Resource Processing And Thermoelectric Properties Optimization Of Processing Waste Of P-Type Bi₂Te₃ Based Refrigerating Crystal Bar

Thermoelectric material is a kind of new functional material and it can realize the direct conversion between heat energy and electric energy,which has broad application prospects in the field of thermoelectric refrigeration and thermoelectric power generation.In view of the present situation that high scrap rate in the processing and production of Bi₂Te₃ based thermoelectric materials in the semiconductor refrigeration industry,and the drawbacks of existing waste recycling technology such as environmentally unfriendly,process complicated,long cycle and high cost,a new technology for recovering processing waste of Bi₂Te₃ based refrigeration crystal bar was proposed.The impurities in the waste were effectively removed through washing,carbonization,smelting and other processes.Then the bulk materials with excellent properties were prepared by composition adjustment and Resistance Pressing Sintering technique.In addition,Bi₂Te₃ based alloys have been widely used in the field of thermoelectric refrigeration as the best thermoelectric material near room temperature,but their applications in thermoelectric power generation are relatively backward.The temperature dependence of the electric-thermal transport properties and the figure of merit of Bi₂Te₃ based thermoelectric materials with different antimony content were studied with the energy band theory.The thermoelectric properties of P-type Bi₂Te₃ based alloy at high temperature were optimized.The results were obtained as follows:1)After simple ultrasonic cleaning and melting process for the processing waste fragments,the impurities in the fragments can be removed and the high purity Bi₂Te₃ based alloy rod can be obtained.The comprehensive performance of the sample in the whole temperature region was significantly improved after the composition adjustment.The ZT values of Bi_0.36Sb_1.64Te₃,Bi_0.4Sb_1.6Te₃ and Bi_0.44Sb_1.56Te₃ reached near about 1.0 in the whole temperature range,and the sample of Bi_0.36Sb_1.64Te₃ obtained the maximum ZT value of 1.21 at 420 K.The recovery rate of waste fragments can reach 98%.2)For mixed waste particles of P and N-type Bi₂Te₃ based refrigeration crystal rod,the impurities mainly by metal oxide and SiO2 were removed and a pure Bi₂Te₃ based alloy was obtained by using ultrasonic washing,reduction,the first smelting and the second smelting process.The conductivity types of the samples changed from N-type to P-type,the electrical conductivity and power factor at room temperature for Bi_0.36Sb_1.64Te₃ and Bi_0.4Sb_1.6Te₃ reached 1000 S×cm-1 and more than 4.0,respectively.The recovery rate of waste particles can reach 97.02%.3)For cutting waste powders from Bi₂Te₃ based refrigeration crystal rods,the impurities from cutting fluid and antimony oxide were removed by vacuum roasting,and the purity of Bi₂Te₃ based alloy was further improved by the first smelting and the second smelting process.Then the P-type bulk materials with excellent thermoelectric properties were prepared by composition adjustment and resistance pressing sintering,where the sample with a nominal composition of Bi_0.36Sb_1.64Te₃ obtained the maximum ZT value of 1.23 at 350 K.The recovery rate of waste powders can reach 85.73%.4)For Bi2-xSbxTe₃ alloys,the band gap and intrinsic excitation temperature were adjusted by doping different content of antimony.The higher the intrinsic excitation temperature was?higher the antimony content was?,faster the electrical conductivity decreased with temperature,and the Seebeck coefficient peaks also occurred at a higher temperature,and meanwhile the contribution of the ambipolar thermal conductivity to the total thermal conductivity was also becoming smaller and smaller.As a result,the corresponding optimal peaks of the figure of merits?ZT?were pushed to a higher temperature.The sample of Bi_0.44Sb_1.56Te₃ obtained the maximum ZT value of 1.22 at 340 K,and the mean ZT values of Bi_0.4Sb_1.6Te₃ and Bi_0.44Sb_1.56Te₃ were all over 1.0 in a wide range of temperature from 300 K to 460 K,which would be very suitable for the low temperature thermoelectric power generation.