Effects of copper addition on thermoelectric properties of B-FeSi2 prepared by mechanical alloying

Abstract

FeSi[subscript 2] were prepared by mechanical alloy (MA) technique using a planetary ball mill. Fe[subscript 30-x]Cu[subscript x]Si[subscript 70] where x = 0, 1, 2 and 5 were selected instead of conventional composition, Fe[subscript 33.33]Si[subscript 66.67], in order to avoid the metallic E-FeSi phase. Each composition was solidified by 2 methods. For the first method, the mixtures were cold pressed with 345 MPa gauge pressure and annealed under Ar atmosphere at 1073K or 1173K. The annealing times were 1, 3 or 5 hours. For the second method, the mixtures were hot pressed with 26 MPa gauge pressure at 1173K and 1 hour soaking time. X-Ray Diffraction technique (XRD) was used to determine B phase of the samples. The B phase fraction and Seebeck coefficient of cold pressed samples increased when %Cu addition increased. Seebeck coefficient of cold pressed samples showed that 0.5%Cu sample annealing at 1173K for 1 hour gives the highest Seebeck coefficient of 16 uV/K at room temperature. Seebeck coefficient of hot pressed samples was greater than that of cold pressed samples. For hot pressed samples, the B phase fraction and Seebeck coefficient is maximize with content of Cu around 0.1% - 0.2%. Seebeck coefficient of hot pressed samples showed that 0.1%Cu sample gives the highest Seebeck coefficient of 66 uV/K at room temperature.