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 2021-09-26 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Ce-(1+x)Fe-(4)Sb-(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,缓慢升温至淬火温度,真空熔融后熔体在饱和食盐水中淬火后放入高温炉中继续退火,将退火样品手工研磨,得到粉末；得到的粉末采用放电等离子体烧结得到低热导率的Ce-(1.25)Fe-(4)Sb-(12)材料。通过对Ce原子填充分数和淬火温度进行优化制备的Ce-(1.25)Fe-(4)Sb-(12)材料具有良好的致密度、多孔的结构和较少的杂质相,这种多孔结构和较少的杂质相使得Ce-(1.25)Fe-(4)Sb-(12)材料具有很低的热导率。(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, which adopts Ce, Fe and Sb as initial raw materials according to the stoichiometric ratio Ce 1+x Fe 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 quenching temperature, vacuum melting, quenching the melt in saturated salt water, and placing the melt in the high temperature furnace for continuous useContinuing annealing, and manually grinding an annealed sample to obtain powder; the obtained powder is sintered by adopting discharge plasma to obtain Ce with low thermal conductivity 1.25 Fe 4 Sb 12 A material. Ce prepared by optimizing Ce atomic packing fraction and quenching temperature 1.25 Fe 4 Sb 12 The material has good compactness, porous structure and less impurity phase, and the porous structure and the less impurity phase enable the Ce to be in a shape of being 1.25 Fe 4 Sb 12 The material has very low thermal 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 of:

s1: ce, Fe and Sb are used as initial raw materials, and the Ce is in stoichiometric ratio_1+xFe₄Sb₁₂Weighing, and then manually mixing uniformly, wherein 1+ x is the filling fraction of Ce, and x is 0.10,0.15,0.25 and 0.30 respectively;

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 ampoules containing the powder with different Ce filling fractions obtained in the step S2 into a high-temperature furnace, slowly heating to a quenching temperature, and quenching the melt in saturated salt water after vacuum melting;

s4: annealing the quartz tubes containing the cast ingots with different Ce filling fractions obtained in the step S3 in a high-temperature furnace, and manually grinding the obtained annealed sample to obtain powder with uniform crystal grain size;

s5: analyzing several annealing powders containing different Ce filling fractions obtained by S4 by adopting an X-ray diffraction technology, and determining the optimal Ce filling fraction;

s6: repeating the steps S1-S4 by selecting the optimal Ce filling fraction to obtain annealing powder with uniform grain size;

s7: and sintering the annealed powder obtained in the step S6 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 according to claim 1, wherein the manual mixing time in the step S1 is 5-10 min.

4. 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.

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 quenching temperature in the step S3 is 1100 ℃.

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 8-10 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 according to claim 1, wherein the optimal filling fraction of Ce element in the step S5 is 1.25.

9. 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 S6, the quenching temperature is 950, 1000, 1100 or 1150 ℃, and the melting time is 8-10 h; the annealing temperature is 670-680 ℃, and the time is 120-168 hours.

10. 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 S7, 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 in the middle temperature region due to its excellent electrical transport propertiesA material. In the last 50 s of the century, researchers in the 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 can adjust and optimize the carrier transport characteristics and further optimize the electrical properties. 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 more or less impurity phases with high thermal conductivity, such as (FeCo) Sb, which are difficult to eliminate, are present during the preparation of p-type filled skutterudite materials₂(FeCo) Sb, Sb or the like (Fe with electron deficiency)₄Sb₁₂Often not stable), which is one reason for its high thermal conductivity. Therefore, the reduction of the impurity phase in the p-type filled skutterudite material in the preparation process is the key to reduce the thermal conductivity and improve the thermoelectric transport performance. 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 solve the problem of how to optimize the quenching temperature of a p-type filled skutterudite material and reduce the formation of impurity phases on the premise of ensuring good sintering compactness so as to obtain the p-type filled skutterudite material with low thermal conductivity, and provides a method for reducing the thermal conductivity of a p-type Ce filled 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 the Ce is in stoichiometric ratio_1+xFe₄Sb₁₂Weighing, and then manually mixing uniformly, wherein 1+ x is the filling fraction of Ce, and x is 0.10,0.15,0.25 or 0.30;

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 ampoules containing the powder with different Ce filling fractions obtained in the step S2 into a high-temperature furnace, slowly heating to a quenching temperature, and quenching the melt in saturated salt water after vacuum melting; the density of the saturated salt solution is greater than that of common water, the cooling speed of the sample is lower than that of common water when the saturated salt solution is adopted for quenching, the quartz tube is not easy to break when the quartz tube is quenched, and on the contrary, the quartz tube is easy to break when the quartz tube is quenched by common water;

s4: putting the quartz tubes containing the cast ingots with different Ce filling fractions obtained in the step S3 into a high-temperature furnace for annealing, manually grinding the obtained annealed sample to obtain powder with uniform grain size, and annealing to ensure that the quenched sample forms a skutterudite phase through long-time peritectic reaction;

s5: analyzing several annealing powders containing different Ce filling fractions obtained by S4 by adopting an X-ray diffraction technology, and determining the optimal Ce filling fraction;

s6: repeating the steps S1-S4 by selecting the optimal Ce filling fraction to obtain annealing powder with uniform grain size;

s7: and sintering the annealed powder obtained in the step S6 in vacuum by adopting a discharge plasma sintering method to obtain the p-type Ce-filled iron-based skutterudite compound thermoelectric material.

The element Ce is easy to be oxidized in the preparation process,if according to the nominal component Ce₁Fe₄Sb₁₂The actual filling fraction of Ce is lower than 1, and the lower filling fraction of Ce is used for preparing the CeFe₄Sb₁₂The material has higher thermal conductivity, thus increasing the filling fraction of Ce (Ce) in the nominal component_1+x) Can ensure that the actual composition of the material is CeFe₄Sb₁₂While reducing the CeFe produced₄Sb₁₂The thermal conductivity of the material, Ce is a filler element, and 1+ x is the amount of Ce that can be filled into the intrinsic voids of the skutterudite 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.

In the step S3, the quenching temperature is 1100 ℃, and the melting time is 8-10 h.

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

The optimal filling fraction of Ce element in the step S5 is 1.25

In the step S6, the quenching temperature is 950 ℃, 1000 ℃, 1100 ℃ or 1150 ℃ respectively, and the melting time is 8-10 h. The annealing temperature is 670-680 ℃, and the time is 120-168 hours.

In the step S7, 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 Ce with low thermal conductivity is prepared by adopting a method of optimizing quenching temperature on the premise of selecting the optimal Ce filling fraction_1.25Fe₄Sb₁₂. The p-type Ce-filled iron-based skutterudite thermoelectric material has the following advantages:

1. the sintering density is good;

2. by controlling the quenching temperature, the p-type Ce filled iron-based skutterudite thermoelectric material has a porous structure, the porous structure can obviously inhibit phonon transport, the thermal conductivity of the material is obviously reduced, the lowest thermal conductivity is only 1.88W/mK, and the amount of pores can be increased by properly increasing the quenching temperature;

3. the p-type Ce filled iron-based skutterudite thermoelectric material has trace impurity phase FeSb by controlling the quenching temperature₂And Sb, impurity phase FeSb₂Sb has higher thermal conductivity, so that the thermal conductivity of the material can be obviously reduced by reducing the impurity phases, and the impurity phases can be obviously reduced by properly increasing the quenching temperature;

these characteristics enable the prepared p-type Ce filled iron-based skutterudite thermoelectric material (Ce)_1.25Fe₄Sb₁₂) Has lower thermal conductivity and competitive ZT value.

Drawings

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

FIG. 2 is Ce in example 1_1+xFe₄Sb₁₂XRD pattern of the annealed sample;

FIG. 3 is an XRD pattern and a glossy SEI and BEI pattern for the sample of example 2;

FIG. 4 is a graph of the thermal conductivity κ test results for the samples of example 2;

FIG. 5 is an XRD pattern and a glossy SEI and BEI pattern for the sample of example 3;

FIG. 6 is a graph of the thermal conductivity κ test results for the samples of example 3;

FIG. 7 is an XRD pattern and a glossy SEI and BEI pattern for the sample of example 4;

FIG. 8 is a graph of the results of the thermal conductivity κ test for the samples in example 4

FIG. 9 is an XRD pattern and a glossy SEI and BEI pattern for the sample of example 5;

fig. 10 is a graph of the thermal conductivity κ test results for the samples in example 5.

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.

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:

example 1

Ce_1+xFe₄Sb₁₂The optimization of the filling fraction of the middle Ce element comprises the following steps:

(1) high-purity Ce (99.9% block), Fe (99% powder) and Sb (99.999% powder) are used as initial raw materials, and the Ce is in stoichiometric ratio_1+xFe₄Sb₁₂(x is 0.10,0.15,0.25 and 0.30).

(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 1100 ℃, melting in vacuum for 10 hours at the temperature, and then placing the melt in saturated salt solution for quenching to obtain Ce_1+xFe₄Sb₁₂Casting blocks; the quartz ampoule containing the quenched ingot was again placed in a high temperature furnace for annealing at 675 deg.C for 168 hours and the annealed sample was hand ground to a finer powder. XRD pattern results for several annealed powder samples with different Ce loading fractions are shown in fig. 2. The results showed that when x was 0.25, the sample contained only a trace amount of impurity phase, while the other samples contained a large amount of impurity phase (FeSb)₂And Sb). Due to FeSb₂Has higher thermal conductivity than Sb, so that compared with Ce_1.25Fe₄Sb₁₂Sample, Ce containing a large amount of impurity phase_1.10Fe₄Sb₁₂,Ce_1.15Fe₄Sb₁₂And Ce_1.30Fe₄Sb₁₂The sample should have a high thermal conductivity. Therefore, the optimum filling fraction of Ce is 1.25.

Example 2

(1) High-purity Ce (99.9% block), Fe (99% powder) and Sb (99.999% powder) are used as initial raw materials, and the Ce is in stoichiometric ratio_1.25Fe₄Sb₁₂And (5) weighing.

(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 950 ℃, melting in vacuum for 10 hours at the temperature, and then placing the melt in saturated salt water for quenching to obtain Ce_1.25Fe₄Sb₁₂Casting blocks; the quartz ampoule containing the quenched ingot was again placed in a high temperature furnace for annealing at 675 deg.C for 168 hours and the annealed sample was hand ground to a finer powder.

(3) And (3) sintering the annealed powder with the optimized filling fraction obtained in the step (2) in vacuum by using a discharge plasma sintering method. The sintering temperature is 500 ℃, the sintering pressure is 50MPa, and the sintering time is 5min, thus obtaining the high-density Ce with the diameter of 15mm and the height of 10mm_1.25Fe₄Sb₁₂The powder X-ray diffraction analysis results of the thermoelectric material and the sintered body show that the main phase of the sintered body is a skutterudite phase and contains much FeSb₂And Sb impurity phase, as shown in fig. 3 a. The BEI profile of the polished facets is consistent with the EDS spectrum results and XRD analysis results, as shown in FIG. 3 c. The glossy SEI image shows that the sample surface is less flat with a small number of pore structures, as in fig. 3 b.

(4) The thermal conductivity of the bulk material after SPS sintering was tested, resulting in a minimum thermal conductivity of 3.84W/mK for this sample, as shown in fig. 4.

Example 3

In this example, the method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material is the same as that in example 2 except for the change in quenching temperature, and the quenching temperature is increased to 1000 ℃.

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 much FeSb₂And Sb impurity phase, as shown in fig. 5 a. The impurity phase was reduced to a small extent compared to example 2. The BEI profile of the polished facets is consistent with the EDS spectrum results and XRD analysis results, as shown in FIG. 5 c. The glossy SEI image shows that the sample surface is relatively flat with a small number of pore structures, as shown in figure 5 b.

The thermal conductivity of the bulk material after SPS sintering was tested, resulting in a minimum thermal conductivity of 2.88W/mK for this sample, as shown in fig. 6.

Example 4

In this example, the method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material is the same as that in example 2 except for the change in the quenching temperature, and the quenching temperature is increased to 1100 ℃.

FIG. 7a is a photograph of the sample obtainedXRD pattern, the main phase of the sample is skutterudite phase and only contains less FeSb₂And an Sb impurity phase. The impurity phase is significantly reduced compared to the samples obtained in examples 2 and 3. Indicating that increasing the quench temperature can significantly reduce the formation of impurity phases. As can be seen from the SEI (fig. 7b) and BEI (fig. 7c) images at the smooth surface of the sample, the surface has a significant increase in the microporous structure, which helps scatter phonons and reduce thermal conductivity, compared to the sample of example 1.

The thermal conductivity of the bulk material after SPS sintering was tested and the lowest thermal conductivity of this sample was obtained to be 1.99W/mK, as shown in fig. 8, which is a substantial reduction in thermal conductivity compared to the samples of examples 2 and 3.

Example 5

In this example, the method for reducing the thermal conductivity of the p-type Ce-filled iron-based skutterudite thermoelectric material is the same as that in example 2 except for the change in quenching temperature, and the quenching temperature is increased to 1150 ℃.

FIG. 9a 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. 9b) and BEI (fig. 9c) images at the sample facets, the surface microporous structure is further increased compared to the sample of example 4. These added porous structures and the large number of micro-nano particles on the walls of the pores (fig. 9d) will help to scatter more phonons, further reducing the thermal conductivity.

The thermal conductivity of the bulk material after SPS sintering was tested and the lowest thermal conductivity for this sample was obtained was only about 1.88W/mK, as shown in fig. 10, which is a significant reduction in thermal conductivity compared to the samples of examples 2 and 3.

The invention shows that p-type Ce filled iron-based skutterudite Ce can be obviously reduced by selecting the optimal Ce filling fraction and properly increasing the quenching temperature_1.25Fe₄Sb₁₂Thermal conductivity of the thermoelectric material. The significant reduction in thermal conductivity benefits from the formation of a porous structure within the material and the significant reduction in impurity phases due to the increased quenching temperature. Lower thermal conductivity without deterioration of electrical properties would be advantageousA high performance thermoelectric material is obtained. Therefore, the selection of the proper Ce filling fraction and 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.