long-term reliability of the device has become a major obstacle to industrial applications. El-Genk et al. found that the output power of the skutterudite device with Cu as the electrode decreased by 70% after the accelerated test at 600 °C for 150 days, and the large increase in the contact resistivity of the high-temperature end interface was the main reason for the decline of the device performance. Heterogeneous interfaces between thermoelectric materials and electrodes play a critical role in device reliability. For devices used in medium and high temperature power generation, the selection and connection technology of high temperature electrode materials are particularly difficult due to the high operating temperature. Among them, as one of the most potential candidates in the mid-temperature region, CoSb ₃ -based skutterudite thermoelectric devices have extremely high conversion efficiencies as high as 12%. At present, the main ways to realize the connection between electrodes and CoSb ₃ -based skutterudite thermoelectric materials include spring pressure contact, brazing, and sintering. In the early days, NASA-JPL proposed the preparation of CoSb ₃ -based thermoelectric power generation devices by spring pressure contact, but the simple mechanical contact made the interface resistance and interface thermal resistance larger, which hindered the improvement of device efficiency (El-Genk MS, Saber HH, Caillat T .Efficient segmented thermoelectric unicouples for space power applications[J]. Energy Conversion & Management, 2003, 44(11):1755-1772. ). For the brazing method, it is difficult to meet the requirements of long-term use due to serious mutual diffusion between the solder and the substrate and poor stability. Fan et al. used Ti as a transition layer and used a two-step SPS method to connect the Mo electrode to the CoSb ₃ material. However, due to the large difference in the thermal expansion coefficients of Mo and CoSb ₃ , the residual stress at the interface is large, and cracks are easily generated, which affects the bonding strength. and device reliability (FanJ, Chen L, Bai S, et al. Joining of Mo to CoSb ₃ by spark plasma sintering by inserting a Ti interlayer[J]. Materials Letters, 2004, 58(30):3876-3878. ) . Later, this technology optimizes the alloy composition through Mo-Cu alloying, the thermal expansion coefficient of Mo-Cu can be adjusted to match the CoSb ₃ -based filled skutterudite, the residual stress at the interface is greatly reduced, and the interface strength and device reliability are obtained. Improve (Zhao D, LiX, He L, et al. Interfacial evolution behavior and reliability evaluation of CoSb ₃ /Ti/Mo-Cu thermoelectric joints during accelerated thermal aging[J]. Journal of Alloys & Compounds, 2009, 477(1-2 ): 425-431. ). However, this method has higher requirements on equipment and molds, it is difficult to obtain higher economic benefits, and the thickness of the transition layer is not easy to control. Therefore, low-cost, efficient and reliable connection methods remain to be developed.

SUMMARY OF THE INVENTION

Aiming at the shortcomings of the existing skutterudite thermoelectric material and electrode connection mode, low efficiency, poor stability, complex process, large equipment investment and high cost, the invention provides a skutterudite thermoelectric material electrode and the electrode and skutterudite thermoelectricity The connection method of the material, the connection method of the electrode and the skutterudite thermoelectric material of the present invention is simple, time-consuming, high efficiency, small equipment investment, low cost, greatly improves the connection efficiency of the skutterudite thermoelectric material electrode, and the obtained electrode and The skutterudite thermoelectric material has tight connections, no cracks, controllable thickness, and firm interface bonding, which can play a good role as an electrode.

The specific technical scheme of the present invention is as follows:

A skutterudite thermoelectric material electrode is made of the following raw materials by mass percentage: 25-35% of aluminum powder, 3-5% of ammonium chloride powder, and the balance of alumina powder.

Further, the electrodes are obtained by uniformly mixing the raw materials of the electrodes and then vacuum calcining them. The roasting temperature is generally 500-550°C, and the roasting time is 0.5-2h. The composition of the electrode obtained by calcination is an aluminum-rich intermetallic compound.

The present invention also provides a method for connecting the skutterudite thermoelectric material and the electrode, comprising the following steps:

(1) Put the uniformly mixed aluminum powder, alumina powder and ammonium chloride powder into the crucible, and then embed the skutterudite thermoelectric material into the mixed powder;

(2) Put the crucible into the quartz tube and vacuum seal;

(3) Raise the quartz tube to the roasting temperature for roasting, cool it after roasting, take out the skutterudite thermoelectric material, and obtain an electrode layer on its surface, which realizes the connection between the skutterudite thermoelectric material and the electrode.

Further, the composition of the skutterudite thermoelectric material in the present invention refers to pure CoSb ₃ , or a doped CoSb ₃ material formed by taking CoSb ₃ as a matrix and filling or doping it with other elements. The element can be one or more of Yb, Li, Ir, Na, K, Ca, La, Al and Pd. The skutterudite thermoelectric material is generally in bulk.

Further, the crucible is a graphite crucible.

Further, in step (1), the raw materials of the electrode are aluminum powder, aluminum oxide powder and ammonium chloride powder, the content of aluminum powder is 25-35 wt %, the content of ammonium chloride powder is 3-5 wt %, and the content of aluminum powder is 3-5 wt %. Make up the balance, the sum of these three is 100wt%. Among them, the aluminum powder provides the elements required for the electrode layer, the aluminum oxide powder plays the role of diluting and filling and preventing the aluminum powder from sticking, and the ammonium chloride powder can promote the generation of active aluminum atoms and accelerate the growth rate of the electrode layer. The content of aluminum powder should not be too high or too low. If it is too low, it is difficult to form a continuous electrode layer. If it is too high, it is easy to cause the aluminum powder to bond and reduce the usage rate of aluminum powder. The content of ammonium chloride powder should not be too high, too high will reduce the quality of the electrode layer, and excessive consumption of aluminum source will cause waste.

Further, the particle size of the aluminum powder is less than or equal to 10 microns, and its purity is greater than or equal to 99.85%; the particle size of the alumina powder is less than or equal to 1 micron, and its purity is greater than or equal to 99.99%. The ammonium chloride powder is AR grade.

Further, in step (1), the aluminum powder, aluminum oxide powder, and ammonium chloride powder can be uniformly mixed in advance by conventional physical mixing methods such as stirring and grinding. method of mixing. Preferably, by wet mixing, the three powders are put into a mortar, anhydrous ethanol is added, manually ground for 10-20 minutes, and dried. The addition of absolute ethanol can prevent the powders from sticking to each other during the grinding process, resulting in uneven mixing.

Further, in step (1), the skutterudite thermoelectric material is embedded in the center of the mixture powder, which is conducive to the formation of a uniform electrode layer.

Further, in step (2), the crucible is put into a quartz tube for vacuum sealing, and the vacuum degree in the quartz tube is above 0.01 MPa, so as to isolate the consumption of aluminum powder caused by oxygen. The present invention must be sealed, otherwise the gas overflow will lead to the failure to form the electrode layer.

Further, in step (3), the calcination temperature is 500-550°C, and the calcination time is 0.5-2h. If the temperature is too low, the electrode layer cannot be formed. If the temperature is too high, there will be many internal defects in the electrode layer, which will affect the quality of the electrode layer and easily cause the decomposition of the skutterudite thermoelectric material matrix. The holding time should not be too long. If the time is too long, the thickness of the electrode layer will not increase significantly, which will cause waste of energy, and the performance of the substrate will also be affected if the time is too long.

Further, the heating rate is preferably 5-10° C./min, and at this heating rate, the performance of the obtained electrode is better.

Further, the thickness of the electrode layer is controlled by controlling the content of aluminum powder, ammonium chloride powder and aluminum oxide powder, calcination temperature and time and other conditions. Generally speaking, within a given range of conditions, the higher the content of aluminum powder, the higher the baking temperature and the longer the time, the thicker the thickness of the obtained electrode layer. The composition of the obtained electrode layer is an aluminum-rich intermetallic compound, and its thickness Typically 15-55 microns. The obtained electrode layer is evenly distributed on the surface of the skutterudite thermoelectric material, the electrode layer is dense, has no cracks, and is firmly bonded to the surface of the skutterudite thermoelectric material.

The present invention has the following beneficial effects:

In the present invention, aluminum powder, alumina powder and ammonium chloride powder are selected as electrode raw materials, and the skutterudite thermoelectric material is embedded in the electrode raw material, reacted and diffused at a certain temperature, and directly on the surface of the skutterudite thermoelectric material. The electrode can be formed in situ, and the quick connection between the skutterudite thermoelectric material and the electrode is realized. The obtained electrode is uniform and dense without cracks, and has metallurgical bonding with _CoSb3 thermoelectric material, and has a good interface bonding state. The method of the invention has the advantages of short production period, small equipment investment, simple operation and the like, greatly improves the connection efficiency between the skutterudite thermoelectric material and the electrode, and is suitable for large-scale production.

Description of drawings

Figure 1 is a schematic diagram of the method of the present invention.

FIG. 2 is a surface distribution diagram of interface elements at the connection between the electrode and the CoSb ₃ thermoelectric material in the product prepared in Example 1. FIG.

3 is a line scan diagram of the interface element at the connection between the electrode and the CoSb ₃ thermoelectric material in the product prepared in Example 1.

4 is a scanning electron microscope photograph of the interface at the connection between the electrode and the CoSb ₃ thermoelectric material in the product prepared in Example 1.

5 is an interface scanning electron microscope photograph of the connection between the electrode and the CoSb ₃ thermoelectric material in the product prepared in Example 2.

FIG. 6 is an interface scanning electron microscope photograph of the connection between the electrode and the CoSb ₃ thermoelectric material in the product prepared in Comparative Example 1.

FIG. 7 is an interface scanning electron microscope photograph of the connection between the electrode and the CoSb ₃ thermoelectric material in the product prepared in Comparative Example 2.

In the figure, 1. Quartz tube, 2. Graphite crucible, 3. Raw material mixed powder, 4. CoSb ₃ bulk material.

Detailed ways

In order to further understand the content of the present invention, the present invention will now be described in detail with reference to specific embodiments.

In the following examples, the particle size of the aluminum powder used is 10 microns, and its purity is 99.85%. The particle size of the alumina powder used was 1 micron and its purity was 99.99%. The ammonium chloride powder used is AR grade.

Example 1

(1) Weigh 20 g of three raw material powders (aluminum powder (25%), alumina powder (71%), and ammonium chloride powder (4%)) by mass percentage. The three powders were put into a mortar, and anhydrous ethanol was added for manual grinding for 10 minutes to make them evenly mixed, and dried at 50°C. Then take 2g of mixed powder into a graphite crucible, and place a _CoSb bulk material in the center of the powder;

(2) Slowly put the graphite crucible into the quartz tube, vacuum and seal, and the vacuum degree is above 0.01MPa;

(3) Put the quartz tube into the tube furnace, set the heating rate to 10°C/min, raise the temperature to 550°C, and keep roasting at this temperature for 2h;

(4) After cooling to room temperature in the furnace, take out the sample, put it into an ultrasonic cleaning machine for ultrasonic cleaning for 5 minutes, and then take out the sample and dry it. After roasting, an electrode layer is obtained on the surface of the CoSb ₃ bulk material, thereby realizing the connection between the skutterudite thermoelectric material and the electrode.

Figures 2 and ₃ are the interface element surface distribution diagram and the interface element line scan diagram of the obtained electrode/CoSb3 thermoelectric material. It can be seen from the figures that the electrode and the thermoelectric material are metallurgically bonded, element diffusion occurs between the two, and aluminum The elements are distributed in the electrode layer in a concentration gradient, and the thickness of the electrode layer is about 50 microns.

Figure 4 is a scanning electron microscope photograph of the interface of the obtained electrode/CoSb ₃ thermoelectric material. It can be seen from the figure that the electrode layer is dense and crack-free, and is well combined with the CoSb ₃ thermoelectric material.

Example 2

An electrode layer was obtained on the _CoSb bulk material according to the method of Example 1, except that in step (3), the temperature was raised to 500°C at a heating rate of 10°C/min, and calcined at this temperature for 2h. The thickness of the resulting electrode layer was about 20 microns.

Figure 5 is a scanning electron microscope photograph of the interface of the obtained electrode/CoSb ₃ thermoelectric material. It can be seen from the figure that the electrode layer is uniform and dense, the interface is smooth and free of cracks, and it is well combined with the CoSb ₃ thermoelectric material.

Example 3

An electrode layer was obtained on the CoSb ₃ bulk material according to the method of Example 1, except that in step (3), the temperature was raised to 550°C at a heating rate of 5°C/min, and calcined at this temperature for 2h. The thickness of the obtained electrode layer is about 50 micrometers, the electrode layer is uniform and dense, the interface is smooth without cracks, and it is well combined with the CoSb ₃ thermoelectric material.

Example 4

An electrode layer was obtained on the CoSb ₃ bulk material according to the method of Example 1, except that in step (3), the temperature was raised to 500°C at a heating rate of 10°C/min, and calcined at this temperature for 30min. The thickness of the obtained electrode layer is about 15 microns, the electrode layer is uniform and dense without cracks, and is well combined with the CoSb ₃ thermoelectric material.

Example 5

According to the method of Example 1, a layer of aluminum electrode layer is obtained from the _CoSb bulk material, the difference is: in step (1), three raw material powders (aluminum powder (35%), alumina Powder (60%), ammonium chloride powder (5%)) total 20g. The thickness of the obtained electrode layer is about 55 micrometers, the electrode layer is uniform and dense without cracks, and is well combined with the CoSb ₃ thermoelectric material.

Comparative Example 1

An electrode layer was obtained on the CoSb ₃ bulk material according to the method of Example 1, except that in step (3), the temperature was raised to 450°C at a heating rate of 10°C/min, and calcined at this temperature for 2h.

Figure 6 is a scanning electron microscope photograph of the interface of the obtained electrode/CoSb ₃ thermoelectric material. It can be seen from the figure that because the heat treatment temperature is too low, there is no continuous electrode layer formed on the surface of CoSb ₃ , and it cannot play the role of an electrode.

Comparative Example 2

An electrode layer was obtained on the CoSb ₃ bulk material according to the method of Example 1, except that in step (3), the temperature was raised to 600°C at a heating rate of 10°C/min, and calcined at this temperature for 2h.

Figure 7 is the SEM photo of the obtained electrode/CoSb ₃ thermoelectric material interface. It can be seen from the figure that due to the high heat treatment temperature, the electrode layer formed on the surface of CoSb ₃ is of poor quality and loose in structure, and causes the appearance inside the CoSb ₃ matrix. cracked.

Comparative Example 3

A layer of electrode layer is obtained on the _CoSb bulk material according to the method of Example 1, the difference is: in step (1), three raw material powders (aluminum powder (15%), alumina Powder (77%), ammonium chloride powder (8%)) total 20g. It was found that because the content of aluminum powder was too small and the content of ammonium chloride was too high, the aluminum powder was excessively consumed by ammonium chloride, which eventually led to the formation of almost no electrode layer on the surface of CoSb ₃ .

Claims (10)

1. A skutterudite thermoelectric material electrode is characterized in that: the feed is prepared from the following raw materials in percentage by mass: 25-35% of aluminum powder, 3-5% of ammonium chloride powder and the balance of alumina powder.

2. The skutterudite thermoelectric material electrode as set forth in claim 1, wherein: the raw materials are evenly mixed and then are roasted in vacuum to obtain the electrode.

3. The skutterudite thermoelectric material electrode as set forth in claim 2, wherein: the roasting temperature is 500-550 ℃, and the roasting time is 0.5-2 h.

4. A method of connecting a skutterudite thermoelectric material to the electrode of claim 1, comprising the steps of:

(1) putting the uniformly mixed aluminum powder, alumina powder and ammonium chloride powder into a crucible, and then embedding the skutterudite thermoelectric material into the mixture powder;

(2) putting the crucible into a quartz tube, and vacuumizing and sealing;

(3) and (3) heating the quartz tube to the roasting temperature for roasting, cooling after roasting, taking out the skutterudite thermoelectric material, and obtaining an electrode layer on the surface of the skutterudite thermoelectric material.

5. The connecting method according to claim 4, wherein: the crucible is a graphite crucible.

6. The connecting method according to claim 4, wherein: the grain diameter of the aluminum powder is less than or equal to 10 microns, and the grain diameter of the aluminum oxide powder is less than or equal to 1 micron.

7. The connecting method according to claim 4, wherein: the aluminum powder, the alumina powder and the ammonium chloride powder are uniformly mixed by adopting a wet mixing method, and the used solvent is ethanol.

8. The connecting method according to claim 4, wherein: the skutterudite thermoelectric material is buried in the center position of the mixture powder.

9. The connecting method according to claim 4, wherein: the roasting temperature is 500-550 ℃, and the roasting time is 0.5-2 h.

10. The connecting method according to claim 4, wherein: the skutterudite thermoelectric material is CoSb₃Or doped CoSb₃A material.

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