ZrNiSn-BASED HALF-HEUSLER THERMOELECTRIC MATERIAL AND PROCESS FOR MANUFACTURING SAME AND FOR REGULATING ANTISITE DEFECTS THEREIN

Abstract

The invention relates to a process for manufacturing a ZrNiSn-based half-Heusler thermoelectric material and regulating antisite defects therein, including the steps of: mixing zirconium (Zr), nickel (Ni), and stannum (Sn) at an atomic ratio of Zr: Ni: Sn=1:1:1; forming an ingot by melting the mixture in a levitation melting furnace; milling the ingot to form a milled powder followed by drying; sintering the dried powder by spark plasma sintering; and placing the sintered powder in a vacuum vessel to be subjected to heat treatment and then quenching treatment to obtain the ZrNiSn-based half-Heusler thermoelectric material. The process is simple, easy to control, and results in a single phase ZrNiSn-based half-Heusler thermoelectric material with antisite defects.

Claims

1. A process for manufacturing a ZrNiSn-based half-Heusler thermoelectric material and regulating antisite defects therein, comprising steps of: mixing zirconium (Zr), nickel (Ni), and stannum (Sn) at an atomic ratio of Zr:Ni:Sn=1:1:1; forming an ingot by melting the mixture in a levitation melting furnace; milling the ingot to form a milled powder followed by drying; sintering the dried powder by spark plasma sintering; and placing the sintered powder in a vacuum vessel to be subjected to heat treatment and then quenching treatment to obtain the ZrNiSn-based half-Heusler thermoelectric material.

2. The process according to claim 1, comprising steps of: (1) mixing Zr, Ni, and Sn at an atomic ratio of Zr: Ni: Sn=1:1:1; (2) forming an ingot by melting the mixture in an argon atmosphere in a levitation melting furnace, with the mixture heated to a temperature of 1600 to 1800 C. and maintained at that temperature for 1 to 5 min; (3) ball-milling the ingot to form a ball-milled powder having a particle size of 0.5 to 2 m followed by natural drying; (4) sintering the dried powder by spark plasma sintering at 900 to 1100 C. under 80 to 100 MPa for 5 to 20 min; (5) placing the sintered powder into a vacuum vessel; (6) placing the vacuum vessel containing the powder into a box-type high-temperature sintering furnace and subjecting the powder to a long-duration diffusion annealing process with an annealing temperature of 800 to 1100 C. and an incubation time of 12 to 36 h; and (7) subjecting the incubated powder to a rapid quenching treatment to form the ZrNiSn-based half-Heusler thermoelectric material.

3. The process according to claim 1, wherein, each of Zr, Ni, and Sn has a purity of greater than or equal to 99.9%.

4. The process according to claim 2, wherein, each of Zr, Ni, and Sn has a purity of greater than or equal to 99.9%.

5. The process according to claim 2, wherein, the melting step (2) is carried out 3 to 6 times.

6. The process according to claim 2, wherein, the argon atmosphere is applied at a pressure of 10.sup.4 to 10.sup.5 Pa.

7. The process according to claim 2, wherein, in step (3), the ingot is initially ground into a powder with a particle size of 0.1 to 1 mm by using a mortar and then subjected to wet-ball-milling in argon atmosphere, wherein, anhydrous ethanol is used as a ball-milling medium, a ball-to-powder ratio is within a range of 10:1 to 20:1, a rotation speed is within a range of 200 to 600 r/min and a milling time is within a range of 5 to 20 h.

8. The process according to claim 2, wherein, in step (3), the ball-milled powder subjected to suction filtration is allowed to dry naturally for 12 to 48 h in argon atmosphere or a sealed and oxygen free environment.

9. The process according to claim 2, wherein, in step (5), a vacuum level of the vacuum vessel is less than or equal to 510.sup.3 Pa.

10. The process according to claim 2, wherein, in step (7), water is used as a quenching medium for the quenching treatment.

11. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 1.

12. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 2.

13. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 3.

14. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 4.

15. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 5.

16. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 6.

17. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 7.

18. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 8.

19. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 9.

20. A ZrNiSn-based half-Heusler thermoelectric material manufactured by the process according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows XRD patterns of different samples sintered by spark plasma sintering;

[0029] FIG. 2 shows electrical conductivity of samples of a ZrNiSn-based half-Heusler thermoelectric material subjected to different heat treatment processes;

[0030] FIG. 3 shows power factor of samples of ZrNiSn-based half-Heusler thermoelectric material subjected to different heat treatment processes; and

[0031] FIG. 4 shows thermoelectric figure of merit of samples of ZrNiSn-based half-Heusler thermoelectric material subjected to different heat treatment processes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0032] The invention will be further described in detail below with reference to examples.

Example 1

[0033] A single phase ZrNiSn-based half-Heusler thermoelectric material having antisite defects was manufactured. Zr, Ni, and Sn were mixed at an atomic ratio of Zr:Ni:Sn=1:1:1. The mixture having 33.3% Zr, 33.3% Ni, and 33.3% Sn was then melted.

[0034] Further, the ZrNiSn-based half-Heusler thermoelectric material with antisite defects, ball-milled, had a grain size of 0.5 to 2 m.

[0035] In particular, the material was manufactured according to the following steps:

[0036] (1) preparing raw material: preparing Zr, Ni, and Sn particles with a diameter of about 2 mm and a length of about 5 mm and a purity of greater than or equal to 99.9% as raw material;

[0037] (2) oxidation prevention: mixing the Zr, Ni, and Sn particles at a nominal atomic ratio of Zr:Ni: Sn=1:1:1 in a glove box;

[0038] (3) melting: melting the mixture in an argon atmosphere (applied at a pressure of 10.sup.4 to 10.sup.5 Pa) in a levitation melting furnace to form an ingot, heating the mixture up to 1600 to 1800 C. and then maintaining that temperature for about 3 min, and re-melting the ingot about four times to ensure component homogeneity in the levitation melting furnace;

[0039] (4) ball-milling: initially grinding the ingot into a powder with a particle size of about 0.1 to 1 mm and then subjecting the ground powder to wet-ball-milling in argon atmosphere, with anhydrous ethanol as a ball-milling medium, a ball-to-powder ratio of 15 to 1, a rotation speed of 500 r/min, and a milling time of 10 h;

[0040] (5) drying: allowing the milled powder subjected to suction filtration to dry naturally for 24 h in a glove box;

[0041] (6) sintering: sintering the dried powder by spark plasma sintering at 1000 C. under 100 MPa for 15 min;

[0042] (7) sealing: placing the sintered powder at a treatment temperature of 900 C. into a quartz glass tube with a diameter of 20 mm, and vacuuming and sealing the tube such that the tube had a degree of vacuum of less than or equal to 510.sup.3 Pa;

[0043] (8) heat treating: subjecting the sample sealed in the vacuum tube to a long-duration diffusion annealing treatment in a box-type high-temperature sintering furnace, with an annealing temperature of 900 C. and an incubation time of 24 h; and

[0044] (9) quenching: subjecting the incubated sample to a rapid quenching treatment with water as a quenching medium, to form the ZrNiSn-based half-Heusler thermoelectric material having a grain size of about 0.5 to 2 m.

Example 2

[0045] (1) preparing raw material: preparing Zr, Ni, and Sn particles with a diameter of 2 mm and a length of 5 mm and a purity of greater than or equal to 99.9% as raw material;

[0046] (2) oxidation prevention: mixing the Zr, Ni, and Sn particles at a nominal atomic ratio of Zr:Ni: Sn=1:1:1 in a glove box;

[0047] (3) melting: melting the mixture in an argon atmosphere (applied at a pressure of 10.sup.4 to 10.sup.5 Pa) in a levitation melting furnace to form an ingot, with the mixture to be heated up to 1600 to 1800 C., maintaining that temperature for 4 min, and re-melting the ingot three times to ensure component homogeneity in the levitation melting furnace;

[0048] (4) ball-milling: initially grinding the ingot into a powder with a particle size of about 0.1 to 1 mm and then subjecting the ground powder to wet-ball-milling in an argon atmosphere, with anhydrous ethanol as a ball-milling medium and a ball-to-powder ratio of 20 to 1, a rotation speed of 600 r/min, and a milling time of 8 h;

[0049] (5) drying: allowing the milled powder subjected to suction filtration to dry naturally for 20 h in a glove box;

[0050] (6) sintering: sintering the dried powder by spark plasma sintering at 950 C. under 90 MPa for 20 mins;

[0051] (7) sealing: placing the sintered powder sample at a temperature of 950 C. into a quartz glass tube with a diameter of 20 mm, and vacuuming and sealing the tube such that the tube had a degree of vacuum of less than or equal to 510.sup.3 Pa;

[0052] (8) heat treating: subjecting the sample sealed in the tube to a long-duration diffusion annealing treatment in a box-type high-temperature sintering furnace, with an annealing temperature of 950 C. and an incubation time of 20 h.

[0053] (9) quenching: subjecting the incubated sample to a rapid quenching treatment with water as a quenching medium, to form the ZrNiSn-based half-Heusler thermoelectric material having a grain size of about 0.5 to 2 m.

[0054] Test Results

[0055] FIG. 1 shows XRD patterns of the as-sintered samples with different heat treatment processes. It can be seen that the samples of the ZrNiSn-based thermoelectric material with different heat treatment processes were of single phase.

[0056] FIG. 2 shows electrical conductivity of the samples of the ZrNiSn-based half-Heusler thermoelectric material with different heat treatment processes. It can be seen that the electrical conductivity of the samples decreased gradually with the increase of the annealing temperature, showing that the electrical conductivity decreased from 7.3510.sup.4 S/m to 6.2510.sup.4 S/m at 923 K.

[0057] FIG. 3 shows the power factor of the samples of the ZrNiSn-based half-Heusler thermoelectric material with different heat treatment processes. It can be seen that the power factor of the samples gradually decreased with the increase of the annealing temperature, showing that the power factor decreased from 3.31 to 2.95 at 923 K.

[0058] FIG. 4 shows thermoelectric figure of merit of the samples of the ZrNiSn-based half-Heusler thermoelectric material with different heat treatment processes. It can be seen that, the thermoelectric figure of merit, ZT, decreased gradually with the increase of the annealing temperature, showing that the ZT decreased from 0.63 to 0.51 at 923 K.

[0059] In the examples, single phase ZrNiSn-based thermoelectric material with different content of antisite defects were manufactured, and the content of antisite defect was regulated by using different heat treatment processes. The XRD results showed that all the samples manufactured were of single phase. Results also showed that the increase of the annealing temperature resulted in a higher driving force for the recovery of the antisite defects, and thus a sample under a higher annealing temperature had fewer antisite defects after the rapid quenching step. The thermoelectric performance results showed that the electrical conductivity and power factor increased gradually with the increase of the antisite defect density, and thus the thermoelectric figure of merit, ZT, was improved. The single phase ZrNiSn-based half-Heusler thermoelectric material having antisite defects was manufactured, and was qualitatively and quantitatively analyzed. The effect of the antisite defects on the thermoelectric performance of the ZrNiSn-based Half-Heusler thermoelectric material was also disclosed.

[0060] It should be noted that the examples above are for the purpose of illustration and not to limit the scope of the invention. Although the invention herein has been described with reference to particular embodiments by way of examples, it should be understood by those skilled in the art, that various modifications or equivalents may be made without departing from the spirit or scope of the invention.