La3-xTe4 thermoelectric material and preparation method thereof

Abstract

The invention discloses a preparation method of a La3-xTe4 thermoelectric material, and belongs to the technical field of thermoelectric materials, and the preparation method comprises the following steps: (1) repeatedly spreading a layer of Te and a layer of La in a boron nitride crucible layer by layer, the outermost layer being Te; (2) putting the boron nitride crucible into high-temperature equipment, and reacting for not less than 3 hours at the temperature of 450-920 DEG C under the protection of argon and micro-positive pressure; (3) cooling to room temperature, then heating, and reacting at 950-1000 DEG C for not less than 1 hour to generate high-temperature alloyed La3-xTe4; and (4) crushing the La3-xTe4 thermoelectric material subjected to high-temperature alloying, carrying out heat preservation for 1 hour at 1250 DEG C, and carrying out hot pressing on the powder through a hot pressing furnace under 90 MPa to prepare the blocky La3-xTe4 thermoelectric material. Through high-temperature equipment such as a high-frequency smelting furnace or a heat treatment furnace, the single-time preparation amount can reach hectogram magnitude.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric materials, and in particular to a La 3-x Te4 thermoelectric material and preparation method thereof. Background Art

[0002] Radioisotope thermoelectric generators (RTGs) based on thermoelectric conversion technology usually have the characteristics of no moving parts, high reliability, long life, and wide application range. As a special power source, they occupy a unique position in deep space exploration, deep sea and other fields. In view of my country's deep space exploration needs for high conversion efficiency and high output power RTGs, traditional germanium silicon thermoelectric materials can no longer meet the requirements of high conversion efficiency due to their relatively low thermoelectric figure of merit. 3-x The average merit of Te4 thermoelectric material is about twice that of germanium silicon material, which can greatly improve the thermoelectric conversion efficiency of RTG. At present, La is generally prepared by high-energy ball milling equipment and mechanical alloying process. 3-x Te4 thermoelectric material, but it cannot be mass-produced due to factors such as material sticking to the wall during ball milling. A large amount of thermoelectric material is required during the RTG development process, so it is urgent to develop a large-scale preparation of La 3-x Processing of Te4 thermoelectric materials. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a La 3-x Te4 thermoelectric material and its preparation method can be prepared in a single time in quantities of up to hundreds of grams through high-temperature equipment such as high-frequency melting furnaces or heat treatment furnaces.

[0004] The present invention is achieved in that a La 3-x The preparation method of Te4 thermoelectric material comprises the following steps:

[0005] (1) In a boron nitride crucible, a layer of Te and a layer of La are repeatedly laid layer by layer, with the outermost layer being Te, showing a single substance Te covering a single substance La, a single layer of La being in the form of a sheet with a thickness of 1 to 3 mm, and a single layer of Te being in the form of a powder with a thickness of 1 to 3 mm;

[0006] (2) placing the boron nitride crucible containing the material into a high-temperature device, using argon protection, the gas pressure is slightly positive, and the first stage La and Te are combined in the temperature range of 450-920° C., and the reaction time is not less than 3 hours;

[0007] (3) After the first stage is completed, the temperature is lowered to room temperature, and then the temperature is raised to carry out the second stage of chemical combination in the temperature range of 950-1000°C. The reaction time is not less than 1 hour to generate high-temperature alloyed La 3-x Te4;

[0008] (4) The high temperature alloyed La was milled by low speed ball milling. 3-x The Te4 thermoelectric material is crushed and hot pressed in a hot press furnace at 1250°C, 1 hour, and 90 MPa to prepare bulk La 3-x Te4 thermoelectric material.

[0009] The high temperature equipment in step (2) is a high frequency melting furnace or a heat treatment furnace.

[0010] The slight positive pressure in step (2) is 0.1 to 0.2 kPa higher than the atmospheric pressure.

[0011] The La obtained in step (4) 3-x Te4 thermoelectric material is in the hundreds of grams level.

[0012] The La prepared by the above preparation method 3-x Te4 thermoelectric material.

[0013] The advantages and positive effects of the present invention are:

[0014] 1. Compared with the low-capacity high-energy ball milling process, the present invention can achieve a single 100-gram scale preparation of La 3-x Te4 thermoelectric material.

[0015] 2. Compared with the traditional ultra-high temperature smelting process, the temperature of the present invention is lower than La 3-x Te4 melting point, material alloying is achieved through solid phase reaction. At a relatively low temperature, the material does not react with the boron nitride mold at high temperature and does not introduce impurities.

[0016] 3. The high-frequency melting furnace, heat treatment furnace, hot pressing furnace, etc. used in the present invention are commonly used equipment, and the process is simple and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the multi-layer paving material of the present invention.

[0018] Figure 2 It is a schematic diagram of the high temperature alloying process of the present invention.

[0019] Figure 3 The La of the present invention 3-x XRD spectrum of Te4 thermoelectric material (the inset is the morphology of the material after high-temperature alloying) DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] The La of the present invention 3-x The preparation method of Te4 thermoelectric material comprises the following steps:

[0022] (1) In a boron nitride crucible, a layer of Te and a layer of La are repeatedly laid layer by layer, with the outermost layer being Te, showing a single substance Te covering a single substance La, a single layer of La being in the form of a sheet with a thickness of 1 to 3 mm, and a single layer of Te being in the form of a powder with a thickness of 1 to 3 mm;

[0023] (2) placing the boron nitride crucible containing the material into a high-temperature device, using argon protection, the gas pressure is slightly positive, and the first stage of La and Te combination is carried out in the temperature range of 450-920°C, and the reaction time is not less than 3 hours;

[0024] (3) After the first stage is completed, the temperature is lowered to room temperature, and then the temperature is raised to carry out the second stage of chemical combination in the temperature range of 950-1000°C. The reaction time is not less than 1 hour to generate high-temperature alloyed La 3-x Te4;

[0025] (4) The high temperature alloyed La is milled by low speed ball milling. 3-x The Te4 thermoelectric material is crushed and hot pressed in a hot press furnace at 1250°C, 1 hour, and 90 MPa to prepare bulk La 3-x Te4 thermoelectric material.

[0026] The high temperature equipment in step (2) is a high frequency melting furnace or a heat treatment furnace.

[0027] The slight positive pressure in step (2) is 0.1 to 0.2 kPa higher than the atmospheric pressure.

[0028] The La obtained in step (4) 3-x Te4 thermoelectric material is in the hundreds of grams level.

[0029] The La prepared by the above preparation method 3-x Te4 thermoelectric material.

[0030] like Figure 1 As shown, in order to increase the contact area between the raw materials La and Te, La needs to be cut into sheets with a thickness of about 2 mm, and the material is laid layer by layer to present the effect of single-element Te covering single-element La. In addition, the container used to hold the raw materials is a boron nitride crucible, because boron nitride has strong high-temperature stability and can avoid the pollution introduced by the high-temperature reaction between the raw materials and the crucible. By adjusting the crucible size and the number of laying layers, the single synthesis amount can be controlled, so that a single alloying preparation of hundreds of grams can be achieved.

[0031] In this embodiment, a layer of Te powder with a thickness of about 1.5 mm and a weight of 21.49 grams is first spread on a boron nitride crucible with a diameter of 70 mm, and a La sheet with a thickness of about 2 mm and a weight of 57.01 grams is spread on it, and then a layer of Te powder with a thickness of about 1.5 mm and a weight of 21.49 grams is spread on the La sheet.

[0032] like Figure 2 As shown, the boron nitride crucible containing the material is placed in a high-frequency melting furnace or a heat treatment furnace or other high-temperature equipment, and argon gas is used for protection, and the gas pressure is slightly positive (0.1 to 0.2 kPa higher than atmospheric pressure). The present invention selects a temperature range of 450 to 920°C to carry out the first stage of La and Te combination, and this temperature range is higher than the melting point of Te and lower than the melting point of La. This temperature range is selected because when the temperature is higher than the melting point of Te (449°C), solid La can react with molten Te at high temperature. When it is higher than the melting point of La (920°C), molten La and Te will react violently, and splashing will occur, causing the final product to deviate from the named composition. The reaction time of this stage is not less than 3 hours.

[0033] After the first stage is completed, it is necessary to lower the temperature to room temperature and then raise the temperature to carry out the second stage of chemical combination. The temperature range selected for this stage is 950-1000℃. After the first stage is completed, the high-temperature reaction of La and Te is not complete, and a large amount of elemental La is still present. Therefore, it is necessary to make the molten La and lanthanum tellurium compound react at a temperature slightly higher than the melting point of La to finally generate the required La. 3-x Te4. The reaction time of this stage is not less than 1 hour.

[0034] In this embodiment, the boron nitride crucible containing the material is placed in a high-frequency melting furnace with argon protection and a gas pressure of 10.3 kPa. The reaction is carried out at a temperature of 700°C for 5 hours. The temperature is lowered to room temperature in 3 hours, and then raised to 950°C. The reaction time in this stage is 2 hours.

[0035] like Figure 3 As shown, the high temperature alloyed La 3-x The XRD pattern of Te4 thermoelectric material is consistent with the standard card pattern, proving that the prepared La 3-x Te4 thermoelectric material.

[0036] Finally, the high temperature alloyed La 3-x The Te4 thermoelectric material was crushed and hot-pressed in a hot press furnace at 1250°C, 1 hour, and 90 MPa to prepare about 99.5 g of bulk La 3-x Te4 thermoelectric material.

[0037] The present invention uses a high-frequency melting furnace or a heat treatment furnace and other high-temperature equipment to alloy La in large quantities. 3-xThe method of using Te4 thermoelectric material can achieve a single preparation amount of hundreds of grams.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A La 3-x The method for preparing Te4 thermoelectric material is characterized in that: The following steps are involved: (1) In a boron nitride crucible, a layer of Te and a layer of La are repeatedly laid layer by layer, with the outermost layer being Te, showing a single substance Te covering a single substance La, a single layer of La being in the form of a sheet with a thickness of 1 to 3 mm, and a single layer of Te being in the form of a powder with a thickness of 1 to 3 mm; (2) placing the boron nitride crucible containing the material into a high-temperature device, using argon protection, the gas pressure is slightly positive, and the first stage of La and Te combination is carried out in the temperature range of 450-920°C, and the reaction time is not less than 3 hours; (3) After the first stage is completed, the temperature is lowered to room temperature, and then the temperature is raised to carry out the second stage of chemical combination in the temperature range of 950-1000°C. The reaction time is not less than 1 hour to generate high-temperature alloyed La 3-x Te4; (4) The high temperature alloyed La was milled by low speed ball milling. 3-x The Te4 thermoelectric material is crushed and hot pressed in a hot press furnace at 1250°C, 1 hour, and 90 MPa to prepare bulk La 3-x Te4 thermoelectric material.

2. according to claim 1 La 3-x The method for preparing Te4 thermoelectric material is characterized in that: The high temperature equipment in step (2) is a high frequency melting furnace or a heat treatment furnace.

3. La according to claim 1 3-x The method for preparing Te4 thermoelectric material is characterized in that: The slight positive pressure in step (2) is 0.1 to 0.2 kPa higher than the atmospheric pressure.

4. La according to claim 1 3-x The method for preparing Te4 thermoelectric material is characterized in that: The La obtained in step (4) 3-x Te4 thermoelectric material is in the hundreds of grams level.

5. La obtained by the preparation method according to any one of claims 1 to 4 3-x Te4 thermoelectric material.

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