Fe—Ni/Ti metalized skutterudite thermoelectric material and method of manufacturing the same

Abstract

This invention relates to a metalized skutterudite thermoelectric material having improved long-term stability and a method of manufacturing the same, wherein the skutterudite thermoelectric material is metalized with a multilayer structure including a Ti layer for preventing the diffusion of the skutterudite thermoelectric material and a FeNi layer for preventing an increase in the thickness of an intermetallic compound layer, whereby the performance of the skutterudite thermoelectric material does not deteriorate due to diffusion and formation of the intermetallic compound even upon long-term use, thus exhibiting improved stability of use, and moreover, the lifetime and stability of a thermoelectric power generation module using the skutterudite thermoelectric material can be increased, whereby the power generation efficiency of the thermoelectric power generation module can be increased in the long term.

Claims

1. A FeNi/Ti metalized skutterudite thermoelectric material, comprising a metalization layer formed on a surface thereof, wherein the metalization layer is configured such that a FeNi layer and a Ti layer are sequentially stacked, wherein the skutterudite thermoelectric material comprises FeSb.sub.3 as a p-type thermoelectric material or CoSb.sub.3 as an n-type thermoelectric material, and wherein the FeNi layer comprises Fe and Ni at a weight ratio ranging from 75:25 to 55:45.

2. The FeNi/Ti metalized skutterudite thermoelectric material of claim 1, wherein the FeNi layer has a thickness of 40 m or more.

3. The FeNi/Ti metalized skutterudite thermoelectric material of claim 2, wherein the FeNi layer has a thickness of 150 m or less.

4. The FeNi/Ti metalized skutterudite thermoelectric material of claim 1, wherein the Ti layer has a thickness of 40 m or more.

5. The FeNi/Ti metalized skutterudite thermoelectric material of claim 4, wherein the Ti layer has a thickness of 150 m or less.

6. A method of manufacturing a FeNi/Ti metalized skutterudite thermoelectric material, comprising forming, on a surface of a skutterudite thermoelectric material, a metalization layer configured such that a FeNi layer and a Ti layer are sequentially stacked, wherein the skutterudite thermoelectric material comprises FeSb.sub.3 as a p-type thermoelectric material or CoSb.sub.3 as an n-type thermoelectric material, and wherein the FeNi layer comprises Fe and Ni at a weight ratio ranging from 75:25 to 55:45.

7. The method of claim 6, wherein the forming the metalization layer is performed by sequentially forming the FeNi layer and the Ti layer on the surface of the skutterudite thermoelectric material.

8. The method of claim 6, wherein the forming the metalization layer is performed in a manner in which a FeNi metal foil and a Ti metal foil are sequentially superimposed on the surface of the skutterudite thermoelectric material and hot pressed.

9. The method of claim 6, wherein the forming the metalization layer is performed in a manner in which a FeNi foil and a Ti foil are sequentially superimposed on a skutterudite powder and pressure sintered, whereby the skutterudite powder is sintered, and simultaneously, the metalization layer, configured such that the FeNi layer and the Ti layer are sequentially stacked, is formed on the surface of the skutterudite thermoelectric material.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view showing that a FeNi/Ti multilayered metalization structure is formed on the surface of a skutterudite thermoelectric material according to an embodiment of the present invention.

(2) FIG. 2A shows the results of EDS (Energy Dispersive X-ray Spectroscopy) when the surface of an n-type skutterudite thermoelectric material is metalized with a Ti powder;

(3) FIG. 2B shows the results of EDS after thermal treatment of the metalized skutterudite thermoelectric material of FIG. 2A at 500 C. for 10 hr;

(4) FIG. 3 shows the results of EDS of a p-type skutterudite thermoelectric material including a FeNi/Ti multilayered metalization structure according to an embodiment of the present invention;

(5) FIG. 4 shows the results of measurement of contact resistance of the metalized p-type skutterudite thermoelectric material of FIG. 3;

(6) FIG. 5 shows the results of EDS of an n-type skutterudite thermoelectric material including a FeNi/Ti multilayered metalization structure according to an embodiment of the present invention;

(7) FIG. 6 shows the results of measurement of contact resistance of the metalized n-type skutterudite thermoelectric material of FIG. 5;

(8) FIG. 7 shows the results of EDS after thermal treatment of the metalized p-type skutterudite thermoelectric material of FIG. 3 at 500 C. for 10 hr;

(9) FIG. 8 shows the results of measurement of contact resistance of the metalized p-type skutterudite thermoelectric material of FIG. 7;

(10) FIG. 9 shows the results of EDS after thermal treatment of the metalized n-type skutterudite thermoelectric material of FIG. 5 at 500 C. for 10 hr; and

(11) FIG. 10 shows the results of measurement of contact resistance of the metalized n-type skutterudite thermoelectric material of FIG. 9.

DESCRIPTION OF SPECIFIC EMBODIMENTS

(12) Hereinafter, a detailed description will be given of embodiments of the present invention with reference to the appended drawings.

(13) The present inventors have ascertained the problems caused when a Ti layer having high diffusion barrier properties is provided alone during the fabrication of a thermoelectric power generation module using a skutterudite thermoelectric material.

(14) FIG. 2A shows the results of EDS when the surface of an n-type skutterudite thermoelectric material is metalized with a Ti powder, and FIG. 2B shows the results of EDS after thermal treatment of the metalized skutterudite thermoelectric material of FIG. 2A at 500 C. for 10 hr.

(15) As shown in FIG. 2A, in which n-type skutterudite is metalized with the Ti powder by applying a pressure of 50 MPa at 650 C. for 10 min, the thickness of the diffusion layer was measured to be 3.4 m through composition analysis.

(16) In order to reproduce the environment in which the thermoelectric power generation module using the thermoelectric material is applied, thermal treatment was performed at 500 C. for 10 hr while maintaining a vacuum atmosphere. As shown in FIG. 2B, the thickness of the diffusion layer was increased to 9.9 m.

(17) The diffusion layer is configured such that elements of skutterudite are diffused to thus form an intermetallic compound with Ti. As seen in FIG. 2A, when the surface of the skutterudite thermoelectric material is metalized with the Ti layer, the intermetallic compound is synthesized upon real-world application, and thus the thickness of the intermetallic compound layer is increased. Since the intermetallic compound, which is formed between the Ti layer and the skutterudite thermoelectric material, has high contact resistance, the thickness of the intermetallic compound layer has to be appropriately adjusted in order to obtain desired efficiency. Even when the intermetallic compound layer is first formed at an adequately controlled thickness, the thickness thereof may increase during actual usage, and thus the contact resistance between the metalization layer and the skutterudite thermoelectric material may increase, ultimately reducing power generation efficiency, which is undesirable. Hence, the skutterudite thermoelectric material metalized with the Ti layer may suffer from stability problems upon long-term use thereof.

(18) Therefore, the present inventors have developed a multilayered metalization structure for use in a skutterudite thermoelectric material, which is configured such that a FeNi layer is interposed between the skutterudite thermoelectric material and the Ti layer having high diffusion barrier performance.

(19) FIG. 3 shows the results of EDS of a p-type skutterudite thermoelectric material including a FeNi/Ti multilayered metalization structure according to an embodiment of the present invention, and FIG. 4 shows the results of measurement of contact resistance of the metalized p-type skutterudite thermoelectric material of FIG. 3.

(20) FIG. 5 shows the results of EDS of an n-type skutterudite thermoelectric material including a FeNi/Ti multilayered metalization structure according to an embodiment of the present invention, and FIG. 6 shows the results of measurement of contact resistance of the metalized n-type skutterudite thermoelectric material of FIG. 5.

(21) The p-type skutterudite thermoelectric material powder comprising FeSb.sub.3 doped with an additive was subjected to pressure sintering, such as SPS (Spark Plasma Sintering), at 650 C. under a pressure of 50 MPa for 10 min. In this procedure, the powder was stacked with a FeNi foil and a Ti foil, whereby the skutterudite thermoelectric material was sintered and simultaneously a metalization layer comprising a FeNi layer and a Ti layer was formed on the surface of the skutterudite thermoelectric material. For an n-type skutterudite thermoelectric material comprising CoSb.sub.3 doped with an additive, the metalization layer comprising a FeNi layer and a Ti layer was formed at the same time as the sintering process, and the SPS process was performed at 650 C. and a pressure of 50 MPa for 10 min.

(22) For the p-type skutterudite thermoelectric material, an intermetallic compound layer having a thickness of 18 m was formed at an interface between the FeNi layer and the skutterudite, and for the n-type skutterudite thermoelectric material, an intermetallic compound layer having a thickness of 13 m was formed at an interface between the FeNi layer and the skutterudite. In these two cases, low contact resistance of about 10.sup.6 cm.sup.2 was measured, resulting in low electrical loss.

(23) FIG. 7 shows the results of EDS after thermal treatment of the metalized p-type skutterudite thermoelectric material of FIG. 3 at 500 C. for 10 hr, and FIG. 8 shows the results of measurement of contact resistance of the metalized p-type skutterudite thermoelectric material of FIG. 7.

(24) FIG. 9 shows the results of EDS after thermal treatment of the metalized n-type skutterudite thermoelectric material of FIG. 5 at 500 C. for 10 hr, and FIG. 10 shows the results of measurement of contact resistance of the metalized n-type skutterudite thermoelectric material of FIG. 9.

(25) Unlike the above Ti layer, the FeNi layer contained in the multilayered metalization structure according to the present embodiment is characterized in that there are no changes in thickness of the intermetallic compound layer despite the same thermal treatment. The contact resistance was slightly increased through thermal treatment, but was still low, to the level of 10.sup.6 cm.sup.2, resulting in no great changes in electrical loss.

(26) In the present embodiment, microcracking and peeling did not occur at the interface between the skutterudite thermoelectric material and the FeNi metalization layer, and very low contact resistance was measured at the interface therebetween, whereby little power loss can be anticipated. Upon thermal treatment for 10 hr at 500 C., similar to the actual use temperature of the thermoelectric device, there was no significant increase in the thickness of the interfacial layer or in the contact resistance. Accordingly, a thermoelectric device having high reliability can be confirmed to be obtained by forming the FeNi layer between the skutterudite thermoelectric material and the Ti metalization layer.

(27) In this embodiment, the FeNi layer was composed of a FeNi alloy comprising Fe and Ni at a weight ratio of 65:35.

(28) Here, the reason why the FeNi alloy is interposed between the Ti layer and the thermoelectric material is that there are differences in properties and performance when Fe or Ni is used alone compared to when the FeNi alloy is used.

(29) When the Fe layer or the Ni layer, in which Fe or Ni is used alone, is interposed between the Ti layer and the skutterudite thermoelectric material, a thick intermetallic compound layer, and thus high contact resistance, may result, compared to when the FeNi alloy is used. Furthermore, problems in which the thickness of the intermetallic compound layer is increased due to thermal treatment still occur. In the case where the Fe layer or the Ni layer is used alone, the formation of the intermetallic compound is deemed to actively progress between the Fe layer or the Ni layer and the thermoelectric material, as in the Ti layer. On the other hand, when the FeNi alloy is applied, Fe and Ni are coupled with each other and thus Fe and Ni contained in the alloy require the energy to be able to break the FeNi bond in order to directly combine with the thermoelectric material. Hence, the formation of the intermetallic compound is regarded as comparatively difficult.

(30) Also, when the Fe layer or the Ni layer is interposed between the Ti layer and the skutterudite thermoelectric material, the metalization layer may crack. This is considered to be due to a difference in coefficient of thermal expansion between Fe or Ni when used alone and the skutterudite thermoelectric material. On the other hand, when the FeNi alloy is applied, a difference in coefficient of thermal expansion from the skutterudite thermoelectric material is small, and thus no cracking occurs.

(31) Consequently, in this embodiment, the FeNi/Ti multilayered metalization structure is applied. When the FeNi alloy is composed of Fe and Ni at a weight ratio ranging from 75:25 to 55:45, the thickness of the intermetallic compound layer is not increased, but is maintained.

(32) Also, in the present invention, the FeNi layer and the Ti layer, which constitute the FeNi/Ti multilayered metalization structure, are formed to respective thicknesses of 40 m or more. Thereby, the Ti layer may play a role in sufficiently performing a diffusion barrier function, and the FeNi layer may satisfactorily function between the Ti layer and the skutterudite thermoelectric material and may also function as a thermal expansion buffer layer. Taking into account the formation of the intermetallic compound layer at the interface between the FeNi layer and the skutterudite thermoelectric material, which are in contact with each other, when the FeNi layer is deposited to a sufficient thickness of 50 m or more, the thickness of the FeNi layer, which is left behind after the formation of the intermetallic compound, may be 40 m or more. The upper limits of the thicknesses of the FeNi layer and the Ti layer are not particularly limited, and may be set to 150 m or less in order to avoid increased material costs and because the properties may deteriorate when being excessively thick.

(33) According to the present invention, forming the multilayered metalization structure on the surface of skutterudite may be conducted using a variety of conventional processes without limitation. In particular, individual layers of the multilayered metalization structure may be sequentially stacked and formed using various deposition processes and hot pressing, and metal foils are superimposed and may be metalized all at once through a process such as hot pressing.

(34) In addition to the formation of the multilayered metalization structure on the surface of the skutterudite thermoelectric material produced in the form of an ingot, it is possible to form the multilayered metalization structure by performing a hot pressing process while the skutterudite thermoelectric material in a powder phase is sintered and manufactured in the form of an ingot, as described above.

(35) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Therefore, the scope of the present invention should be interpreted not by specific embodiments but by the accompanying claims, and it is to be understood that all technical ideas within the claims fall within the purview of the present invention.