CN112582527A

CN112582527A - Preparation method of graphite-doped GeS2 thermoelectric material

Info

Publication number: CN112582527A
Application number: CN202011457393.0A
Authority: CN
Inventors: 宋吉明; 胡泽青
Original assignee: Anhui University
Current assignee: Anhui University
Priority date: 2020-12-13
Filing date: 2020-12-13
Publication date: 2021-03-30
Anticipated expiration: 2040-12-13
Also published as: CN112582527B

Abstract

The invention discloses a graphite-doped GeS₂A preparation method of thermoelectric material belongs to the technical field of energy conversion. Is prepared by adopting a solid-phase reaction method combined with a high-frequency furnace heating and hot-pressing sintering process and is prepared by GeS₂And graphite (abbreviated as G) as a raw material, formula G_xGeS₂Wherein x is graphite in GeS₂Is 0, and<x<0.5. firstly, weighing a proper amount of graphite and GeS according to a certain stoichiometric ratio₂Grinding fully and mixing uniformly, preparing into G by adopting a solid-phase reaction method_xGeS₂Precursor powder, then carrying out hot-pressing sintering on the precursor powder under proper pressure and temperature to obtain G_xGeS₂A bulk thermoelectric material. G prepared by the invention_xGeS₂The thermoelectric material has an electrical conductivity of 136034852S/m, and a thermal conductivity of 0.87-2.0W/mK. The preparation of G by adopting a solid-phase reaction method combined with high-frequency furnace heating and hot-pressing sintering_xGeS₂The thermoelectric material has the advantages of low sintering temperature, short preparation period, simple and convenient operation, low requirement on equipment and the like. The invention solves the problem of the existing GeS₂The thermoelectric material has a large resistivity.

Description

Preparation method of graphite-doped GeS2 thermoelectric material

Technical Field

The invention relates to a novel thermoelectric material, namely a preparation method of a graphite-doped GeS2 thermoelectric material, belonging to the field of energy conversion.

Background

The thermoelectric material is a material capable of realizing mutual conversion of heat energy and electric energyThe material can be used for thermoelectric refrigeration and thermoelectric power generation. At present, thermoelectric devices assembled by utilizing P-type and N-type semiconductor thermoelectric materials have the advantages of high stability, small volume, long service life, environmental protection and the like, so that the thermoelectric devices have wide application prospects in the fields of sensors, refrigeration, waste heat recycling, aerospace and the like. However, the performance of thermoelectric materials is usually measured by the thermoelectric figure of merit, ZT = S²Sigma T/K, wherein S is the Seebeck coefficient, sigma is the electric conductivity, T is the absolute temperature, and K is the thermal conductivity. The power factor of the material is PF = S²And sigma. Therefore, excellent thermoelectric materials require a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity at the same time.

Due to germanium disulfide (GeS)₂) Has unique optical and electrical properties and is therefore considered to be an excellent functional material. In the past 20 years, GeS₂The potential application in the fields of optical fibers, lithium ion batteries, waveguide materials and the like is widely explored. Considering GeS₂Is a semiconductor material with stable physical and chemical properties, and is GeS in the application₂As a matrix, by doping techniques, in GeS₂The medium doped Graphite (Graphite is abbreviated as G) improves the thermoelectric performance of the sample. Firstly, a solid-phase reaction method is adopted to prepare precursor powder (G) of thermoelectric material_xGeS₂) Then combining with the high-frequency furnace heating and hot-pressing sintering process to prepare the block G with high density_xGeS₂A thermoelectric material.

Heretofore, a precursor powder (G) of a thermoelectric material has been prepared by a solid-phase reaction method_xGeS₂) And the G with good crystallinity is prepared by combining the hot-pressing sintering process_xGeS₂Bulk thermoelectric materials have not been reported.

Disclosure of Invention

The invention relates to a graphite-doped GeS₂Method for producing thermoelectric material with GeS₂Doping graphite as raw material, and synthesizing G by solid-phase reaction_xGeS₂A precursor powder of a thermoelectric material, wherein 0<x<0.5, combining with the high-frequency furnace heating and hot-pressing sintering process to be 450-580^oC preparation of G_xGeS₂The block body improves the thermoelectric performance of the block body.

The invention is realized by the following technical scheme:

graphite-doped GeS₂The preparation method of the thermoelectric material is characterized in that GeS is used₂And graphite as a raw material, wherein the graphite is expanded graphite. According to the general formula G_xGeS₂Weighing appropriate amount of GeS according to the stoichiometric ratio₂And graphite, uniformly mixing the graphite and the graphite in an agate mortar, and fully grinding to obtain a ground mixed sample; then putting the graphite powder into an alumina crucible, putting the alumina crucible into a tubular furnace, vacuumizing the tubular furnace, and carrying out solid-phase reaction in a flowing weak reducing atmosphere to obtain graphite-doped germanium disulfide precursor powder; then the mixture is put into a graphite grinding tool, and G with good crystallinity and high purity is prepared by high-frequency furnace heating and hot-pressing sintering_xGeS₂A bulk thermoelectric material.

Further, the synthesis method comprises the following specific steps:

(1) solid-phase reaction: weighing appropriate amount of GeS according to stoichiometric ratio₂And expanded graphite, placing the two into an agate mortar, uniformly mixing and fully grinding to obtain a ground mixed sample; then uniformly mixing the two in an agate mortar, and fully grinding to obtain a ground mixed sample; then the mixture is put into an alumina crucible and put into a tube furnace for vacuum pumping, and solid phase reaction is carried out in flowing weak reducing atmosphere to obtain graphite doped germanium disulfide precursor powder, namely G_xGeS₂Thermoelectric material raw materials.

(2) The high-frequency furnace heating and hot-pressing sintering process comprises the following steps: g obtained in the step (1)_xGeS₂The precursor powder is put into a graphite grinding tool, sealed by a carbon rod from top to bottom and wrapped by carbon paper, and subjected to axial pressure of 35-65 MPa and axial pressure of 450-580 MPa^oC, hot pressing for 10-30 min in the environment to obtain G with high density and high purity_xGeS₂A bulk thermoelectric material.

(3) Further the conditions of the solid phase reaction are: 5 to 15 times of^oHeating to 500-600 ℃ at a rate of C/min^oC, preserving heat for 5-20 hours, and then cooling along with the furnaceAnd then cooled to room temperature. The diameter of the used quartz tube is 50 mm, the wall thickness is 2 mm, and the vacuum degree of the quartz tube is kept at minus 0.1 to minus 0.2 Pa in the vacuum pumping process.

(4) G obtained according to the above preparation method_xGeS₂The thermoelectric material has good crystallinity, high density and high purity, the electric conductivity is 1360-34852S/m, and the thermal conductivity is 0.87-2.0W/mK. The thermal conductivity of the material is measured by a Netzsch LFA-457 laser thermal conductivity instrument (Germany Chi resistant company); the conductivity of the material is obtained by measuring relevant parameters on a German LSR-3 Seebeck coefficient/resistance tester and calculating.

(5) The invention prepares G by combining a solid-phase reaction method with a high-frequency furnace heating and hot-pressing sintering process_xGeS₂Bulk thermoelectric materials have two distinct advantages: firstly, a new G is prepared by adopting a solid-phase reaction method at a lower temperature_xGeS₂The method for preparing the precursor thermoelectric material is simple to operate and has low requirements on experimental equipment. Secondly, G with excellent performance is prepared by high-frequency furnace heating and hot-pressing sintering process_xGeS₂A bulk thermoelectric material.

Description of the drawings:

FIG. 1 shows sample G_0.45GeS₂X-ray diffraction pattern (XRD) of the bulk;

FIG. 2 shows sample G_0.45GeS₂SEM picture of block after hot pressing sintering;

FIG. 3 is a graph of thermal conductivity data for examples 1, 2 and 3 of the present invention;

FIG. 4 is a graph of conductance data for examples 1, 2 and 3 of the present invention;

the specific implementation mode is as follows:

graphite-doped GeS₂The preparation method of the thermoelectric material specifically comprises the following steps:

(1) solid-phase reaction: weighing appropriate amount of GeS according to stoichiometric ratio₂And graphite, wherein the graphite is expanded graphite, and the expanded graphite and the graphite are uniformly mixed in an agate mortar and are fully ground to obtain a ground mixed sample; then placing the mixture into an alumina crucible, placing the alumina crucible into a tubular furnace, vacuumizing, and carrying out solid-phase reaction in a flowing weak reducing atmosphere to obtain the stonePrecursor powder of ink-doped germanium disulfide, i.e. G_xGeS₂Thermoelectric material raw materials.

(2) The high-frequency furnace heating and hot-pressing sintering process comprises the following steps: g obtained in the step (1)_xGeS₂Putting the powder into a graphite grinding tool, sealing the upper part and the lower part by using a carbon rod, wrapping the powder by using carbon paper, and performing axial pressure of 35-65 MPa and axial pressure of 450-580 MPa^oC, hot pressing for 10-30 min in the environment to obtain G with high density_xGeS₂A bulk thermoelectric material.

(3) The conditions of the solid phase reaction are as follows: 5 to 15 times of^oHeating to 500-600 ℃ at a rate of C/min^oC, preserving heat for 5-20 hours, and then cooling to room temperature along with the furnace; the diameter of the used quartz tube is 50 mm, the wall thickness is 2 mm, and the vacuum degree of the quartz tube is kept at minus 0.1 to minus 0.2 Pa in the vacuum pumping process.

Example 1

Graphite doped G with x = 0.1_xGeS₂The preparation of the heat conducting material comprises the following specific preparation processes:

(1) solid-phase reaction: x = 0.1, according to GeS₂2.31 g of GeS are weighed out in stoichiometric ratio to graphite₂And 0.23G of graphite G, and the two were uniformly mixed in an agate mortar and sufficiently ground to obtain a ground mixed sample. Then the mixture is put into an alumina crucible and put into a tube furnace for vacuum pumping, and solid phase reaction is carried out in flowing weak reducing atmosphere to obtain precursor powder G of graphite-doped germanium disulfide_0.1GeS₂Thermoelectric material raw materials.

(2) The high-frequency furnace heating and hot-pressing sintering process comprises the following steps: g obtained in the step (1)_0.1GeS₂Loading the powder into graphite grinding tool with inner diameter of 13 mm, sealing with carbon rod, wrapping with carbon paper, and applying axial pressure of 50 MPa and 530 deg.C^oHot pressing for 25 min in the environment of C, then cooling, releasing pressure, closing the hot pressing instrument, naturally cooling the sample to obtain G_0.1GeS₂A thermoelectric material.

Example 2

Graphite doped G with x = 0.25_xGeS₂The preparation of the heat conducting material comprises the following specific preparation processes:

(1) solid-phase reaction: x = 0.25, according to GeS₂2.31 g of GeS are weighed out in stoichiometric ratio to graphite₂And 0.57G of graphite G, and the two were uniformly mixed in an agate mortar and sufficiently ground to obtain a ground mixed sample. Then the mixture is put into an alumina crucible and put into a tube furnace for vacuum pumping, and solid phase reaction is carried out in flowing weak reducing atmosphere to obtain precursor powder G of graphite-doped germanium disulfide_0.25GeS₂Thermoelectric material raw materials.

(2) The high-frequency furnace heating and hot-pressing sintering process comprises the following steps: g obtained in the step (1)_0.25GeS₂Loading the powder into graphite grinding tool with inner diameter of 13 mm, sealing with carbon rod, wrapping with carbon paper, and applying axial pressure of 50 MPa and 530 deg.C^oHot pressing for 25 min in the environment of C, then cooling, releasing pressure, closing the hot pressing instrument, naturally cooling the sample to obtain G_0.25GeS₂A thermoelectric material.

Example 3

Graphite doped G with x = 0.45_xGeS₂The preparation of the heat conducting material comprises the following specific preparation processes:

(1) solid-phase reaction: x = 0.45, according to GeS₂2.31 g of GeS are weighed out in stoichiometric ratio to graphite₂And 1.04G of graphite G, and the two were uniformly mixed in an agate mortar and sufficiently ground to obtain a ground mixed sample. Then the mixture is put into an alumina crucible and put into a tube furnace for vacuum pumping, and solid phase reaction is carried out in flowing weak reducing atmosphere to obtain precursor powder G of graphite-doped germanium disulfide_0.45GeS₂Thermoelectric material raw materials.

(2) The high-frequency furnace heating and hot-pressing sintering process comprises the following steps: g obtained in the step (1)_0.45GeS₂The powder was loaded into a graphite grinding tool with an inner diameter of 13 mm, sealed with carbon rods up and down and wrapped with carbon paper. Axial pressure at 50 MPa, 530^oHot pressing for 25 min in the environment of C, then cooling, releasing pressure, closing the hot pressing instrument, naturally cooling the sample to obtain G_0.45GeS₂A thermoelectric material.

Example 4

The samples obtained in example 1, example 2 and example 3 were subjected to phase, thermal and electrical conductivity tests: the samples of example 1, example 2 and example 3 were cut into pieces by a diamond wire cutter of the type of Shenyang Coco STX-202A, and then subjected to characterization of thermoelectric properties. By aligning the hot pressed blocks G_0.45GeS₂The sample is tested, and the phase mainly existing in the sample is GeS according to the X-ray diffraction pattern (figure 1)₂(PDF # 27-0238) and a characteristic peak of graphite (PDF # 41-1487) is also present in the sample. FIG. 2 is G_0.45GeS₂SEM image of bulk thermoelectric material. As shown in FIG. 3, the sample doped with graphite has a gradually decreasing thermal conductivity with increasing temperature, and at 819K, sample G_0.1GeS₂The thermal conductivity of (A) was 0.76W/mK. As shown in FIG. 4, the conductivity of the sample doped with graphite gradually increased with the temperature, and at 819K, the sample G_0.45GeS₂Has an electrical conductivity of 34851S/m.

Claims

1. Graphite-doped GeS₂The preparation method of the thermoelectric material is characterized in that GeS is used₂And graphite as raw material, wherein the chemical formula of the thermoelectric material is G_xGeS₂Wherein 0 is<x<0.5, the graphite is expanded graphite, and the implementation steps are as follows:

(1) solid-phase reaction: weighing appropriate amount of GeS according to stoichiometric ratio₂And graphite, the two are uniformly mixed in an agate mortar and fully ground to obtain a ground mixed sample, then the mixed sample is put into an alumina crucible and put into a tubular furnace, the tubular furnace is vacuumized, and solid-phase reaction is carried out in a flowing weak reducing atmosphere to obtain precursor powder of graphite-doped germanium disulfide, namely G_xGeS₂Thermoelectric material raw materials;

(2) the high-frequency furnace heating and hot-pressing sintering process comprises the following steps: g obtained in the step (1)_xGeS₂Putting the powder into a graphite grinding tool, sealing the upper part and the lower part by using a carbon rod, wrapping the powder by using carbon paper, and performing axial pressure of 35-65 MPa and axial pressure of 450-580 MPa^oC environmentG with high density and high purity is obtained by medium-heat pressing for 10-30 min_xGeS₂A bulk thermoelectric material.

2. The graphite-doped GeS of claim 1₂The preparation method of the thermoelectric material is characterized in that the solid-phase reaction process comprises the following steps: 5 to 15 times of^oHeating to 500-600 ℃ at a rate of C/min^oC, preserving heat for 5-20 hours, and then cooling to room temperature along with the furnace; the diameter of the used quartz tube is 50 mm, the wall thickness is 2 mm, and the vacuum degree of the quartz tube is kept at minus 0.1 to minus 0.2 MPa in the vacuum pumping process.