Preparation method of bismuth telluride protective coating

Abstract

The invention relates to the field of thermoelectric materials, in particular to a preparation method of a bismuth telluride protective coating, which comprises the following steps: (1) immersing bismuth telluride into a chemical etching agent for chemical etching, dust removal and cleaning; (2) mixing the bismuth telluride treated in the step (1) with an energizing material; (3) putting the bismuth telluride and the energizing material into a chemical plating solution together for chemical plating, wherein the bismuth telluride, the energizing material and the chemical plating solution form a primary battery during the chemical plating; and cleaning to obtain the bismuth telluride with the protective coating. By applying continuous and stable weak voltage to the surfaces of the bismuth telluride crystal grains, autocatalysis of the bismuth telluride crystal grains is realized, the catalytic efficiency is high, the preparation process is simple, and the binding force and uniformity of a chemical plating layer can be improved so as to enhance the protection effect of bismuth telluride.

Description

Technical Field

[0001] The invention relates to the field of thermoelectric materials, and in particular to a method for preparing a bismuth telluride protective coating. Background Art

[0002] Bismuth telluride is a thermoelectric power generation material with excellent performance, and is often used in thermoelectric conversion devices. Since most thermoelectric conversion devices use soldering to connect the P and N type thermoelectric arms to the copper electrodes, the copper element will diffuse into the bismuth telluride base along with the tin-based alloy, causing the thermoelectric refrigeration material to fail. Therefore, a protective coating needs to be set around the bismuth telluride for protection.

[0003] In the art, micro-diameter bismuth telluride grains are usually protected around them, and then surface treated by electrochemical barrel plating to form a protective coating. However, chemical plating agents cannot react directly with bismuth telluride grains, and electroplating catalysis is required to form micro-grains on the grains. The chemical plating agent and the micro-grains react continuously. The current electroplating catalysis method cannot make all protected grains evenly energized. After the protective treatment, a good path cannot be formed around the grains, resulting in uneven chemical plating, broken plating, and leaking plating, which affects the protective effect of bismuth telluride. Therefore, it is crucial to find a method for preparing bismuth telluride that can improve the efficiency and quality of chemical plating to obtain excellent protective effects. Summary of the invention

[0004] In order to solve the above-mentioned technical problems of low quality of chemical plating and poor protective effect of bismuth telluride, the present invention provides a method for preparing a bismuth telluride protective coating, which can continuously induce the micro-grains required for chemical plating by applying a continuous and stable weak voltage on the surface of bismuth telluride grains, realize self-catalysis of bismuth telluride grains, and form good pathways around the grains, thereby improving the efficiency and quality of chemical plating and enhancing the protective effect of bismuth telluride.

[0005] The specific technical solution of the present invention is: a method for preparing a bismuth telluride protective coating, comprising the following steps: (1) immersing bismuth telluride in a chemical etchant to perform chemical etching, dust removal, and cleaning; (2) mixing the bismuth telluride treated in step (1) with a charge-bearing material; (3) placing bismuth telluride and a charge-bearing material together in a chemical plating solution for chemical plating, during which the bismuth telluride, the charge-bearing material and the chemical plating solution constitute a primary cell; and washing to obtain bismuth telluride with a protective coating.

[0006] Chemical etching forms a rough micro-nano structure on the surface of bismuth telluride. Then, using the principle of the primary cell, the chemically etched bismuth telluride undergoes an oxidation-reduction reaction with the charge-bearing material. The charge-bearing material serves as the anode and the bismuth telluride serves as the cathode. A potential difference, i.e., voltage, is generated between them, so that the surface of the bismuth telluride grains is endowed with a continuous and stable weak voltage, eliminating the electroplating catalytic step and achieving self-catalysis of the bismuth telluride grains. Since a good path is formed around the grains, the chemical plating efficiency is high and the quality is good, and the bonding strength and uniformity of the coating are improved, thereby enhancing the protective effect of bismuth telluride.

[0007] Furthermore, in step (1), the chemical etchant includes one or more of hydrofluoric acid, nitric acid and sodium dodecylbenzene sulfonate.

[0008] Furthermore, in step (1), the chemical etchant is composed of hydrofluoric acid, nitric acid and sodium dodecylbenzene sulfonate, and the mass volume ratio of hydrofluoric acid, nitric acid and sodium dodecylbenzene sulfonate is (5-30) ml: (10-30) ml: (0.1-0.5) g.

[0009] Furthermore, in step (1), the bismuth telluride has a diameter Bismuth telluride with an organic insulating protective coating all around.

[0010] Furthermore, in step (1), bismuth telluride is placed in a polytetrafluoroethylene rolling net for chemical etching.

[0011] Furthermore, in step (2), the charge-bearing material is a metal or non-metal material whose electrode potential is lower than the hydrogen potential.

[0012] Preferably, in step (2), the charge-imparting material is a zinc sheet, wherein the zinc content is 1 to 20%, and the size is (0.1 to 0.5) mm×(2 to 10) mm×(2 to 10) mm.

[0013] Zinc has a relatively low potential and is highly active, making it easier to form a primary cell with materials and plating solutions.

[0014] Preferably, in step (2), the zinc content of the zinc sheet is 10% and the size is 0.1×4×4 mm.

[0015] Furthermore, in step (3), the protective coating contains one or more elements selected from the group consisting of nickel, gold, palladium and tin.

[0016] Furthermore, in step (3), the chemical plating solution is a nickel solution, the chemical plating temperature is 82-92° C., and the time is 30-60 min.

[0017] Compared with other metal elements, the work function of nickel is more closely matched to bismuth telluride, and can better block the diffusion of welding materials and copper electrodes into bismuth telluride.

[0018] Preferably, in step (3), the chemical plating solution is nickel solution, the chemical plating temperature is 87° C., and the time is 30 min.

[0019] Furthermore, in step (3), bismuth telluride and charge-bearing material are placed in a drum for chemical plating.

[0020] Furthermore, in step (3), the drum speed is 10 to 200 rpm / min.

[0021] Preferably, in step (3), the drum speed is 60 rpm / min.

[0022] The preparation method of bismuth telluride used in step (1) of the present invention is: Firstly, a micro-diameter bismuth telluride crystal rod with a diameter of 0.5 to 3.0 mm is prepared by hot extrusion or zone melting, epoxy adhesive is dipped during preparation, and then the rod is cut into bismuth telluride grains with a height of 0.5 to 2.0 mm.

[0023] Compared with the prior art, the present invention has the following advantages: The present invention applies a continuous and stable weak voltage on the surface of bismuth telluride grains to achieve self-catalysis of bismuth telluride grains, which can continuously trigger the grains required for chemical plating, improve catalytic efficiency, save the electroplating catalytic step, simplify the preparation process, and shorten the preparation time; a good passage is formed around the bismuth telluride grains, which improves the efficiency and quality of chemical plating, improves the bonding strength and uniformity of the coating, and enhances the protective effect of bismuth telluride. Thermoelectric conversion devices prepared using this method have a longer service life and better adaptability, and can be used in more and more extreme working environments. DETAILED DESCRIPTION

[0024] The present invention is described below by specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be thought of by those skilled in the art are included in the present invention, and the attached claims and any equivalents thereof are the protection scope of the present invention.

[0025] Unless otherwise defined, all technical terms and scientific terms used in the present invention have the same meanings as those commonly understood by ordinary technicians in the field to which the present disclosure belongs. Unless otherwise specified, the raw materials and equipment used in the present invention are conventional raw materials and equipment in the field and can be obtained from conventional commercial channels; unless otherwise specified, the methods used in the present invention are conventional methods in the field.

[0026] Example 1 This embodiment provides a method for preparing a bismuth telluride protective coating, and the specific process is as follows: 1. Chemical etching 1) Prepare materials: Take 100 grains of bismuth telluride, the bismuth telluride is a micro-diameter (i.e., diameter ) Bismuth telluride surrounded by an organic insulating protective coating.

[0027] 2) Prepare a chemical etchant: Mix 5 ml of hydrofluoric acid, 25 ml of nitric acid and 0.1 g of sodium dodecylbenzene sulfonate to form a chemical etchant.

[0028] 3) Chemical etching: Place 100 grains of bismuth telluride into a polytetrafluoroethylene rolling net, ensure that the bismuth telluride is evenly distributed on the rolling net, immerse in a chemical etchant for 1 minute to make the bismuth telluride rough. After completion, take it out and use an ultrasonic cleaning device to remove the dust on the surface of the bismuth telluride, and then thoroughly clean it with pure water to ensure that all chemical etchants and residues are completely removed.

[0029] 2. Pre-treatment of electrification 1) Prepare materials: Select zinc sheets with a zinc content of 10% and a size of 0.1×4×4 mm as the charge-bearing material.

[0030] 2) Mixing: Mixing the chemically etched bismuth telluride with the zinc sheet.

[0031] 3. Chemical plating treatment 1) Prepare materials: Mix 10 g of sodium hypophosphite, 30 g of nickel chloride, 5 g of sodium acetate, and 30 g of sodium citrate, add water to dissolve, add ammonia water dropwise to the solution to adjust the pH value to 4.6, and then add water to a total volume of 1 L to prepare a nickel solution as the chemical plating solution of this embodiment.

[0032] 2) Chemical plating: put the bismuth telluride mixed with zinc sheet into a drum, put the drum into nickel liquid, set the drum speed to 60rpm / min, set the nickel liquid temperature to 87℃, and process for 30min. During this period, bismuth telluride, zinc sheet and nickel liquid form a primary battery, and nickel ions form a uniform coating on the surface of bismuth telluride.

[0033] 3) Post-treatment: The nickel-plated bismuth telluride and zinc sheets are taken out of the drum and repeatedly washed in pure water to ensure that all chemical nickel plating liquid and residues are completely removed. After washing, the quality and integrity of the bismuth telluride coating are checked to obtain bismuth telluride with a protective coating on all sides.

[0034] Example 2 This embodiment provides a method for preparing a bismuth telluride protective coating, and the specific process is as follows: 1. Chemical etching 1) Prepare materials: Take 100 particles of bismuth telluride, wherein the bismuth telluride is bismuth telluride with a micro-diameter and an organic insulating protective coating around the periphery.

[0035] 2) Prepare a chemical etchant: Mix 5 ml of hydrofluoric acid, 30 ml of nitric acid and 0.2 g of sodium dodecylbenzene sulfonate to form a chemical etchant.

[0036] 3) Chemical etching: Place 100 grains of bismuth telluride into a polytetrafluoroethylene rolling net, ensure that the bismuth telluride is evenly distributed on the rolling net, immerse in a chemical etchant for 2 minutes to make the bismuth telluride rough. After completion, take it out and use an ultrasonic cleaning device to remove the dust on the surface of the bismuth telluride, and then thoroughly clean it with pure water to ensure that all chemical etchants and residues are completely removed.

[0037] 2. Pre-treatment of electrification 1) Prepare materials: Select zinc sheets with a zinc content of 20% and a size of 0.1×2×2 mm as the charge-bearing material.

[0038] 2) Mixing: Mixing the chemically etched bismuth telluride with the zinc sheet.

[0039] 3. Chemical plating treatment 1) Prepare materials: Select nickel solution as the chemical plating solution. The preparation method of the nickel solution is the same as that of Example 1.

[0040] 2) Chemical plating: put the bismuth telluride mixed with zinc sheet into a drum, put the drum into nickel liquid, set the drum speed to 10rpm / min, set the nickel liquid temperature to 93°C, and the processing time to 60min. During this period, bismuth telluride, zinc sheet and nickel liquid form a primary battery, and nickel ions form a uniform coating on the surface of bismuth telluride.

[0041] 3) Post-treatment: The nickel-plated bismuth telluride and zinc sheets are taken out of the drum and repeatedly washed in pure water to ensure that all chemical nickel plating liquid and residues are completely removed. After washing, the quality and integrity of the bismuth telluride coating are checked to obtain bismuth telluride with a protective coating on all sides.

[0042] Example 3 This embodiment provides a method for preparing a bismuth telluride protective coating, and the specific process is as follows: 1. Chemical etching 1) Prepare materials: Take 100 particles of bismuth telluride, wherein the bismuth telluride is bismuth telluride with a micro-diameter and an organic insulating protective coating around the periphery.

[0043] 2) Prepare a chemical etchant: Mix 30 ml of hydrofluoric acid, 10 ml of nitric acid and 0.3 g of sodium dodecylbenzene sulfonate to form a chemical etchant.

[0044] 3) Chemical etching: Place 100 grains of bismuth telluride into a polytetrafluoroethylene rolling net, ensure that the bismuth telluride is evenly distributed on the rolling net, immerse in a chemical etchant for 1 minute to make the bismuth telluride rough. After completion, take it out and use an ultrasonic cleaning device to remove the dust on the surface of the bismuth telluride, and then thoroughly clean it with pure water to ensure that all chemical etchants and residues are completely removed.

[0045] 2. Pre-treatment of electrification 1) Prepare materials: Select zinc sheets with a zinc content of 5% and a size of 0.5×10×10 mm as the charge-bearing material.

[0046] 2) Mixing: Mixing the chemically etched bismuth telluride with the zinc sheet.

[0047] 3. Chemical plating treatment 1) Prepare materials: Select nickel solution as the chemical plating solution. The preparation method of the nickel solution is the same as that of Example 1.

[0048] 2) Chemical plating: put the bismuth telluride mixed with zinc sheet into a drum, put the drum into nickel liquid, set the drum speed to 100rpm / min, set the nickel liquid temperature to 82℃, and process for 40min. During this period, bismuth telluride, zinc sheet and nickel liquid form a primary battery, and nickel ions form a uniform coating on the surface of bismuth telluride.

[0049] 3) Post-treatment: The nickel-plated bismuth telluride and zinc sheets are taken out of the drum and repeatedly washed in pure water to ensure that all chemical nickel plating liquid and residues are completely removed. After washing, the quality and integrity of the bismuth telluride coating are checked to obtain bismuth telluride with a protective coating on all sides.

[0050] Example 4 This embodiment provides a method for preparing a bismuth telluride protective coating, and the specific process is as follows: 1. Chemical etching 1) Prepare materials: Take 100 particles of bismuth telluride, wherein the bismuth telluride is bismuth telluride with a micro-diameter and an organic insulating protective coating around the periphery.

[0051] 2) Prepare a chemical etchant: Mix 15 ml of hydrofluoric acid, 15 ml of nitric acid and 0.3 g of sodium dodecylbenzene sulfonate to form a chemical etchant.

[0052] 3) Chemical etching: Place 100 grains of bismuth telluride into a polytetrafluoroethylene rolling net, ensure that the bismuth telluride is evenly distributed on the rolling net, immerse in a chemical etchant for 3 minutes to make the bismuth telluride rough. After completion, take it out and use an ultrasonic cleaning device to remove the dust on the surface of the bismuth telluride, and then thoroughly clean it with pure water to ensure that all chemical etchants and residues are completely removed.

[0053] 2. Pre-treatment of electrification 1) Prepare materials: Select zinc sheets with a zinc content of 2% and a size of 0.3×8×8 mm as the charge-bearing material.

[0054] 2) Mixing: Mixing the chemically etched bismuth telluride with the zinc sheet.

[0055] 3. Chemical plating treatment 1) Prepare materials: Select nickel solution as the chemical plating solution. The preparation method of the nickel solution is the same as that of Example 1.

[0056] 2) Chemical plating: put the bismuth telluride mixed with zinc sheet into a drum, put the drum into nickel liquid, set the drum speed to 200rpm / min, set the nickel liquid temperature to 82℃, and process for 30min. During this period, bismuth telluride, zinc sheet and nickel liquid form a primary battery, and nickel ions form a uniform coating on the surface of bismuth telluride.

[0057] 3) Post-treatment: The nickel-plated bismuth telluride and zinc sheets are taken out of the drum and repeatedly washed in pure water to ensure that all chemical nickel plating liquid and residues are completely removed. After washing, the quality and integrity of the bismuth telluride coating are checked to obtain bismuth telluride with a protective coating on all sides.

[0058] Example 5 This embodiment provides a method for preparing a bismuth telluride protective coating, and the specific process is as follows: 1. Chemical etching 1) Prepare materials: Take 100 particles of bismuth telluride, wherein the bismuth telluride is bismuth telluride with a micro-diameter and an organic insulating protective coating around the periphery.

[0059] 2) Prepare a chemical etchant: Mix 5 ml of hydrofluoric acid, 25 ml of nitric acid and 0.1 g of sodium dodecylbenzene sulfonate to form a chemical etchant.

[0060] 3) Chemical etching: Place 100 grains of bismuth telluride into a polytetrafluoroethylene rolling net, ensure that the bismuth telluride is evenly distributed on the rolling net, immerse in a chemical etchant for 1 minute to make the bismuth telluride rough. After completion, take it out and use an ultrasonic cleaning device to remove the dust on the surface of the bismuth telluride, and then thoroughly clean it with pure water to ensure that all chemical etchants and residues are completely removed.

[0061] 2. Pre-treatment of electrification 1) Prepare materials: Select an iron sheet with an iron content of 10% and a size of 0.1×4×4 mm as the charging material.

[0062] 2) Mixing: Mixing the chemically etched bismuth telluride with the iron sheet.

[0063] 3. Chemical plating treatment 1) Prepare materials: Mix 10 g of sodium hypophosphite, 4 g of palladium chloride, and 27 g of ammonium chloride, add water to dissolve, add 4 ml of concentrated hydrochloric acid to the solution, add ammonia water to adjust the pH value to 9.8, and then add water to a total volume of 1 L to prepare a palladium solution as the chemical plating solution of this embodiment.

[0064] 2) Chemical plating: put the bismuth telluride mixed with iron sheet into a drum, put the drum into palladium liquid, set the drum speed to 60rpm / min, set the palladium liquid temperature to 68°C, and the processing time to 5min. During this period, the bismuth telluride, iron sheet and palladium liquid form a primary battery, so that the palladium ions form a uniform coating on the surface of the bismuth telluride.

[0065] 3) Post-treatment: The bismuth telluride and iron sheet after palladium plating are taken out of the drum and repeatedly washed in pure water to ensure that all chemical palladium plating liquid and residues are completely removed. After the cleaning is completed, the quality and integrity of the bismuth telluride coating are checked to obtain bismuth telluride with a protective coating on all sides.

[0066] Example 6 This embodiment provides a method for preparing a bismuth telluride protective coating, and the specific process is as follows: 1. Chemical etching 1) Prepare materials: Take 100 particles of bismuth telluride, wherein the bismuth telluride is bismuth telluride with a micro-diameter and an organic insulating protective coating around the periphery.

[0067] 2) Prepare a chemical etchant: Mix 5 ml of hydrofluoric acid, 25 ml of nitric acid and 0.1 g of sodium dodecylbenzene sulfonate to form a chemical etchant.

[0068] 3) Chemical etching: Place 100 grains of bismuth telluride into a polytetrafluoroethylene rolling net, ensure that the bismuth telluride is evenly distributed on the rolling net, immerse in a chemical etchant for 1 minute to make the bismuth telluride rough. After completion, take it out and use an ultrasonic cleaning device to remove the dust on the surface of the bismuth telluride, and then thoroughly clean it with pure water to ensure that all chemical etchants and residues are completely removed.

[0069] 2. Pre-treatment of electrification 1) Prepare materials: Select aluminum sheets with an aluminum content of 10% and a size of 0.1×4×4mm as the charge-bearing material.

[0070] 2) Mixing: Mixing the chemically etched bismuth telluride with the aluminum sheet.

[0071] 3. Chemical plating treatment 1) Prepare materials: Mix 10 g of sodium hypophosphite, 2 g of potassium gold cyanide, 75 g of ammonium chloride and 50 g of sodium citrate, add water to a total volume of 1 L, and prepare a gold solution as the chemical plating solution of this embodiment.

[0072] 2) Chemical plating: put the bismuth telluride mixed with aluminum sheet into a drum, put the drum into gold liquid, set the drum speed to 60rpm / min, set the gold liquid temperature to 75℃, and process for 5min. During this period, bismuth telluride, aluminum sheet and gold liquid form a primary battery, and gold ions form a uniform coating on the surface of bismuth telluride.

[0073] 3) Post-treatment: The gold-plated bismuth telluride and aluminum sheet are taken out of the drum and repeatedly washed in pure water to ensure that all chemical gold plating liquid and residues are completely removed. After the washing is completed, the quality and integrity of the bismuth telluride coating are checked to obtain bismuth telluride with a protective coating on all sides.

[0074] Example 7 This embodiment provides a method for preparing a bismuth telluride protective coating, and the specific process is as follows: 1. Chemical etching 1) Prepare materials: Take 100 particles of bismuth telluride, wherein the bismuth telluride is bismuth telluride with a micro-diameter and an organic insulating protective coating around the periphery.

[0075] 2) Prepare a chemical etchant: Mix 5 ml of hydrofluoric acid, 25 ml of nitric acid and 0.1 g of sodium dodecylbenzene sulfonate to form a chemical etchant.

[0076] 3) Chemical etching: Place 100 grains of bismuth telluride into a polytetrafluoroethylene rolling net, ensure that the bismuth telluride is evenly distributed on the rolling net, immerse in a chemical etchant for 1 minute to make the bismuth telluride rough. After completion, take it out and use an ultrasonic cleaning device to remove the dust on the surface of the bismuth telluride, and then thoroughly clean it with pure water to ensure that all chemical etchants and residues are completely removed.

[0077] 2. Pre-treatment of electrification 1) Prepare materials: Select zinc sheets with a zinc content of 10% and a size of 0.1×4×4 mm as the charge-bearing material.

[0078] 2) Mixing: Mixing the chemically etched bismuth telluride with the zinc sheet.

[0079] 3. Chemical plating treatment 1) Prepare materials: Mix 90 g of sodium hypophosphite, 20 g of stannous chloride, 75 g of thiourea and 1 g of dodecylpyridinium chloride, add water to dissolve, then add 80 ml of concentrated hydrochloric acid, and add water to a total volume of 1 L to prepare a tin solution as the chemical plating solution of this embodiment.

[0080] 2) Chemical plating: put the bismuth telluride mixed with zinc sheet into a drum, put the drum into tin liquid, set the drum speed to 60rpm / min, set the tin liquid temperature to 38°C, and the processing time to 30min. During this period, bismuth telluride, zinc sheet and tin liquid form a primary battery, and tin ions form a uniform coating on the surface of bismuth telluride.

[0081] 3) Post-treatment: The tin-plated bismuth telluride and zinc sheets are taken out of the drum and repeatedly washed in pure water to ensure that all chemical tin plating liquid and residues are completely removed. After the washing is completed, the quality and integrity of the bismuth telluride coating are checked to obtain bismuth telluride with a protective coating on all sides.

[0082] Comparative Example 1 In this comparative example, bismuth telluride with a protective coating is prepared by electrochemical barrel plating, and the specific process is as follows: 1. Chemical etching 1) Prepare materials: Take 100 particles of bismuth telluride, wherein the bismuth telluride is bismuth telluride with a micro-diameter and an organic insulating protective coating around the periphery.

[0083] 2) Prepare a chemical etchant: Mix 5% by volume of hydrofluoric acid, 25% by volume of nitric acid and 0.1 g of sodium dodecylbenzene sulfonate to form a chemical etchant.

[0084] 3) Chemical etching: Place 100 grains of bismuth telluride into a polytetrafluoroethylene rolling net, ensure that the bismuth telluride is evenly distributed on the rolling net, immerse in a chemical etchant for 1 minute to make the bismuth telluride rough. After completion, take it out and use an ultrasonic cleaning device to remove the dust on the surface of the bismuth telluride, and then thoroughly clean it with pure water to ensure that all chemical etchants and residues are completely removed.

[0085] 2. Electroplating 1) Preparation of electrolyte: Mix 250 g of nickel chloride, 50 g of nickel sulfate and 30 g of sodium chloride, add 35 ml of hydrochloric acid, and then add water to a total volume of 1 L to prepare an electrolyte.

[0086] 2) Electroplating: Place the chemically etched bismuth telluride into an electrolyte with a current density of 1-5A / dm 2 , temperature is 50℃, power on for 5 minutes.

[0087] 3. Chemical plating treatment 1) Prepare materials: Select nickel solution as the chemical plating solution.

[0088] 2) Chemical plating: put the electroplated bismuth telluride into a drum, put the drum into nickel liquid, set the drum speed to 60 rpm / min, set the nickel liquid temperature to 87° C., and the treatment time to 30 min.

[0089] 3) Post-treatment: The nickel-plated bismuth telluride is taken out of the drum and repeatedly washed in pure water to obtain bismuth telluride with a protective coating on all sides.

[0090] The bismuth telluride with protective coating prepared in Examples 1-7 and Comparative Example 1 was respectively applied to three groups of identical thermoelectric conversion devices to test their accelerated lifespans. The results are shown in Table 1.

[0091] Table 1 Accelerated life test results of three groups of products When the resistance change rate exceeds 10%, the product is judged to be invalid. It can be seen from Table 1 that the products of Examples 1-7 remain effective when the number of cycles reaches 30,000, indicating that the bismuth telluride obtained by this method has a good protective effect and can increase the service life of the thermoelectric conversion device. The resistance change rate of the product of Comparative Example 1 increases with the increase in the number of cycles, and it has failed when the number of cycles reaches 30,000; while the resistance change rate of the product of Example 1 has been maintained at 1-2%. The accelerated life data of the product of Example 1 is better than that of Comparative Example 1. This is because Example 1 uses the principle of the primary battery to directly obtain a chemical nickel plating layer. The plating layer has a stronger bonding force with bismuth telluride and better uniformity. It has a higher ability to protect the diffusion of electrode elements and elements in welding materials, prevents changes in the composition of bismuth telluride, and performance loss, thereby extending the service life of the electrical conversion device.

[0092] The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0093] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a bismuth telluride protective coating, characterized in that: The following steps are involved: (1) immersing bismuth telluride in a chemical etchant to perform chemical etching, dust removal, and cleaning; (2) mixing the bismuth telluride treated in step (1) with a charge-bearing material; (3) placing bismuth telluride and a charge-bearing material together in a chemical plating solution for chemical plating, during which the bismuth telluride, the charge-bearing material and the chemical plating solution constitute a primary cell; and washing to obtain bismuth telluride with a protective coating.

2. The method for preparing a bismuth telluride protective coating according to claim 1, characterized in that: In step (1), the chemical etchant includes one or more of hydrofluoric acid, nitric acid and sodium dodecylbenzene sulfonate.

3. The method for preparing a bismuth telluride protective coating according to claim 2, characterized in that: In step (1), the chemical etchant is composed of hydrofluoric acid, nitric acid and sodium dodecylbenzene sulfonate, and the mass volume ratio of hydrofluoric acid, nitric acid and sodium dodecylbenzene sulfonate is (5-30) ml: (10-30) ml: (0.1-0.5) g.

4. The method for preparing a bismuth telluride protective coating according to claim 1 or 2, characterized in that: In step (1), the bismuth telluride has a diameter Bismuth telluride with an organic insulating protective coating all around.

5. The method for preparing a bismuth telluride protective coating according to claim 1, characterized in that: In step (2), the charge-bearing material is a metal or non-metal material whose electrode potential is lower than the hydrogen potential.

6. The method for preparing a bismuth telluride protective coating according to claim 5, characterized in that: In step (2), the charge-bearing material is a zinc sheet, wherein the zinc content is 1-20% and the size is (0.1-0.5) mm×(2-10) mm×(2-10) mm.

7. The method for preparing a bismuth telluride protective coating according to claim 1, characterized in that: In step (3), the protective coating contains one or more elements selected from the group consisting of nickel, gold, palladium and tin.

8. The method for preparing a bismuth telluride protective coating according to claim 1, characterized in that: In step (3), bismuth telluride and charge-bearing materials are placed in a drum for chemical plating.

9. The method for preparing a bismuth telluride protective coating according to claim 8, characterized in that: In step (3), the drum speed is 10 to 200 rpm / min.

10. The method for preparing a bismuth telluride protective coating according to claim 1, characterized in that: In step (3), the chemical plating solution is nickel solution, the chemical plating temperature is 82-92° C., and the time is 30-60 min.

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