A barrier layer for improving high temperature stability of thermoelectric module and preparation method thereof

Abstract

The invention discloses a barrier layer for improving the high temperature stability of a thermoelectric module and a preparation method thereof, and relates to the technical field of thermoelectric materials. The preparation method comprises: S1, cleaning and drying a substrate; S2, microetching to form a substrate with a surface roughness of Ra 0.5-1.2 μm; S3, activation; S4, pre-plating a nickel-cobalt layer: placing the activated substrate in a chemical pre-plating solution containing nickel salt, cobalt salt, reducing agent and complexing agent to form a nickel-cobalt transition layer with a thickness of 0.5-1.0 μm; S5, chemical plating composite layer: placing the pre-plated substrate in a chemical plating solution containing nickel salt, cobalt salt, rare earth salt, reducing agent and stabilizer to form a nickel-cobalt-rare earth element composite barrier layer with a thickness of 3-5 μm; S6, washing and drying the substrate after chemical plating. The present invention improves the traditional nickel barrier layer, adds rare earth elements, and performs chemical plating. The prepared composite barrier layer maintains stability during high temperature service, and can extend the service life to a certain extent.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric materials, and in particular to a barrier layer for improving the high-temperature stability of a thermoelectric module and a preparation method thereof. Background Art

[0002] A thermoelectric module is a device that can convert thermal energy into electrical energy or electrical energy into thermal energy. Its working principle is based on the thermoelectric effect. The thermoelectric effect refers to the electric field or potential difference generated between two different metals or semiconductor materials when the temperatures at the two ends are different. Specifically, when the electrons in the two materials are excited by thermal energy, they will move along the temperature gradient to form a potential difference. Thermoelectric modules are composed of N-type and P-type thermoelectric materials, with barrier layers, solder layers and metal electrodes at both ends in turn. N-type and P-type thermoelectric materials are used to realize the conversion of electrical energy and thermal energy; the barrier layer can prevent the diffusion of elements between the thermoelectric material and the solder, thereby improving the performance of the thermoelectric module and extending its service life; the metal electrode is generally a copper electrode, which is used to connect the thermoelectric materials in series to form a closed loop between the N-type and P-type thermoelectric materials; the solder is used to connect the thermoelectric material to the metal electrode. Thermoelectric materials are divided into three categories:

[0003] (1) Low-temperature thermoelectric materials (below 300°C) mainly used in thermoelectric refrigeration and low-temperature waste heat temperature difference power generation, mainly Bi 2 Te 3 , Sb 2 Te 3 etc. and their solid solutions;

[0004] (2) Medium-temperature thermoelectric materials (around 500°C) mainly used in medium-temperature power generation, including Mg 2 Si, PbTe, CoSb 3 Thermoelectric materials;

[0005] (3) High temperature thermoelectric materials (above 700°C), mainly including: CrSi 2 , Half-Heusler, SiGe, etc.

[0006] At present, Bi2Te3 is the most commonly used thermoelectric material, with an applicable temperature of 0~250℃ and a ZT value of 1.3~1.4 at room temperature. After optimization by methods such as doping and band engineering to control carrier concentration, the ZT value can even reach above 1.8, showing high thermoelectric performance. 2 Te 3 When encapsulating the base thermoelectric module, Ni is usually used as the material of the barrier layer. Although the electroplated Ni barrier layer can prevent electrode diffusion to a certain extent, it will diffuse into the Bi 2 Te 3 and form a brittle NiTe phase, and Ni and Bi2 Te 3 The interface between the substrates exhibits ohmic contact. During long-term service, coupled with the huge thermal stress generated during service, the interface between the Ni barrier layer and the thermoelectric material cracks, causing the performance and service life of the thermoelectric device to decline. In addition, the pure nickel coating has a low hardness (about 200 HV) and poor wear resistance, and is prone to wear failure after long-term use. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a barrier layer and a preparation method thereof for improving the high-temperature stability of a thermoelectric module. By introducing rare earth elements into the barrier layer and preparing a composite barrier layer by chemical plating, the stability of the barrier layer can be greatly improved and its service life can be extended.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a barrier layer for improving high temperature stability of a thermoelectric module comprises:

[0010] S1, pretreatment: cleaning the substrate to remove surface stains and then drying;

[0011] S2, immersing the pretreated substrate in a micro-etching solution for micro-etching to form a substrate with a surface roughness of Ra 0.5-1.2 μm;

[0012] S3, activating the micro-etched substrate surface;

[0013] S4, pre-plating nickel-cobalt layer: placing the activated substrate into a chemical pre-plating solution containing nickel salt, cobalt salt, reducing agent and complexing agent to form a nickel-cobalt transition layer with a thickness of 0.5-1.0 μm;

[0014] S5, chemical plating composite layer: placing the pre-plated substrate in a chemical plating solution containing nickel salt, cobalt salt, rare earth salt, reducing agent and stabilizer to form a nickel-cobalt-rare earth element composite barrier layer with a thickness of 3-5 μm;

[0015] S6, washing and drying the substrate after chemical plating.

[0016] Furthermore, in step S1, the surface of the substrate is cleaned with an alkaline cleaning agent and deionized water in sequence.

[0017] Furthermore, in step S2, the micro-etching solution comprises: 2 SO 4 80~90 mL / L, H 2 O 225~28 mL / L, polytetrafluoroethylene dispersion 25~28 mL / L, sodium citrate 1~2 g / L, the solvent is deionized water; the micro-etching time is 5~6min.

[0018] Furthermore, in step S3, the activation solution is 80-100 mL / L concentrated hydrochloric acid, and the activation time is 50-60 s.

[0019] Furthermore, in step S4, the pre-plating solution comprises: nickel sulfate (NiSO 4 6H 2 O) 20~30 g / L, cobalt sulfate (CoSO 4 7H 2 O) 5~8 g / L, sodium hypophosphite (NaH 2 PO 2 ·H 2 O) 20~30 g / L, sodium citrate 10~15 g / L, thiourea 0.5~1.0 mg / L, and the solvent is deionized water.

[0020] Furthermore, in step S4, chemical pre-plating is performed at a temperature of 60-80° C. and a pH of 8.5-9.5 for 10-15 minutes.

[0021] Further, in step S5, the composition of the chemical plating solution includes: 25-35 g / L nickel sulfate, 8-12 g / L cobalt sulfate, 4-5 mg / L rare earth salt, 30-40 g / L sodium hypophosphite, 15-20 g / L sodium citrate, 1-2 mg / L sodium thiosulfate, and the solvent is deionized water.

[0022] Furthermore, in step S5, chemical plating is performed at a temperature of 70-85° C. and a pH of 9.0-10.0 for 30-45 min, and the rare earth salt is selected from chlorides or sulfates of lanthanum, cerium or neodymium.

[0023] Furthermore, mechanical stirring or ultrasonic assistance is used during the pre-plating in step S4 and the chemical plating in step S5.

[0024] Furthermore, the present invention also provides a barrier layer for improving the high-temperature stability of a thermoelectric module, which is prepared by the above-mentioned preparation method. The barrier layer is a nickel-cobalt-rare earth element ternary composite barrier layer, wherein the rare earth element is uniformly distributed at the grain boundary, the mass fraction of the rare earth element in the composite barrier layer is 0.5~1.0%, and the Vickers hardness of the barrier layer is ≥420HV, and the interface contact resistance is ≤1.5 μΩ·cm² after aging for 1000 hours at 300°C.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention improves the traditional nickel barrier layer by adding rare earth elements. Rare earth elements have properties such as high corrosion resistance, high wear resistance, and superconductivity. The barrier layer formed by rare earth elements and nickel also has these properties. The barrier layer can maintain stability during high-temperature service, which can extend the service life to a certain extent.

[0027] (2) The present invention uses sodium hypophosphite as a reducing agent during chemical plating, stabilizes metal ions through a complexing agent (sodium citrate), and uses thiourea or sodium thiosulfate as a stabilizer to prevent decomposition of the plating solution. The key to the co-deposition of rare earth salts with nickel and cobalt is to adjust the pH value and temperature. The present invention adjusts the pH of chemical plating to an alkaline condition and controls the temperature at 70-85°C. By adjusting the pH and temperature, the reduction of rare earth ions can be promoted and embedded in the grain boundaries of the coating.

[0028] (3) The present invention adopts chemical plating to prepare the barrier layer, and adds a pre-nickel-cobalt plating process. This is to strengthen the bonding force between the substrate and the composite layer and effectively prevent the main plating solution (i.e., chemical plating solution) from causing excessive corrosion to the substrate. Mechanical stirring or ultrasonic assisted stirring is used during the chemical plating process to eliminate the pores in the coating and improve the density.

[0029] (4) The present invention adds a micro-etching step after cleaning the substrate to increase the surface roughness of the substrate, thereby increasing the bonding strength between the barrier layer and the substrate; in addition, the micro-etching treatment can also effectively remove the cuts and oxide layer on the surface of the substrate. Therefore, in the pretreatment stage of the present invention, there is no need to add an additional sandpaper polishing step to remove the oxide layer.

[0030] (5) Through reasonable design, the present invention can prepare a highly stable barrier layer by chemical plating, and the barrier layer has strong bonding force and high hardness. Compared with electroplating, chemical plating does not require power supply equipment, which reduces energy consumption to a certain extent. In addition, chemical plating is also suitable for substrates with complex shapes. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with embodiments, and the embodiments of the present invention include but are not limited to the following embodiments.

[0032] Example 1

[0033] This embodiment provides a method for preparing a barrier for improving the high temperature stability of a thermoelectric module, and the process is as follows:

[0034] (1) Pretreatment: The P-type and N-type substrates (thermoelectric materials to be packaged) with a diameter of 30 mm and a thickness of 1.6 mm were rinsed with an alkaline cleaning agent (NaOH 65 g / L) and deionized water to remove surface stains, and then dried.

[0035] (2) Micro-etching treatment: Immerse both ends of the cleaned substrate in the micro-etching solution for 5 minutes. The process is carried out at room temperature to form a substrate with a surface roughness of Ra 0.5μm. The composition of the micro-etching solution is: H 2 SO 4 80mL / L, H 2 O 2 25 mL / L, polytetrafluoroethylene dispersion 25 mL / L, sodium citrate 1 g / L, the solvent is deionized water;

[0036] Micro-etching can form a microscopic rough surface at both ends of the substrate, thereby increasing the bonding strength between the substrate and the barrier layer. In this embodiment, a suitable micro-etching solution is designed and the micro-etching time is controlled. After testing, the roughness of the substrate surface is Ra 0.5μm. In addition, micro-etching can remove cuts and oxide layers on the substrate surface.

[0037] (3) Activation: At room temperature, place the substrate in 80 mL / L hydrochloric acid solution for activation treatment to increase the activity of the substrate surface for 50 seconds.

[0038] (4) Pre-plating of nickel-cobalt layer: The activated substrate is placed in a chemical pre-plating solution containing nickel salt, cobalt salt, reducing agent and chelating agent, and chemically plated for 10 min at a temperature of 60°C and a pH of 8.5 to form a nickel-cobalt transition layer with a thickness of 0.5 μm; mechanical stirring (speed 150 rpm) is used for auxiliary stirring during the pre-plating process;

[0039] The composition of the chemical pre-plating solution is: nickel sulfate (NiSO 4 6H 2 O) 20g / L, cobalt sulfate (CoSO 4 7H 2 O) 5 g / L, sodium hypophosphite (NaH 2 PO 2 ·H 2 O) 20 g / L, sodium citrate 10 g / L, thiourea 0.5 mg / L, and the solvent was deionized water.

[0040] (5) Chemical plating composite layer: The pre-plated substrate is placed in a chemical plating solution containing nickel salt, cobalt salt, rare earth salt, reducing agent and stabilizer, and chemically plated for 30 minutes at a temperature of 70°C and a pH of 9.0 to form a nickel-cobalt-rare earth composite barrier layer. After testing, the barrier layer is 3 μm; wherein the rare earth salt is lanthanum chloride; mechanical stirring (rotation speed 150 rpm) is used during the chemical plating process to promote the uniformity of the coating;

[0041] The composition of the chemical plating solution (main plating solution) is: nickel sulfate (NiSO 4 6H 2 O) 25g / L, cobalt sulfate (CoSO4 7H 2 O) 8g / L, rare earth salt 4mg / L, sodium hypophosphite (NaH 2 PO 2 ·H 2 O) 30 g / L, sodium citrate 15 g / L, sodium thiosulfate 1 mg / L, and the solvent was deionized water.

[0042] (6) Post-treatment: After the chemical plating is completed, it is thoroughly washed with water and dried to remove the residual impurities on the surface of the coating to obtain a composite barrier layer.

[0043] The rare earth element selected in this embodiment is one of lanthanum, cerium, and neodymium. Rare earth elements have properties such as high corrosion resistance, high wear resistance, and superconductivity. Cobalt also has high corrosion resistance and conductivity. Adding rare earth elements and cobalt to the chemical plating solution can improve the stability of the plating solution, make the barrier layer formed by chemical plating uniform and dense, and improve the hardness, corrosion resistance, and wear resistance of the barrier layer, thereby maintaining a high stability during high-temperature service.

[0044] After testing, it was found that the mass fraction of the rare earth element lanthanum in the barrier layer prepared by the above method was 0.7%.

[0045] Example 2

[0046] (1) Pretreatment: The P-type and N-type substrates with a diameter of 30 mm and a thickness of 1.6 mm were rinsed with an alkaline detergent (NaOH 70 g / L) and deionized water to remove surface stains, and then dried.

[0047] (2) Micro-etching treatment: The two ends of the cleaned substrate are immersed in the micro-etching solution for 6 minutes. The process is carried out at room temperature to form a substrate with a surface roughness of Ra 1.2μm. The composition of the micro-etching solution is: H 2 SO 4 90mL / L, H 2 O 2 28 mL / L, polytetrafluoroethylene dispersion 28 mL / L, sodium citrate 2 g / L, and the solvent is deionized water.

[0048] (3) Activation: At room temperature, place the substrate in a 100 mL / L hydrochloric acid solution for activation treatment to increase the activity of the substrate surface for 60 seconds.

[0049] (4) Pre-plating of nickel-cobalt layer: The activated substrate is placed in a chemical pre-plating solution containing nickel salt, cobalt salt, reducing agent and chelating agent, and chemically plated for 15 min at a temperature of 80 °C and a pH of 9.5 to form a nickel-cobalt transition layer with a thickness of 1.0 μm; ultrasonic stirring (frequency 40 kHz) is used during the pre-plating process;

[0050] The composition of the chemical pre-plating solution is: nickel sulfate (NiSO 4 6H 2 O) 30g / L, cobalt sulfate (CoSO 4 7H 2 O) 8g / L, sodium hypophosphite (NaH 2 PO 2 ·H 2 O) 30g / L, sodium citrate 15g / L, thiourea 1.0 mg / L, and the solvent was deionized water.

[0051] (5) Chemical plating composite layer: The pre-plated substrate is placed in a chemical plating solution containing nickel salt, cobalt salt, rare earth salt, reducing agent and stabilizer, and chemically plated for 45 minutes at a temperature of 85°C and a pH of 10.0 to form a nickel-cobalt-rare earth composite barrier layer. After testing, the barrier layer is 5 μm; wherein the rare earth salt is lanthanum chloride; ultrasonic assistance (frequency 40 kHz) is used in the chemical plating process to promote the uniformity of the coating;

[0052] The composition of the chemical plating solution (main plating solution) is: nickel sulfate (NiSO 4 6H 2 O) 35 g / L, cobalt sulfate (CoSO 4 7H 2 O) 12 g / L, rare earth salt 5 mg / L, sodium hypophosphite (NaH 2 PO 2 ·H 2 O) 40 g / L, sodium citrate 20 g / L, sodium thiosulfate 2 mg / L, and the solvent was deionized water.

[0053] (6) Post-treatment: After the chemical plating is completed, it is thoroughly washed with water and dried to remove the residual impurities on the surface of the coating to obtain a composite barrier layer.

[0054] After testing, it was found that the mass fraction of the rare earth element lanthanum in the barrier layer prepared by the above method was 1.0%.

[0055] Example 3

[0056] (1) Pretreatment: The P-type and N-type substrates with a diameter of 30 mm and a thickness of 1.6 mm were rinsed with an alkaline detergent (NaOH 68 g / L) and deionized water to remove surface stains, and then dried.

[0057] (2) Micro-etching treatment: The two ends of the cleaned substrate are immersed in the micro-etching solution for 5 minutes. The process is carried out at room temperature to form a substrate with a surface roughness of Ra 0.8μm. The composition of the micro-etching solution is: H 2 SO 4 85 mL / L, H 2 O2 26 mL / L, polytetrafluoroethylene dispersion 27 mL / L, sodium citrate 1.5 g / L, the solvent is deionized water;

[0058] (3) Activation: At room temperature, place the substrate in a 90 mL / L hydrochloric acid solution for activation treatment to increase the activity of the substrate surface for 55 seconds.

[0059] (4) Pre-plating of nickel-cobalt layer: The activated substrate is placed in a chemical pre-plating solution containing nickel salt, cobalt salt, reducing agent and chelating agent, and chemically plated for 12 min at a temperature of 70 °C and a pH of 9.0 to form a nickel-cobalt transition layer with a thickness of 0.7 μm; mechanical stirring is used during the pre-plating process (speed 180 rpm);

[0060] The composition of the chemical pre-plating solution is: nickel sulfate (NiSO 4 6H 2 O) 25 g / L, cobalt sulfate (CoSO 4 7H 2 O) 6 g / L, sodium hypophosphite (NaH 2 PO 2 ·H 2 O) 25 g / L, sodium citrate 12 g / L, thiourea 0.8 mg / L, and the solvent was deionized water.

[0061] (5) Chemical plating composite layer: the pre-plated substrate is placed in a chemical plating solution containing nickel salt, cobalt salt, rare earth salt, reducing agent and stabilizer, and chemically plated for 40 minutes at a temperature of 80°C and a pH of 9.5 to form a nickel-cobalt-rare earth composite barrier layer. After testing, the barrier layer is 4 μm; wherein the rare earth salt is lanthanum chloride; mechanical stirring (rotation speed 180 rpm) is used during the chemical plating process;

[0062] The composition of the chemical plating solution (main plating solution) is: nickel sulfate (NiSO 4 6H 2 O) 30 g / L, cobalt sulfate (CoSO 4 7H 2 O) 10 g / L, rare earth salt 4.5 mg / L, sodium hypophosphite (NaH 2 PO 2 ·H 2 O) 35 g / L, sodium citrate 18 g / L, sodium thiosulfate 1.5 mg / L, and the solvent was deionized water.

[0063] (6) Post-treatment: After the chemical plating is completed, it is thoroughly washed with water and dried to remove the residual impurities on the surface of the coating to obtain a composite barrier layer.

[0064] After testing, it was found that the mass fraction of the rare earth element lanthanum in the barrier layer prepared by the above method was 0.8%.

[0065] Example 4

[0066] This embodiment provides a method for preparing a barrier layer for improving the high temperature stability of a thermoelectric module. On the basis of Embodiment 1, lanthanum chloride is replaced with cerium chloride, and other processes are the same as those of Embodiment 1.

[0067] After testing, it was found that the mass fraction of the rare earth element cerium in the barrier layer prepared by this embodiment was 0.5%.

[0068] Example 5

[0069] This embodiment provides a method for preparing a barrier layer for improving the high temperature stability of a thermoelectric module. On the basis of Embodiment 1, lanthanum chloride is replaced with neodymium chloride, and other processes are the same as those in Embodiment 1.

[0070] After testing, it was found that the mass fraction of the rare earth element neodymium in the barrier layer prepared by this embodiment was 0.7%.

[0071] Example 6

[0072] This embodiment provides a method for preparing a barrier layer for improving the high temperature stability of a thermoelectric module. Based on Embodiment 1, lanthanum chloride is replaced with lanthanum sulfate, and other processes are the same as those in Embodiment 1.

[0073] After testing, it was found that the mass fraction of the rare earth element lanthanum in the barrier layer prepared by this embodiment was 0.9%.

[0074] Example 7

[0075] This embodiment provides a method for preparing a barrier layer for improving the high temperature stability of a thermoelectric module. On the basis of Embodiment 1, lanthanum chloride is replaced with cerium sulfate, and other processes are the same as those of Embodiment 1.

[0076] After testing, it was found that the mass fraction of the rare earth element cerium in the barrier layer prepared by this embodiment was 0.6%.

[0077] Example 8

[0078] This embodiment provides a method for preparing a barrier layer for improving the high temperature stability of a thermoelectric module. Based on Embodiment 1, lanthanum chloride is replaced with neodymium sulfate, and other processes are the same as Embodiment 1.

[0079] After testing, it was found that the mass fraction of the rare earth element neodymium in the barrier layer prepared by this embodiment was 0.8%.

[0080] Comparative Example 1

[0081] The barrier layer was prepared by the method of Example 1, and the chemical pre-plating solution and the chemical plating solution contained only a nickel source, and did not contain a cobalt salt and a rare earth salt.

[0082] Comparative Example 2

[0083] The barrier layer is prepared by the method of Example 1, and the chemical plating solution does not contain rare earth salt.

[0084] Comparative Example 3

[0085] The barrier layer was prepared by the method of Example 1, and the pretreated substrate was directly activated and chemically pre-plated without micro-etching.

[0086] Comparative Example 4

[0087] The barrier layer was prepared by the method of Example 1, the chemical pre-plating solution and the chemical plating solution only contained a nickel source, and the pre-treated substrate was directly activated and chemically pre-plated without micro-etching.

[0088] The barrier layers prepared in Examples 1 to 8 and Comparative Examples 1, 2, 3, and 4 were subjected to the following performance tests:

[0089] (1) Contact resistance test: The barrier layer materials prepared in the examples and comparative examples were annealed at 280°C (553K) for 30 days. The P-type and N-type Bi 2 Te 3 The contact resistance between the thermoelectric material and the barrier layer is less than 1 μΩ·cm 2 , P-type and N-type Bi in the comparative example 2 Te 3 The contact resistance between the thermoelectric material and the barrier layer is greater than 3 μΩ·cm 2 . Contact resistance is an important parameter to measure the degree of interface diffusion between the barrier layer and the thermoelectric material. The barrier layer provided in this embodiment has a lower contact resistance, which indicates that its interface diffusion degree is lower. In addition, the interface between the thermoelectric material and the barrier layer after annealing for 30 days was observed. The materials prepared by the methods provided in Examples 1 to 8 did not show obvious cracking, while cracking occurred in Comparative Examples 1, 2, and 4. The degree of cracking in Comparative Example 4 and Comparative Example 1 was stronger than that in Comparative Example 2. This is related to whether the composite barrier layer contains cobalt and rare earth elements. No obvious cracking occurred in Comparative Example 3 because the barrier layer prepared in Comparative Example 3 contains cobalt and rare earth elements. These two elements can increase interface stability and improve interface bonding strength to a certain extent.

[0090] (2) Bonding strength test: The bonding strength between the coating (barrier layer) and the substrate (thermoelectric material) is tested by tensile test and other methods. The test results are as follows:

[0091]

[0092] The bonding strength between the composite barrier layer prepared in Examples 1 to 8 and the thermoelectric substrate reaches more than 14 MPa, which has a high bonding force, indicating that the composite barrier layer prepared by the preparation method provided by the present invention has a relatively excellent bonding strength; the Vickers hardness of the composite barrier layer prepared in Examples 1 to 8 is greater than 420 HV. After consulting the data, the barrier layer is prepared by electroplating, and its maximum Vickers hardness can reach more than 450 HV. The present invention adopts chemical plating to prepare the composite barrier layer, and its hardness is slightly lower than that of the electroplated layer. This is related to the presence of sulfur impurities in the composite barrier layer prepared by chemical plating. However, the present invention can still meet the hardness ≥ 420 HV requirement through solid solution strengthening of cobalt and rare earth.

[0093] In Comparative Example 1, the barrier layer only contains a nickel source, which is a commonly used barrier layer in the prior art, and its bonding strength is 10.5 MPa; in Comparative Example 2, a cobalt source is added, but no rare earth elements are contained, and its interface bonding strength reaches 11.4 MPa. After adding the cobalt element, the interface bonding strength can be improved to a certain extent; in Comparative Example 3, cobalt and rare earth elements are added, but the surface of the substrate is not roughened. Compared with the prior art (Comparative Example 1), its interface bonding strength is enhanced, but its effect is still lower than that of Examples 1 to 8; in Comparative Example 4, neither cobalt nor rare earth elements are added, nor is micro-etching performed, and its interface bonding strength is relatively low.

[0094] The present invention improves the traditional nickel barrier layer by adding rare earth elements. Rare earth elements have properties such as high corrosion resistance, high wear resistance, and superconductivity. The barrier layer formed by the rare earth elements and nickel also has these properties, and the barrier layer maintains stability during high-temperature service, which can extend the service life to a certain extent. In the present invention, the interface between the substrate and the barrier layer is micro-etched, and the micro-etching liquid and the micro-etching time are reasonably controlled to maintain a reasonable roughness on the surface of the substrate. In addition, the effect of the cobalt element can improve the interface bonding force between the thermoelectric material and the barrier layer; in addition, after adding the rare earth elements, a dense composite coating is formed, and the elements are evenly distributed, which can further improve the interface bonding force, so that the thermoelectric material is not easy to crack after being encapsulated into a thermoelectric module (device), and it remains stable for a long time during service, thereby extending the service life.

[0095] The above embodiment is only one of the preferred implementation modes of the present invention and should not be used to limit the protection scope of the present invention. Any changes or modifications that are made to the main design concept and spirit of the present invention and have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention.

Claims

1. A method for preparing a barrier layer for improving the high temperature stability of a thermoelectric module, characterized in that: include: S1, pretreatment: cleaning the substrate to remove surface stains and then drying; S2, immersing the pretreated substrate in a micro-etching solution for micro-etching to form a substrate with a surface roughness of Ra 0.5-1.2 μm; S3, activating the micro-etched substrate surface; S4, pre-plating nickel-cobalt layer: placing the activated substrate into a chemical pre-plating solution containing nickel salt, cobalt salt, reducing agent and complexing agent to form a nickel-cobalt transition layer with a thickness of 0.5-1.0 μm; S5, chemical plating composite layer: placing the pre-plated substrate in a chemical plating solution containing nickel salt, cobalt salt, rare earth salt, reducing agent and stabilizer to form a nickel-cobalt-rare earth element composite barrier layer with a thickness of 3-5 μm; the rare earth salt is selected from chlorides or sulfates of lanthanum, cerium or neodymium; S6, washing and drying the substrate after chemical plating.

2. The method for preparing a barrier layer for improving high temperature stability of a thermoelectric module according to claim 1, characterized in that: In step S1, the surface of the substrate is cleaned with an alkaline cleaning agent and deionized water in sequence.

3. The method for preparing a barrier layer for improving high temperature stability of a thermoelectric module according to claim 2, characterized in that: In step S2, the micro-etching solution comprises: H2SO4 80-90 mL / L, H2O2 25-28 mL / L, polytetrafluoroethylene dispersion 25-28 mL / L, sodium citrate 1-2 g / L, and the solvent is deionized water; the micro-etching time is 5-6 min.

4. The method for preparing a barrier layer for improving high temperature stability of a thermoelectric module according to claim 3, characterized in that: In step S3, the activation solution is 80-100 mL / L concentrated hydrochloric acid, and the activation time is 50-60 s.

5. The method for preparing a barrier layer for improving high temperature stability of a thermoelectric module according to claim 4, characterized in that: In step S4, the composition of the pre-plating solution includes: NiSO4·6H2O 20~30 g / L, CoSO4·7H2O 5~8 g / L, NaH2PO2·H2O 20~30 g / L, sodium citrate 10~15 g / L, thiourea 0.5~1.0 mg / L, and the solvent is deionized water.

6. The method for preparing a barrier layer for improving high temperature stability of a thermoelectric module according to claim 5, characterized in that: In step S4, chemical pre-plating is performed at a temperature of 60-80° C. and a pH of 8.5-9.5 for 10-15 minutes.

7. The method for preparing a barrier layer for improving high temperature stability of a thermoelectric module according to claim 6, characterized in that: In step S5, the composition of the chemical plating solution includes: 25-35 g / L nickel sulfate, 8-12 g / L cobalt sulfate, 4-5 mg / L rare earth salt, 30-40 g / L sodium hypophosphite, 15-20 g / L sodium citrate, 1-2 mg / L sodium thiosulfate, and the solvent is deionized water.

8. The method for preparing a barrier layer for improving high temperature stability of a thermoelectric module according to claim 7, characterized in that: In step S5, chemical plating is performed at a temperature of 70-85° C. and a pH of 9.0-10.0 for 30-45 minutes.

9. The method for preparing a barrier layer for improving high temperature stability of a thermoelectric module according to claim 8, characterized in that: During the pre-plating in step S4 and the chemical plating in step S5, mechanical stirring or ultrasonic assistance is used.

10. A barrier layer for improving the high temperature stability of a thermoelectric module, prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The barrier layer is a nickel-cobalt-rare earth element ternary composite barrier layer, wherein the rare earth element is uniformly distributed at the grain boundary, the mass fraction of the rare earth element in the composite barrier layer is 0.5-1.0%, and the Vickers hardness of the barrier layer is ≥420 HV, and the interface contact resistance is ≤1.5 μΩ·cm² after aging for 1000 hours at 300°C.

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