KR102234203B1 - Alloy for thermoelectric device and fabrication method thereof - Google Patents

Abstract

The present invention relates to an alloy for a thermoelectric element composed of 0.01 to 0.07 wt% of copper and 99.93 to 99.99 wt% of a p-type Bi-Sb-Te-based alloy. A manufacturing method of the alloy comprises: a first step of preparing a molten alloy by mixing and dissolving Bi, Te and Sb, and preparing a thermostar powder therefrom; a second step of preparing a composite powder by mixing the thermostar powder and copper powder; and a third step of sintering the composite powder by an electric pressure sintering method.

Description

Alloy for thermoelectric device and manufacturing method thereof TECHNICAL FIELD OF THE INVENTION

The present invention relates to an alloy for a thermoelectric element exhibiting a high thermoelectric performance index and a method of manufacturing the same.

Due to the acceleration of global warming and the trend of depletion of fossil fuels, research and development on various alternative energy sources to replace existing fossil fuels are actively progressing. Among them, the most notable alternative energy sources include power generation using solar power, wind power, and geothermal heat, and in addition, interest in thermoelectric power generation using waste heat is increasing.

Thermoelectric power generation is due to a thermoelectric shape, which means direct energy conversion between heat and electricity, and this thermoelectric phenomenon can be viewed as a phenomenon that occurs due to the movement of charge carriers such as electrons and holes in a material.

Thermoelectric phenomena are divided into a Peltier effect that causes heat absorption on one side and heat generation on the other side according to the flow of current, and a Seebeck effect through which current flows due to temperature difference.The power generation by this thermoelectric phenomenon is simple in structure, easy to maintain, and semi-permanent. There is an advantage that can be used as.

The performance of such a thermoelectric material can be expressed as a "ZT value" commonly referred to as a dimensionless figure of merit, which is "ZT = S ² σT/k (S is Seebeck coefficient, σ is electrical conductivity, T Is the absolute temperature and k is the thermal conductivity.)", and appropriate control of Seebeck coefficient, electrical conductivity and thermal conductivity are required to improve thermoelectric performance, and various studies are being conducted to improve thermoelectric performance. .

Republic of Korea Patent Publication No. 10-2019-0007235

An object of the present invention is to provide an alloy for a thermoelectric device that exhibits excellent thermoelectric performance at medium temperature through dispersion of copper in a Bi-Sb-Te alloy.

The alloy for a thermoelectric device according to the present invention is characterized in that it is made of 0.01 to 0.07% by weight of copper and 99.93 to 99.99% by weight of a p-type Bi-Sb-Te-based alloy.

In the alloy for a thermoelectric device according to an embodiment of the present invention, the p-type Bi-Sb-Te-based alloy may satisfy Equation 1 below.

[Equation 1]

_{Bi 0 .5- x Sb 1 .5+ x} Te 3 (-0.1≤X≤0.1)

In the alloy for a thermoelectric device according to an embodiment of the present invention, the alloy for a thermoelectric device may be made of 0.03 to 0.05% by weight of copper.

In the alloy for a thermoelectric device according to an embodiment of the present invention, the alloy for a thermoelectric device may exhibit a thermoelectric performance index (ZT) of 1.0 or more at 400 to 450 K.

The present invention also provides a method for manufacturing an alloy for a thermoelectric device.

The method for manufacturing an alloy for a thermoelectric device according to the present invention comprises: a first step of mixing and dissolving Bi, Te, and Sb to prepare a molten alloy, and preparing a thermoelectric powder therefrom;

A second step of preparing a composite powder by mixing the thermoelectric powder and the copper powder;

And a third step of sintering the composite powder by an electric current pressure sintering method.

In the method of manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the first step may include generating thermoelectric powder by spraying water on Bi, Te, and Sb.

In the method of manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the thermoelectric powder may be made of 70 to 80% by weight of Sb ₂ Te ₃ and 20 to 30% by weight of Bi ₂ Te ₃ .

In the method for manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the mixing may be performed using a ball mill.

In the method for manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the ball mill may be performed under an argon atmosphere.

In the method for manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the ball mill may be performed at 200 to 600 rpm for 1 to 10 hours.

In the method for manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the copper powder may be manufactured by treating molten copper by gas atomization using an inert gas.

The method of manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention may further include a heat treatment step of heat-treating the composite powder after the second step and before the third step.

In the method of manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the heat treatment step may be performed in a vacuum atmosphere of 400 to 550°C.

In the method for manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the third step may be characterized in that it proceeds for 3 minutes or more under a condition of a temperature of 300 to 550° C. and a pressure of 30 to 65 MPa.

In the alloy for a thermoelectric device according to the present invention, since 0.01 to 0.07% by weight of copper is mixed with the p-type Bi-Sb-Te-based alloy, not only the thermoelectric performance but also the driving temperature range having the optimum performance can be controlled.

1 is a diagram illustrating and measuring Seebeck coefficient, electrical conductivity, and output factor of an alloy for a thermoelectric device according to an embodiment of the present invention.
2 shows the thermal conductivity and thermoelectric performance index of an alloy for a thermoelectric device according to an embodiment of the present invention.
3 shows the thermal conductivity and thermoelectric performance index of an alloy for a thermoelectric device according to another embodiment of the present invention.
4 is an analysis of the shape and particle size distribution of the powder according to the ball milling time in the method of manufacturing an alloy for a thermoelectric device according to the present invention.
5 is an Atom probe tomography analysis on the sintered body manufactured according to an embodiment of the present invention and shows the results.

Advantages and features of the embodiments of the present invention, and a method of achieving them will be apparent with reference to the embodiments described later in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in a variety of different forms, and only these embodiments make the disclosure of the present invention complete, and common knowledge in the technical field to which the present invention pertains. It is provided to completely inform the scope of the invention to those who have, and the invention is only defined by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

In describing the embodiments of the present invention, if it is determined that a detailed description of a known function or configuration may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted. In addition, terms to be described later are terms defined in consideration of functions in an embodiment of the present invention, which may vary according to the intention or custom of users or operators. Therefore, the definition should be made based on the contents throughout the present specification.

The present invention relates to an alloy for a thermoelectric element comprising 0.01 to 0.07% by weight of copper and 99.93 to 99.99% by weight of a p-type Bi-Sb-Te-based alloy.

Conventionally _{, a thermoelectric material using a Bi 2} Te ₃ alloy exhibits excellent thermoelectric performance at room temperature or in a low temperature range, but there is a problem in that the thermoelectric performance rapidly decreases with an increase in temperature. The applicant of the present invention attempted to solve this problem to develop an alloy for thermoelectric devices that exhibits high thermoelectric performance even at medium temperature. There is an advantage in that the application range of the Bi ₂ Te _{3 series thermoelectric device is further expanded.} In addition, in the present invention, the term "medium temperature" means a temperature of 350 to 500 K. Conventional BiTe-based thermoelectric materials have a relatively low temperature range indicating an optimum ZT value, and thus have a limit that is only used for cooling. By showing, there is an advantage that it can be used not only for cooling but also for power generation.

Specifically, in the alloy for a thermoelectric device according to an embodiment of the present invention, the p-type Bi-Sb-Te-based alloy may satisfy Equation 1 below.

[Equation 1]

_{Bi 0 .5- x Sb 1 .5+ x} Te 3 (-0.1≤X≤0.1)

By using a Bi-Sb-Te-based alloy that satisfies the above-described range, there is an advantage in that it is possible to manufacture an alloy having more excellent thermoelectric performance by improving the thermal conductivity of an alloy for a thermoelectric element manufactured. Accordingly, the alloy for a thermoelectric device according to an embodiment of the present invention has an advantage of exhibiting a thermoelectric performance index (ZT) of 1.0 or more, preferably 1.1 or more, and more preferably 1.15 to 1.3 at 400 to 450 K.

The alloy for a thermoelectric device according to the present invention contains 0.01 to 0.07% by weight, preferably 0.02 to 0.06% by weight of copper as described above. By adding copper, there is an advantage in that it is possible to manufacture an alloy for a thermoelectric element exhibiting high performance at medium temperature by controlling the Seebeck coefficient according to temperature change.

Specifically, the performance of a thermoelectric material can be expressed as a "ZT value" commonly referred to as a dimensionless figure of merit, which is "ZT = S ² σT/k (S is Seebeck coefficient, σ is electrical conductivity). , T is the absolute temperature, k is the thermal conductivity.)", and the higher the Seebeck coefficient and the electrical conductivity and the lower the thermal conductivity, the better the thermoelectric performance.

When copper is added, the Seebeck coefficient is partially lowered at low temperatures, which seems to be due to an increase in the hole concentration. However, as the temperature rises to the mid-temperature region, the Seebeck coefficient of the alloy to which copper is added is higher than that of the alloy without the addition of copper. In addition, in the medium temperature range of 400 K or higher, there is a problem that the thermal conductivity of an alloy containing no copper increases rapidly, and accordingly, the thermoelectric performance decreases at medium temperature, but when copper is added, the thermal conductivity is prevented from rapidly increasing, As a result, there is an advantage in that it is possible to manufacture an alloy for a thermoelectric device having excellent thermoelectric performance in a medium temperature range.

Advantageously, the alloy for a thermoelectric device according to an embodiment of the present invention may contain 0.03 to 0.05% by weight of copper, and has an advantage of showing a high thermoelectric performance of 1.2 or more based on 400 to 450 K in this range, which It is judged to be the influence of the tendency that thermal conductivity and electrical conductivity increase as the content of copper increases.

The present invention also provides a method for manufacturing an alloy for a thermoelectric device. The method for manufacturing an alloy for a thermoelectric device according to the present invention may be a method for manufacturing the alloy for a thermoelectric device described above, but the present invention is not limited thereto.

The method for manufacturing an alloy for a thermoelectric device according to the present invention comprises: a first step of mixing and dissolving Bi, Te, and Sb to prepare a molten alloy, and preparing a thermoelectric powder therefrom;

A second step of preparing a composite powder by mixing the thermoelectric powder and the copper powder;

And a third step of molding the composite powder by energizing pressurization sintering.

The method of manufacturing an alloy for a thermoelectric device according to the present invention has the advantage of showing excellent thermoelectric performance at medium temperature by adding copper to an alloy material including Bi, Te, and Sb, and mixing them. In addition, there is a problem that a lot of energy is required when copper is made and added to an alloy, but the present invention has the advantage of showing an excellent thermoelectric performance index by the addition of copper while using a milling process that requires relatively little energy. .

Specifically, in the method of manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the first step is a step of heating and melting Bi, Te, and Sb, and spraying water to the molten alloy to generate a thermoelectric powder. It may include. The thermoelectric powder according to an embodiment of the present invention manufactures thermoelectric powder by spraying water into the molten alloy as described above, thereby producing thermoelectric powder having a uniform size, and then forming a dense and uniform thermoelectric powder in the third step of molding. There is an advantage that it is possible to manufacture an alloy for an element.

Specifically, in the step of spraying water, the molten alloy is lowered into the chamber through an orifice and water is sprayed obliquely, so that the molten alloy is solidified and a thermoelectric powder can be produced. At this time, the average particle diameter of the resulting thermoelectric powder may be 3 to 120 µm, specifically 40 to 60 µm, and there is an advantage that it is possible to manufacture an alloy for a thermoelectric element having a compact structure in this range.

In this case, the molten alloy may satisfy Equation 1 for the p-type Bi-Sb-Te-based alloy. By using a Bi-Sb-Te-based molten alloy that satisfies the above range, the thermal conductivity of an alloy for a thermoelectric element manufactured is improved, thereby making it possible to manufacture an alloy having more excellent thermoelectric performance.

The method of manufacturing an alloy for a thermoelectric device according to the present invention includes a second step of preparing a composite powder by mixing the thermoelectric powder and the copper powder. Advantageously, the mixing may be performed using a ball mill, and by producing the thermoelectric powder and copper powder while applying a physical impact like a ball mill, it is possible to improve the electrical conductivity of the alloy for thermoelectric elements, and as a result There is an advantage that it is possible to manufacture an alloy for a thermoelectric device having excellent thermoelectric performance.

Specifically, the ball mill may be performed in an inert gas atmosphere such as argon, and the ball mill may be performed at a rotation speed of 200 to 600 rpm, preferably 250 to 500 rpm, for 1 to 10 hours, preferably 2 to 8 hours. , More preferably, it may be performed for 2.5 to 7, and in this range, an effect of improving thermoelectric performance due to grain reduction or the like may be achieved. Specifically, when the ball mill time is less than 1 hour, there is a problem that it is difficult to achieve the effect of the above-described ball mill, and when the ball mill time exceeds 10 hours, strain occurs in the particles and the melting point decreases, as a result of which will be described later. During the performing of the sintering step, recrystallization of grains occurs at a low temperature, which may cause a problem in that physical properties such as conductivity are deteriorated.

In the method of manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention, the copper powder may be manufactured by treating molten copper with gas atomization. By producing copper powder through such atomization, there is an advantage that it is possible to manufacture copper powder having fine grains. At this time, atomization may be performed by injecting an inert gas such as argon, but the present invention is not limited thereto. The average particle diameter of the copper powder may be 3 to 200 μm, preferably 40 to 50 μm.

The method of manufacturing an alloy for a thermoelectric device according to an embodiment of the present invention may further include a heat treatment step of heat-treating the composite powder after the second step and before the third step. By adding such a heat treatment step, there is an advantage in that the thermoelectricity increase index can be higher than that of the case where the heat treatment is not performed.

Specifically, the heat treatment step may be performed in a vacuum atmosphere at 400 to 550 °C, and the heat treatment time may vary depending on the amount of the composite powder to be heat treated, but specifically 10 to 120 minutes, more specifically 30 to 90 minutes. It may be performed for a minute, but the present invention is not limited thereto.

The method of manufacturing an alloy for a thermoelectric device according to the present invention includes a third step of forming the composite powder by energizing pressurization sintering. By using the energization pressurization sintering, there is an advantage that it is possible to manufacture an alloy for a uniform thermoelectric element within a short time, and accordingly, it is possible to produce an alloy for a thermoelectric element with high reliability. Specifically, the third step may be performed for 3 minutes or more, preferably 5 to 30 minutes, under the condition that the temperature is 300 to 550 °C and the pressure is 30 to 65 MPa.

By manufacturing an alloy for a thermoelectric device through the above-described process, there is an advantage of exhibiting high thermoelectric performance at medium temperature, and accordingly, there is an advantage of expanding the application range of _{the Bi 2} Te _{3 based thermoelectric device.}

Hereinafter, the present invention will be described in detail by examples and comparative examples. The following examples are only intended to aid understanding of the present invention, and the scope of the present invention is not limited by the following examples.

[Production Example 1]

1. Manufacture of thermoelectric powder

After measuring 99.999% (5N) of Bi, Te, and Sb elements respectively and charging them into a carbon crucible, P-type 75at.%Sb ₂ Te ₃ -25at.%Bi ₂ Te ₃ (2wt.%) using a high-frequency induction furnace. Te dopping) (hereinafter referred to as thermoelectric powder) to prepare a molten alloy having the composition. The molten alloy was lowered to the chamber through an orifice and water was sprayed toward the molten alloy to produce a powder, and the average particle diameter of the prepared thermoelectric powder was confirmed to be about 50 µm.

2. Manufacture of copper powder

After loading 5N copper into a carbon crucible, it was melted using a high-frequency induction furnace, and the molten copper was lowered to the chamber through an orifice and at the same time, argon gas was sprayed to prepare copper powder. The average particle diameter of the prepared copper powder was 40 µm. Confirmed as.

3. Preparation of composite powder

To prepare a composite powder of thermoelectric powder and copper powder, put 400g of 0.5ø zirconia balls and 40g of 0.05wt.%Cu powder together with the above-specified thermoelectric powder in a stainless steel ball milling vessel with an inner diameter of 50°, and in an Ar atmosphere at 400rpm for 1 hour. A composite powder was prepared by ball milling.

4. Molding

Molding was performed by sintering through pressurization sintering.To manufacture a sintered body, 32g of the powder prepared before was charged into a cylindrical mold with an outer diameter of 60ø, an inner diameter of 20ø, and a height of 60mm, and then using a punch made of graphite material at the top and bottom, respectively. The charged powder was fixed. Sintering was carried out in a vacuum atmosphere (10-3torr), the temperature was raised at a rate of 50°C/min and the temperature was increased to 400°C, and the temperature was maintained at 400°C for 10 minutes for sufficient sintering. In addition, during the sintering process, a pressure of 50 Mpa was applied to the sintered body through a punch fixed at the upper and lower parts. Finally, an alloy for a thermoelectric element in the form of a cylinder having a diameter of 20 ø and a thickness of about 12 mm was manufactured.

[Production Examples 2 to 4]

Manufactured in the same manner as in Preparation Example 1, 3. In the manufacturing process of the composite powder, the ball mill was performed for 3 hours (Production Example 2), 6 hours (Production Example 3) and 10 hours (Production Example 4), respectively, to prepare a sintered body. I did.

[Production Example 5]

It was prepared in the same manner as in Preparation Example 3, but the composite powder before the molding step of 4 was heat-treated ^{at 470° C. for 1 hour in a vacuum atmosphere (10 -3 torr).}

[Comparative Preparation Example 1]

It was manufactured in the same manner as in Preparation Example 1, but the milling process was omitted and an alloy for a thermoelectric element was manufactured.

[Comparative Production Example 2]

It was prepared in the same manner as in Preparation Example 1, but an alloy for a thermoelectric element was prepared without adding copper.

1. Evaluation of properties of alloys for thermoelectric elements according to ball milling time

The Seebeck coefficient, electrical conductivity, and output factor of the alloy for thermoelectric elements prepared in Preparation Examples 1 to 4 and Comparative Preparation Example 1 (shown as Raw in the drawing) were measured, and the results are shown in FIG. The thermoelectric performance was measured and shown in FIG. 2.

The Seebeck coefficient measured the amount of electromotive force generated by giving the temperature difference at both ends, and the electrical conductivity was measured in a temperature range of 25 ~ 100 ℃ using a 4 point probe method (TEP-1000). The thermal conductivity was measured by grinding the alloy for a thermoelectric element into a disk shape having a diameter of 12.7 mm and a thickness of 1 mm. The thermal conductivity (κ) was calculated using Equation 1 below, and the thermoelectric performance was calculated and derived based on the measured Seebeck coefficient, electrical conductivity, and thermal conductivity.

[Equation 1]

κ = λ × Cp × d

In Equation 1, λ is the thermal diffusivity of the large-area Bi-Sb-Te-based sintered gold, Cp is the specific heat of the large-area Bi-Sb-Te-based sintered gold, and d is the large-area Bi-Sb-Te-based sintering It means the density of the alloy.

The output factor (P.F) was calculated by Equation 2 below using the Seebeck coefficient and electrical conductivity.

[Equation 2]

PF = α ² × σ

In Equation 2, α denotes Seebeck coefficient and σ denotes electrical conductivity.

Referring to FIG. 1, Comparative Preparation Example 1 exhibits the highest Seebeck coefficient value at room temperature, but shows a tendency that the Seebeck coefficient rapidly decreases with an increase in temperature, whereas Preparation Examples 1 to 4 show a tendency to decrease rapidly with an increase in temperature. It can be seen that the Seebeck coefficient is gradually increased, and it can be seen that the Seebeck coefficient is higher than that of the comparative example at 450K or higher. In addition, considering the time of the ball mill, it can be seen that the highest Seebeck coefficient is displayed when the ball mill is performed for 1 to 6 hours, which is a phenomenon that occurs when the grain and particle size decrease by performing the ball mill for the above-described time. Seems to be. It can be seen that the output factor also shows the highest value when ball milling for 6 hours, and in the case of electrical conductivity, it can be seen that the electrical conductivity is significantly increased in the copper-added composite powder, which is due to the increase in hole concentration due to the addition of copper. It is judged to be the cause.

Referring to FIG. 2, in the case of the comparative manufacturing example, the thermal conductivity is high at room temperature, but the thermal conductivity tends to increase rapidly with the increase of the temperature.However, in the case of the alloy for thermoelectric elements manufactured in Preparation Examples 1 to 4, It can be seen that there is no increase in thermal conductivity. As a result, it can be seen that Preparation Examples 2 and 3, in which the ball mill was performed for 3 hours and 6 hours, exhibited a thermoelectric performance of 1.0 or more, and among them, the alloy for a thermoelectric element manufactured by performing the ball mill for 6 hours as in Preparation Example 3 was It can be seen that the thermoelectric performance is the most excellent in the range of 350 to 400K, and specifically 1.0 or more, more specifically 1.1 or more.

2. Evaluation of thermoelectric performance according to the presence or absence of heat treatment

Preparation Example 3 (represented by 6h) milling for 6 hours, 5 (represented by 6h + MW) and Comparative Preparation Example 1 (represented by Raw) in the production of heat treatment after the milling process for 6 hours. The properties of the alloy for thermoelectric elements were evaluated, and the results are shown in FIG. 4.

Referring to FIG. 3, it can be seen that Preparation Example 5, in which the heat treatment step before sintering was added, exhibits excellent thermoelectric performance index (ZT) at a temperature of 400 to 450 K compared to Preparation Example 3 without heat treatment. It was confirmed that it had a thermoelectric performance index (ZT) of 1.29.

3. Analysis of particle size distribution according to ball milling time

Powder shape and particle size analysis of Comparative Preparation Example 1 (Raw, Fig. 4a) and Preparation Examples 1 to 4 (each b to e in Fig. 4) was performed, and the results are shown in Fig. 4.

Referring to FIG. 4, it can be seen that the average particle diameter of the powder before performing the ball mill is 51 μm, the average particle size gradually decreases as the milling time increases, and does not decrease to 21 μm or less after 6 hours.

4. Atom probe Tomography analysis

Atom probe tomography analysis was performed on the sintered body prepared in Preparation Example 3, and a schematic diagram of the result and atomic distribution is shown in FIG. 5.

Referring to the atomic distribution analysis (top), while other materials were relatively uniformly distributed, Cu was mainly concentrated at the grain boundaries, which was sintered in the BiSbTe-Cu alloy alloyed through milling as shown in the lower schematic diagram of FIG. 5. In the process, it is judged that diffusion proceeded along the grain boundaries due to heat and pressure.

Claims (13)

A first step of mixing and dissolving Bi, Te, and Sb to prepare a molten alloy, and preparing a thermoelectric powder therefrom;
A second step of preparing a composite powder by mixing the thermoelectric powder and the copper powder with a ball mill at 200 to 600 rpm for 2.5 to 7 hours in an argon atmosphere;
Including; a third step of sintering the composite powder by a energization pressurization sintering method,
The thermoelectric powder satisfies the following formula 1,
It is characterized in that the thermoelectric performance index (ZT) is 1.15 to 1.3 at 400 to 450K,
A method for manufacturing an alloy for a thermoelectric device comprising 0.01 to 0.07% by weight of copper and 99.93 to 99.99% by weight of a p-type Bi-Sb-Te-based alloy.
[Equation 1]
Bi _0.5-x Sb _1.5+x Te ₃ (-0.1≤X≤0.1) The method of claim 1,
The first step is a method of manufacturing an alloy for a thermoelectric device comprising the step of generating thermoelectric powder by spraying water on the molten Bi, Te, and Sb. delete delete delete The method of claim 1,
The copper powder is a method of manufacturing an alloy for a thermoelectric device that is manufactured by treating molten copper by atomization using a gas inert gas. The method of claim 1,
After the second step and before the third step, the method of manufacturing an alloy for a thermoelectric device further comprising a heat treatment step of heat-treating the composite powder. The method of claim 7,
The heat treatment step is a method of manufacturing an alloy for a thermoelectric device performed in a vacuum atmosphere of 400 to 550 ℃. The method of claim 1,
The third step is a method of manufacturing an alloy for a thermoelectric device, characterized in that the temperature is 300 to 550 ℃, the pressure is 30 to 65 MPa, characterized in that the process proceeds for more than 3 minutes under the condition. delete delete delete delete

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