Thermoelectric Properties of Mg2Si Produced by New Chemical Route and SPS

Wilfried Wunderlich,Masashi Sato,Yoshihito Suzuki,Atta Khan,Takao Mori,Muayyad Al-Abandi,Takahiro Ohkuma,Naoto Gibo

doi:10.3390/inorganics2020351

Wilfried Wunderlich, Masashi Sato + Show 6 more

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https://doi.org/10.3390/inorganics2020351

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Abstract

This paper reports about a new synthesis method for preparing Mg2Si in an efficient way. The intermetallic Mg2Si-phase forms gradually from a mixture of Mg and Si fine powder during exposure to hydrogen atmosphere, which reacts in a vacuum vessel at 350 °C. The resulting powder has the same particle size (100 µm) compared with commercial Mg2Si powder, but higher reactivity due to large surface area from particulate morphology. Both types of powders were compacted by spark plasma sintering (SPS) experiments at 627, 602, 597, and 400 °C for 600 s with a compaction pressure of 80 MPa. The thermoelectric characterization was performed with low and high temperature gradients of ΔT = 10 K up to 600 K. The results confirmed a Seebeck coefficient of −0.14 mV/K for specimens sintered from both powders. The small difference in total performance between purchased and produced power is considered to be due to the effect of impurities. The best values were obtained for n-type Mg2Si doped with 3% Bi yielding a Seebeck coefficient of −0.2 mV/K, ZT = 0.45) and electric output power of more than 6 µW.

Highlights

IntroductionCompared with PbTe and CoSb3 or other TEs usable in the same temperature range, silicides have advantages as they are considered as environmental-friendly materials, because they consist of elements which are abundant in the earth’s crust and they are nontoxic
Mg2Si-based thermoelectric (TE) materials were reported in the early 1960s [1,2] as promising devices for heat-into-electricity-conversion in the middle temperature range, because of their attractive figure-of-merit ZT = 1.3 [3,4,5]
For the first time, the Sieverts’ method of controlling the pressure, composition and temperature as a new and efficient synthesis method for producing Mg2Si powders

Summary

Introduction

Compared with PbTe and CoSb3 or other TEs usable in the same temperature range, silicides have advantages as they are considered as environmental-friendly materials, because they consist of elements which are abundant in the earth’s crust and they are nontoxic. Since they are composed of light metals, they have low densities in the range of 2–3.6 g/cm which is a favorable feature for heat recovery in automobile applications. Measurements of Seebeck coefficient [34,35,36] and electric output power are described, and all results are discussed

Results and Discussion

Experimental Section

Conclusions