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http://dx.doi.org/10.3740/MRSK.2002.12.5.375

Phase Transformation and Thermoelectric Properties of N-tyre β Processed by Mechanical Alloying  

Eo, Sun-Cheol (Dept. of Materials Science and Engineering/Nano Technology Lab., Chungju National University)
Publication Information
Korean Journal of Materials Research / v.12, no.5, 2002 , pp. 375-381 More about this Journal
Abstract
N-type ${\beta}-FeSi_2$ with a nominal composition of $Fe_{0.98}Co_{0.02}Si_2$ powders has been produced by mechanical alloying process and consolidated by vacuum hot pressing. As-milled powders were of metastable state and fully transformed to ${\beta}-FeSi_2$ phase by subsequent isothermal annealing. However, as-consolidated $Fe_{0.98}Co_{0.02}Si_2$ consisted of untransformed mixture of ${\alpha}-Fe_2Si_ 5$ and $\varepsilon$-FeSi phases. Isothermal annealing has been carried out to induce the transformation to a thermoelectric semiconducting ${\beta}-FeSi_2$ phase. The transformation behavior of ${\beta}-FeSi_2$ was investigated by utilizing DTA, a modified TGA under magnetic field, SEM, and XRD analyses. Isothermal annealing at $830^{\circ}C$ in vacuum led to the thermoelectric semiconducting ${\beta}-FeSi_2$ phase transformation, but some residual metallic $\alpha$ and $\varepsilon$ phases were unavoidable even after prolonged annealing. Thermoelectric properties were remarkably improved by isothermal annealing due to the transformation from metallic $\alpha$ and $\varepsilon$ phases to semiconducting phases.
Keywords
Iron-silitide; ${\beta}-FeSi_2$; mechanical alloying; thermoelectric; isothermal annealing; MF-TGA;
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