TWI541382B - A coating for thermoelectric materials and a device containing the same - Google Patents

Description

Thermoelectric material coating film and device therewith

The invention relates to a coating of a thermoelectric material and a structure and a preparation method thereof for an element (or device) containing the same, and belongs to the field of thermoelectric materials and devices.

Thermoelectric power generation is a power generation technology that directly converts thermal energy (temperature difference) into electrical energy by using the Seebeck effect of semiconductor thermoelectric materials. The thermoelectric power generation system is compact in structure, reliable in performance and good in mobility. It is environmentally friendly green energy technology because it has no running parts, no noise, no wear and no leakage. It is suitable for low energy density recycling, in industrial waste heat and The field of recycling and utilization of exhaust heat of automobiles has broad application prospects. The thermoelectric conversion efficiency mainly depends on the dimensionless performance index ZT=S ² σ T/κ of the material, where S is the Seebeck coefficient, σ conductivity, κ thermal conductivity and T is the absolute temperature. The higher the ZT value of the material, the higher the efficiency of thermoelectric conversion.

CoSb ₃ based skutterudite thermoelectric materials are present between 500-850K due to their large unit cell, heavy atomic mass and large carrier mobility characteristics, and the presence of filling atoms in the Sb dodecahedron. Excellent high temperature thermoelectric properties, wherein the highest ZT values of n-type Yb _y Co ₄ Sb ₁₂ (800K) and p-type Ca _x Ce _y Co _2.5 Fe _1.25 Sb ₁₂ (750K) are 1.4 and 1.2, respectively. Comprehensive performance, price, safety and preparation methods. Among many new thermoelectric material systems, CoSb ₃ square cobalt is the most promising commercial medium and high temperature thermoelectric material, which is expected to replace the commonly used PbTe thermoelectric materials.

Since the best thermoelectric properties of the thermoelectric material CoSb ₃ based skutterudite located between 500-850K, so CoSb ₃ based skutterudite thermoelectric device near the end of the thermoelectric element temperature up to operating temperature of 850K. Due to the high vapor pressure of Sb element (see Figure 1), it is about 10Pa at 850K, which is 12 orders of magnitude higher than other elements Fe, Co and Ce (David R.Lide, CRC Handbook of Chemistry and Physics, CRC Press, 2005), so the performance deterioration of the thermoelectric device due to the high temperature loss of the Sb element is very serious.

In order to avoid deterioration of device performance due to volatilization of the thermoelectric material during use at high temperatures, the surface of the material must be coated and packaged. This measure of coating protection of thermoelectric materials in high temperature applications can be traced back to earlier SiGe thermoelectric materials. The high temperature end of the SiGe thermoelectric element can be used up to 1273K. The SiGe thermoelectric material can be well protected by coating the Si ₃ N ₄ coating. The thickness of the coating is millimeter (Kelly CE Proceedings of the 10th intersociety energy conversion engineering conferenc, American Institute of Chemical Engineers, New York 1975, p. 880-6). Essential for the CoSb ₃ based skutterudite thermoelectric materials Sb high temperature problems, Mohamed put forward surface material cobaltite square method to solve a metal coating (Mohamed S.El-Genk et al, Energy Conversion and Management, 47 (2006 ) 174; Hamed H. Saber, Energy Conversion and Management, 48 (2007) 1383). It is recommended to segment the device (p-type component: CeFe _3.5 Co _0.5 Sb ₁₂ +Bi _0.4 Sb _1.5 Te ₃ , n-type component: CoSb ₃ +Bi ₂ Te _2.95 Se _0.05 ). The metal elements available for coating are Ta, Ti. Mo, V, the thickness of the metal coating should be 1-10 microns, the theoretical derivation shows that the higher the conductivity of the metal coating or the thicker the coating, the higher the peak output power, but the higher the peak conversion efficiency low. The paper does not mention the preparation of the coating and the comparison of the experimental data of the four coatings.

Mohamed et al. proposed a method of coating a metal coating on the surface of a specific component CoSb ₃ skutter cobalt ore material, although it provides a way of thinking about the high temperature volatilization problem of Sb, but the coverage is too narrow and fails to solve the CoSb ₃ basal cobalt. The high temperature oxidation of materials that mineral materials and their components need to face in the actual use environment.

Therefore, there is an urgent need in the art for a coating for a thermoelectric material that can solve the problem of high temperature oxidation and a device containing the same.

It is an object of the present invention to obtain a coating for a thermoelectric material that can solve the problem of high temperature oxidation.

A second object of the present invention is to obtain a device containing the material which can solve the problem of high temperature oxidation.

A third object of the present invention is to obtain a method for preparing a coating for a thermoelectric material which can solve the problem of high temperature oxidation.

In a first aspect of the invention, there is provided a coating comprising: a thermoelectric layer comprising a thermoelectric material; one or more metal coatings, wherein the metal coating forms a surface in contact with the thermoelectric layer and a facing surface; One or more layers of a metal oxide coating comprising a metal oxide, wherein the metal oxide coating forms a surface in contact with the opposing surface.

In a specific embodiment, the thermoelectric material is selected from the group consisting of filled and/or doped skutterudite.

In a specific embodiment, the filled and/or doped skutterudite is selected from the group consisting of CoSb ₃ skutter cobalt ore.

In a specific embodiment, the metal coating layer contains Ta, Nb, Ti, Mo, V, Al, Zr, Ni, NiAl, TiAl, NiCr, or a combination thereof.

In one specific embodiment, the metal oxide coating containing _{TiO 2, Ta 2 O 5,} Nb 2 O 5, Al 2 O 3, ZrO 2, NiO, SiO 2 , or combinations thereof.

In a specific embodiment, the thickness is from 10 to 500 microns.

In a specific embodiment, the thickness is from 50 to 200 microns.

In a specific embodiment, the metal coating has a thickness of from 0.01 to 20 microns.

In a specific embodiment, the metal coating has a thickness of 0.2 to 2 microns.

In a specific embodiment, the thermoelectric layer has a thickness L _T , and the metal coating and the metal oxide coating each have a thickness of L _{M & MOx} , wherein L _{M & MO} x ≦ L _T , and (L _T -L _M&MOx ) / L _T ≦ 0.4.

A second aspect of the invention resides in obtaining a device comprising a coating of the invention.

A third aspect of the present invention is to provide a method of producing the coating, comprising: providing a thermoelectric layer containing a thermoelectric material; forming one or more metal coating layers on the thermoelectric layer, wherein the metal coating is formed and a surface in contact with the thermoelectric layer and another facing surface; forming one or more layers of a metal oxide coating on the metal coating, the metal oxide coating containing a metal oxide, wherein the metal oxide is formed The surface of the metal coating that is in contact with the facing surface.

In some embodiments, the all or part of the metal coating is formed by thermal evaporation arc spraying, plasma spraying, flame spraying, vacuum sputtering, electrochemical vapor deposition plating, or no electricity. Electroless deposition.

In some embodiments, the all or part of the metal oxide coating is formed by a thermal evaporation deposition method, a vacuum sputtering method, a plasma spray method, a sol-gel method, or a chemical solution deposition method. (chemical solution deposition), or chemical vapor deposition.

In certain embodiments, the metal oxide coating is contacted with the facing surface of the metal coating by at least partial oxidation of the metal coating.

Figure 1 shows the high temperature vapor pressure of some of the elements.

2 is a CoSb ₃ based skutterudite π-type device with a multilayer coating.

3 is a top cross-sectional view corresponding to the multilayered package thermoelectric element of FIG. 2 (left: circular, right: square).

Figure 4 is a SEM photograph of the interface of the Yb _0.3 Co ₄ Sb ₁₂ core cladding material.

The inventors have conducted extensive and intensive research to form a multilayer coating of metal and oxide on the surface of a thermoelectric material (represented by a CoSb ₃ skutter cobalt ore material) by an improved preparation process using physical and chemical methods. It achieves the dual problem of preventing Sb volatilization and inhibiting oxidation of materials at high temperature, and improves the durability and reliability of CoSb ₃ skutter cobalt ore and its devices. The present invention has been completed on this basis.

The present invention is directed to the surface of a CoSb ₃ skutterite material or component by physical or chemical preparation methods for the needs of thermoelectric materials (typically such as CoSb ₃ skutter cobalt ore) and the use of components and the lack of prior art. A multilayer coating of two types of metals and oxides to prevent volatilization of Sb elements and oxidation of materials in high temperature applications.

The invention relates to a method for preparing a thermoelectric material and a component thereof having a multi-layer coating structure, and belongs to the field of thermoelectric materials and devices. The composition of the material is called SKT/M/MO _x , where SKT includes, but is not limited to, CoSb ₃ octagonal cobalt ore compound, doped CoSb ₃ -based skutterudite compound, CoSb ₃ -based skutterudite compound, doped CoSb ₃ -based filled skutterudite compound; M represents a metal coating, including but not limited to one of Ta, Nb, Ti, Mo, V, Al, Zr, Ni, NiAl, TiAl, NiCr or two or more of them alloy; MO _x represents a metal oxide coating, including, but not limited to, _{TiO 2, Ta 2 O 5,} Nb 2 O 5, Al 2 O 3, ZrO ₂ one kind _2, NiO, SiO, or wherein two or more A composite or a multilayer structure composed of two or more oxides. The material or component presented by SKT/M/MO _x has a multi-layer cladding structure, that is, a metal M layer is coated on the surface of the SKT material, and one or more layers of MO _{x are} coated on the surface of the M layer. The role of the coating is to inhibit the volatilization of Sb in SKT and the oxidation of the SKT material. The main role of the metal M layer is to improve the density, continuity and bonding strength of the MO _x cladding layer. The method for preparing the coating layer includes thermal evaporation, physical sputtering, arc spraying, plasma thermal spraying, electrochemical deposition, chemical vapor deposition, solution chemical deposition, and pulse electrodeposition. The total thickness of the coating is typically from 10 to 500 microns, with the M layer having a thickness of from 0.01 to 20 microns and the MO _x layer having a thickness of from 9.99 to 499.9 microns. The invention can effectively prevent the high temperature volatilization of Sb and the oxidation of SKT in the material as a preparation method of the CoSb ₃ based skutter ore multi-layer material. The high temperature aging results show that the conversion efficiency of the coated layer π-type component is 1000 hours and high temperature aging. After the test, it remained substantially unchanged, while the conversion efficiency of the same π-shaped element without the coating layer was reduced by 70% after 1000 hours of aging. The invention significantly improves the durability of the CoSb ₃ skutter cobalt ore material and its device, and can be used as a practical thermoelectric material and device for a long period of time at a temperature of about 600 ° C.

As used herein, "opposing" means that the positional relationship between the two faces each other.

Various aspects of the invention will be described in detail below.

As shown in Figures 2 and 3, a coating or element of a coated multi-layered structure is shown, the structure of which can be described as SKT/M/MO _x (see Figures 2 and 3). That is, the structure of the thermoelectric material (SKT) / coating (M / MO _x ).

Wherein SKT by CoSb ₃ based skutterudite materials, doped CoSb ₃ based skutterudite compounds, CoSb ₃ based filled skutterudite compounds, doped CoSb ₃ based filled skutterudite compound selected, and the above compound as a main phase Composite material; may also be a cage compound thermoelectric material, a semi-Hasler thermoelectric material, a BiTe-based material, a doped BiTe-based compound, a BiTe-based filling compound, a doped BiTe-based filling compound, and the above compound as a main phase Composite material. Preferably, the SKT is composed of a CoSb ₃ octagonal cobalt ore material, a CoSb ₃ -based skutterudite compound, a CoSb ₃ -based skutterudite compound, a doped CoSb ₃ -based skutterudite compound, and the above compounds. The composite is chosen.

The metal coating M is a film-like coating of a metal or an alloy, including but not limited to one of Ta, Nb, Ti, Mo, V, Al, Zr, Ni, NiAl, TiAl, NiCr or two or more of them. Alloy.

MO _x is a coating of a metal oxide, and may be one of TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₃ , Al ₂ O ₃ , ZrO ₂ , NiO, SiO ₂ or a composite of two or more thereof, Or a composite composed of two or more oxides or a multilayer structure composed of two or more oxides thereof.

The invention provides a CoSb ₃ skutter cobalt compound material containing a multi-layer coating layer and a preparation method thereof. The core of the preparation method is to form a strong adhesion on the outer layer or the outer layer by physical or chemical methods. An oxide layer with high density and continuity, and the inner layer is one or more layers of metal. The metal transition layer can prevent the high temperature volatilization of the Sb element and improve the bonding between the oxide layer and the skutterudite material. strength.

The all or part of the metal coating may be formed by thermal evaporation, arc spraying, plasma spraying, flame spraying, vacuum sputtering, electrochemical vapor deposition, electroplating, or electroless deposition. (electroless depositlon).

The all or part of the metal oxide coating may be formed by thermal evaporation, vacuum sputtering, plasma spraying, sol-gel, chemical solution deposition, or chemistry. Chemical vapor deposit (chemical vapor deposit).

In a preferred embodiment of the invention, the invention preferably employs a filled (and/or) doped CoSb ₃ -based skutterudite compound material or component as a core, by thermal evaporation, physical sputtering, arc spraying One or more layers of M transition layer material are formed on the surface of the skutterudite material by a method such as pulse electrodeposition, electrochemical deposition or electroplating. Next, the surface of the M layer is subjected to methods such as thermal evaporation, physical sputtering, plasma thermal spraying, Sol-Gel, chemical solution deposition, and chemical vapor deposition (Chemical Vapor Deposition). One or more oxide MO _x layers are formed. For those metal elements which are easily oxidized, the MO _x layer can also be directly oxidized by a metal M layer under a suitable partial pressure of oxygen, at which time the partial pressure of oxygen and its temperature are controlled by thickness. Important process parameters.

In the two types of coatings, the inner layer M transition layer is relatively thin, 0.01-20 microns, mainly to increase the bonding strength of the MO _x layer. The total thickness of the M layer depends on the composition of the core and the M layer itself, the thermal conductivity and electrical conductivity of the skutterudite material, the method of forming the M layer, the composition of the MO _x layer, etc. The key to controlling the thickness of the M layer is to prevent A fast bypass path that creates heat flow and current. The outer MO _x protective layer is relatively thick, and the thickness of the MO _x layer depends on the material composition, the method of forming the MO _x layer, the density and thermal conductivity of the MO _x layer, and the like. The two types of coatings have a total thickness of from 10 to 500 microns.

If the CoSb ₃ skutter cobalt multi-layer cladding material is used as a thermoelectric element to form a device, the length (high) of the peripheral coating of the component should be less than or equal to the length (high) of the component, if less than the length (high) of the component When the component is near the low temperature end, an uncoated region not exceeding 40% of the total length of the component may be left. The length (height) of the coating depends on the length (high) of the component, the temperature at the high temperature end, the thickness of the coating, especially the M transition layer, and the thermal properties of the core of the skutterite component. In a π-type device, if the length of the surface coating of the element is less than the length of the element, the length of the coating on the p-type and n-type elements may be different as long as the temperature of use of the uncoated portion of the two elements is close.

The advantages of the invention are:

1. The π-type device prepared by the present invention has a marked improvement in durability and reliability in continuous use in a high temperature environment. Although the device composed of the coating-coated material has a slight decrease in thermoelectric conversion efficiency and electric power compared with the device composed of the uncoated material, the deterioration of the running performance at a high temperature (850K) for a long time (1000 hours) is not significant. The non-coating protection device has a thermoelectric conversion efficiency of about 70% after long-term operation at high temperatures.

2. The coating material can effectively prevent the high temperature volatilization of Sb element and the oxidation of SKU in SKU material; among them, the main functions of M layer include (1) preventing the high temperature volatilization of Sb element, and (2) improving the adhesion of MO _x layer. , density, continuity and bonding strength.

Unless otherwise specified, various starting materials of the present invention can be obtained commercially, or can be prepared according to conventional methods in the art. All professional and scientific terms used herein have the same meaning as those skilled in the art, unless otherwise defined or indicated. Furthermore, any methods and materials similar or equivalent to those described may be employed in the methods of the invention.

Other aspects of the invention will be apparent to those skilled in the art from this disclosure.

The invention is further illustrated below in conjunction with specific embodiments. It is to be understood that the examples are not intended to limit the scope of the invention. The experimental methods in the following examples which do not specify the specific conditions are usually carried out according to conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise stated, all parts are by weight, all percentages are by weight, and the molecular weight of the polymer is number average molecular weight.

Unless otherwise defined or indicated, all of the professional and scientific terms used herein have the same meaning as those skilled in the art. Furthermore, any methods and materials similar or equivalent to those described may be employed in the methods of the invention.

Example 1:

The nominal composition of the CoSb ₃ -based filled n-type skutterudite material is Ba _0.24 Co ₄ Sb ₁₂ , and the sintered bulk material is processed into a 3 x 3 x 15 mm ³ cuboid sample. Firstly, a layer of about 5 micron NiCrMo (Ni:Cr:Mo=68:24:8) is formed by arc spraying on the peripheral surface of the material. The arc spraying process parameters are: arc voltage 28-30V, working current 180-200A, The gas pressure is 0.4-0.6 MPa and the spraying distance is 150-200 mm. A layer of about 60 micron SiO ₂ is formed by plasma spraying on the NiCrMo coating. The process parameters of the plasma spraying are: spraying distance 70-100mm, powder feeding rate 0.5-1g/min, spraying current 70-100A, ion The gas Ar flow rate is 1-1.5 L/min, and the flow rate of the powdered Ar gas is 1-3 L/min.

Example 2;

The nominal composition of the CoSb ₃ -based filled n-type skutterudite material is Ba _0.18 Ce _0.06 Co ₄ Sb ₁₂ , and the sintered bulk material is processed into a 3 x 3 x 15 mm ³ cuboid sample. A layer of Al of about 2 microns was first formed by magnetron sputtering on the peripheral surface of the material. The Al target has a diameter of 75 mm and a thickness of 5 mm, and the sputtering gas is high purity argon gas (Ar purity is 99.999%), and the argon gas flow rate is 15 mL/min. The system has a background vacuum of 10 Pa and a working pressure of 0.2 Pa. Further, the sample temperature was normal temperature (20 ° C), the sputtering power was 40 W, and the film deposition rate was about 12 nm/min. Finally, the aluminum-coated sample was oxidized in air at 150 ° C for 1 hour to form an Al ₂ O ₃ coating on the surface.

Example 3:

Examples of CoSb ₃ using the filled skutterudite-based core with a multilayer cover element consisting of π-type device of this embodiment. The nominal composition of the p-type element is Ce _0.9 Co _2.5 Fe _1.5 Sb ₁₂ , and the nominal composition of the n-type element is Yb _0.3 Co ₄ Sb ₁₂ . The sintered bulk material was processed into a 3 x 3 x 15 mm ³ rectangular parallelepiped sample. First, the end faces (including the end faces) of the p-type and n-type members were covered with carbon paper by about 3.5 and 5.5 mm, respectively, while the other end was coated with the same material to cover the end faces. A 6-micron Mo coating was applied to the exposed surface of the two components by arc spraying, and a 20 μm ZrO _{2 was} sprayed onto the Mo coating by plasma spraying. Finally, the carbon paper for covering was removed to obtain p-type and n-type elements having coating lengths of 16.5 and 14.5 mm, respectively (see Fig. 4).

All documents mentioned in the present application are hereby incorporated by reference in their entireties as if they do In addition It is to be understood that various changes and modifications may be made by those skilled in the art in the light of the scope of the invention.

Claims (15)

A coating for a thermoelectric material, comprising: a thermoelectric layer comprising a thermoelectric material; one or more metal coatings, wherein the metal coating forms a surface in contact with the thermoelectric layer and a facing surface; one or more layers of a metal oxide coating comprising a metal oxide, wherein the metal oxide coating forms a surface in contact with the opposing surface. The coating of claim 1 wherein the thermoelectric material is selected from the group consisting of filled and/or doped skutterudite. The coating of claim 2, wherein the filled and/or doped skutterudite is selected from the group consisting of CoSb ₃ octagonal cobalt ore. The coating of claim 1, wherein the metal coating comprises Ta, Nb, Ti, Mo, V, Al, Zr, Ni, NiAl, TiAl, NiCr, or a combination thereof. The coating of the requested item 1, wherein said metal oxide coating containing _{TiO 2, Ta 2 O 5,} Nb 2 O 5, Al 2 O 3, ZrO 2, NiO, SiO 2 , or combinations thereof. The coating of claim 1 wherein the coating has a thickness of from 10 to 500 microns. The coating of claim 6 wherein the coating is thick The degree is 50-200 microns. The coating of claim 1 wherein the metal coating has a thickness of from 0.01 to 20 microns. The coating of claim 8 wherein the metal coating has a thickness of from 0.2 to 2 microns. The coating of the requested item 1, wherein the pyroelectric layer having a height of L _T, and the metal coating and the metal oxide coating each having a height of L _{M & MOx,} where L _{M & MOx} ≦ L _T, and (L _T -L _M&MOx /L _T )≦0.4. A device comprising the coating of claim 1. A method for preparing a coating according to claim 1, comprising the steps of: providing a thermoelectric layer containing a thermoelectric material; forming one or more metal coating layers on the thermoelectric layer, wherein the metal Forming a surface in contact with the thermoelectric layer and another opposing surface; forming one or more layers of a metal oxide coating on the metal coating, the metal oxide coating comprising a metal oxide, wherein The metal oxide coating forms a surface that is in contact with the opposing surface of the metal coating. The preparation method of claim 12, comprising the steps of: Forming all or part of the metal coating by one or more of the following methods: thermal evaporation, arc spray, plasma spray, flame spray, vacuum sputtering, electrochemical vapor deposition, Electroplating, or electroless deposition. The preparation method according to claim 12, comprising the steps of: forming all or part of the metal oxide coating layer by one or more of the following methods: thermal evaporation method, vacuum sputtering method, plasma spraying method , sol-gel, chemical solution deposition, or chemical vapor deposition. The preparation method of claim 12, comprising the step of at least partially oxidizing the metal coating such that the metal oxide coating is in contact with the facing surface of the metal coating.