CN107814571B

CN107814571B - SnTe nano composite material and preparation method and application thereof

Info

Publication number: CN107814571B
Application number: CN201711059730.9A
Authority: CN
Inventors: 李洪涛; 郅惠博; 王彪; 赵永胜; 杨曼曼; 宿太超
Original assignee: Shanghai Customs Industrial Products And Raw Material Testing Technology Center
Current assignee: Shanghai Customs Industrial Products And Raw Material Testing Technology Center
Priority date: 2017-11-01
Filing date: 2017-11-01
Publication date: 2021-03-02
Anticipated expiration: 2037-11-01
Also published as: CN107814571A

Abstract

The invention provides a SnTe nano composite material and a preparation method thereof, wherein the preparation method comprises the following steps: 1) placing Ge powder, Sn powder and Te powder which are mixed according to a certain molar ratio into a closed container; 2) absolute ethyl alcohol is injected into the closed container, deoxidation and/or protection treatment is carried out, and then the closed container is fixed on a ball mill for ball milling; 3) drying the ball-milled product to obtain dry powder; 4) pressing the resulting dry powder into a block; 5) and (4) performing pressure sintering on the pressed block to obtain the compact SnTe nano composite material. The preparation method has the advantages of low cost, short preparation period, simple process, low synthesis temperature, energy conservation and suitability for large-scale industrial production, and the prepared block nano composite material has high density and low thermal conductivity.

Description

SnTe nano composite material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of new energy materials, and particularly relates to a SnTe nano composite material and a preparation method and application thereof.

Background

The thermoelectric material can realize the direct conversion of heat energy and electric energy, and a thermoelectric generator made of the thermoelectric material can effectively utilize heat sources such as industrial waste heat, automobile waste gas and the like to carry out thermoelectric generation. Because no mechanical moving part is arranged, the thermoelectric device has the advantages of portability, no pollution, no noise and the like. The existing thermoelectric material in the intermediate temperature region suitable for thermoelectric power generation is mainly a sulfur group lead compound represented by PbTe, but heavy metal Pb has great harm to the environment and human body.

The search for lead-free high-performance thermoelectric materials is an important direction in the field of thermoelectric research at present. Cheap and nontoxic Sn and Pb belong to the same group elements, and SnTe has the same structure with PbTe, so that SnTe is considered as an important candidate material for replacing PbTe. At present, the preparation method of the SnTe material is mainly a vacuum melting and mechanical alloying method, and the SnTe material can be obtained only by long-time high-temperature heating or mechanical ball milling, so the samples prepared by the two methods have the defects of long preparation period, high cost and the like. Furthermore, the higher intrinsic thermal conductivity of SnTe affects its properties and its further applications.

Disclosure of Invention

In order to solve the defects in the prior art, the invention provides a novel SnTe nano composite material (Ge-Sn-Te or Ag-Sb-Sn-Te nano composite material) containing Ge, Ag or Sb and a preparation method thereof.

The invention provides a preparation method of a SnTe nano composite material, which comprises the following steps:

step 1), batching: putting raw materials into a closed container (such as a ball milling tank), wherein the raw materials comprise Ge powder, Sn powder and Te powder which are mixed according to a certain molar ratio, or Ag powder, Sb powder, Sn powder and Te powder;

step 2) wet ball milling: injecting an organic solvent into the closed container, performing deoxidation and/or protection treatment, fixing the treated closed container on a ball mill, performing ball milling at a certain rotating speed for a preset time;

step 3) drying: drying the product obtained after the wet ball milling in the step 2) to obtain dry powder;

step 4), pressing: grinding the dry powder obtained in the step 3), and pressing the ground powder into a block;

step 5), sintering: carrying out pressure sintering on the block pressed in the step 4) to obtain a compact Ge-Sn-Te or Ag-Sb-Sn-Te nano composite material; the method specifically comprises the following steps: applying a preset pressure to the block sample and heating to a first preset temperature to perform first-stage sintering; after the sintering is finished, quickly cooling to a second preset temperature, and performing second-stage sintering; and after the reaction is finished, quickly cooling to room temperature and releasing the pressure to obtain the Ge-Sn-Te or Ag-Sb-Sn-Te nano composite material.

Wherein, in the step 1), when the raw materials are Ge powder, Sn powder and Te powder, the molar ratio of the elements of the Ge powder, the Sn powder and the Te powder is (0.05-0.4): 0.6-0.95): 1; preferably, 0.1:0.9: 1; when the raw materials are Ag powder, Sb powder, Sn powder and Te powder, the molar ratio of the Ag powder, the Sb powder, the Sn powder and the Te powder is (0.05-0.25): (0.05-0.25): 0.5-0.9): 1; preferably, it is 0.08:0.08:0.84: 1.

Wherein, the finally prepared Ge-Sn-Te or Ag-Sb-Sn-Te nano composite material has lower thermal conductivity.

Wherein, in the step 1), the mass ratio of the ball material (the mass ratio of the grinding ball to the raw material) is (5-20) to 1; preferably 15:1, 20: 1.

In the step 1), the purity of Sn, Te, Ge, Ag and Sb powder serving as raw materials is higher than 99.9%.

Wherein in the step 2), the volume ratio of the raw materials to the absolute ethyl alcohol is 1 (1-3); preferably, it is 1: 2.

Wherein, in the step 2), the organic solvent includes but is not limited to one or more of absolute ethyl alcohol, acetone and diethyl ether; preferably, it is absolute ethanol.

Wherein, in the step 2), the deoxidation and/or protection treatment step comprises the following steps: and vacuumizing the ball milling tank, introducing high-purity inert gas, and repeatedly vacuumizing and introducing the high-purity inert gas for several times. Preferably, the inert gas is introduced along with the deoxidation and/or protection treatmentThe wall of the ball milling tank is injected into the ball milling tank from the upper part of the ball milling tank. Wherein the inert gas is selected from Ar, He and N₂And the like, preferably Ar gas.

Wherein, in the step 2), the predetermined rotation speed may be, but is not limited to, 200-; preferably 250 rpm and 300 rpm.

Wherein, in the step 2), the preset time is 30-500 minutes; preferably, 120-; further preferably 200 minutes.

Wherein, in the step 3), the drying treatment can adopt any common drying method, including but not limited to, placing the product after the wet grinding in the step 2) into a vacuum drying oven, and the vacuum degree is 10-200Pa, preferably 50 Pa; vacuum drying for 3-10 hours, preferably 4-8 hours, and more preferably 6 hours; the drying temperature is 50 to 70 ℃, preferably 50 to 60 ℃ or 60 to 70 ℃, and more preferably 60 ℃.

Wherein, in the step 4), the pressing can be performed by any common pressing method, including but not limited to hydraulic pressure.

Wherein in the step 5), the predetermined pressure is 2-5 GPa; preferably 4 GPa.

In the step 5), the heating rate of heating to the first preset temperature is 200-400 ℃/min; preferably 300 deg.c/min.

Wherein in the step 5), the first preset temperature is 850-1050 ℃; preferably, it is 1000 ℃.

Wherein, in the step 5), the sintering time of the first stage is 3-40 minutes; preferably, it is 10 to 15 minutes.

In the step 5), after the sintering in the first stage is finished, cooling at the speed of 50-200 ℃/second; preferably 60 deg.C/sec, 100 deg.C/sec or 200 deg.C/sec.

Wherein, in the step 5), the second predetermined temperature is 700-; preferably 750 deg.c.

Wherein, in the step 5), the second-stage sintering time is 5-20 minutes; preferably, it is 10 to 15 minutes.

In the step 5), after the second-stage sintering is finished, cooling at a speed of 100-200 ℃/min; preferably 100 deg.C/min and 200 deg.C/min.

In one embodiment, the step 5) comprises: and applying a preset pressure to the block sample, adding the block sample to a first preset temperature, sintering for 10-15 minutes, then cooling at a speed of 60 ℃/second to quickly cool to a second preset temperature, sintering for 10-15 minutes again, cooling at a speed of 200 ℃/minute to quickly cool to room temperature and releasing pressure to obtain the Ge-Sn-Te or Ag-Sb-Sn-Te nanocomposite.

In step 5) of the method, the heating process in the sintering process for preparing the nano composite material is extremely important, the first preset temperature heating process for the Ge-containing sample is that Ge, Sn and Te are completely in a molten state, and the second preset temperature is Ge-Te rich in Ge (Ge-Te refers to GeTe and GeTe₄) Crystallizing and solidifying, wherein Sn-Te (Sn-Te refers to SnTe) is still in a molten state process, and the process from the first preset temperature to the second preset temperature needs high-speed temperature reduction to promote Ge-Te to be separated out from liquid containing three elements and keep the nanometer scale; the sintering time of the second stage needs to be controlled within 20 minutes, so that the solid solution alloy is prevented from being easily formed after too long time. The first predetermined temperature heating process for the Ag and Sb-containing samples was for the Ag, Sb, Sn and Te to be completely molten, the second predetermined temperature was for the Sn-rich Sn-Te (Sn-Te means SnTe phase) to crystallize and solidify, and for the Ag and Sb-rich Ag-Sb-Te₂(Ag-Sb-Te₂Refers to AgSbTe₂) While still in the molten state, the first to second predetermined temperatures₂Crystallized into nano-scale and enriched at Sn-Te crystal boundary; the sintering time of the second stage still needs to be controlled within 20 minutes, and the solid solution alloy is prevented from being easily formed after the sintering time is too long.

The method adopts a two-stage heating process, namely: firstly heating to a temperature above the melting point of the raw materials to ensure that all elements are fully melted, and then cooling to a matrix phase (SnTe phase) and a nano second phase compound (Ge-Te phase or AgSbTe phase)₂) So that one material solidifies out first and the other remains in the molten state. And finally, cooling to prepare the nano composite material.

The invention also provides the SnTe nano composite material prepared by the preparation method.

The invention also provides a SnTe nano composite material, which mainly comprises a Sn-Te phase with a face-centered cubic structure and crystal grains of 2-10 micron scale and a Ge-Te phase or Ag-Sb-Te phase with the crystal grains of nano scale, namely, the product Ge-Sn-Te or Ag-Sb-Sn-Te nano composite material prepared by the invention is a composite material containing a nano second phase, and the nano composite material has very low thermal conductivity of 1.25-2W/mK.

The invention also provides the application of the Ge-Sn-Te or Ag-Sb-Sn-Te nano composite material in the field of thermoelectric generation.

The invention has the beneficial effects that a, the cost of the raw materials is low, the tin powder is mainly adopted to replace the lead raw material, the source is rich, the environment is not harmful, and the price is low. b. The preparation material period is short and the process is simple. The invention has the advantages of simple process, rapid material synthesis, low temperature, energy saving and suitability for large-scale industrial production. c. The prepared SnTe block nano composite material has high density and low thermal conductivity (1.25-2W/mK).

Additional advantages, objects, and features of the invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Drawings

FIG. 1 is an X-ray diffraction pattern (XRD) of Ge-Sn-Te nanocomposites prepared in examples 1-4.

FIG. 2 shows Ge-Sn-Te (containing Ge 10% and having a specific composition of Ge) prepared in example 1_0.1Sn_0.9Te) electron Scanning Electron Micrographs (SEM) and electron energy spectra of the nanocomposite. A is an SEM atlas of a sample, and the micro appearance of the sample mainly comprises micron-scale grains and a large number of nano grains which are dispersed and distributed; and B, the electron energy spectrum analysis is carried out on micron crystal grains and nanometer crystal grains, wherein the micron crystal grains mainly comprise Sn and Te elements, and the nanometer crystal grains contain three elements of Ge, Sn and Te.

FIG. 3 is a graph comparing thermal conductivities of Ge-Sn-Te nanocomposites prepared with different Ge contents in examples 1-4.

FIG. 4 is an XRD of Ag-Sb-Sn-Te nanocomposites prepared in example 9 with different contents of Ag and Sb.

FIG. 5 shows Ag-Sb-Sn-Te (containing 10% of each of Ag and Sb, and having a specific composition of Ag) prepared in example 9_0.1Sb_0.1Sn_0.8Te) electron Scanning Electron Micrographs (SEM) and electron energy spectra of the nanocomposite. A is an SEM image of a sample, and the micro appearance of the sample is mainly seen to comprise micron-scale grains and nano grains distributed at grain boundaries; the B diagram is an electron spectrum analysis of the white line portion region in the A diagram, and it can be observed that the Sn content is small and the Ag and Sb contents are high at the grain boundary.

Detailed Description

The present invention will be described in further detail with reference to the following specific examples and the accompanying drawings. The procedures, conditions, experimental methods and the like for carrying out the present invention are general knowledge and common general knowledge in the art except for the contents specifically mentioned below, and the present invention is not particularly limited.

Examples 1 to 4

In this embodiment, the process of fabricating the thermoelectric material of the present invention is described in detail, taking the process of fabricating Ge-Sn-Te as an example, and the fabrication process includes the following steps: 1) a step of burdening; 2) a wet ball milling step; 3) a drying step; 4) a pressing step; 5) and (5) sintering.

The above-described five steps will be described in detail below, respectively.

1) Step of compounding

Ge powder, Sn powder and Te powder are taken as main raw materials, and the Ge powder, the Sn powder and the Te powder are mixed according to a certain molar ratio and are placed in a stainless steel ball milling tank. The molar ratio of Ge powder, Sn powder and Te powder is (0.05-0.4): 0.6-0.95): 1. In this example, experiments were performed using different molar ratios of Ge powder, Sn powder, and Te powder, respectively, and various properties of the obtained product were tested, with the results shown in fig. 1 to 4.

In the embodiment, high-purity Ge powder (with the purity of 99.999%), Sn powder (with the purity of 99.9%) and Te powder (with the purity of 99.9%) are adopted as raw materials; according to Ge_xSn_1-xTe stoichiometry is compared with the raw materialsThe total weight is 20g, wherein x is 0-0.5(x is the molar content of Ge relative to the molar content of Te, and the sum of Ge and Sn is 1), preferably 0.1. The ball to feed ratio was set at 15: 1.

2) Wet ball milling

Anhydrous ethanol is injected into the ball mill pot and the feedstock is typically deoxygenated and/or protected prior to mixing with the feedstock added to the ball mill pot. The deoxidation and/or protection treatment comprises vacuumizing the ball milling tank, introducing high-purity Ar gas, and repeating the operations of vacuumizing and introducing high-purity Ar for a plurality of times, such as 3-5 times, so as to ensure that oxygen in the ball milling tank is exhausted.

After deoxidation and/or protection treatment, the ball milling tank is fixed on a ball mill, and wet ball milling is carried out at a preset rotation speed of 250 rpm for 200 minutes at a preset time.

3) Drying

After wet grinding, collecting a sample in a ball milling tank, then placing a product after the wet grinding in a vacuum drying oven for drying treatment, and volatilizing all absolute ethyl alcohol to obtain dry powder; wherein, the vacuum condition is as follows: the vacuum degree is 50 Pa; vacuum drying is carried out for 6 hours at a drying temperature of 60 ℃.

4) Pressing

The resulting dry powder was placed in a mold and pressed into a block using a tablet press.

5) Sintering

And finally, performing pressure sintering on the pressed block to obtain the compact Ge-Sn-Te nano composite material. And applying a preset pressure of 4GPa on the block sample, heating the block sample to 1000 ℃ at a heating rate of 300 ℃/min, cooling the block sample at a speed of 60 ℃/sec after 10 minutes of first sintering time, quickly cooling the block sample to 750 ℃ at a second preset temperature, cooling the block sample at a speed of 100 ℃/min for 15 minutes, quickly cooling the block sample to room temperature, and releasing the pressure to obtain the Ge-Sn-Te nano composite material.

The heating process in the preparation process of the Ge-Sn-Te nano composite material is extremely important, the first preset temperature heating process is that Ge, Sn and Te are completely in a molten state, the second preset temperature is that Sn-Te crystal rich in Sn is solidified and Ge-Te is still in the molten state, and the process from the first preset temperature to the second preset temperature needs high-speed temperature reduction to promote Ge-Te to be separated out from molten liquid Ge-Sn-Te and keep the nano scale. The sintering time of the second stage needs to be controlled within 20 minutes, so that the solid solution alloy is prevented from being easily formed after too long time.

According to the method, the Ge-Sn-Te nano composite material with the Ge mole percent of 0%, 10%, 20% and 30% is respectively prepared.

FIGS. 1 and 2 are the X-ray diffraction patterns of the four Ge-Sn-Te nanocomposites prepared in example 1 and the SEM images of the nanocomposites with a Ge mole percentage of 10%, respectively. The XRD spectrum of figure 1 shows that Ge-Te phase appears in the sample after Ge is doped, and the SEM result of figure 2 shows that the sample has higher density and a large amount of nano-crystalline grains are dispersedly distributed on the grain boundary and crystal face of SnTe phase with 2-5 microns magnitude; the energy spectrum analysis in figure 2 and the XRD spectrum in figure 1 show that the nanophase of the Ge-Sn-Te nano composite material obtained by the invention is the Ge-Te phase, namely the material obtained by the invention belongs to a micro-nano composite material.

In order to verify the performance difference of the obtained four Ge-Sn-Te nano composite materials, the obtained Ge-Sn-Te nano composite materials are cut and polished, the thermal diffusion coefficient of the Ge-Sn-Te nano composite materials is tested by using LFA-457, and then the thermal conductivity is calculated, and the numerical value of the thermal conductivity is shown in figure 3; in the legend of fig. 3, 0, 0.1, 0.2, and 0.3 represent 0%, 10%, 20%, and 30% mole percent of Ge in the Ge — Sn — Te nanocomposite, respectively. As can be seen from FIG. 3, the average thermal conductivity of Ge-Sn-Te nanocomposites containing Ge is much lower than that of Sn-Te phase (i.e. Ge-Sn-Te nanocomposites containing 0% Ge by mole percentage) in the temperature range of 300K to 700K, mainly due to the decrease of lattice thermal conductivity caused by scattering medium-short wave phonons as the nanophase of Ge-rich Ge-Sn-Te nanocomposites precipitates on the crystal surface and grain boundaries; the thermal conductivity of the nano composite material containing 10% of Ge in a test temperature range (300K-700K) is smaller than that of Sn-Te containing no Ge, the thermal conductivity of the nano composite material further increasing the Ge content is increased under a high temperature condition, and the structure of the nano composite material is damaged mainly because a sample tends to be amorphous due to the increase of the Ge content.

Examples 5 to 8

According to SnTe and Ge_0.1Sn_0.9Te (molar contents of Ge and Sn relative to that of Te were 10% and 90%, respectively) samples were prepared at different sintering pressures, and the sintering pressures in step 5 were set to 2GPa, 3GPa, 4GPa, and 5GPa, respectively, and the other steps were the same as in example 1.

The thermal conductivity of the nano composite material obtained by the experiment under the room temperature condition is shown in table 1, the thermal conductivity of the nano composite material is gradually reduced along with the increase of the sintering pressure in the range of 2-4GPa, the reduction of the thermal conductivity in the range of 2-4GPa is mainly caused by lattice distortion due to high pressure, and further defects such as dislocation and the like are introduced, and the existence of a large number of defects can cause phonon scattering to reduce the thermal conductivity. Further increase of the sintering pressure after 4GPa has no effect on the thermal conductivity value, which indicates that the defect concentration of the sample after 4GPa reaches the limit, i.e. 4GPa is the optimum sintering pressure.

TABLE 1 thermal conductivity of samples obtained under different sintering pressure conditions

Examples	Sintering pressure (GPa)	Thermal conductivity (Wm) of SnTe^-1K^-1)	Ge_0.1Sn_0.9Thermal conductivity (Wm) of Te^-1K^-1)
				5	2	6.452	2.657
6	3	6.299	2.575
				7	4	6.167	2.531
8	5	6.168	2.531

Example 9

Ag and Sb are used for replacing Ge to prepare the Ag-Sb-Sn-Te composite material, and the element proportion is (AgSb)_xSn_1-2xTe, the sintering conditions in the step 5 are as follows: the first predetermined temperature is 1000 deg.C, the second predetermined temperature is 700 deg.C, and other steps are the same as example 1.

FIG. 4 is an X-ray diffraction pattern of the Ag-Sb-Sn-Te nanocomposite material prepared in example 9, and it can be seen that the sample contains SnTe and AgSbTe2 phases. The scanning electron micrograph of figure 5 shows that the sample contains both micron-sized grains and small nano-sized grains, and the energy spectrum analysis of figure 5 shows that the micron phase is a Sn-rich phase and the grain boundary-derived nano-size is an AgSb-rich phase, and the XRD pattern combined with figure 4 shows that the micron phase is SnTe and the nano-phase is AgSbTe 2.

Table 2 shows the results of thermal conductivity measurements of Ag-Sb-Sn-Te nanocomposites prepared in example 9 at room temperature, since a large amount of AgSbTe2 is concentrated at the grain boundary, which constitutes strong scattering for phonons, resulting in a significant decrease in the thermal conductivity of SnTe, where the thermal conductivity of the sample is the smallest at an AgSb content of 0.125.

TABLE 2 thermal conductivity of samples of different AgSb content

Content of AgSb, x	Thermal conductivity (Wm)^-1K^-1)
		0	6.167
0.1	3.234
		0.125	2.675
0.16	2.847

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and other modifications or equivalent substitutions made by the technical solutions of the present invention by those of ordinary skill in the art should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. The preparation method of the SnTe nano composite material is characterized by comprising the following steps:

step 1) placing raw materials into a closed container, wherein the raw materials comprise Ge powder, Sn powder and Te powder which are mixed according to a certain molar ratio, or Ag powder, Sb powder, Sn powder and Te powder;

step 2) injecting an organic solvent into the closed container, performing deoxidation and/or protection treatment, and then performing ball milling; the rotation speed of the ball milling is 200-350 r/m; the ball milling time is 30-500 minutes;

step 3) drying the product after ball milling to obtain dry powder;

step 4) grinding the obtained dry powder, and pressing the ground powder into a block;

step 5) carrying out pressure sintering on the pressed block to obtain a Ge-Sn-Te or Ag-Sb-Sn-Te nano composite material; the method specifically comprises the following steps: applying a preset pressure to the block sample and heating to a first preset temperature to perform first-stage sintering; after the sintering is finished, quickly cooling to a second preset temperature, and performing second-stage sintering; after the reaction is finished, rapidly cooling to room temperature and releasing the pressure to obtain the Ge-Sn-Te or Ag-Sb-Sn-Te nano composite material;

wherein the predetermined pressure is 2-4 GPa;

the first preset temperature is 850-1050 ℃, and the sintering time of the first stage is 3-40 minutes;

the second preset temperature is 700-800 ℃, and the second-stage sintering time is 5-20 minutes.

2. The method of claim 1, wherein in step 1), when the raw materials are Ge powder, Sn powder and Te powder, the molar ratio of the Ge powder, Sn powder and Te powder is (0.05-0.4): 1 (0.6-0.95); when the raw materials are Ag powder, Sb powder, Sn powder and Te powder, the mol ratio of the Ag powder, the Sb powder, the Sn powder and the Te powder is (0.05-0.25): (0.05-0.25):(0.5-0.9):1.

3. The method according to claim 1, wherein in the step 1), the mass ratio of the ball materials is (5-20): 1; and/or the volume ratio of the raw material to the absolute ethyl alcohol is 1 (1-3).

4. The method of claim 1, wherein in step 2), the organic solvent comprises one or more of absolute ethyl alcohol, acetone and diethyl ether.

5. The method according to claim 1, wherein in the step 3), the drying treatment is to place the product after the wet grinding in the step 2) in a vacuum drying oven with the vacuum degree of 10-200 Pa; vacuum drying for 3-10 hr; the drying temperature is 50-70 ℃.

6. The method according to claim 1, wherein in step 5), the heating rate of the heating to the first predetermined temperature is 200 to 400 ℃/min; after the sintering of the first stage is finished, cooling at the speed of 50-200 ℃/second; and after the second-stage sintering is finished, cooling at the speed of 100-200 ℃/min.

7. A Ge-Sn-Te or Ag-Sb-Sn-Te nanocomposite material prepared by the method according to any one of claims 1 to 6.

8. Use of the nanocomposite material of claim 7 in the field of thermoelectric power generation.