METHOD OF PREPARING THERMOELECTRIC MATERIAL COMPRISING IRON-SULFUR COMPOUND

Abstract

A method of preparing a thermoelectric material comprising an iron-sulfur compound, the method including: 1) weighing, grinding, and mixing an iron salt and a sulfur-containing source to obtain a mixed powder; 2) carrying out a hydrothermal reaction with the mixed powder to obtain a black precipitate; 3) washing the precipitate; 4) drying the precipitate under vacuum to obtain FeS.sub.2 powder; 5) annealing the FeS.sub.2 powder under inert atmosphere to obtain annealed powder, where a heating temperature is from 300 C. to 1000 C., a heating time is from 2 hours to 24 hours, and a flow rate of an inert gas is from 30 mL/min to 200 mL/min; and 6) sintering the annealed powder to obtain a thermoelectric material including an iron-sulfur compound.

Claims

1. A method of preparing a thermoelectric material comprising an iron-sulfur compound, the method comprising: 1) weighing, grinding, and mixing an iron salt and a sulfur-containing source to obtain a mixed powder, wherein the sulfur-containing source is a mixture of sodium hyposulfite (Na.sub.2S.sub.2O.sub.3) and elemental sulfur; 2) carrying out a hydrothermal reaction with the mixed powder to obtain a black precipitate; 3) washing the precipitate; 4) drying the precipitate under vacuum to obtain FeS.sub.2 powder; 5) annealing the FeS.sub.2 powder under inert atmosphere to obtain annealed powder, wherein a heating temperature is from 300 C. to 1000 C., a heating time is from 2 hours to 24 hours, and a flow rate of an inert gas is from 30 mL/min to 200 mL/min; and 6) sintering the annealed powder to obtain a thermoelectric material comprising an iron-sulfur compound.

2. The method of claim 1, wherein in 1), the iron salt is ferrous sulfate.

3. The method of claim 1, wherein a reaction temperature is from 160 and 200 C., and a reaction time is from 18 to 30 h in 2).

4. The method of claim 1, wherein the black precipitate is washed by CS.sub.2, deionized water, and ethyl alcohol successively in 3).

5. The method of claim 1, wherein a drying temperature is from 50 to 100 C., and a drying time is from 4 to 10 h in 4).

6. The method of claim 1, wherein hot-pressing sintering or discharge plasma sintering is adopted in 6), a sintering temperature is from 430 to 700 C., a pressure is from 50 to 80 mPa, and a time is from 3 to 20 min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a preparation process diagram of a thermoelectric material comprising an iron-sulfur compound according to one embodiment of the disclosure.

[0021] FIG. 2 is an XRD spectra of FeS.sub.2 powder synthesized by the hydrothermal method; different symbols in the figure represent different phases of FeS.sub.2; the XRD spectra demonstrate that FeS.sub.2 has been synthesized successfully.

[0022] FIG. 3 is an XRD spectra of FeS.sub.2 powder annealed at different temperatures. Compounds with different phases and different molar ratios of Fe and S are obtained at different annealing temperatures (FeS.sub.2 annealed at 700 C. has also been studied but not presented here due to complex component).

[0023] FIG. 4 is temperature dependent electrical conductivity of the thermoelectric material in Example 2, compared with reference data from Christian Uhlig. The electrical conductivities in this invention reach up to 136 S/cm at room temperature and 240 S/cm at 600 K, which are respectively much higher than reported results of 3.1 S/cm (300 K) and 7.8 S/cm (600 K).

[0024] FIG. 5 is temperature dependent Seebeck coefficient of a thermoelectric material in Example 2, compared with reference data from Christian Uhlig.

[0025] FIG. 6 is temperature dependent power factor of a thermoelectric material in Example 2, compared with reference data from Christian Uhlig.

[0026] FIG. 7 is temperature dependent thermal conductivity of a thermoelectric material in Example 2, compared with reference data from Christian Uhlig. The sample synthesized by this invention possesses higher thermal conductivity, because of the weaker phonon scattering caused by larger particles.

[0027] FIG. 8 is temperature dependent ZT values of a thermoelectric material in Example 2, compared with reference data from Christian Uhlig. ZT value in this invention is higher than that of reported result from Christian Uhlig at room temperature.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] For further illustrating the invention, experiments detailing a method of preparing a thermoelectric material comprising an iron-sulfur compound are described below.

[0029] As shown in FIG. 1, this disclosure provides a method of preparing a thermoelectric material comprising an iron-sulfur compound, the method comprising: [0030] 1) weighing, grinding, and mixing an iron salt and a sulfur-containing source to obtain a mixed powder; [0031] 2) carrying out a hydrothermal reaction with the mixed powder to obtain a black precipitate, where the reaction temperature is from 160 and 200 C., and a reaction time is from 18 to 30 h; [0032] 3) washing the black precipitate using CS.sub.2, deionized water, and ethyl alcohol successively; [0033] 4) drying the precipitate under vacuum to obtain FeS.sub.2 powder, where the drying temperature is from 50 to 100 C., and the drying time is from 4 to 10 h; [0034] 5) annealing the FeS.sub.2 powder under inert atmosphere to obtain annealed powder, wherein a heating temperature is from 300 C. to 1000 C., a heating time is from 2 hours to 24 hours, and a flow rate of an inert gas is from 30 mL/min to 200 mL/min; and [0035] 6) sintering the annealed powder to obtain a thermoelectric material comprising an iron-sulfur compound; specifically, hot-pressing sintering or discharge plasma sintering is adopted, a sintering temperature is from 430 to 700 C., a pressure is from 50 to 80 mPa, and a time is from 3 to 20 min.

Example 1

[0036] Step 1: 7.6 g FeSO.sub.4, 7.9 g Na.sub.2S.sub.2O.sub.3 and 0.8 g S were weighed, and were ground sufficiently in a mortar.

[0037] Step 2: The mixture obtained in step 1 was dissolved in 50 mL deionized water and transferred into a reactor for hydrothermal reaction at 180 C. for 24 h.

[0038] Step 3: FeS.sub.2 precipitate was obtained by filtering after the hydrothermal reactor cooled to room temperature. Then the precipitate was washed with CS.sub.2, deionized water and ethyl alcohol several times.

[0039] Step 4: The precipitate obtained in step 3 was dried at 80 C. for 6 h under vacuum, and FeS.sub.2 powder were obtained.

[0040] Step 5: The powder obtained in step 4 were transferred into a graphite die and densified by discharge plasma sintering at 500 C. and under 72 mPa for 10 min, then iron sulfide bulk thermoelectric material were obtained.

Example 2

[0041] The powder was transferred into a tube furnace and heated to 500 C., 600 C., and 700 C. for 240 min respectively for annealing in step 5 of Example 1, and other operation steps are as same as that in Example 1.

[0042] Unless otherwise indicated, the numerical ranges involved in the invention include the end values. While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.