KR101104677B1 - A Method for fabricating thermoelectric material by mechano-chemical process - Google Patents

Abstract

Method for producing a thermoelectric material by the mechanical-chemical reaction according to an embodiment of the present invention, the method for producing a thermoelectric material by the mechanical-chemical reaction according to the present invention for achieving the above object, copper (Cu) extraction from the ore At least one of HNO ₃ and H ₂ SO ₄ in the material preparation step of preparing an aqueous solution containing tellurium as a by-product generated during the production process, an impurity removing step of removing impurities contained in the aqueous solution, and the aqueous solution from which the impurities are removed Neutralization step of neutralizing the aqueous solution by adding, Tellurium oxide extraction step of extracting the tellurium oxide powder formed by reacting in the neutralized aqueous solution, and mixing the tellurium oxide powder and bismuth salt by mechanical milling process to prepare a mixed powder A mechanical mixing step, an oxidation heat treatment step of manufacturing a Bi-Te-based composite oxide by heat-treating the mixed powder in an oxidizing atmosphere, and the Bi-Te-based composite A mechanical grinding step of controlling the powder size of the oxide using a mechanical milling process, and a reduction heat treatment step of forming a thermoelectric material by reducing heat treatment of the pulverized Bi-Te based composite oxide. According to the present invention configured as described above, it is possible to manufacture the thermoelectric material by recycling the by-products generated during the ore smelting can reduce the manufacturing cost, there is an advantage to maximize the resource recycling rate.

Description

A method for fabricating thermoelectric material by mechano-chemical process

The present invention extracts tellurium oxide (TeO ₂ ) from the tellurium-sodium hydroxide (NaOH) solution generated as a by-product during copper (Cu) extraction from the ore, and the oxidation and calcination after bismuth salt and mechanical milling Bi oxide The present invention relates to a method of manufacturing a thermoelectric material by a mechanical-chemical reaction, which enables the production of a thermoelectric material (Bi ₂ Te ₃ ) made of bismuth and tellurium by reducing heat treatment after preparing a composite oxide made of a Te oxide.

A thermoelectric material is an energy conversion material in which electrical energy is generated when a temperature difference is applied between both ends of a material, and conversely, a temperature difference is generated between both ends of a material when an electric energy is applied to a material.

After the discovery of thermoelectric phenomena such as Seebeck effect, Peltier effect, and Thomson effect in the early 19th century, thermoelectric materials have been developed in the late 1930s. It is developed as a material and recently used as a special power supply device for mountain wallpaper, space, military, etc. using thermoelectric power generation, and precise temperature control or computer-related small cooler in semiconductor laser diode, infrared detection device using thermoelectric cooling, It is used for optical communication laser chiller, chiller and water cooler, semiconductor temperature control device, heat exchanger and so on.

Bismuth Telluride (Bi ₂ Te ₃ ), the core material of the most promising thermoelectric material, is bismuth (Bi) and tellurium (Te). Of the two metal elements, tellurium (Te) is imported at a price comparable to that of platinum due to its low reserves in the world, especially in developed countries, and high raw material prices.

In addition, conventional thermoelectric materials were manufactured by melting and pulverizing ingots of Bi and Te, which are raw materials, into powders, and then sintering them again. Therefore, the manufacturing process is complicated, and the problem of incorporation of impurities during melting and grinding of the ingot manufactured and manufactured. Difficult particle size control problems remain a challenge.

However, the extraction of the thermal power material directly from the ore stage and manufacturing it into the desired thermal powder material may solve the above problems, and the use of salt powders, which are inexpensive even when mixing the raw materials and the purity of the raw materials, increases during processing. By finally manufacturing in the state of alloy powder consisting of only Bi and Te, it is possible to simplify the manufacturing process and reduce the cost of raw material costs.

An object of the present invention is to solve the conventional problems, more specifically, to extract the tellurium contained in the sodium hydroxide (NaOH) solution which is a by-product generated when extracting copper (Cu) from the ore in the form of oxide, The present invention provides a method of manufacturing a thermoelectric material by a mechanical-chemical reaction, in which a composite oxide is prepared by a mechanical milling process with a bismuth salt, followed by reduction, thereby producing a thermoelectric material consisting of bismuth and tellurium. .

Method for producing a thermoelectric material by the mechanical-chemical reaction according to the present invention for achieving the above object, the material preparation step of preparing an aqueous solution containing tellurium which is a by-product generated during copper (Cu) extraction from the ore, An impurity removal step of removing impurities contained in the aqueous solution, a neutralization step of neutralizing the aqueous solution by adding one or more of HNO ₃ and H ₂ SO ₄ to the aqueous solution from which the impurities are removed, and tellurium formed by reacting in the neutralized aqueous solution The tellurium oxide extraction step of extracting the oxide powder, the mechanical mixing step of preparing a mixed powder by mixing the tellurium oxide powder and bismuth salt in a mechanical milling process, and heat treatment the mixed powder in an oxidizing atmosphere to Bi-Te system Oxidation heat treatment step of producing a composite oxide, and mechanically controlling the powder size of the Bi-Te-based composite oxide using a mechanical milling process By reducing the heat treatment step with the chain, the pulverized Bi-Te based composite oxide comprises a reducing heat treatment to form a thermoelectric material.

The impurity removing step may be a process of removing impurities including Cu and Fe contained in the aqueous solution by adding NaSH.

The neutralization step is characterized in that to remove the NaOH contained in the aqueous solution to form tellurium oxide.

In the tellurium oxide extracting step, a surfactant which is either SDS or SDBS is added to control the size of the tellurium oxide powder.

In the mechanical mixing step, the tellurium oxide powder is TeO ₂ , the bismuth salt is one or more of bismuth nitride, bismuth chloride, bismuth sulfide is applied, tellurium and bismuth is characterized in that mixed in a molar ratio of 3: 2. .

The oxidizing heat treatment step, a sulfate (SO ₄₎ contained in the bismuth salts ^- is characterized in that the process of removing ^-, nitrate (NO ₃₎ ^-, chlorine salt (Cl).

The oxidation heat treatment step is characterized in that the bismuth salt is made of bismuth oxide and complexed with tellurium oxide.

The oxidation heat treatment step is characterized in that carried out at a temperature of 350 ℃ in the oxygen atmosphere.

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The reduction heat treatment step is characterized in that the process to minimize the volatilization of tellurium by heating at a temperature of less than 350 ℃ in a hydrogen atmosphere.

The thermoelectric material prepared in the reduction heat treatment step is characterized in that the powder form having a Bi ₂ Te ₃ phase.

As described above, in the present invention, by extracting tellurium oxide contained in the sodium hydroxide (NaOH) solution, which is a by-product generated when extracting copper (Cu) from the ore, and mixed with and reacted with bismuth salt to binary or ternary thermoelectric It was possible to prepare a powder.

Therefore, it is possible to manufacture the thermal starch powder by recycling the by-products containing tellurium generated during the ore smelting without disposing, thus reducing the manufacturing cost compared to the method of purchasing the existing ingot and remelting and crushing in multiple stages. There is an advantage to maximize the recycling rate.

1 is a process flowchart showing a method of manufacturing a thermoelectric material by a mechanical-chemical reaction according to the present invention.
Figure 2a is a SEM photograph showing the tellurium oxide powder prepared after the neutralization step of the present invention.
Figure 2b is a table showing the elemental component analysis of the tellurium oxide powder prepared after the neutralization step of the present invention.
Figure 2c is an XRD graph showing the phase analysis of the tellurium oxide powder prepared after the neutralization step of the present invention.
FIG. 2d is a SEM photograph showing tellurium oxide powder having a particle size of 50 nm controlled by an SDS surfactant added during the neutralization step of the present invention.
Figure 3a is a SEM photograph showing the thermoelectric powder prepared after the oxidation heat treatment and milling in accordance with the thermoelectric material manufacturing method according to an embodiment of the present invention
Figure 3b is an XRD graph showing the results of the phase analysis of the thermoelectric powder prepared after the oxidation heat treatment and milling in accordance with the thermoelectric material manufacturing method according to an embodiment of the present invention
Figure 4a is a SEM photograph showing the thermoelectric powder prepared after the reduction heat treatment according to the thermoelectric material manufacturing method according to an embodiment of the present invention
Figure 4b is an XRD graph showing the phase analysis results of the thermoelectric powder prepared after the reduction heat treatment according to the thermoelectric material manufacturing method according to an embodiment of the present invention

Hereinafter, a method of manufacturing a thermoelectric material according to the present invention will be described with reference to FIG. 1.

1 is a process flowchart showing a method of manufacturing a thermoelectric material by a mechanical-chemical reaction according to the present invention.

Referring to the method of manufacturing a thermoelectric material by a mechanical-chemical reaction according to a preferred embodiment of the present invention, tellurium oxide is extracted from an aqueous solution which is a by-product generated in the process of extracting a copper source ore from the ore collected from the mine, The extracted tellurium oxide is mixed with a bismuth salt, followed by oxidative heat treatment, pulverization and reduction heat treatment in order to obtain Bi ₂ Te ₃ as a thermoelectric material.

To this end, the thermoelectric material is a material preparation step (S100) of preparing an aqueous solution containing tellurium, which is a by-product generated when copper (Cu) is extracted from ore, and metal impurities such as copper or iron by adding NaSH to the aqueous solution. Impurity removal step (S200) to precipitate, neutralization step (S300) to neutralize the aqueous solution by adding one or more of HNO ₃ and H ₂ SO ₄ to the aqueous solution from which impurities are removed, and a reducing agent and a surfactant in the neutralized aqueous solution Tellurium oxide extraction step (S400) for extracting tellurium oxide powder by adding, the mechanical mixing step (S500) and mixing the tellurium oxide powder and bismuth salts in a mechanical milling process to prepare a mixed powder, and the mixed powder Oxidation heat treatment step (S500) of producing a Bi-Te-based composite oxide by heat-treating it in an oxidizing atmosphere, and controlling the powder size of the Bi-Te-based composite oxide using a mechanical milling process. Ever and the milling step (S600), a reducing heat treatment to the pulverized Bi-Te based composite oxide is produced via the reduction heat treatment step (S700) of forming a thermoelectric material.

In the aqueous solution preparation step (S100), the aqueous solution of NaOH is contained in the aqueous solution, and copper (Cu), iron (Fe), and tellurium (Te) are also dissolved together.

The aqueous solution containing tellurium and NaOH is prepared through the impurity removal step (S200) to produce a NaOH solution containing only tellurium.

The impurity removal step (S200) is a process for precipitating copper, iron, tellurium, and the like, which are metals contained in the aqueous solution, and is possible by adding NaSH to the aqueous solution.

In more detail, the impurity removal step (S200) is to dissolve NaSH in the aqueous solution to extract the iron and copper easy to form sulfide in the form of sulfide to precipitate in the solution. At this time, the precipitate is precipitated with trace elements such as copper and iron remaining in the ore solution. The precipitate is filtered, and only NaOH and tellurium are dissolved in the solution from which the precipitate is removed.

Thereafter, a neutralization step (S300) is performed in which nitric acid (HNO ₃ ) or sulfuric acid (H ₂ SO ₄ ) is added to extract only tellurium from the solution of NaOH containing only tellurium.

In the neutralization step (S200), TeO ₂ may be precipitated and extracted, and a surfactant such as SDS or SDBS having high affinity with an aqueous solution may be used to control the particle size of the tellurium oxide powder.

After the neutralization step (S200), the precipitated tellurium oxide powder is extracted through the tellurium oxide extraction step (S400). In this case, the tellurium oxide powder may be extracted through a filtering method or a centrifugal separation method, and the extracted tellurium oxide powder may be dried at a predetermined time and temperature.

Tellurium (Te) extracted from the aqueous solution through the tellurium oxide extraction step (S400) is separated into TeO ₂ powder and then subjected to a mechanical mixing step (S500).

The mechanical mixing step (S500) is a process of mixing TeO ₂ powder and Bi (SO4) ₃ powder or Bi chloride or Bi nitride, which are produced by the tellurium oxide extraction step (S400), with Bi chloride or Bi nitride, by a mechanical milling process.

At this time, the TeO ₂ powder and bismuth salt powder are finally mixed so that the Te and Bi contained in the oxide and salt powder each have a molar ratio of 3: 2.

And due to the frictional heat generated during the mechanical mixing step (S500), a part of the mixed powder is synthesized as a BI-Te-based oxide, a part may be present in the state of Bi (SO ₄ ) ₃ -TeO ₂ mixed powder.

After the oxidation heat treatment step (S600) is carried out. The oxidation heat treatment step (S600) is a process of manufacturing a Bi-Te-based composite oxide by heat-treating the mixed powder in an oxidizing atmosphere to remove sulfates, chlorine salts, and nitrates contained in bismuth salts.

That is, the bismuth salt is based on bismuth sulfide (Bi (SO ₄ ) ₃ ), which is a by-product of bismuth, and bismuth chlorine salt (BiCl ₃ ) or bismuth nitrate (Bi (NO ₃ ) ₃ ) is used. In order to remove sulfuric acid group, nitric acid group and chlorine group, the mixed powder is charged inside the heat treatment furnace, and air or oxygen is continuously supplied to the inside of the heat treatment furnace so that an oxidizing atmosphere can be continuously formed. Sulfuric acid groups, nitric acid groups and chlorine groups are separated from Bi by thermal energy, and Bi is oxidized by supplied oxygen.

At this time, the organic material is removed from the bismuth salt to the outside by heat treatment, and Bi-Te-based composite oxide may be prepared by reaction with TeO ₂ .

After the mechanical grinding step (S700) is carried out. The mechanical grinding step (S700) is to control the powder size of the Bi-Te-based composite oxide, a mechanical milling process is applied.

The Bi-Te-based composite oxide whose size is controlled in the mechanical grinding step (S700) is finally formed through the reduction heat treatment step (S700) to form a thermoelectric material.

In the reduction heat treatment step (S800), a hydrogen reduction heat treatment process was applied in an embodiment of the present invention, whereby the Bi-Te-based composite oxide is a thermoelectric material having a Bi ₂ Te ₃ phase.

Hereinafter, preferred embodiments of the present invention will be described.

[Example]

Impurity removal step (S200) was performed by adding 2% NaSH to 500 ml of an aqueous solution containing tellurium (Te). The neutralization step (S300) was performed by adding 60% sulfuric acid solution to 500 ml of NaOH solution in which impurities were removed and only tellurium was dissolved.

Then, the tellurium oxide (TeO ₂ ) powder extracted in the tellurium oxide extraction step (S400) is mixed with Bi (SO ₄ ) ₃ powder, which is a bismuth salt, in a molar ratio of 3: 2, and then mixed by a mechanical milling method ( Mechanical mixing step: S500).

The mixed powder is present in the state of BI-Te-based oxide and Bi (SO ₄ ) ₃ -TeO ₂ mixed powder, charged in a heat treatment furnace and sulfated through the oxidation heat treatment step (S600) of the air atmosphere at 350 ° C. SO ₄₎ ^- to remove to prepare a Bi-Te based composite oxide.

The Bi-Te composite oxide was pulverized by a mechanical milling process to control the powder size (mechanical grinding step: S700), followed by reduction heat treatment in a hydrogen atmosphere to prepare a thermoelectric powder. (Reduction heat treatment step: S800)

The thermoelectric material made according to such a process is as shown in FIG. 2.

That is, Figure 2a is a SEM photograph showing the produced tellurium oxide prepared after the tellurium oxide extraction step of the thermoelectric material manufacturing method according to the present invention, it can be confirmed that the size of the oxide powder is 1 ~ 2㎛.

Figures 2b and 2c is a table and XRD graph showing the composition of the tellurium oxide prepared after the tellurium oxide extraction step of the thermoelectric material manufacturing method according to the present invention it can be confirmed that the TeO ₂ phase was formed clearly.

In the composition table, Si and excess O were derived from the Si substrate used in the SEM observation, and it was confirmed as a measurement error. Figure 2d is a SEM photograph showing the TeO ₂ powder prepared by nanoparticles to 50nm when the surfactant was added in the neutralization step.

In addition, Figure 3a is a SEM photograph showing the composite oxide prepared after the oxidation heat treatment and mechanical grinding step in the thermoelectric material manufacturing method according to the present invention can be seen that the size of the primary particle is controlled to several hundred nm level.

In FIG. 3B, an XRD graph showing a phase of a composite oxide is representative of TeO ₂ and Bi ₂ O ₃ based on a composite oxide of Bi ₂ TeO ₅ . This confirms that the organic material contained in Bi is completely removed and the composite oxide phase is prepared by reacting with TeO ₂ .

Figure 4a is a SEM photograph showing the thermal powder prepared after the reduction heat treatment step can confirm that the particle size is turned on compared to before reduction and can be seen that the Bi ₂ Te ₃ phase is formed as can be seen in the XRD results of Figure 4b have.

Embodiments of the present invention described so far are only specific examples of the technical idea of the present invention, and processing conditions such as temperature, time, volume fraction of a reducing agent and surfactant, etc. may be selectively modified by those skilled in the art. will be.

S100. Material preparation step S200. Impurity Removal Step
S300. Neutralization step S400. Tellurium Oxide Extraction Step
S500. Mechanical mixing step S600. Oxidation heat treatment step
S700. Mechanical grinding step S800. Reduction heat treatment step

Claims (11)

A material preparation step of preparing an aqueous solution containing tellurium, a by-product generated when copper (Cu) is extracted from the ore,
An impurity removal step of removing impurities contained in the aqueous solution;
Neutralizing the aqueous solution by adding one or more of HNO ₃ and H ₂ SO ₄ to the aqueous solution from which the impurities are removed;
Tellurium oxide extraction step of extracting the tellurium oxide powder formed by reacting in a neutralized aqueous solution,
A mechanical mixing step of preparing the mixed powder by mixing the tellurium oxide powder and the bismuth salt by a mechanical milling process;
An oxidation heat treatment step of producing a Bi-Te-based composite oxide by heat-treating the mixed powder in an oxidizing atmosphere;
A mechanical grinding step of controlling the powder size of the Bi-Te-based composite oxide using a mechanical milling process;
A method of manufacturing a thermoelectric material by a mechanical-chemical reaction, characterized in that the reduction heat treatment step of forming a thermoelectric material by reducing heat treatment of the pulverized Bi-Te-based composite oxide. The method of claim 1, wherein the impurity removing step,
Method for producing a thermoelectric material by a mechanical-chemical reaction, characterized in that for removing impurities including Cu, Fe, etc. contained in the aqueous solution by adding NaSH. The method of claim 2, wherein the neutralizing step,
Method of producing a thermoelectric material by a mechanical-chemical reaction, characterized in that to remove the NaOH contained in the aqueous solution to form tellurium oxide. According to claim 1, In the tellurium oxide extraction step,
Method for producing a thermoelectric material by a mechanical-chemical reaction, characterized in that the surfactant of any one of SDS or SDBS is added to control the size of the tellurium oxide powder. The method of claim 4, wherein in the mechanical mixing step, the tellurium oxide powder is TeO ₂ , bismuth salt is applied at least one of bismuth nitride, bismuth chloride, bismuth sulfide, tellurium and bismuth in a molar ratio of 3: 2 Method for producing a thermoelectric material by a mechanical-chemical reaction, characterized in that the mixing. The method of claim 1, wherein the oxidizing heat treatment step, a sulfate (SO ₄₎ contained in the bismuth salt ^-, nitrate (NO ₃₎ ^-, chlorine salt (Cl) ^- machine, characterized in that the process for removing - chemical reaction Thermoelectric material manufacturing method by 7. The method of claim 1 or 6, wherein the oxidation heat treatment step is a process of preparing bismuth salts into bismuth oxides and complexing them with tellurium oxides. The method of claim 7, wherein the oxidation heat treatment step is performed at a temperature of 350 ° C. under an oxygen atmosphere. delete The method of claim 8, wherein the reducing heat treatment is a process of minimizing the volatilization of tellurium by heating at a temperature of 350 ° C. or less in a hydrogen atmosphere. The method of claim 1, wherein the thermoelectric material prepared in the reducing heat treatment step is a powder form having a Bi ₂ Te ₃ phase.

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