Nanometer aluminum oxide composite thermoelectric material based on bismuth telluride waste reutilization and preparation method of nanometer aluminum oxide composite thermoelectric material

Abstract

The invention provides a nanometer aluminum oxide composite thermoelectric material based on bismuth telluride waste reutilization and a preparation method of the nanometer aluminum oxide composite thermoelectric material, bismuth telluride waste is used as a main raw material, and the nanometer aluminum oxide composite thermoelectric material aims at solving the following defects in the prior art: (1) the waste recovery efficiency is low, and the resource utilization is insufficient; and (2) the stability of the material is influenced due to non-uniform dispersion of the nanophase. The thermoelectric property and the mechanical property of the composite product are improved compared with those of a commercial bismuth telluride material by combining the outstanding electrical property and the mechanical property of the nano aluminum oxide and then through a ball-milling mixing and hot extrusion preparation process. According to the method, collaborative optimization of thermoelectric performance and mechanical performance is well achieved, and the method has a great promotion effect on expansion of the application range of a current bismuth telluride material.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, specifically relating to a nano-alumina composite thermoelectric material based on the reuse of bismuth telluride waste and its preparation method. Background Technology

[0002] Thermoelectric materials are functional materials that can convert heat energy into electrical energy and vice versa. They have advantages such as simple structure, no pollution, and long lifespan, and are widely used in waste heat recovery, thermoelectric power generation, and space power sources. Bismuth telluride-based materials are thermoelectric materials with excellent performance in the room temperature range, but their production process generates a large amount of waste, such as powder and scrap from machining, cutting, and grinding. These wastes are rich in Bi2Te3, and direct disposal not only wastes resources but may also lead to environmental pollution.

[0003] In existing technologies, the preparation of bismuth telluride-based thermoelectric materials mainly employs zone melting and powder metallurgy methods. For example, CN108103534A discloses a method for preparing Bi2Te3-based thermoelectric materials through melting and hot pressing, but does not consider waste recycling; CN112951975A describes a silicon carbide nanocomposite bismuth telluride-based thermoelectric material based on the recycling of bismuth telluride processing waste, which achieves waste recycling through ball milling and hot pressing, but the composite phase is silicon carbide (SiC), limiting the optimization of thermoelectric performance.

[0004] Nanocomposite technology can optimize thermoelectric properties by introducing nanoparticles, such as reducing thermal conductivity (κ) and improving the thermoelectric figure of merit (ZT) by scattering phonons. Studies have shown that embedding nano-Al₂O₃ into a Bi₂Te₃ matrix can form an interfacial barrier, increasing the Seebeck coefficient and reducing κ. However, current methods are mostly based on pure raw materials, resulting in low waste utilization and performance fluctuations due to uneven dispersion. While ball milling is used for powder mixing, it is prone to introducing defects in traditional applications; hot extrusion can achieve densification, but it is rarely used in waste composites. Summary of the Invention

[0005] To address the above problems, this invention provides a nano-alumina composite thermoelectric material with bismuth telluride waste as the main raw material and its preparation method, aiming to solve the following shortcomings of the prior art: (1) low waste recycling efficiency and insufficient resource utilization; (2) uneven dispersion of nano-phase, affecting the stability of the material.

[0006] The method of this invention uses bismuth telluride waste as the main raw material, introduces nano-alumina, uses ball milling to achieve uniform dispersion, and prepares high-performance composite thermoelectric materials through hot extrusion, thereby realizing efficient utilization of waste and performance improvement.

[0007] The specific technical solution of the present invention is as follows:

[0008] In a first aspect, this invention provides a method for preparing a nano-alumina composite thermoelectric material based on the reuse of bismuth telluride waste, comprising the following steps:

[0009] 1) Collect bismuth telluride processing waste and pre-treat it, then clean, dry and crush it to obtain waste powder with a particle size of less than 100 μm;

[0010] 2) Mix the powder with nano-alumina particles and ball mill at low speed in a ball mill to achieve uniform compounding;

[0011] 3) The mixed powder is cold-pressed by a hydraulic press and then vacuum sintered to obtain a bismuth telluride-based bulk composite material;

[0012] 4) The bismuth telluride matrix composite material is placed in a hot extrusion die to obtain composite material ingots, and finally annealed.

[0013] The optimal conditions for the four processes are as follows:

[0014] In step 1),

[0015] The pretreatment method for bismuth telluride processing waste is as follows: the waste is initially screened to remove visible foreign objects (such as plastic, metal shavings, dust, etc.). If the waste is too large, it can be coarsely crushed first to increase the cleaning contact area.

[0016] The cleaning steps are as follows: Completely immerse the waste material in an organic cleaning solvent, preferably under ultrasonic assistance, for 10-30 minutes to remove surface grease. The cavitation effect of ultrasound can penetrate deep into crevices and thoroughly remove contaminants. After degreasing, rinse repeatedly with fresh, identical solvent, high-purity ethanol, or deionized water until the rinsing solution is clear and transparent, with no oil floating on the surface.

[0017] Preferably, the organic solvent has good volatility, strong degreasing ability, and relatively low toxicity, with acetone, isopropanol, and ethanol being the most preferred.

[0018] The drying steps are as follows: Transfer the cleaned wet material to a sieve or porous container, let it drain naturally in a ventilated place until most of the liquid has drained, and then transfer it to a vacuum drying oven to dry at 60~80℃ and a vacuum degree <100 Pa. This will completely remove any residual solvent or moisture from the cleaning step and prevent clumping or the introduction of new impurities during the crushing process.

[0019] This invention preferably utilizes a vacuum drying environment, which significantly reduces the partial pressure of oxygen, effectively preventing the material from oxidizing during heating. Simultaneously, the boiling point of the solvent is lowered, resulting in faster and more thorough drying; furthermore, the drying temperature should not be too high to prevent tellurium oxidation.

[0020] The pulverization steps are as follows: the dried material is ground using a high-energy ball mill, and then the slurry is sieved through a 100-mesh standard sieve to obtain powder within the target particle size range.

[0021] During the grinding process, materials with high hardness, high wear resistance and low susceptibility to contamination must be used, such as cemented carbide (WC-Co), zirconium oxide (ZrO2) or agate. Stainless steel should be avoided to prevent contamination by iron (Fe) impurities.

[0022] Wet grinding media are preferred: anhydrous ethanol or acetone are used as the wet grinding media. Wet grinding can prevent powder from overheating, oxidizing, and adhering to the tank wall, resulting in higher efficiency and more uniform particle size distribution.

[0023] Further atmospheric protection: grinding in a vacuum or argon / nitrogen-filled ball mill jar is the most effective way to prevent bismuth telluride oxidation.

[0024] In addition, if the dried waste still has large lumps, it can be coarsely crushed into millimeter-sized particles using a jaw crusher or hammer crusher.

[0025] Furthermore, in step (2), the ball milling process is as follows: rotation speed 100~500r / min, ball milling time 1~5min.

[0026] Furthermore, in step (2), the mass fraction of nano-alumina powder is 0.2%~1.0%.

[0027] Furthermore, in step (3), the cold pressing conditions are: axial pressure of 800~1200kN, and pressure holding for 3~10min.

[0028] Furthermore, in step (3), the vacuum sintering conditions are: vacuum degree less than 1MPa, and heat preservation at 400~600℃ for 6~10h.

[0029] Furthermore, in step (4), the hot extrusion temperature is set to 300~400℃, and a pressure of 100~300MPa is applied in the extrusion direction.

[0030] Furthermore, in step (4), the annealing temperature is set to 300~380℃ and the time is 5~10h.

[0031] In a second aspect, the present invention provides a nano-alumina composite thermoelectric material prepared by the above method.

[0032] The role and effect of invention

[0033] 1) This application avoids reliance on traditional pure raw materials by using bismuth telluride processing waste as the base material, significantly reducing costs and environmental impact. Compared with existing recycling methods, this invention directly utilizes waste powder, simplifying pretreatment and improving resource recycling efficiency.

[0034] 2) Low-speed ball milling is used to achieve uniform dispersion of nano-alumina in bismuth telluride waste, avoiding crystal damage caused by high-energy ball milling. This method forms a nanoscale composite interface, effectively scattering phonons, reducing thermal conductivity, while maintaining high electrical conductivity and improving the thermoelectric figure of merit. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of the preparation process of the nano-alumina composite thermoelectric material based on the reuse of bismuth telluride waste according to the present invention. Detailed Implementation

[0036] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, the following embodiments should not be construed as limiting the scope of the present invention.

[0037] Example 1

[0038] 1) Collect bismuth telluride processing waste and pre-treat it, then clean, dry, and pulverize it to obtain waste powder with a particle size of less than 100 μm. The specific steps are as follows:

[0039] 1-1) Pretreatment

[0040] The waste material is initially screened to remove visible foreign objects such as plastic, metal shavings, and dust. If the waste material is too large, it can be coarsely crushed first to increase the cleaning contact area.

[0041] The cleaning steps are as follows: Immerse the waste material completely in ethanol and clean it for 20 minutes with ultrasonic assistance to remove the grease attached to the surface; after degreasing, rinse it multiple times with fresh solvent of the same type until the rinsing solution is clear and transparent with no oil floating on it.

[0042] 1-2) Drying

[0043] After washing, transfer the wet material to a sieve or porous container and allow it to drain naturally in a ventilated area until most of the liquid has evaporated. Then, transfer it to a vacuum drying oven and dry it at 60°C and a vacuum degree <100 Pa to completely remove any residual solvent or moisture from the washing process, preventing clumping or the introduction of new impurities during crushing. If the dried waste material still has large lumps, it can be coarsely crushed to millimeter-sized particles using a jaw crusher or hammer crusher.

[0044] The vacuum environment significantly reduces the partial pressure of oxygen, effectively preventing the material from oxidizing during heating. Simultaneously, the boiling point of the solvent decreases, resulting in faster and more thorough drying; however, the drying temperature should not be too high to prevent tellurium oxidation.

[0045] 1-3) Crushing

[0046] The dried material was ground using a high-energy ball mill. Anhydrous ethanol was used as the wet grinding medium during the grinding process. The grinding was carried out in a ball mill jar filled with argon / nitrogen. The slurry was then sieved through a standard sieve with a mesh size of 100 to obtain powder within the target particle size range.

[0047] Grinding jars and grinding rods must be made of materials with high hardness, high wear resistance and low susceptibility to contamination, such as cemented carbide (WC-Co), zirconium oxide (ZrO2) or agate. Stainless steel should be avoided to prevent contamination by iron (Fe) impurities.

[0048] 2) After mixing bismuth telluride waste powder with nano alumina powder, the mixture was ball-milled at 100 r / min for 5 min to obtain a composite bismuth telluride powder material doped with 0.2% nano alumina.

[0049] 3) The obtained composite powder material is cold-pressed into a blank under an axial pressure of 800kN by a hydraulic press; then vacuum sintered for 10h under a vacuum degree of less than 1MPa and a temperature of 400℃.

[0050] 4) Place the sintered billet into the hot extrusion mold, and place it into the heater together with the mold. Set the heater temperature to 365℃. Apply a pressure of 200MPa in the extrusion direction and extrude a 30cm diameter rod in the pressure direction. After the extruded rod is held at 380℃ for 10 hours, it is annealed.

[0051] Example 2

[0052] 1) Collect bismuth telluride processing waste and pre-treat it, then clean, dry, and pulverize it to obtain waste powder with a particle size of less than 100 μm. The specific steps are as follows:

[0053] 1-1) Pretreatment

[0054] The waste material is initially screened to remove visible foreign objects such as plastic, metal shavings, and dust. If the waste material is too large, it can be coarsely crushed first to increase the cleaning contact area.

[0055] The cleaning steps are as follows: Immerse the waste material completely in isopropanol and clean it for 20 minutes with ultrasonic assistance to remove the grease attached to the surface; after degreasing, rinse it multiple times with fresh solvent of the same type until the rinsing solution is clear and transparent with no oil floating on it.

[0056] 1-2) Drying

[0057] After washing, transfer the wet material to a sieve or porous container and allow it to drain naturally in a ventilated area until most of the liquid has evaporated. Then, transfer it to a vacuum drying oven and dry it at 70°C and a vacuum degree <100 Pa to completely remove any residual solvent or moisture from the washing process, preventing clumping or the introduction of new impurities during crushing. If the dried waste material still has large lumps, it can be coarsely crushed to millimeter-sized particles using a jaw crusher or hammer crusher.

[0058] 1-3) Crushing

[0059] The dried material was ground using a high-energy ball mill. Acetone was used as the wet grinding medium during the grinding process. The grinding was carried out in a ball mill jar filled with argon / nitrogen. The slurry was then sieved through a standard sieve with a mesh size of 100 to obtain powder within the target particle size range.

[0060] 3) After mixing the bismuth telluride waste powder with nano alumina powder, the mixture was ball-milled at 300 r / min for 5 min to obtain a composite bismuth telluride powder material with 0.6% nano alumina doping.

[0061] 3) The obtained composite powder material is cold-pressed into a blank under an axial pressure of 1000kN using a hydraulic press; then it is vacuum sintered for 10h under a vacuum degree of less than 1MPa and a temperature of 500℃.

[0062] 4) Place the sintered billet into the hot extrusion mold, and place it into the heater together with the mold. Set the heater temperature to 365℃. Apply a pressure of 200MPa in the extrusion direction and extrude a 30cm diameter rod in the pressure direction. After the extruded rod is held at 380℃ for 10 hours, it is annealed.

[0063] Example 3

[0064] 1) Collect bismuth telluride processing waste and pre-treat it, then clean, dry, and pulverize it to obtain waste powder with a particle size of less than 100 μm. The specific steps are as follows:

[0065] 1-1) Pretreatment

[0066] The waste material is initially screened to remove visible foreign objects such as plastic, metal shavings, and dust. If the waste material is too large, it can be coarsely crushed first to increase the cleaning contact area.

[0067] The cleaning steps are as follows: Immerse the waste material completely in isopropanol and clean it for 20 minutes with ultrasonic assistance to remove the grease attached to the surface; after degreasing, rinse it multiple times with fresh solvent of the same type until the rinsing solution is clear and transparent with no oil floating on it.

[0068] 1-2) Drying

[0069] After washing, transfer the wet material to a sieve or porous container and allow it to drain naturally in a ventilated area until most of the liquid has evaporated. Then, transfer it to a vacuum drying oven and dry it at 80°C and a vacuum degree <100 Pa to completely remove any residual solvent or moisture from the washing process, preventing clumping or the introduction of new impurities during crushing. If the dried waste material still has large lumps, it can be coarsely crushed to millimeter-sized particles using a jaw crusher or hammer crusher.

[0070] 1-3) Crushing

[0071] The dried material was ground using a high-energy ball mill. Acetone was used as the wet grinding medium during the grinding process. The grinding was carried out in a ball mill jar filled with argon / nitrogen. The slurry was then sieved through a standard sieve with a mesh size of 100 to obtain powder within the target particle size range.

[0072] 4) After mixing the bismuth telluride waste powder with the nano alumina powder, the mixture was ball-milled at 500 r / min for 5 min to obtain a composite bismuth telluride powder material with 1.0% nano alumina doping.

[0073] 3) The obtained composite powder material is cold-pressed into a blank under an axial pressure of 1200kN using a hydraulic press; then it is vacuum sintered for 10h under a vacuum degree of less than 1MPa and a temperature of 600℃.

[0074] 4) Place the sintered billet into the hot extrusion mold, and place it into the heater together with the mold. Set the heater temperature to 365℃. Apply a pressure of 200MPa in the extrusion direction and extrude a 30cm diameter rod in the pressure direction. After the extruded rod is held at 380℃ for 10 hours, it is annealed.

[0075] The undescribed parts of this invention are the same as or implemented using existing technology. The applicant declares that this invention is illustrated through the above embodiments, but the invention is not limited to the above detailed methods, i.e., it does not mean that the invention must rely on the above detailed methods to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. A method for preparing nano-alumina composite thermoelectric materials based on the reuse of bismuth telluride waste, characterized in that, Includes the following steps: 1) Collect bismuth telluride processing waste and pre-treat it, then clean, dry and crush it to obtain waste powder with a particle size of less than 100μm; 2) Mix the powder with nano-alumina particles and ball mill at low speed in a ball mill to achieve uniform compounding; 3) The mixed powder is cold-pressed by a hydraulic press and then vacuum sintered to obtain a bismuth telluride-based bulk composite material; 4) The bismuth telluride matrix composite material is placed in a hot extrusion die to obtain composite material ingots, and finally annealed.

2. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that: in, In step (1), the pretreatment method for bismuth telluride processing waste is as follows: the waste is initially screened to remove visible foreign objects, and the waste that is too large is coarsely crushed.

3. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that: in, In step (1), the cleaning steps are as follows: the waste material is completely immersed in an organic cleaning solvent and cleaned for 10-30 minutes with ultrasonic assistance to remove the grease attached to the surface; then it is rinsed multiple times with fresh solvent of the same kind, high-purity ethanol or deionized water until the rinsing solution is clear and transparent and no oil stains float.

4. The method for preparing the bismuth telluride-based thermoelectric material according to claim 3, characterized in that: in, The organic cleaning solvent is selected from acetone, isopropanol, or ethanol.

5. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that: in, In step (1), the drying step is as follows: the cleaned wet material is transferred to a sieve or porous container, and after most of the liquid is drained naturally in a ventilated place, it is transferred to a vacuum drying oven for drying. It is dried at 60~80℃ and vacuum degree <100 Pa to completely remove the solvent or water remaining in the cleaning step and prevent clumping or introduction of new impurities during the crushing process.

6. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that: in, In step (1), the pulverization step is as follows: using a high-energy ball mill, with anhydrous ethanol or acetone as the wet grinding medium, the dried material is ground in a vacuum or argon / nitrogen-filled ball mill jar, and then the slurry is sieved through a 100-mesh standard sieve to obtain powder within the target particle size range.

7. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that: in, In step (2), the rotation speed is 100~500 r / min and the ball milling time is 1~5 min; the mass fraction of nano alumina powder is 0.2%~1.0%.

8. The method for preparing the bismuth telluride-based thermoelectric material according to claim 1, characterized in that: in, In step (3), the cold pressing conditions are: axial pressure of 800~1200kN, holding pressure for 3~10min; the vacuum sintering conditions are: vacuum degree less than 1MPa, holding temperature at 400~600℃ for 6~10h.

9. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that: in, In step (4), the hot extrusion conditions are as follows: the hot extrusion temperature is set to 300~400℃, and a pressure of 100~300MPa is applied in the extrusion direction; the annealing temperature is set to 300~380℃, and the time is 5~10h.

10. A nano-alumina composite thermoelectric material, characterized in that, It is prepared by the method described in any one of claims 1 to 9.

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