Progress on Searching Optimal Thermal Spray Parameters for Magnesium Silicide
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Progress on Searching Optimal Thermal Spray Parameters for Magnesium Silicide Gaosheng Fu1, Lei Zuo*1, Jon Longtin1, Yikai Chen2 and Sanjay Sampath2 Department of Mechanical Engineering, and 2Department of Material Science and Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794, U.S.A. (*[email protected], 631-632-9327) ABSTRACT The thermoelectric properties of Mg2Si coatings prepared by Atmospheric Plasma Spray (APS), and Vacuum Plasma Spray (VPS) are presented. Seebeck coefficient results of both APS and VPS have been reported. XRD and SEM analysis of the samples are also presented to understand how microstructure influences the coating thermoelectric properties. The results suggest significant improvements can be made on the reduction of impurity including oxidation and pure silicon by using proper spray method and parameters. Thermal spray has been demonstrated before to be effective way to reduce thermal conductivity which may due to the coating microstructure. VPS result shows higher Seebeck coefficient than APS which may due to lower level of oxidization. 1
Key words: thermoelectric material, Mg2Si, thermal spray, APS, VPS 1. INTRODUCTION Magnesium silicide (Mg2Si) is particularly interesting at a temperature range from 400 to 800K as a thermoelectric solid-state power generator material [1, 2]. Mg2Si is abundant on earth, thus making it much less expensive than traditional Bismuth Telluride thermoelectric material. It is also non-toxic and friendly to the environment. The conversion efficiency of the thermoelectric material is determined by its figure of merit, ZT= S2T/k, where S is the Seebeck coefficient; is the electrical conductivity; k is the thermal conductivity; and T is the absolute temperature. Extensive research has been done to synthesize and solidify Mg2Si and its solid solutions, Zaitsev et al used direct melting Mg2Si and got a maximum ZT of 1.1[3]. Riffel and Schilz investigated mechanical alloying method followed by hot-pressing process [4]. Jung and Kim tried solid state reactions then hot press (HP) and obtained maximum ZT of 0.7 at 830K with Bi doped Mg2Si [5]. Kajikawa et al. [6, 7] and Tani[8] used spark plasma sintering and got maximum ZT of 0.86 at 862K with Bi doped Mg2Si. The vertical Bridgman method has also been applied for the single crystal growth by Akasaka et al. [9] and Tamura et al. [10]. Meltspinning followed by spark plasma synthesis (SPS) or hot pressing has been used to synthesis thermoelectric material by Q. Li and demonstrated thermoelectric properties could be enhanced by non-equilibrium technique [11]. As a flexible, industry-scalable and cost-effective manufacturing process, thermal spray has been traditionally used for protective barrier coating. In the past decade Sampath et al [12] extended it for material synthesis of functional electronics and sensors. Thermal spray has a very high quenching rate (10^6-7 K/sec) similar as the melt spinning [13], we would like to enable integrated manufacturing of thermoelectric devices on the
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