Preparation method of thermoelectric composite material with same composition and different structure

Abstract

The present invention belongs to the technical field of functional material preparation, and specifically relates to a method for preparing a thermoelectric composite material with the same composition and different structure. The preparation method comprises the following steps: Step 1: Mixing Co, Sb, and Se as raw materials, and placing them in a stainless steel ball mill; Step 2: Wet milling: Deoxidizing the ball mill and injecting a volatile liquid into the ball mill. The treated ball mill is fixed to a ball mill and wet milled at a predetermined speed for a predetermined period of time; Step 3: Drying: Drying the wet-milled product to obtain a dry powder precursor; Step 4: Pressing: Pressing the obtained dry powder precursor into a block; Step 5: Sintering: High-pressure synthesis of the pressed block to obtain a Pnm21 and P213 two-phase composite thermoelectric material. The present invention can produce high-performance thermoelectric materials suitable for operation in the temperature range of 500-700K, shortening the preparation cycle, improving repeatability, and reducing costs and energy consumption.

Description

Technical Field

[0001] The invention belongs to the technical field of functional material preparation, and in particular relates to a method for preparing a thermoelectric composite material with the same composition and different structures. Background Art

[0002] Thermoelectric materials are functional materials that can achieve direct conversion between heat and electricity. They can be used to make thermoelectric power generation devices, which can effectively utilize large amounts of waste heat from industry and automobiles to generate electricity. They can also provide special power sources for exploration in extreme environments such as deep space.

[0003] The working efficiency of thermoelectric materials mainly depends on their thermoelectric figure of merit ZT value (ZT = TS 2 / ρκ), which requires the material to have a high Seebeck coefficient, low resistivity, and low thermal conductivity. However, these three thermoelectric parameters are closely related to factors such as carrier concentration. Therefore, optimizing the performance of thermoelectric materials requires the coordinated regulation of thermoelectric parameters.

[0004] Structuring composite materials is one of the most effective means to achieve coordinated regulation of thermoelectric parameters. Most of the thermoelectric composite materials reported so far are two-phase composites with different compositions and the same structure or different compositions and different structures. Therefore, the difference in composition leads to certain limitations in preparation cycle, cost, repeatability, etc. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing thermoelectric composite materials with the same composition and different structures, which can produce high-performance thermoelectric materials suitable for working in the temperature range of 500-700K, shorten the preparation cycle, improve repeatability, and reduce costs and energy consumption.

[0006] The technical solutions adopted by the present invention are as follows:

[0007] A method for preparing a thermoelectric composite material with the same composition and different structures, the method comprising the following steps:

[0008] Step 1: Co, Sb, and Se with a purity of ≥99% are mixed in a molar ratio of CoSbSe and placed in a stainless steel ball mill.

[0009] Step 2: wet milling: the ball mill jar was deoxidized and injected with anhydrous ethanol. The treated ball mill jar was fixed on the ball mill and wet milled at 300 rpm for 240 minutes.

[0010] Step 3: Drying: Dry the wet-milled product by vacuum drying for 5-10 hours at a drying temperature of 50-70° C. to obtain a dry powder precursor;

[0011] Step 4: Pressing, pressing the obtained dry powder precursor into a block;

[0012] Step 5: Sintering: The pressed block is subjected to high-pressure synthesis at a synthesis pressure of not less than 1 GPa to obtain a thermoelectric material composed of two phases of Pnm21 and P213;

[0013] Step 6: The sample after the primary sintering is crushed and ground, and then sintered for the second time under the same pressure and temperature conditions as in step 5.

[0014] Furthermore, the high-pressure synthesis in step 5 is carried out on a high-temperature and high-pressure device, and the synthesis process includes wrapping the bulk sample with a boron nitride insulating tube, placing it in a pyrophyllite synthesis block, and performing high-pressure synthesis.

[0015] Furthermore, the sintering pressure used in step 5 is 1-6 GPa, the sintering temperature is 950-1150° C., the heating rate is 100-200° C. / min, and the sintering time is 30 min.

[0016] Furthermore, the sintering pressure used in step 5 is 4 GPa.

[0017] Furthermore, the sintering pressure used in step 5 is 1-5 GPa, the sintering temperature is 900-1100°C, the heating rate is 100-200°C / min, and the sintering time is 15-30 min.

[0018] Furthermore, the deoxygenation protection treatment in step 2 includes the following steps:

[0019] After evacuating the ball mill jar, introduce high-purity Ar gas, and then repeat the operation of evacuating the jar and introducing high-purity Ar gas 3-5 times.

[0020] The technical effects achieved by the present invention are:

[0021] (1) The method for preparing a thermoelectric composite material with the same composition and different structure of the present invention mainly utilizes high-voltage induced phase transformation to realize the construction of a composite material with the same composition and different structure. It belongs to a new type of thermoelectric composite material, so as to obtain a high-performance thermoelectric material suitable for operating in the temperature range of 500-700K, shorten the preparation cycle, improve repeatability, and reduce costs and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the X-ray diffraction pattern of CoSbSe synthesized under different pressure conditions of the present invention;

[0023] Figure 2 is a two-phase ratio diagram of CoSbSe samples synthesized at different pressures according to the present invention;

[0024] Figure 3Graph showing the variation of the Seebeck coefficient of CoSbSe synthesized under different pressure conditions according to the present invention with temperature;

[0025] Figure 4 Graph showing the change in resistivity of CoSbSe synthesized under different pressure conditions according to the present invention as a function of temperature;

[0026] Figure 5 is a graph showing the change in quality factor of CoSbSe synthesized under different pressure conditions according to the present invention as a function of temperature;

[0027] Figure 6 The CoSb synthesized under 0GPa pressure conditions of the present invention 1-x Se 1+x X-ray diffraction pattern of

[0028] Figure 7 The CoSb synthesized under 1GPa pressure conditions of the present invention 1-x Se 1+x X-ray diffraction pattern of

[0029] Figure 8 The CoSb synthesized under 1GPa pressure conditions of the present invention 1-x Se 1+x Two-phase ratio diagram;

[0030] Figure 9 The CoSb synthesized under the pressure conditions of 0GPa and 1GPa of the present invention 1-x Se 1+x The quality factor of the graph changes with temperature;

[0031] Figure 10 The CoSb synthesized under the pressure conditions of 0GPa and 1GPa of the present invention 1-x Se 1+x The Seebeck coefficient of the graph changes with temperature. DETAILED DESCRIPTION

[0032] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is described in detail below with reference to the following examples. It should be understood that the following text is only used to describe one or more specific embodiments of the present invention and does not strictly limit the scope of protection of the present invention.

[0033] like Figure 1-5 As shown, a method for preparing a thermoelectric composite material with the same composition and different structure includes the following steps:

[0034] Step 1: Mix Co, Sb, and Se as raw materials in a molar ratio of CoSbSe and place them in a stainless steel ball mill;

[0035] The raw materials are Co powder, Sb powder and Se powder with a purity of ≥99%, and can also be doped with elements Te or Sn; the raw materials are weighed according to the stoichiometric ratio of CoSbSe, with a total weight of 6g, and the ball-to-material ratio can be set to 10:1.

[0036] Step 2: Wet grinding. Before wet grinding the raw materials added to the ball mill, it is usually necessary to perform deoxidation protection treatment on the ball mill;

[0037] After deoxygenation treatment, a volatile liquid such as anhydrous ethanol is injected, and the treated ball mill jar is fixed on a ball mill (e.g., a planetary ball mill) and wet ball milled at a predetermined speed for a predetermined period of time. The predetermined speed here is preferably 300 rpm, and the predetermined period of time is preferably 240 minutes.

[0038] Wherein, the deoxygenation protection treatment comprises the following steps:

[0039] After evacuating the ball mill jar, high-purity Ar gas is introduced. Then, the operation of evacuating the ball mill jar and introducing high-purity Ar gas is repeated several times, for example, 3-5 times, to ensure that all oxygen inside the ball mill jar is exhausted.

[0040] Step 3: Drying. After wet grinding, collect the sample in the ball mill, and then dry the wet-milled product. Vacuum dry it for a period of time to evaporate all the organic liquid (alcohol) to obtain a dry powder precursor.

[0041] The drying process adopted in step 3 is as follows: placing the wet-grinded product in a vacuum drying oven and vacuum drying it for 5-10 hours at a drying temperature of 50-70°C, preferably 60°C.

[0042] Step 4: Pressing: Place the dry powder precursor obtained after drying into a mold and press it into a block using a tablet press.

[0043] Step 5: Sintering, subjecting the pressed block to high-pressure synthesis to obtain a thermoelectric material composed of two phases of Pnm21 and P213, i.e., a dense CoSbSe bulk thermoelectric material.

[0044] The high-pressure synthesis in step 5 is carried out on a high-temperature and high-pressure device. The synthesis process includes wrapping the block sample with a boron nitride insulating tube, placing it in a pyrophyllite synthesis block, and performing high-pressure synthesis. The synthesis pressure used is not less than 1 GPa.

[0045] Specifically, experiments have shown that the best experimental results are achieved when the sintering pressure is 1-6 GPa, the sintering temperature is 950-1150°C, the heating rate is 100-200°C / min, and the sintering time is 30 minutes.

[0046] Step 6: The sample after the primary sintering is crushed and ground, and then sintered for the second time under the same pressure and temperature conditions as in step 5.

[0047] Step 6 can achieve uniform and sufficient reaction of the sample and improve the preparation purity. The specific X-ray diffraction structure is shown in Figure 1 ,from Figure 1 It can be seen that the 1GPa sample has a Pnm21 structure, which is consistent with the structure prepared by conventional solid-phase reaction method, the 5GPa sample has a P213 structure, and a mixed phase of Pnm21 and P213 structures appears at 2-4GPa. XRD refinement shows that the ratio of the two phases can be continuously adjusted by changing the pressure (such as Figure 2 ).

[0048] In order to characterize the performance of the samples, the CoSbSe samples synthesized at different pressures were cut and polished, and the resistivity, Seebeck coefficient and thermal conductivity of the samples were tested using CTA-3 and LFA-457, and the quality factor was calculated, such as Figure 3 As shown in Figure 2, the Seebeck coefficient of the Pnm21 structure sample is very small, close to that of metal, and is not suitable as a thermoelectric material; the resistivity of the P213 sample is relatively high (e.g. Figure 4 ), which needs to be reduced, and the Seebeck coefficient and resistivity of the two-phase mixed sample are continuously adjustable, and the best thermoelectric figure of merit is obtained under 4GPa conditions (such as Figure 5 ), which is a high-performance thermoelectric material suitable for working in the temperature range of 500-700K.

[0049] Example 2:

[0050] In this embodiment, based on the embodiment 1, a thermoelectric material CoSb1-xSe1+x (x=0-0.4) is prepared, preferably, x=0.3-0.4.

[0051] In the process of preparing the thermoelectric material CoSb1-xSe1+x, similar steps as those in Example 1 are adopted, except that some numerical values ​​are slightly different, and specifically include the following steps:

[0052] Step 1: Ingredients: Co, Sb, and Se are used as raw materials. The raw material weight is calculated based on the value of x in CoSb1-xSe1+x and the mass of the sample. They are mixed in a molar ratio according to the CoSbSe molecular formula and placed in a stainless steel ball mill.

[0053] The raw materials used are Co powder, Sb powder and Se powder with a purity of ≥99%. The raw materials are weighed according to the stoichiometric ratio of CoSbSe, with a total weight of 6 g. The ball-to-material ratio can be set to 10:1.

[0054] Step 2: Wet grinding. Before wet grinding the raw materials added to the ball mill, it is usually necessary to perform deoxidation protection treatment on the raw materials;

[0055] After deoxygenation treatment, a volatile liquid such as anhydrous ethanol is injected, and the treated ball mill jar is fixed on a ball mill (e.g., a planetary ball mill) and wet ball milled at a predetermined speed for a predetermined period of time. The predetermined speed here is preferably 300 rpm, and the predetermined period of time is preferably 240 minutes.

[0056] Wherein, the deoxygenation protection treatment comprises the following steps:

[0057] After evacuating the ball mill jar, high-purity Ar gas is introduced. Then, the operation of evacuating the ball mill jar and introducing high-purity Ar gas is repeated several times, for example, 3-5 times, to ensure that all oxygen inside the ball mill jar is exhausted.

[0058] Step 3: Drying. After wet grinding, collect the sample in the ball mill, and then dry the wet-milled product. Vacuum dry it for a period of time to evaporate all the organic liquid (alcohol) to obtain a dry powder precursor.

[0059] The drying process adopted in step 3 is as follows: placing the wet-grinded product in a vacuum drying oven and vacuum drying it for 5-10 hours at a drying temperature of 50-70°C, preferably 60°C.

[0060] Step 4: Pressing: Place the dry powder precursor obtained after drying into a mold and press it into a block using a tablet press.

[0061] Step 5: Sintering, subjecting the pressed block to high-pressure synthesis to obtain a thermoelectric material composed of two phases of Pnm21 and P213, i.e., a dense CoSbSe bulk thermoelectric material.

[0062] The high-pressure synthesis in step 5 is carried out on a high-temperature and high-pressure device. The synthesis process includes wrapping the block sample with a boron nitride insulating tube, placing it in a pyrophyllite synthesis block, and performing high-pressure synthesis. The synthesis pressure used is not less than 1 GPa.

[0063] Specifically, experiments have shown that the sintering pressure used in the sintering process is 1-5 GPa, the sintering temperature is 900-1100°C, the heating rate is 100-200°C / min, and the sintering time is 15-30 min;

[0064] Step 6: The sample after the first sintering is crushed and ground, and then sintered for the second time under the same pressure and temperature conditions.

[0065] The sintering pressure in step 5 is preferably 1 GPa. In order to compare the effect of pressure, the present invention also uses a solid-phase reaction combined with a spark plasma sintering method under pressureless conditions (i.e., 0 GPa) to prepare CoSb1-xSe1+x; the sintered samples were tested by X-ray diffraction and found that all samples under 0 GPa conditions had a Pnm21 structure (such as Figure 6 ), while the use of Se instead of Sb under 1GPa conditions can induce the sample to transform into a composite material with coexistence of Pnm21 and P213 phases (such as Figure 7 ), and the ratio of the two phases changes with the change of Se content (e.g. Figure 8 ). This indicates that pressure assistance is the key factor in inducing the structural transformation and two-phase recombination of CoSbSe.

[0066] like Figure 9 As shown in Figure 2, the thermoelectric properties of CoSb1-xSe1+x (x ≥ 0.1) samples synthesized at 0 GPa are much lower than those of doped samples prepared at 1 GPa. The main reason is that the structure of the samples at 0 GPa is Pmn21, which is a low Seebeck phase. However, under the combined action of pressure (1 GPa) and Se doping, CoSbSe is transformed from a single Pmn21 structure to a composite structure with coexistence of Pnm21 and P213 phases, which increases the Seebeck coefficient (e.g. Figure 10 ), thereby improving the thermoelectric figure of merit.

[0067] In summary, the present invention mainly utilizes high-voltage-induced phase transformation to realize the construction of composite materials with the same composition but different structures. It belongs to a new type of thermoelectric composite material, so as to obtain high-performance thermoelectric materials suitable for operating in the temperature range of 500-700K, shorten the preparation cycle, improve repeatability, and reduce costs and energy consumption.

[0068] The foregoing is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained herein shall, unless otherwise specified or limited, be implemented in accordance with conventional means in the art.

Claims

1. A method for preparing a thermoelectric composite material with the same composition and different structure, characterized by: The preparation method comprises the following steps: Step 1: Ingredients, using Co, Sb, and Se as raw materials, CoSb 1-x Se 1+x The molecular formulas are mixed in a molar ratio and placed in a stainless steel ball mill, wherein x = 0.1 to 0.4; Step 2: wet milling, the ball mill jar is treated with deoxidation protection and injected with volatile liquid. The treated ball mill jar is fixed on the ball mill and wet milled at a predetermined speed for a predetermined period of time; Step 3: Drying: Drying the wet-milled product to obtain a dry powder precursor; Step 4: Pressing, pressing the obtained dry powder precursor into a block; Step 5: Sintering: subjecting the pressed block to high-pressure synthesis with a synthesis pressure of not less than 1 GPa to obtain a thermoelectric material of a two-phase composite of Pnm21 and P213.

2. The method for preparing a thermoelectric composite material with the same composition and different structure according to claim 1, characterized in that: Also includes: Step 6: The sample after the primary sintering is crushed and ground, and then sintered for the second time under the same pressure and temperature conditions as in step 5.

3. A method for preparing a thermoelectric composite material with the same composition and different structure according to any one of claims 1 to 2, characterized in that: The high-pressure synthesis in step 5 is carried out on a high-temperature and high-pressure device. The synthesis process includes wrapping the bulk sample with a boron nitride insulating tube, placing it in a pyrophyllite synthesis block, and performing high-pressure synthesis.

4. The method for preparing a thermoelectric composite material with the same composition and different structure according to claim 1, characterized in that: The predetermined rotation speed in step 2 is 300 rpm, and the predetermined time period is 240 minutes.

5. The method for preparing a thermoelectric composite material with the same composition and different structure according to claim 1, characterized in that: The deoxygenation protection treatment in step 2 includes the following steps: After evacuating the ball mill jar, introduce high-purity Ar gas, and then repeat the operation of evacuating the jar and introducing high-purity Ar gas 3-5 times.

6. The method for preparing a thermoelectric composite material with the same composition and different structure according to claim 1, characterized in that: The volatile liquid in step 2 is anhydrous ethanol.

7. The method for preparing a thermoelectric composite material with the same composition and different structure according to claim 1, characterized in that: The drying process adopted in step 3 comprises the following steps: The wet-ground product is placed in a vacuum drying oven and vacuum-dried for 5-10 hours at a drying temperature of 50-70°C.

8. A method for preparing a thermoelectric composite material with the same composition and different structure according to any one of claims 1-2, characterized in that: The sintering pressure used in step 5 is 1-5 GPa, the sintering temperature is 900-1100° C., the heating rate is 100-200° C. / min, and the sintering time is 15-30 min.

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