Method for realizing low-temperature and low-voltage connection of skutterudite and metal electrode based on nano-silver paper

Abstract

The invention discloses a method for realizing low-temperature and low-voltage connection of skutterudite and a metal electrode based on nano-silver paper, and relates to the technical field of dissimilar material connection. The invention aims to solve the problems that the connection strength of a joint is reduced and the contact resistance and the contact thermal resistance of an interface are increased due to serious interface chemical reaction caused by over-high connection temperature of the skutterudite and a metal electrode in the prior art, so that the conversion efficiency of a thermoelectric device is low. By controlling the connection temperature, the heat preservation time and the sintering pressure of the nano-silver paper, the sintered silver tissue structure can be effectively controlled, and then the joint tissue and performance are controlled; compared with common brazing and diffusion welding methods, the welding temperature is low, and the welding pressure is small; and compared with nano-silver paste sintering, the sintering quality is high, and the cost is low. The method for realizing low-temperature and low-voltage connection of skutterudite and the metal electrode based on the nano-silver paper can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of connecting dissimilar materials, and in particular to a method for connecting skutterudite and a metal electrode at low temperature and low pressure based on nano silver paper. Background Art

[0002] The medium temperature zone of skutterudite is one of the thermoelectric materials with the greatest potential for practical applications. For actual skutterudite thermoelectric devices, in addition to the performance of skutterudite thermoelectric materials, the connection quality between skutterudite thermoelectric materials and metal electrodes is also a key factor affecting the output performance of thermoelectric devices. However, conventional welding methods such as brazing and diffusion welding have high welding temperatures (>600°C), which will intensify the chemical reaction at the electrode connection interface, resulting in an increase in the interface contact resistance and contact thermal resistance, thereby reducing the output performance of the thermoelectric device.

[0003] Conventional nano silver solder paste can achieve the connection of thermoelectric materials at a relatively low temperature (about 300°C), but the connection atmosphere of nano silver paste usually requires a certain amount of oxygen, which will cause oxidation of the skutterudite thermoelectric material. Vacuum sintering of nano silver paste will have defects such as too fast solvent evaporation and insufficient decomposition resulting in holes. Therefore, it is urgent to develop a method that can connect skutterudite and metal electrodes under low temperature (<500°C) and low pressure (<15MPa) conditions in a vacuum. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the connection temperature of the existing skutterudite and metal electrode is too high, which leads to serious interfacial chemical reaction, reduces the connection strength of the joint and increases the contact resistance and contact thermal resistance of the interface, thereby leading to low conversion efficiency of the thermoelectric device, and to provide a method for low-temperature and low-pressure connection of skutterudite and metal electrode based on nano silver paper.

[0005] A method for connecting skutterudite and a metal electrode at low temperature and low pressure based on nano silver paper is carried out in the following steps:

[0006] Step S1, preparing the skutterudite thermoelectric material to be welded:

[0007] The skutterudite thermoelectric material powder is sequentially sintered and connected with the element barrier layer and the welding transition layer in one step to obtain a skutterudite block with the barrier layer and the transition layer; the skutterudite block is cut, and then the surface to be welded of the skutterudite block is sequentially ground, polished, ultrasonically cleaned and blown dry to obtain the skutterudite thermoelectric material to be welded;

[0008] Step S2: preparing the metal electrode to be welded:

[0009] The surface of the metal electrode to be welded is sequentially ground, polished, ultrasonically cleaned and blown dry to obtain the metal electrode to be welded;

[0010] Step S3, connecting the skutterudite thermoelectric material to be welded and the metal electrode to be welded:

[0011] The nano silver paper to be welded is placed between the skutterudite thermoelectric material to be welded obtained in step S1 and the metal electrode to be welded obtained in step S2 for assembly to obtain a connecting piece to be welded; the connecting piece to be welded is heated to 400-550°C in a vacuum environment, and is kept warm at 400-550°C for 5-60 minutes; after the insulation is completed, the temperature is cooled to room temperature to complete the low-temperature and low-pressure connection of the skutterudite and the metal electrode based on the nano silver paper.

[0012] Beneficial effects of the present invention:

[0013] (1) The present invention uses nano silver paper to achieve the connection between skutterudite and copper electrode. Specifically, nano silver paper without organic solvent is used as the welding material of skutterudite thermoelectric material, which can effectively reduce the connection temperature of conventional brazing and diffusion welding, as well as the problem of excessive organic content of nano silver paste; it can also effectively reduce the interface reaction problem of skutterudite thermoelectric joint. At the same time, the metal electrode, nano silver paper, welding transition layer and element barrier layer have good metallurgical bonding, only limited element diffusion exists, and brittle intermetallic compounds are not generated. The present invention realizes the low-temperature and low-pressure reliable connection between metal electrode and skutterudite, and the service temperature of the joint can exceed 600°C, which fully meets the high-temperature service requirements; at the same time, the interface connection strength is high, and the room temperature shear strength is as high as 30MPa.

[0014] (2) The present invention can effectively control the sintered silver structure and thus the joint structure and performance by controlling the nano-silver paper connection temperature, insulation time and sintering pressure; compared with the commonly used soldering and diffusion welding methods, the welding temperature is low and the welding pressure is small; compared with the nano-silver paste sintering, the sintering quality is high and the cost is low.

[0015] The present invention can obtain a method for realizing low-temperature and low-voltage connection between skutterudite and a metal electrode based on nano silver paper. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The porosity SEM structure diagram of the nano silver paper after sintering in Example 1 is shown;

[0017] Figure 2 The SEM image of the interface of the nano silver paper connected to the Cu electrode / p-type skutterudite (p-SKD) in Example 1;

[0018] Figure 3 The stress-strain curve of the nanosilver paper connected to the Cu electrode / p-type skutterudite (p-SKD) in Example 1 is shown. DETAILED DESCRIPTION

[0019] Specific implementation method 1: This implementation method is a method for connecting skutterudite and a metal electrode at low temperature and low pressure based on nano silver paper, which is carried out according to the following steps:

[0020] Step S1, preparing the skutterudite thermoelectric material to be welded:

[0021] The skutterudite thermoelectric material powder is sequentially sintered and connected with the element barrier layer and the welding transition layer in one step to obtain a skutterudite block with the barrier layer and the transition layer; the skutterudite block is cut, and then the surface to be welded of the skutterudite block is sequentially ground, polished, ultrasonically cleaned and blown dry to obtain the skutterudite thermoelectric material to be welded;

[0022] Step S2: preparing the metal electrode to be welded:

[0023] The surface of the metal electrode to be welded is sequentially ground, polished, ultrasonically cleaned and blown dry to obtain the metal electrode to be welded;

[0024] Step S3, connecting the skutterudite thermoelectric material to be welded and the metal electrode to be welded:

[0025] The nano silver paper to be welded is placed between the skutterudite thermoelectric material to be welded obtained in step S1 and the metal electrode to be welded obtained in step S2 for assembly to obtain a connecting piece to be welded; the connecting piece to be welded is heated to 400-550°C in a vacuum environment, and is kept warm at 400-550°C for 5-60 minutes; after the insulation is completed, the temperature is cooled to room temperature to complete the low-temperature and low-pressure connection of the skutterudite and the metal electrode based on the nano silver paper.

[0026] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the element barrier layer described in step S1 is any one metal or an alloy composed of multiple elements among Al, Ti, V, Cr, Fe, Co, Ni, Zr, Nb, Mo, Ag, Au and Pt.

[0027] The other steps are the same as those in the first specific implementation.

[0028] Specific implementation method three: The difference between this implementation method and specific implementation method one or two is that the welding transition layer described in step S1 is any one metal of Cu, Ag and Au or an alloy composed of multiple elements.

[0029] The other steps are the same as those in the first or second embodiment.

[0030] Specific implementation method 4: The difference between this implementation method and specific implementation methods 1 to 3 is that the metal electrode described in step S2 is any one metal of Cu, Ag, Fe, Ni and Co or an alloy composed of multiple elements.

[0031] The other steps are the same as those in Specific Embodiments 1 to 3.

[0032] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that: the element barrier layer is Fe 80 V 20 alloy layer; the welding transition layer is a Cu metal layer; the metal electrode is a Cu electrode.

[0033] The other steps are the same as those in Specific Embodiments 1 to 4.

[0034] Specific implementation method six: The difference between this implementation method and specific implementation methods one to five is that: in step S1, a diamond wire cutting machine is used to cut the cobaltite block into pieces with a size of (2-5) mm×(2-5) mm×(3-10) mm; the surface to be welded of the cobaltite block is grinded with 800#, 1000#, 1500# and 2000# metallographic sandpaper in turn, and then polished, and then placed in ethanol and acetone solutions for ultrasonic cleaning for 3-20 minutes, and finally blown dry with cold air from a hair dryer.

[0035] The other steps are the same as those in Specific Embodiments 1 to 5.

[0036] Specific implementation method seven: The difference between this implementation method and specific implementation methods one to six is ​​that in step S2, the surface to be welded of the metal electrode is grinded and polished using 800#, 1000#, 1500# and 2000# metallographic sandpapers in sequence, and then placed in ethanol and acetone solutions for ultrasonic cleaning for 3 to 20 minutes, and finally blown dry with cold air from a hair dryer.

[0037] The other steps are the same as those in Specific Embodiments 1 to 6.

[0038] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the vacuum degree in step S3 is 5×10 -3 ~10×10 -3 Pa.

[0039] The other steps are the same as those in Specific Embodiments 1 to 7.

[0040] Specific embodiment 9: The difference between this embodiment and specific embodiments 1 to 8 is that the welding pressure of the connecting piece to be welded in step S3 is 2.5-20 MPa.

[0041] The other steps are the same as those in Specific Embodiments 1 to 8.

[0042] Specific embodiment ten: The difference between this embodiment and specific embodiments one to nine is that in step S3, the heating rate is 5 to 30°C / min, and the cooling rate is 5 to 30°C / min.

[0043] The other steps are the same as those in Specific Embodiments 1 to 9.

[0044] The following examples are used to verify the beneficial effects of the present invention:

[0045] Example 1: A method for connecting skutterudite and a metal electrode at low temperature and low pressure based on nano silver paper, which is carried out according to the following steps:

[0046] Step S1, preparing the skutterudite thermoelectric material to be welded:

[0047] The skutterudite thermoelectric material powder is sequentially mixed with the element barrier layer Fe 80 V 20 and the welding transition layer Cu are sintered in one step (the sintering process is the sintering process of the skutterudite material), and a skutterudite block with a barrier layer and a transition layer is obtained; the skutterudite block is cut into pieces with a size of 5 mm×5 mm×8 mm using a diamond wire cutting machine, and then the surface to be welded of the skutterudite block is polished with 800#, 1000#, 1500# and 2000# metallographic sandpaper in sequence, and then polished, and then ultrasonically cleaned in ethanol and acetone solutions for 20 minutes in sequence, and finally dried with cold air from a hair dryer to obtain the skutterudite thermoelectric material to be welded, and placed in a sealed bag for storage for standby use;

[0048] The skutterudite is p-type skutterudite;

[0049] Step S2: preparing the metal electrode to be welded:

[0050] The surface of the Cu electrode to be welded was ground and polished using 800#, 1000#, 1500# and 2000# metallographic sandpapers, and then ultrasonically cleaned in ethanol and acetone solutions for 20 minutes, and finally dried with cold air from a hair dryer to obtain the Cu electrode to be welded, which was then stored in a sealed bag for later use;

[0051] Step S3, connecting the skutterudite thermoelectric material to be welded and the metal electrode to be welded:

[0052] The nano silver wire is reduced by polyol method or purchased by filtration-drying to obtain nano silver paper to be welded; the nano silver paper to be welded is placed between the skutterudite thermoelectric material to be welded obtained in step S1 and the Cu electrode to be welded obtained in step S2 to obtain a connecting piece to be welded; the connecting piece to be welded is placed in a vacuum degree of 5×10 -3 Pa, the temperature was raised to 500°C at a rate of 30°C / min, and kept at 500°C for 30 minutes, with a welding pressure of 15MPa; after the insulation, the temperature was lowered to room temperature at a rate of 10°C / min, completing the low-temperature and low-pressure connection of cobaltite and metal electrode based on nanosilver paper.

[0053] After testing, this embodiment achieves low-temperature and low-pressure reliable connection between the Cu electrode and the cobaltite, and the service temperature of the joint can exceed 600°C, meeting the high-temperature service requirements; the interface connection strength is high, and the room temperature shear strength is as high as 30MPa.

[0054] Figure 1 The porosity SEM structure diagram of the nano silver paper after sintering in Example 1 is shown; Figure 1 As shown in the figure, the porosity of the nanosilver sintered body reaches one of the highest values ​​of nanosilver sintered bodies at present. The extremely low porosity ensures that the sintered body has ultra-high thermal conductivity. By calculation, it can be obtained that the thermal conductivity of sintered silver is 394W·m when the porosity is 5.5%. -1 ·K -1 , reaching 92% of the pure silver block.

[0055] Figure 2 The SEM image of the interface of the nano silver paper connected to the Cu electrode / p-type skutterudite (p-SKD) in Example 1 is shown; Figure 2 As shown, in this embodiment, the welding interface is uniform and flat, without obvious welding defects such as pores, no intermetallic compounds are generated at the electrode / nanosilver paper / transition layer / barrier layer interface, and metallurgical bonding occurs by element diffusion (red arrow). The joint welding strength is high, and compared with the conventional brazing interface, the interface resistance and interface thermal resistance in this embodiment are lower.

[0056] Figure 3 : represents the stress-strain curve of the nano silver paper connected to the Cu electrode / p-type skutterudite (p-SKD) in Example 1; Figure 3 As shown, the shear strength of the welded joints in this embodiment has high repeatability and can reach the p-SKD base material strength (30 MPa).

[0057] This embodiment uses organic solvent-free nano silver paper as a connecting material for skutterudite thermoelectric materials, which can effectively reduce the welding temperature between the electrode and the skutterudite. Compared with conventional brazing and diffusion welding, the welding temperature and pressure are low. This embodiment can effectively achieve good metallurgical bonding between skutterudite and Cu electrode by optimizing the welding transition layer material, with high interface connection strength and no intermetallic compound generation. The performance of the brazed connection joint of the cobalt intermediate layer diffusion connection skutterudite and copper electrode in this embodiment is tested, and the test results show that the sintered porosity of the nano silver paper is only 5.5%, and the shear strength of the joint can reach 30MPa at room temperature, while the shear strength of the conventional welding joint at room temperature is less than 20MPa.

Claims

1. A method for connecting skutterudite and a metal electrode at low temperature and low pressure based on nano silver paper, characterized in that The connection method is carried out as follows: Step S1, preparing the skutterudite thermoelectric material to be welded: The skutterudite thermoelectric material powder is sequentially sintered and connected with the element barrier layer and the welding transition layer in one step to obtain a skutterudite block with the barrier layer and the transition layer; the skutterudite block is cut, and then the surface to be welded of the skutterudite block is sequentially ground, polished, ultrasonically cleaned and blown dry to obtain the skutterudite thermoelectric material to be welded; Step S2: preparing the metal electrode to be welded: The surface of the metal electrode to be welded is sequentially ground, polished, ultrasonically cleaned and blown dry to obtain the metal electrode to be welded; Step S3, connecting the skutterudite thermoelectric material to be welded and the metal electrode to be welded: The nano silver paper to be welded is placed between the skutterudite thermoelectric material to be welded obtained in step S1 and the metal electrode to be welded obtained in step S2 for assembly to obtain a connecting piece to be welded; the connecting piece to be welded is heated to 400-550°C in a vacuum environment, and is kept warm at 400-550°C for 5-60 minutes; after the insulation is completed, the temperature is cooled to room temperature to complete the low-temperature and low-pressure connection of the skutterudite and the metal electrode based on the nano silver paper.

2. The method of claim 1 for realizing low-temperature and low-pressure connection between skutterudite and metal electrode based on nano silver paper, characterized in that The element barrier layer described in step S1 is any one metal of Al, Ti, V, Cr, Fe, Co, Ni, Zr, Nb, Mo, Ag, Au and Pt, or an alloy composed of multiple elements.

3. The method of claim 1 for realizing low-temperature and low-pressure connection between skutterudite and metal electrode based on nano silver paper, characterized in that The welding transition layer described in step S1 is any one metal of Cu, Ag and Au or an alloy composed of multiple elements.

4. The method of claim 1 for realizing low-temperature and low-pressure connection between skutterudite and metal electrode based on nano silver paper, characterized in that The metal electrode in step S2 is any one of Cu, Ag, Fe, Ni and Co or an alloy composed of multiple elements.

5. A method for connecting skutterudite and a metal electrode at low temperature and low pressure based on nano silver paper according to claim 2, 3 or 4, characterized in that The element barrier layer is Fe 80 V 20 alloy layer; the welding transition layer is a Cu metal layer; the metal electrode is a Cu electrode.

6. The method of claim 1 for realizing low-temperature and low-pressure connection between skutterudite and metal electrode based on nano silver paper, characterized in that In step S1, a diamond wire cutting machine is used to cut the cobaltite block into pieces with a size of (2-5) mm×(2-5) mm×(3-10) mm; the surface to be welded of the cobaltite block is grinded and polished using 800#, 1000#, 1500# and 2000# metallographic sandpapers in sequence, and then placed in ethanol and acetone solutions for ultrasonic cleaning for 3-20 minutes in sequence, and finally dried with cold air from a hair dryer.

7. The method of claim 1 for realizing low-temperature and low-pressure connection between skutterudite and metal electrode based on nano silver paper, characterized in that In step S2, the surface of the metal electrode to be welded is grinded and polished using 800#, 1000#, 1500# and 2000# metallographic sandpapers in sequence, and then ultrasonically cleaned in ethanol and acetone solutions for 3 to 20 minutes, and finally dried with cold air from a hair dryer.

8. The method of claim 1 for realizing low-temperature and low-pressure connection between skutterudite and metal electrode based on nano silver paper, characterized in that The vacuum degree in step S3 is 5×10 -3 ~10×10 -3 Pa.

9. The method of claim 1 for realizing low-temperature and low-pressure connection between skutterudite and metal electrode based on nano silver paper, characterized in that The welding pressure of the connecting piece to be welded in step S3 is 2.5-20 MPa.

10. The method of claim 1 for realizing low-temperature and low-pressure connection between skutterudite and metal electrode based on nano silver paper, characterized in that In step S3, the heating rate is 5 to 30°C / min, and the cooling rate is 5 to 30°C / min.

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