A method for realizing low-temperature and low-pressure connection of skutterudite and metal electrode based on nano-silver paper

Abstract

The application relates to a method for connecting a low-temperature and low-pressure fulling cobalt with a metal electrode based on nano-silver paper, and relates to the technical field of heterogeneous material connection. The application aims to solve the problems of high connection temperature of the existing fulling cobalt and metal electrode, serious interface chemical reaction, reduced connection strength of the joint, increased contact resistance and contact thermal resistance of the interface, and low conversion efficiency of a thermoelectric device. The application can effectively control the sintered silver organization structure, and then control the joint organization and performance by controlling the nano-silver paper connection temperature, holding time and sintering pressure. Compared with the commonly used brazing and diffusion welding method, 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. The application can obtain a method for connecting a low-temperature and low-pressure fulling cobalt with a metal electrode based on nano-silver paper.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of heterogeneous material connection, in particular to a method for connecting skutterudite and metal electrodes at low temperature and low pressure based on a nano-silver paper. BACKGROUND

[0002] The medium-temperature zone of skutterudite is one of the most practically applicable thermoelectric materials. For an actual skutterudite thermoelectric device, in addition to the performance of the skutterudite thermoelectric material, the connection quality of the skutterudite thermoelectric material and the metal electrode is also a key factor affecting the output performance of the thermoelectric device. However, the welding temperature of conventional welding methods such as brazing and diffusion welding is relatively high (> 600 DEG C), which can aggravate the chemical reaction at the electrode connection interface, increase the interface contact resistance and contact thermal resistance, and thus reduce the output performance of the thermoelectric device.

[0003] However, the connection atmosphere of the conventional nano-silver solder paste usually requires a certain amount of oxygen, which can cause the oxidation of the skutterudite thermoelectric material. The vacuum sintering of the nano-silver solder paste can cause problems such as too fast solvent volatilization and insufficient decomposition to generate pores. Therefore, it is urgent to develop a method for connecting skutterudite and metal electrodes at low temperature (< 500 DEG C) and low pressure (< 15 MPa) in a vacuum. SUMMARY

[0004] The application aims to solve the problems of high connection temperature of the existing skutterudite and metal electrodes, serious interface chemical reaction, reduced connection strength of the joint, increased interface contact resistance and contact thermal resistance, and low conversion efficiency of the thermoelectric device, and provides a method for connecting skutterudite and metal electrodes at low temperature and low pressure based on a nano-silver paper.

[0005] A method for connecting skutterudite and metal electrodes at low temperature and low pressure based on a nano-silver paper, which is performed according to the following steps:

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

[0007] The skutterudite thermoelectric material powder is sequentially sintered with an element barrier layer and a welding transition layer to obtain a skutterudite block with the barrier layer and the transition layer; the skutterudite block is cut, and then the welding surface of the skutterudite block is sequentially polished, polished, ultrasonically cleaned and dried to obtain the skutterudite thermoelectric material to be welded;

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

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

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

[0011] The to-be-welded nanosilver paper is arranged between the to-be-welded skutterudite thermoelectric material obtained in step S1 and the to-be-welded metal electrode obtained in step S2 to obtain a to-be-welded connecting piece; the to-be-welded connecting piece is heated to 400-550 DEG C under a vacuum environment, and is kept at the temperature of 400-550 DEG C for 5-60 min; after the keeping, the temperature is reduced to room temperature, and the connection of the skutterudite and the metal electrode based on the nanosilver paper is completed at low temperature and low pressure.

[0012] The present application has the following beneficial effects:

[0013] (1) The present application uses the nanosilver paper to realize the connection of the skutterudite and the copper electrode, specifically, the nanosilver paper without organic solvent is used as the welding material of the skutterudite thermoelectric material, which can effectively reduce the connection temperature of the conventional brazing and diffusion welding, and the problem of excessive organic content of the nanosilver paste; the interface reaction problem of the skutterudite thermoelectric joint can also be effectively reduced, and the metallurgical combination between the metal electrode, the nanosilver paper, the welding transition layer and the element barrier layer is good, only limited element diffusion exists, and no brittle intermetallic compound is generated. The present application realizes the reliable connection of the metal electrode and the skutterudite at low temperature and low pressure, and the service temperature of the joint can exceed 600 DEG C, which fully meets the high-temperature service requirement; meanwhile, the interface connection strength is high, and the room temperature shear strength is as high as 30 MPa.

[0014] (2) The present application can effectively control the sintered silver organization structure, and further control the joint organization and performance by controlling the connection temperature, holding time and sintering pressure of the nanosilver paper; compared with the conventional brazing and diffusion welding method, the welding temperature is low, and the welding pressure is small; compared with the nanosilver paste sintering, the sintering quality is high, and the cost is low.

[0015] The present application can obtain a method for realizing the connection of the skutterudite and the metal electrode at low temperature and low pressure based on the nanosilver paper. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The porosity SEM organization diagram of the nanosilver paper after sintering in embodiment 1 is shown;

[0017] Figure 2 The interface SEM diagram of the nanosilver paper connecting the Cu electrode / p-type skutterudite (p-SKD) in embodiment 1 is shown;

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

[0019] Embodiment I: The embodiment is a method for connecting skutterudite and metal electrode at low temperature and low pressure based on nano-silver paper, which is performed according to the following steps:

[0020] Step S1: Preparing skutterudite thermoelectric material to be welded:

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

[0022] Step S2: Preparing metal electrode to be welded:

[0023] The welding surface of the metal electrode is sequentially polished, polished, ultrasonically cleaned and dried 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 to obtain a welding connector; the welding connector is heated to 400-550 DEG C in a vacuum environment, and is kept at a temperature of 400-550 DEG C for 5-60 min; after the heat preservation is completed, it is cooled to room temperature, and the connection of skutterudite and metal electrode at low temperature and low pressure based on nano-silver paper is completed.

[0026] Embodiment II: The difference between the embodiment and embodiment I is that the element barrier layer in step S1 is any one of Al, Ti, V, Cr, Fe, Co, Ni, Zr, Nb, Mo, Ag, Au and Pt or an alloy composed of multiple elements.

[0027] The other steps are the same as those in embodiment I.

[0028] Embodiment III: The difference between the embodiment and embodiment I or II is that the welding transition layer in step S1 is any one of Cu, Ag and Au or an alloy composed of multiple elements.

[0029] The other steps are the same as those in embodiment I or II.

[0030] Embodiment IV: The difference between the embodiment and any one of embodiments I to III is that the metal electrode in step S2 is any one of Cu, Ag, Fe, Ni and Co or an alloy composed of multiple elements.

[0031] The other steps are the same as those in embodiment I to III.

[0032] Specific implementation five: the difference between this implementation and one of the specific implementations one to four is that the element barrier layer is Fe 80 V 20 alloy layer; the welding transition layer is a Cu metal layer; and the metal electrode is a Cu electrode.

[0033] The other steps are the same as those in the specific implementations one to four.

[0034] Specific implementation six: the difference between this implementation and one of the specific implementations one to five is that the diamond wire cutting machine is used to cut the skutterudite block into a size of (2-5) mm x (2-5) mm x (3-10) mm in step S1; the welding surface of the skutterudite block is polished using 800#, 1000#, 1500# and 2000# metallographic sandpaper in turn, and then polished, and then placed in ethanol and acetone solution for ultrasonic cleaning for 3-20 min in turn, and finally dried by cold air blowing of a hair dryer.

[0035] The other steps are the same as those in the specific implementations one to five.

[0036] Specific implementation seven: the difference between this implementation and one of the specific implementations one to six is that the welding surface of the metal electrode is polished using 800#, 1000#, 1500# and 2000# metallographic sandpaper in turn in step S2, and then polished, and then placed in ethanol and acetone solution for ultrasonic cleaning for 3-20 min in turn, and finally dried by cold air blowing of a hair dryer.

[0037] The other steps are the same as those in the specific implementations one to six.

[0038] Specific implementation eight: the difference between this implementation and one of the specific implementations one to seven is that the vacuum degree in step S3 is 5 x 10 -3 -10 x 10 -3 Pa.

[0039] The other steps are the same as those in the specific implementations one to seven.

[0040] Specific implementation nine: the difference between this implementation and one of the specific implementations one to eight is that the pressure of the welding of the to-be-welded connecting piece in step S3 is 2.5-20 MPa.

[0041] The other steps are the same as those in the specific implementations one to eight.

[0042] Specific implementation ten: the difference between this implementation and one of the specific implementations one to nine is that the heating rate in step S3 is 5-30 ℃ / min, and the cooling rate is 5-30 ℃ / min.

[0043] The other steps are the same as those in the specific implementations one to nine.

[0044] The beneficial effects of the present application are verified by the following examples:

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

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

[0047] The skutterudite thermoelectric material powder is sequentially sintered with the element barrier layer Fe 80 V 20 and the welding transition layer Cu (the sintering process is the sintering process of the skutterudite material) to obtain a skutterudite block with a barrier layer and a transition layer; the skutterudite block is cut into a size of 5mm×5mm×8mm using a diamond wire cutting machine, and then the welding surface of the skutterudite block is sequentially polished using 800#, 1000#, 1500# and 2000# metallographic sandpaper, and then polished, and then sequentially placed in ethanol and acetone solution for ultrasonic cleaning for 20min, and finally dried with cold air using a hair dryer, to obtain a skutterudite thermoelectric material to be welded, which is stored in a sealed bag for later use;

[0048] The skutterudite is a p-type skutterudite;

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

[0050] The welding surface of the Cu electrode is sequentially polished using 800#, 1000#, 1500# and 2000# metallographic sandpaper, and then polished, and then sequentially placed in ethanol and acetone solution for ultrasonic cleaning for 20min, and finally dried with cold air using a hair dryer, to obtain a Cu electrode to be welded, which is 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 obtained by reduction by the polyol method or purchased is subjected to suction filtration-drying to obtain a 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 heated at a rate of 30℃ / min to 500℃ under a vacuum degree of 5×10 -3 Pa, and held at a temperature of 500℃ for 30min, the welding pressure is 15MPa; after holding, it is cooled to room temperature at a rate of 10℃ / min, to complete the low-temperature and low-pressure connection of skutterudite and metal electrode based on nano-silver paper.

[0053] Tests have shown that this embodiment achieves a reliable low-temperature, low-pressure connection between the Cu electrode and cobaltite, with a joint service temperature exceeding 600°C, meeting the requirements for high-temperature service; the interface connection strength is high, with a room temperature shear strength of up to 30 MPa.

[0054] Figure 1 This shows the SEM microstructure of the nano-silver paper after sintering in Example 1; as shown. Figure 1 As shown, the porosity of the sintered nano-silver body reaches one of the highest values ​​to date. This extremely low porosity ensures the sintered body possesses ultra-high thermal conductivity. Calculations show that the thermal conductivity of sintered silver with a porosity of 5.5% is 394 W·m. -1 ·K -1 It reaches 92% of the purity of the silver block.

[0055] Figure 2 This shows a SEM image of the interface between the silver nanopaper and the Cu electrode / p-type cobaltite (p-SKD) in Example 1; as shown. Figure 2 As shown, the welding interface in this embodiment is uniform and flat, with no obvious welding defects such as pores. No intermetallic compounds are generated at the electrode / nanosilver paper / transition layer / barrier layer interface. Metallurgical bonding occurs through element diffusion (red arrow). The joint has high welding strength, and the interface resistance and interface thermal resistance are lower in this embodiment compared with conventional brazing interfaces.

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

[0057] This embodiment uses solvent-free nano-silver paper as the connecting material for cobaltite thermoelectric materials, which can effectively reduce the welding temperature between the electrode and cobaltite. Compared with conventional brazing and diffusion welding, the welding temperature and pressure are lower. By optimizing the welding transition layer material, this embodiment can effectively achieve a good metallurgical bond between cobaltite and Cu electrodes, with high interfacial bonding strength and no intermetallic compounds generated. The performance of the brazed joint connecting cobaltite and copper electrodes in this embodiment was tested. The test results show that the sintered porosity of the nano-silver paper is only 5.5%, and the shear strength of the joint at room temperature can reach 30 MPa, while the shear strength of the traditional welded joint at room temperature is less than 20 MPa.

Claims

1. A method for achieving low-temperature, low-pressure connection between cobaltite and a metal electrode based on nano-silver paper, characterized in that... The connection method is performed according to the following steps: Step S1: Prepare the cobalt ore thermoelectric material to be welded. The cobaltite thermoelectric material powder is sequentially sintered with an element barrier layer and a welding transition layer in one step to obtain a cobaltite block with a barrier layer and a transition layer; the cobaltite block is cut, and then the surface of the cobaltite block to be welded is sequentially ground, polished, ultrasonically cleaned and dried to obtain the cobaltite thermoelectric material to be welded. Step S2: Prepare the metal electrode to be soldered. The surfaces of the metal electrodes to be welded are successively ground, polished, ultrasonically cleaned, and dried to obtain the metal electrodes to be welded. 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; Step S3: Connect the cobalt ore thermoelectric material to be welded to the metal electrode to be welded. The nano-silver paper to be welded is placed between the cobaltite thermoelectric material to be welded obtained in step S1 and the metal electrode to be welded obtained in step S2 to form a weldable connector; the weldable connector is heated to 400~550℃ in a vacuum environment and kept at 400~550℃ for 5~60min; after the holding time is completed, it is cooled to room temperature to complete the low-temperature, low-pressure connection between cobaltite and metal electrode based on nano-silver paper; The silver nanowires are filtered and dried to obtain silver nanopaper to be soldered. The vacuum degree in step S3 is 5×10 -3 ~10×10 -3 The welding pressure of the connecting parts to be welded is 2.5~20 MPa, the heating rate is 5~30℃ / min, and the cooling rate is 5~30℃ / min.

2. The method for achieving low-temperature, low-pressure connection between cobaltite and metal electrodes based on nano-silver paper according to claim 1, characterized in that... In step S1, the cobaltite block is cut into (2~5) mm × (2~5) mm × (3~10) mm using a diamond wire cutter. The surfaces of the cobaltite block to be welded are polished in sequence with 800#, 1000#, 1500# and 2000# metallographic sandpaper, then polished, and then ultrasonically cleaned in ethanol and acetone solutions for 3~20 minutes. Finally, it is dried with a hair dryer using cold air.

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

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