Method for rapidly preparing half-Heusler alloy through deep supercooling

Abstract

The invention discloses a method for rapidly preparing a half-Heusler alloy through deep supercooling. The method comprises the steps that elementary substance raw materials are weighed according to the chemical general formula of a half-Heusler compound; the simple substance raw materials are sequentially put into a crucible, and a glass cleaning agent is laid on the top of the crucible; the glass cleaning agent and the elementary substance raw material in the crucible are located at the heating position of the high-frequency induction coil through the electric push rod device; vacuumizing the vacuum chamber to 10 <-3 > Pa, and reversely filling high-purity argon; heating the glass purifying agent and the elementary substance raw material through a high-frequency induction coil, sequentially realizing melting coating of the glass purifying agent on the surface of the alloy and melting of the elementary substance raw material, fully mixing by electromagnetic stirring, cooling and solidifying, and repeatedly heating and cooling and solidifying until a proper supercooling degree is obtained; and cooling to obtain the half Heusler alloy. The prepared half-Heusler alloy has the advantages that the solidification process is easy to control, the component loss is small, volatilization of low-melting-point elements can be fully inhibited, the preparation speed is high, and the performance is excellent.

Description

Technical Field

[0001] The invention relates to the field of thermoelectric materials, and in particular to a method for rapidly preparing a half-Heusler alloy through deep undercooling. Background Art

[0002] Half-Heusler alloys are a class of intermetallic compounds with highly ordered crystal structures. Their general chemical formula is XYZ, where X is a transition element or a rare earth element, Y is a transition element, and Z is a main element. The elements are widely distributed and have a rich alloy system. Therefore, half-Heusler alloys have very rich and novel physical properties, such as thermoelectric effect, semi-metallic properties, ferromagnetism, magnetoresistance effect, superconductivity, magneto-martensitic phase transition, anomalous Hall effect, anomalous Nernst effect, etc., showing almost all kinds of physical phenomena covering the entire condensed matter physics and materials science. These characteristics make half-Heusler alloys have great research value and application prospects in hot functional application fields such as thermoelectric devices, spintronics devices, magnetic refrigeration, shape memory alloys, rare-earth magnetic semiconductors and topological insulators, especially in the field of clean energy.

[0003] In the thermoelectric material system, half-Heusler alloys have unique and excellent thermoelectric properties, such as high Seebeck coefficient, excellent electrical conductivity and good thermal stability. In addition, they have abundant raw materials, relatively low cost and are environmentally friendly. They are considered to be one of the most promising thermoelectric materials.

[0004] At present, the main process steps of the preparation method of half-Heusler alloy include synthesis, powder making, and sintering. Because it contains both high-melting-point refractory metals and low-melting-point metals, such as Nb, Ti, V and other metals with melting points exceeding 2000°C, and Sn, Sb, Te and other metals with melting points below 1000°C, some melting processes can melt refractory metals, but at the same time cause a large amount of low-melting-point metals to volatilize, making the alloy composition difficult to control. In addition, the traditional preparation process requires the process of crushing, powder making and sintering into blocks after synthesis. The process is not only cumbersome, but also has high requirements on equipment and preparation process, resulting in a long time and high cost for sample preparation, and some impurities will also be introduced in the process. Therefore, it is urgent to develop a new preparation process to meet the needs of rapid preparation of pure half-Heusler thermoelectric materials. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a method for rapidly preparing a half-Heusler alloy by deep supercooling, aiming at rapidly and efficiently mass-producing half-Heusler thermoelectric materials by deep supercooling.

[0006] In one aspect, the present invention provides a method for rapidly preparing a half-Heusler alloy by deep undercooling, comprising:

[0007] Step 1, weighing the single substance raw materials of X, Y and Z according to the chemical formula XYZ of the half-Heusler compound;

[0008] Step 2, the weighed single-element raw materials are placed in a crucible in order from the bottom to the top according to the melting point, and a certain amount of glass purifier is placed on the top;

[0009] Step 3, controlling the crucible to move vertically up and down along the central axis of the high-frequency induction coil by an electric push rod device, so that the glass purifier and the single-element raw material in the crucible are at a heating position in a vertical direction of the high-frequency induction coil;

[0010] Step 4: Evacuate the vacuum chamber to 10 -3 After Pa, high-purity argon gas is backfilled for atmosphere protection;

[0011] Step 5, heating the glass purifier and the single-element raw material by the high-frequency induction coil, so that the glass purifier melts and covers the surface of the single-element raw material and the single-element raw material melts in turn, the single-element raw material is fully mixed by electromagnetic stirring and then cooled and solidified, and the heating and cooling and solidification are repeated until a suitable degree of supercooling is obtained; after cooling, the half-Heusler alloy is obtained.

[0012] Preferably, X is at least one of Sc, Y, La, Ti, Zr, Hf, V, Nb, and Ta, Y is at least one of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt, and Z is at least one of Ge, Sn, Sb, and Bi.

[0013] Preferably, the X, Y, Z single substance raw materials are in the form of flakes or particles, and the purity is higher than 99.99%.

[0014] As a preferred technical solution of the present invention, in the step 2, the amount of the glass purifier placed on the top is such that it can cover the single element raw material thereunder.

[0015] As a preferred technical solution of the present invention, in step 3, the glass purifier and the single substance raw material in the crucible are placed at the center of the high-frequency induction coil.

[0016] As a preferred technical solution of the present invention, in step 4, the vacuum degree of the vacuum chamber is evacuated to at least 10 -3 Pa.

[0017] As a preferred technical solution of the present invention, in step 5, the glass purifier and the single substance raw material are heated to 1073-1173°C by the high-frequency induction coil, the softening of the glass purifier is observed by a high-speed charge coupled device (CCD), and the temperature is kept for 100s to allow the glass purifier to melt and coat the surface of the single substance raw material; the temperature is raised to 1500°C to melt all the single substance raw materials, the alloy components are fully mixed by electromagnetic stirring, and the high-frequency induction coil is closed to cool and solidify; the temperature curve collected by the infrared probe is observed, and when the temperature drops to 400°C, the high-frequency induction coil is opened to continue heating; the temperature is quickly raised to 1500°C, and then the high-frequency induction coil is closed to cool and solidify; the previous step is repeated until a suitable degree of supercooling is obtained; after cooling, a half-Heusler alloy sample with uniform composition is taken out.

[0018] Preferably, the crucible is one of a boron nitride crucible, a quartz crucible, an alumina crucible, and a graphite crucible.

[0019] Preferably, the glass purifier is composed of Na 2 O·CaO·6SiO 2 of glass.

[0020] In another aspect, the present invention provides a half-Heusler alloy prepared according to the above method.

[0021] Compared with the prior art, the technical solution provided by the embodiment of the present invention has the following gain effects:

[0022] The present invention uses a high-frequency induction heating device and a combination of molten glass purification and cyclic superheating methods to achieve deep supercooling and rapid preparation of high-performance half-Heusler alloys. The alloys have the characteristics of easy control of the solidification process, small component loss, sufficient suppression of volatilization of low-melting-point elements, fast preparation speed, and superior performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the method for preparing a half-Heusler alloy described in Example 1 of the present invention.

[0024] Figure 2 These are the solidified structures of NbCoSn with different undercooling degrees prepared in Example 1 of the present invention.

[0025] Figure 3 1 is the thermoelectric performance curve of the deeply undercooled and non-undercooled NbCoSn prepared in Example 1 of the present invention.

[0026] Figure 4 It is the morphology picture of the samples prepared in Example 2, Example 3 and Example 4 of the present invention.

[0027] exist Figure 1 middle:

[0028] 1- Glass purifier 2- Single material 3- Electric push rod device 4- Workbench

[0029] 5- High-speed CCD 6- Infrared thermometer 7- Vacuum pump 8- Industrial computer DETAILED DESCRIPTION

[0030] In order to make those skilled in the art better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, rather than to limit the protection scope of the present invention.

[0031] The method for rapidly preparing a half-Heusler alloy by deep undercooling of the present invention is exemplarily described below.

[0032] The embodiment of the present invention provides a method for rapidly preparing a half-Heusler alloy under deep supercooling conditions. The deep supercooling process of the alloy in the preparation method is carried out by a high-frequency induction heating device and a combination of molten glass purification and cyclic superheating methods. During the smelting process, each alloy raw material element is first placed in a crucible from bottom to top in order of melting point from high to low, and a glass purifier is added to the top layer of the alloy raw material. During smelting, the glass purifier is melted and coated on the alloy surface and the metal raw material is melted by heating with a high-frequency induction coil. After the alloy liquid is fully mixed, it is cooled and solidified, and the heating and cooling and solidification are repeated until deep supercooling is obtained, so as to prepare an alloy ingot with performance far superior to that without supercooling. Wherein, the crucible includes a boron nitride crucible, a quartz crucible, an alumina crucible, a graphite crucible, and a multilayer structure crucible composed of the above crucibles.

[0033] Example 1

[0034] Step 1, using each element as raw material, weigh each element metal single substance according to the atomic mass percentage of each element of NbCoSn half-Heusler alloy Nb:Co:Sn=1:1:1, and prepare 20g of raw material; the metal single substances used correspond to metal particles of Nb, Co, and Sn elements respectively;

[0035] Step 2, select a cylindrical boron nitride crucible with an inner diameter of 26 mm, an outer diameter of 29 mm, and a height of 48 mm, and put the prepared raw materials into the boron nitride crucible in sequence. When placing the raw materials, according to the melting point, they are placed in the boron nitride crucible in the order of glass purifier, Nb, Co, and Sn from top to bottom; secondly, the amount of glass purifier used is 5 g, and the height of the alloy raw material added is 2 / 3 of the height of the boron nitride crucible. Preferably, the glass purifier used is composed of Na 2 O·CaO·6SiO 2 The glass purifier can completely cover the metal raw material after it is completely melted;

[0036] Step 3: Use an electric push rod device to control the boron nitride crucible to move vertically up and down along the central axis of the high-frequency induction coil. In order to ensure that all the raw materials are melted and obtain a suitable degree of supercooling, place the purifier and metal raw material in the boron nitride crucible at the center of the high-frequency coil so that the purifier and metal raw material are in the heating position of the high-frequency induction coil. Figure 1 This is a schematic diagram of a boron nitride crucible and sample loading;

[0037] Step 4: After closing the vacuum chamber, use a vacuum pump to pump the vacuum degree in the vacuum chamber to 10 -3 Pa and above, close the exhaust valve, open the air inlet valve, backfill with high-purity argon gas to 0.5 standard atmospheric pressure, close the air inlet valve, repeat the gas washing twice, and then close the air inlet valve;

[0038] Step 5, heat the alloy to 1073-1173℃ through a high-frequency induction coil. Observe the softening degree of the glass purifier through a high-speed CCD, keep warm for 100s to allow the glass purifier to melt and coat the surface of the single-element raw material, and after the glass purifier is completely spread on the alloy surface, heat the alloy to 1500℃. At this time, the Nb and Co metal raw materials are wrapped by the liquid melt Sn. The temperature around the Nb and Co metals is increased by thermal radiation and heat conduction, which accelerates the melting of the Nb and Co metal raw materials. The alloy liquid is fully mixed by electromagnetic stirring, and the high-frequency induction coil is turned off for cooling and solidification; observe the temperature curve collected by the infrared probe, and turn on the high-frequency induction coil to continue heating when the temperature drops to 400℃. After rapidly heating to 1500℃, turn off the high-frequency induction coil for cooling and solidification; repeat the previous step 4-5 times, and end when the appropriate supercooling is obtained; after cooling for 30 minutes, take out a cylindrical semi-Heusler alloy sample with uniform composition, Figure 2 The solidification microstructure diagram of NbCoSn with different undercooling degrees prepared in this example is shown in Figure 2. Figure 3 It can be seen that compared with NbCoSn without undercooling, deeply undercooled NbCoSn has a higher ZT value in the high temperature region greater than 600K.

[0039] Example 2

[0040] The preparation process is consistent with that of Example 1. The metal raw material is VFeSb. According to V:Fe:Sb=1:1:1, 50 g of each element metal single substance is weighed. The appearance morphology of the prepared Figure 4 shown.

[0041] Example 3

[0042] The preparation process is consistent with that of Example 1. The metal raw material is VFeSb and the rare earth element Sm is added. According to V:Fe:Sb:Sm=1:1:1:0.1, 30 g of each metal element is weighed. The appearance morphology of the prepared metal is shown in FIG. Figure 4 shown.

[0043] Example 4

[0044] The preparation process is the same as that of Example 1. The metal raw material is NbFeSb. According to the ratio of Nb:Fe:Sb=1:1:1, 60 g of each metal element is weighed. Figure 4 As shown in the figure, by comparing conventional induction melting and molten glass purification, it can be seen that molten glass purification effectively inhibits the volatilization of element Sb. In addition, the bulk sample prepared by molten glass purification has a denser structure and no pores inside.

[0045] It should be noted that the above-described embodiments are only preferred embodiments of the present invention. For those skilled in the art, without departing from the principles of the present invention, the present invention may be modified, improved and replaced with equivalents, and these modifications, improvements and equivalent replacements are also considered to fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a half-Heusler alloy, comprising: Step 1, weighing the single substance raw materials of X, Y and Z according to the chemical formula XYZ of the half-Heusler compound; Step 2, the weighed single-element raw materials are placed in a crucible in order from the bottom to the top according to the melting point, and a certain amount of glass purifier is placed on the top; Step 3, controlling the crucible to move vertically up and down along the central axis of the high-frequency induction coil by an electric push rod device, so that the glass purifier and the single-element raw material in the crucible are at a heating position in a vertical direction of the high-frequency induction coil; Step 4: Evacuate the vacuum chamber to 10 -3 After Pa, high-purity argon gas is backfilled for atmosphere protection; Step 5, heating the glass purifier and the single-element raw material by the high-frequency induction coil, so that the glass purifier melts and covers the surface of the single-element raw material and the single-element raw material melts in turn, the single-element raw material is fully mixed by electromagnetic stirring and then cooled and solidified, and the heating and cooling and solidification are repeated until a suitable degree of supercooling is obtained; after cooling, the half-Heusler alloy is obtained.

2. The method for preparing a half-Heusler alloy according to claim 1, characterized in that: The X is at least one of Sc, Y, La, Ti, Zr, Hf, V, Nb, and Ta, the Y is at least one of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt, and the Z is at least one of Ge, Sn, Sb, and Bi.

3. The method for preparing a half-Heusler alloy according to claim 1, characterized in that: The X, Y, Z single substance raw materials are in the form of flakes or particles, and the purity is higher than 99.99%.

4. The method for preparing a half-Heusler alloy according to claim 1, characterized in that: In step 2, the amount of the glass purifier placed on the top is such that it can cover the single element raw material thereunder.

5. The method for preparing a half-Heusler alloy according to claim 1, characterized in that: In the step 3, the glass purifier and the single substance raw material in the crucible are placed at the center of the high-frequency induction coil.

6. The method for preparing a half-Heusler alloy according to claim 1, characterized in that: In step 4, the vacuum degree of the vacuum chamber is evacuated to at least 10 -3 Pa.

7. The method for preparing a half-Heusler alloy according to claim 1, characterized in that: In step 5, the glass purifier and the single substance raw material are heated to 1073-1173° C. by the high-frequency induction coil, the softening of the glass purifier is observed by a high-speed charge coupled device, and the temperature is kept for 100 seconds to allow the glass purifier to melt and coat the surface of the single substance raw material; the temperature is raised to 1500° C. to melt all the single substance raw materials, and the single substance raw materials are fully mixed by electromagnetic stirring, and the high-frequency induction coil is closed to cool and solidify; the temperature curve collected by the infrared probe is observed, and when the temperature drops to 400° C., the high-frequency induction coil is opened to continue heating; the high-frequency induction coil is closed after the temperature is quickly raised to 1500° C. to cool and solidify; Repeat the above steps until a suitable undercooling degree is obtained; after cooling, take out a half-Heusler alloy sample with uniform composition.

8. The method for preparing a half-Heusler alloy according to any one of claims 1 to 7, characterized in that: The crucible is one of a boron nitride crucible, a quartz crucible, an alumina crucible and a graphite crucible.

9. The method for preparing a half-Heusler alloy according to claim 1, characterized in that: The glass purifier is glass with a composition of Na2O·CaO·6SiO2.

10. A half-Heusler alloy prepared by the method according to any one of claims 1 to 9.

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