Preparation of Mg<SUB>2</SUB>Si-FeSi<SUB>2</SUB> Thermoelectric Device by MA-Pulsed Current Sintering Process

The formation process and Seebeck coefficient of a Mg2Si-FeSi2 thermoelectric device made by mechanical alloying (MA) and pulsed current sintering was investigated.The MA was performed in a planetary ball mill using three elemental powders. The powders were prepared by the mixing of Mg2Si-xmass%FeSi2(x=0, 20, 40, 60 ,80, 100). The MA powders were consolidated by pulsed current sintering method. The Seebeck coefficient of Mg2Si sintered at 823 K under 350 MPa was −366 μV/K at room temperature. However, the Seebeck coefficient of Co doped FeSi2 sintered at 1073 K was 4 μV/K because the sintered structure of FeSi2 was consisted of α and ε phase. After heat treatment at 973 K for 108 ks, the structure of FeSi2 became almost pure β phase and the Seebeck coefficient became −245 μV/K. Mg2Si-80 mass%FeSi2 was held at 823 K for 180 s and at 1073 K for 600 s during pulsed current sintering, in order to attain the densification. After sintering, the sample was heat treated at 973 K for 108 ks. Therefore, Mg2Si phase and β-FeSi2 phase coexisted in the sample. However, the Seebeck coefficient of Mg2Si-80 mass%FeSi2 was about −110 μV/K. There was no improvement of the Seebeck effect.