阅读说明：本技术 一种降低p型Ce填充铁基方钴矿热电材料热导率的方法 (Method for reducing thermal conductivity of p-type Ce-filled iron-based skutterudite thermoelectric material ) 是由 刘志愿 童鑫 朱江龙 夏爱林 于 2020-12-07 设计创作，主要内容包括：本发明涉及新能源材料领域,具体涉及一种降低p型Ce填充铁基方钴矿热电材料热导率的方法,采用Ce、Fe和Sb为初始原料,按化学计量比CeFe-4Sb-(12)称量后手工混合均匀；将混合好的粉末置于干净的石墨坩埚中,在真空条件下将石墨坩埚密封于石英管中,得到石英安瓿；将得到的石英安瓿置于高温炉中,缓慢升温至1000～1150℃,真空熔融后熔体在油中淬火,铸锭再次密封在石英管中,退火后将得到的退火样品手工研磨,得到粉末；将得到的粉末采用放电等离子体烧结法于真空下烧结得到p型Ce填充铁基方钴矿化合物热电材料,这种降低p型Ce填充铁基方钴矿热电材料热导率的方法,优化了p型填充方钴矿材料的淬火温度保证良好的烧结致密度、较低的热导率前提下减少杂质相的形成。(The invention relates to the field of new energy materials, in particular to a method for reducing the thermal conductivity of p-type Ce filled iron-based skutterudite thermoelectric material, which adopts Ce, Fe and Sb as initial raw materials and CeFe according to stoichiometric ratio 4 Sb 12 Weighing and then manually mixing uniformly; placing the mixed powder in a clean graphite crucible, and sealing the graphite crucible in a quartz tube under a vacuum condition to obtain a quartz ampoule; placing the obtained quartz ampoule in a high-temperature furnace, slowly heating to 1000-1150 ℃, quenching the melt in oil after vacuum melting, sealing the ingot in a quartz tube again, and annealingManually grinding the obtained annealed sample to obtain powder; the obtained powder is sintered in vacuum by adopting a discharge plasma sintering method to obtain the p-type Ce filled iron-based skutterudite compound thermoelectric material, and the method for reducing the heat conductivity of the p-type Ce filled iron-based skutterudite thermoelectric material optimizes the quenching temperature of the p-type filled skutterudite material, ensures good sintering compactness and reduces the formation of impurity phases on the premise of lower heat conductivity.)

1. A method for reducing the thermal conductivity of a p-type Ce filled iron-based skutterudite thermoelectric material is characterized by comprising the following steps:

s1: ce, Fe and Sb are used as initial raw materials, and CeFe is used according to the stoichiometric ratio₄Sb₁₂Weighing and then manually mixing uniformly;

s2: putting the mixed powder in the step S1 into a clean graphite crucible, and sealing the graphite crucible in a quartz tube under a vacuum condition to obtain a quartz ampoule;

s3: placing the quartz ampoule obtained in the step S2 in a high-temperature furnace, slowly heating to 1000-1150 ℃, and quenching the melt in oil after vacuum melting to obtain a cast ingot;

s4: sealing the ingot obtained in the step S3 in a quartz tube again, and manually grinding an obtained annealed sample after annealing to obtain powder with uniform grain size;

s5: and sintering the powder obtained in the step S4 in vacuum by adopting a discharge plasma sintering method to obtain the p-type Ce-filled iron-based skutterudite compound thermoelectric material.

2. The method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material as claimed in claim 1, wherein in the step S1, Ce is 99.9% high-purity Ce, Fe is 99% high-purity Fe, and Sb is 99.999% high-purity Sb.

3. The method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material as claimed in claim 1, wherein in the step S1, Ce is bulk, Fe is powder, and Sb is powder.

4. The method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material according to claim 1, wherein the manual mixing time in the step S1 is 9-11 min.

5. The method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material as claimed in claim 1, wherein the vacuum condition in the step S2 is a vacuum degree of less than 0.1 MPa.

6. The method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material according to claim 1, wherein the melting time in the step S3 is 8-11 h.

7. The method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material as claimed in claim 1, wherein the annealing temperature in the step S4 is 670-680 ℃ for 120-168 h.

8. The method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material as claimed in claim 1, wherein in the step S5, the sintering temperature is 490-510 ℃, the sintering pressure is 50-60 MPa, and the sintering time is 5-15 min.

Technical Field

The invention relates to the field of new energy materials, in particular to a method for reducing the thermal conductivity of a p-type Ce filled iron-based skutterudite thermoelectric material.

Background

The thermoelectric material is a new energy material which can realize the direct interconversion of heat energy and electric energy and can be used for power generation and refrigeration. The thermoelectric device made of thermoelectric material is an all-solid-state energy conversion device, has many advantages which other energy conversion devices do not have, such as small volume, simple structure, no noise, high reliability, long service life, environmental friendliness, wide applicable temperature range and the like, and has important functions in the fields of aerospace, military, medicine, microelectronics and the like.

The performance of the thermoelectric material is comprehensively represented by a dimensionless figure of merit (ZT), and the larger the ZT value is, the higher the thermoelectric conversion efficiency of the material under a certain temperature difference is. The ZT value is related to the Seebeck coefficient, electrical conductivity and thermal conductivity of the material. Good thermoelectric materials have high electrical conductivity and Seebeck coefficient and low thermal conductivity. Depending on the applicable temperature of the thermoelectric material, the thermoelectric material is classified into Bi₂Te₃Low-temperature thermoelectric materials typified by PbTe, medium-temperature thermoelectric materials typified by PbTe, and high-temperature thermoelectric materials typified by SiGe. Of these thermoelectric material systems, skutterudite is recognized as the most promising thermoelectric material in the middle temperature region due to its excellent electrical transport properties. In the last 50 s, researchers in the former soviet union have conducted detailed and systematic studies on the properties of skutterudites and their alloys and their applications in the field of thermoelectricity. They found that binary skutterudite has better electrical properties but higher thermal conductivity, resulting in very low ZT values. Due to the unique icosahedral void crystal structure of skutterudite, the scholars propose that other atoms are introduced into the voids of skutterudite to form a filled skutterudite compound, the small ionic radius of the filled atoms and the weak combination of the filled atoms and adjacent atoms can generate local disturbance strong resonance scattering phonons in crystal lattices, so that the thermal conductivity of the crystal lattices is remarkably reduced; secondly, the introduced filler atoms enable the regulation and optimization of the current carryingThe sub-characteristics further optimize electrical performance. Therefore, the filled skutterudite has better comprehensive thermoelectric performance.

Compared with the n-type filled skutterudite material, the single-phase p-type filled skutterudite material is difficult to prepare. Because the p-type filled skutterudite material is more or less subjected to impurity phases (Fe with electron deletion) which are difficult to eliminate in the preparation process₄Sb₁₂Often not stable), which is one reason for poor thermoelectric performance. Therefore, the reduction of the impurity phase in the p-type filled skutterudite material in the preparation process is the key to improve the thermoelectric transport performance of the p-type filled skutterudite material. In the conventional process for preparing skutterudite thermoelectric materials, the quenching process is a very critical step. The quenching temperature plays an important role in finally forming single-phase compact skutterudite, so that the optimization of the quenching temperature is also the key for preparing high-performance skutterudite thermoelectric materials, particularly p-type Fe-based skutterudite materials. However, the quenching temperature of the p-type filled skutterudite material is optimized, so that the formation of impurity phases is reduced on the premise of ensuring good sintering compactness and lower thermal conductivity, and the research on improving the electrothermal transport performance is less.

In view of the above-mentioned drawbacks, the inventors of the present invention have finally obtained the present invention through a long period of research and practice.

Disclosure of Invention

The invention aims to optimize the quenching temperature of a p-type filling skutterudite material, ensure good sintering compactness and reduce the formation of impurity phases on the premise of lower heat conductivity, thereby improving the electric heat transport performance and providing a method for reducing the heat conductivity of the p-type Ce filling iron-based skutterudite thermoelectric material.

The invention adopts the technical scheme that a method for reducing the thermal conductivity of a p-type Ce filled iron-based skutterudite thermoelectric material is disclosed, and the method comprises the following steps:

s1: ce, Fe and Sb are used as initial raw materials, and CeFe is used according to the stoichiometric ratio₄Sb₁₂Weighing and then manually mixing uniformly;

s2: putting the mixed powder in the step S1 into a clean graphite crucible, and sealing the graphite crucible in a quartz tube under a vacuum condition to obtain a quartz ampoule;

s3: placing the quartz ampoule obtained in the step S2 in a high-temperature furnace, slowly heating to 1000-1150 ℃, and quenching the melt in oil after vacuum melting to obtain a cast ingot;

s4: sealing the ingot obtained in the step S3 in a quartz tube again, and manually grinding an obtained annealed sample after annealing to obtain powder with uniform grain size;

s5: and sintering the powder obtained in the step S4 in vacuum by adopting a discharge plasma sintering method to obtain the p-type Ce-filled iron-based skutterudite compound thermoelectric material.

And in the step S1, the manual mixing time is 9-11 min, so that the materials are fully and uniformly mixed.

In the step S2, the vacuum degree is less than 0.1MPa, and the finished product is sealed in vacuum, so that the purity of the finished product is improved.

The melting time in the step S3 is 8-11 h.

In the step S4, the annealing temperature is 670-680 ℃, and the time is 120-168 hours.

In the step S5, the sintering temperature is 490-510 ℃, the sintering pressure is 50-60 MPa, and the sintering time is 5-15 min.

Compared with the prior art, the invention has the beneficial effects that: the p-type Ce-filled iron-based skutterudite compound thermoelectric material is obtained by adopting a process of combining melting-quenching-annealing with spark plasma sintering, and the p-type Ce-filled iron-based skutterudite thermoelectric material prepared by adopting a method for optimizing quenching temperature has the following advantages:

1. a porous structure;

2. the sintering density is good;

3. a trace amount of impurity phase.

These characteristics enable the prepared p-type Ce filled iron-based skutterudite thermoelectric material (CeFe)₄Sb₁₂) Has lower thermal conductivity and competitive thermoelectric performance figure of merit ZT value.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is an XRD pattern and a glossy SEI and BEI pattern for the sample of example 1;

FIG. 3 is the thermoelectric figure of merit ZT value of the sample of example 1;

FIG. 4 is an XRD pattern and a glossy SEI and BEI pattern for the sample of example 2;

FIG. 5 is the thermoelectric figure of merit ZT value of the sample of example 2;

FIG. 6 is an XRD pattern and a glossy SEI and BEI pattern for the sample of example 3;

FIG. 7 is the thermoelectric figure of merit ZT values for the samples of example 3;

figure 8 is the thermal conductivity of the samples of examples 1-3.

Detailed Description

The above and further features and advantages of the present invention are described in more detail below with reference to the accompanying drawings.

Example 1

As shown in fig. 1, a method for reducing the thermal conductivity of a p-type Ce-filled iron-based skutterudite thermoelectric material comprises the following steps:

(1) using high-purity Ce (99.9% block), Fe (99% powder) and Sb (99.999% powder) as initial raw materials, according to the stoichiometric ratio CeFe₄Sb₁₂Weighed and weighed a total of 10 g.

(2) Mixing the raw materials by hand for 10min to mix them uniformly. Then putting the mixed powder into a clean graphite crucible; sealing the graphite crucible in a quartz tube under the condition that the vacuum degree is less than 0.1MPa, placing the quartz crucible in a program temperature control melting furnace, slowly heating to 1000 ℃, melting in vacuum for 10 hours at the temperature, and then placing the melt in oil for quenching to obtain CeFe₄Sb₁₂Casting blocks; the quenched sealed quartz ampoule containing the ingot was again placed in a high temperature furnace for annealing at 650 ℃ for 168h and the annealed sample was hand ground to a finer powder.

(3) And (3) sintering the powder obtained in the step (2) in vacuum by using a discharge plasma sintering method. The sintering temperature is 500 ℃, the sintering pressure is 50MPa, the sintering time is 5min, the high-density p-type Ce filled iron-based skutterudite thermoelectric material with the diameter of 15mm and the height of 10mm is obtained, and the powder X-ray diffraction analysis result of the sintered body shows that the main phase of the sintered body is a skutterudite phase and contains more FeSb₂And Sb impurity phase, as shown in fig. 2 a. BEI diagram of a smooth surfaceConsistent with the EDS spectra results and XRD analysis results, as shown in figure 2 c. The SEI image of the shiny side shows that the sample surface is relatively flat with a small number of pore structures, as shown in figure 2 b.

(4) The seebeck coefficient, the electrical conductivity and the thermal conductivity of the bulk material obtained after SPS sintering were measured and the ZT value was calculated with a maximum value of only 0.3, as shown in fig. 3.

Example 2

In this example, the preparation method of the p-type Ce-filled iron-based skutterudite thermoelectric material is the same as that of example 1 except that the quenching temperature is changed. The quenching temperature was raised to 1100 ℃.

FIG. 4a is the XRD pattern of the sample obtained, the main phase of the sample is skutterudite phase, and only the FeSb is less₂And an Sb impurity phase. The impurity phase is significantly reduced compared to the sample obtained in example 1. Indicating that increasing the quench temperature can significantly reduce the formation of impurity phases. As can be seen from the SEI image (fig. 4b) and the BEI image (fig. 4c) at the smooth surface of the sample, the surface has a significantly increased microporous structure compared to the sample of example 1, and these porous structures help to scatter phonons, reduce thermal conductivity, and improve the thermal transport properties of the sample.

The ZT value of the sample was calculated from the Seebeck coefficient, the electrical conductivity and the thermal conductivity obtained from the tests, as shown in fig. 5. The maximum ZT value of the sample was 0.78, which was significantly improved compared to the sample of example 1.

Example 3

In this example, the preparation method of the p-type Ce-filled iron-based skutterudite thermoelectric material is the same as that of examples 1 and 2 except that the quenching temperature is changed. The quenching temperature was raised to 1150 ℃.

FIG. 6a is the XRD pattern of the sample obtained, the main phase of which is the skutterudite phase and also contains less FeSb₂And an Sb impurity phase. FeSb comparison with the sample obtained in example 2₂And Sb impurity content did not vary much, but was significantly lower than in example 1. As can be seen from the SEI (fig. 6b) and BEI (fig. 6c) images at the smooth surface of the sample, the surface has a further increased microporous structure compared to the sample of example 2. Further addition of these porous structures further contributes to scattering more phonons, further reducingLow thermal conductivity and high heat transport performance. The ZT value of the sample was calculated from the Seebeck coefficient, the electrical conductivity and the thermal conductivity obtained from the tests, as shown in fig. 7. The optimum ZT value for the sample reached about 0.9, which was further improved compared to the sample of example 2.

The invention shows that the p-type Ce filled iron-based skutterudite CeFe can be obviously improved by properly increasing the quenching temperature₄Sb₁₂Thermoelectric properties of the thermoelectric material. This significant increase in thermoelectric performance benefits from a significant reduction in thermal conductivity due to the increased quenching temperature, as shown in fig. 8. Therefore, the selection of an appropriate quenching temperature is very important to obtain a p-type Ce-filled iron-based skutterudite compound thermoelectric material with high performance.

The foregoing is merely a preferred embodiment of the invention, which is intended to be illustrative and not limiting. It will be understood by those skilled in the art that various changes, modifications and equivalents may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.