Technical Study On The Preparation Of Bi₂Se_0.3Te_2.7 Thermoelectric Materials By Thermal Spraying

The thermoelectric device works through the thermoelectric effect and can transform the heat and electric energy into each other.It has the advantages of no pollution,small volume and high reliability.Thermoelectric materials are the basis of thermoelectric devices.Bi₂Te₃compounds are the best and most widely used thermoelectric materials at room temperature.At present,the ZT value of commercial Bi₂Te₃ block thermoelectric materials prepared by zone melting process is near 1.However,the low hardness and the big brittleness of zone melting materials are not conducive to the processing and application of materials.In addition,the preparation process of thermoelectric devices is tedious and long,which makes the device cost high and yield low.Therefore,it is of great significance to explore new process for thermoelectric devices.Thermal spraying is an important technology of surface engineering.It has the characteristics of strong binding force,fast film forming speed and adjustable film thickness.Thermal spraying technology is used to spray the thermoelectric materials directly on the copper ceramic substrate,which can greatly reduce the fabrication process of the device,reduce the production cost and improve the yield.For this,the powder must have good fluidity.In this paper,the n type Bi₂Se_0.3Te_2.7.7 was used as the raw material,and the powder fluidity of Bi₂Se_0.3Te_2.7.7 was improved by the method of polymer granulation,and the physical properties and thermoelectric properties of the samples before and after granulation were compared.Then,by plasma spraying and high velocity oxygen fuel technology,by the Bi₂Se_0.3Te_2.7.7 after granulation powder as the research object,for the preparation of Bi₂Se_0.3Te_2.7.7 coating to explore and research its craft,for Bi₂Se_0.3Te_2.7.7 coating thermoelectric performance of prophase research job.The main research contents and results are as follows:?1?The Bi₂Se_0.3Te_2.7.7 powder and PVA?polyvinyl alcohol in a 10%proportion of the water solution?are mixed and grind for granulation.The powders before and after granulation and the blocks made by hot pressing are tested and characterized respectively.The results showed that the fluidity of Bi₂Se_0.3Te_2.7.7 powder increased significantly after granulation,and the granulation sample with PVA and Bi₂Se_0.3Te_2.7.7 powder at mass ratio of 1:10 had the best fluidity;Granulation had no effect on the microhardness of the samples,which were all around 80 HV;The thermoelectric properties of Bi₂Se_0.3Te_2.7.7 were not reduced,and the ZT values are all around 0.56,of which is close to the ZT values of the granulation sample with PVA and Bi₂Se_0.3Te_2.7.7 powder at mass ratio of 1:10 and the non granulation Bi₂Se_0.3Te_2.7sample.?2?Taking PVA and Bi₂Se_0.3Te_2.7.7 mass ratio of 1:10 granulation sample as the research object,the related process of Bi₂Se_0.3Te_2.7.7 coating prepared by plasma spraying was explored.The results show that the velocity of plasma spraying is low in the research scope of this paper,so that the microhardness and bonding strength of the coating are not high.When the hydrogen flow rate is 1.5 L/min and the pressure is 0.4 MPa,the argon flow rate is 10 L/min and the pressure is 0.8 MPa,the optimum spraying distance and the powder feed rate are 6 cm and 20 g/min respectively,and the coating microhardness and bonding strength are 251 HV and 4.5 MPa,respectively.?3?Taking the granulation sample of PVA and Bi₂Se_0.3Te_2.7.7 mass ratio at 1:10 as the research object,the related process of Bi₂Se_0.3Te_2.7.7 coating prepared by high velocity oxygen fuel was explored.The results show that the high velocity oxygen fuel can provide high speed,and the coating with high microhardness and high bonding strength is obtained.And in this paper,when the flow rate of oxygen is 873 L/min and the flow rate of fuel is 0.38 L/min,the optimum spray distance and the powder feed rate are 30 cm and 90 g/min,respectively,and the coating microhardness and bonding strength are 593 HV and 36 MPa,respectively.?4?The fluidity of Bi₂Se_0.3Te_2.7.7 powder can be improved by the method of polymer granulation,and then the Bi₂Se_0.3Te_2.7.7 powder after granulation can be used as the research object for thermal spraying.Bi₂Se_0.3Te_2.7.7 coatings were obtained by plasma spraying and high velocity oxygen fuel process respectively.Comparing the properties of two kinds of thermal sprayed coatings,it is found that the high velocity oxygen fuel is superior to plasma spraying.It is indicated that the high velocity oxygen fuel process is more suitable for the preparation of Bi₂Se_0.3Te_2.7.7 coatings.And it is the basis for the preparation of related thermoelectric devices.