Thermoelectric properties of FeSi sub 2 sintered thermoelectric using granulated powders by spray drying method

FeSi sub 2 alloys doped with Mn or Co (p-type Fe sub 0.92 Mn sub 0.08 Si sub 2 , n-type Fe sub 0.98 Co sub 0.02 Si sub 2 ) were prepared by vacuum induction melting. The ingots were pulverized in a jet mill, and the powders were granulated by spray drying method using aqueous polyvinylalcohol (PVA) binder, in order to investigate the possibility of production on a large scale. The powders granulated exhibited excellent characteristics of fluidity, leading to smoothly feed it into a die cavity. To remove the binder from a compacted body, it was debindered at 723K for 1 h in H 2 , and then sintered at 1423K for 5 h in H sub 2 , so that the residual carbon and oxygen contents in a sintered body approached those of the starting powder. Subsequently it was annealed at 1113K for 100 h in Ar, so that it was almost composed of beta -FeSi sub 2 . The thermoelectric figures of merit (Z) for optimal p- and n-type FeSi sub 2 thermoelectric are 1.75x10 exp -4 (K exp -1 ) and 2.0x10 exp -4 (K exp -1 ), respectively, which are slightly higher than those obtained by H. Nagai on a laboratory scale.