Bonding And Prepareing Of Cu Electrode With Mg₂Si Thermoelectric Material And The Performance Revolution

Mg₂Si-based thermoelectric materials are promising candidate materials for thermoelectric power generation applications in the middle temperature range for the advantages of high performance,light weight,environmentally friendly and high abundance of constituents in the earth's crust.In order to put it into practice,the stability in working temperature,thermal stresses relaxation and contact resistance have great influence in the performance of the thermoelectric devices.Therefore it is of great importance to prepare the electrode,study the high-temperature stability and reliability of the joint between Mg₂Si-based thermoelectric materials and electrode.In order to choose better preparation technology of Mg₂Si bulk material for studying the revolution of the joints between Mg₂Si and the electrode in high-temperature for basic scientific research.A systematic study was conducted to study the synthesis temperature and pressure effect on the thermoelectric properties and microstructure.The results showed that the density of the sample and the carrier concentration increased with the sintering temperature and pressure increasing.Mg₂Si was prepared under different pressure?50 MPa,80 MPa,120 MPa?and same temperature?590??,the highest power factor was 5.33×10^-55 Wm^-1K^-22 under the pressure of 80 MPa.Mg₂Si was also prepared under different temperature?640?,690?,740?,780??and same pressure?50 MPa?,the highest power factor was1.82×10^-4 Wm^-1K^-22 under the temperature of 780?.Different kind of metallic materials were in comparison as to select the suitable electrode.Cu can be the suitable electrode because of the good physical and chemical property.In order to understand the regularity of the joint interface structure with time and temperature,samples were annealed at different temperatureand different time.A reaction layer was formed after SPS,Cu,Mg and Si was found at the reaction layer.After annealing at 500?for different time,the joint bond well and no crack was found at the interface.The interlayer was sintered as to study the phase composition and the properties.Cu₅Mg₂Si and Cu_1.44MgSi_0.56 were found at the interface and it has good thermal property and electric property.The overall performance of the Cu/Mg₂Si joints after bonding was studied.Four-probe electrical resistivity measuring technique was carried out to measure the contact resistance,the contact resistance and the resistance of Mg₂Si increased over time.Before annealing,the contact resistance was 0.08?,after annealing for 72 h,the contact resistance increased to 0.9?.After thermal conductivity test of Mg₂Si/Cu joints,theoretical thermal diffusion coeffient differ by about 4 mm²s^-11 from the experimental value.After annealing at 500?for different time,thermal diffusion coefficient decreased with the increase of time.Shearing test was carried out to study the mechanical property of the joint,the shear strength decreased after time growth,after annealing for 72 h,the shear strength was decreased by 44%compared with the sample before annealing.In order to understand the changes in structure of the joints at higher temperature,after annealing at 550?,small crack was found at the interface.After annealing at 580?for different time,the ratio of the elements changed and the crack extend with the increase of time,indicate that they are not suitable for running at high temperature.