日本金属学会誌

J. Japan Inst. Metals, Vol. 63, No. 3 (1999),
pp. 391-396

Thermal Shock Resistance and Thermoelectric Properties ofBoron Doped Iron Disilicides

Yukihiro Isoda1, Yoshikazu Shinohara1, Yoshio Imai1,Isao Albart Nishida1 and Osamu Ohashi2

1National Research Institute for Metals, Ibaraki 305-0047
2Graduate School of Science and Technology, Niigata University, Niigata 950-2181

Abstract:

The phase analysis was carried out for the (1-x)FeSi2+xBSi2 system in the composition range of 0{≤q}x{≤q}0.08 by an X-ray technique. It was found that B atoms in FeSi2 were substituted by Fe atoms and that a solid solution Fe1-xBxSi2 was formed in the composition range of x{≤q}0.03. The thermal shock resistance was estimated by the number of quenching cycle times, before crack was initiated by heating to 1073 K and subsequently water quenching to 300 K. For x=0, a crack was initiated on the specimen surface with one quenching cycle, while no crack was found until forty quenching cycles for x=0.03. The effect of B atoms on thermoelectric properties of the sintered (1-x)FeSi2+xBSi2 have been investigated at 300 K, and the thermoelectromotive force E0 and effective mean resistivity re were observed up to a temperature difference of 800 K. It was found that B atoms acted as the donors. The absolute value of the Seebeck coefficient at 300 K was 103.5 μV K-1 for x=0 and increased up to 681 μV K-1 for x=0.03. Lattice thermal conductivity at 300 K decreased with increasing x and the reduction ratio was 12% for x=0.03. The effective maximum power Pe(=E02/4re) of p-type FeSi2 doped with Mn and B was lower than that of Mn doped FeSi2, while Pe of n-type FeSi2 doped with Co and B was equivalent to that of un-doped B. A p-type or n-type thermoelectric material with a high thermal shock resistance was formed by double doping of FeSi2 with Mn and B or with Co and B, respectively.


(Received September 2, 1998; In Final Form November 30, 1998)

Keywords:

iron disilicide, boron, thermal shock resistance, Seebeck coefficient, thermal conductivity, resistivity, thermoelectric property


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