Processing And Mechanism Of Joining Bi_0.5Sb_1.5Te₃ Thermoelectric Material With Nanostructure

Thermoelectric materials are functional materials which are capable of direct conversion of electrial energy and thermal energy.To use thermoelectric materials can realize the thermoelectric power generation and thermoelectric cooling.In practical applications,it is necessary to connect thermoelectric modules to electrode devices.Therefore,the thermoelectric conversion efficiency is determined by both the thermoelectric properties of the thermoelectric material and the connecting joint.Bi₂Te₃-based thermoelectric materials are the best thermoelectric materials at room temperature,usually used in the field of cooling.Thermoelectric property of commercial Bi₂Te₃ is still poor,whicn can not meet the requirements of the use of thermoelectric power generation.In this paper,a P-type Bi_0.5Sb_1.5Te₃ thermoelectric material with high thermoelctirc properties was prepared,and the properties of the materials were characterized.Joining of Bi_0.5Sb_1.5Te₃ thermoelectric material to Cu electrode was realized.Melt spin rejection is a rapid solidification method.In the rapid solidification process,the grain size can be significantly inhibited.In this paper,the P-type Bi_0.5Sb_1.5Te₃ was first smelted,and then the molten ingot was melt spin into a thin ribbon.The microstructure showed that the grain size was less than 500 nm.The XRD test showed that the ribbon was pure Bi_0.5Sb_1.5Te₃ phase.The ribbons were ground into powders and then hot pressed to obtain a bulk P-type Bi_0.5Sb_1.5Te₃ material.The structure and structural characterization indicated that the bulk material was still pure phase of Bi_0.5Sb_1.5Te₃ and retained the nanostructures of the ribbons.The properties of the materials prepared under the optimum process parameters were characterized.Its ZT value is 1.01 at 300 K,and the ZT value is 0.82 at 420 K,which greatly improves the single crystal material prepared by the fusion method.It is shown that the nanostructures in the P-type Bi_0.5Sb_1.5Te₃ materials prepared by melt-spinning combined with hot-pressing sintered form effective scattering to low-frequency phonons,which greatly reduces the lattice thermal conductivity and improves the thermoelectric properties.By using different brazing methods,it is found that the brazing joint of Bi_0.5Sb_1.5Te₃ and Cu can be realized by SAC305 as brazing filler metal,rosin as flux and heating table heating method.The typical interfacial microstrcture of the joint was Bi_0.5Sb_1.5Te₃/SnTe+SnSb/?Sn+Bi+Cu6Sn5+Ag3Sn/Cu6Sn5/Cu.The effects of different process parameters on the microstructure and mechanical properties of the interface were investigated.The results show that the effect of holding time on the interface and mechanical properties of the joint is greater than the brazing temperature.With the change of process parameters,the mechanical properties of the joints increased first and then decreased.When the brazing temperature is 250?,and holding time is 3min,the maximum shear strength could be obtained,which is 18 MPa.The fracture position of the joint was the the solder zone and Cu-Sn compound zone near the Cu region.In order to achieve the joint at low temperature and working at high temperature,nanosilver particles with a average dimension of 40 nm and good dispersibility were prepared.The results showed that the grain size was small and uniform at a drop rate of 10 m L/min.The nanosilver particles were arranged as solder paste to realize the reliable joinning of Bi_0.5Sb_1.5Te₃ and Cu.The influence of process parameters on the microstructure and mechanical properties of interconnected joints was investigated.It was found that the optimum parameters of the joint were ethanol as the solvent of nanosilver solder paste,the joining temperature was,300?,the holding time was 30 min,and the pressure was 10 MPa.In this process,the resulting joint had no obvious defects,shear strength was 5MPa.