Preparation And Performance Of Mg₂Si Based Thermoelectric Materials From MgH₂Reaction

Thermoelectric material is a kind of functional materials that can convert heat to electricity directly. The thermoelectric devices own some advantages like silent, clean, and high security, which is to applied in saving and recycling waste heat, including heat of exhausted gases and fumes from viecles, factories, and thermoelectric refrigeration. Among all TE materials, the compounds Mg2X (X=Si, Ge, Sn) and their solid solutions are characterized by abundant raw materials, non-toxic, security, and have attracted considerable attention in recent years.In this work, aimed at the problems arise from the vaporization of Mg and its oxidation reactivity, Tube furnace reaction followed by Field-Activated and Pressure-Assisted Synthesis (FAPAS) was used to prepare the Mg2Si based thermoelectric materials. Bi doped Mg2Si, Y doped Mg2Sn and the Mg2(Si, Sn) thermoelectric materials were prepared, and their thermoelectric properties were valuated. The main research results are summarized as follows:Thermoelectric (TE) materials of pure Mg2Si, and1%Bi-doped Mg2Si were prepared by tube reaction. The thermoelectric properties of Mg2Si and1%Bi doped Mg2Si based thermoelectric material shows that:Reaction between silicon and magnesium hydride instead of pure magnesium minimizes the oxidation and vaporization of magnesium. The prepared TE materials had a grain size of500nm. Compared with pure Mg2Si, its electrical conductivity is increased, and its ZT value is also improved to0.58at750K.Mg2Sn based thermoelectric (TE) materials were prepared by a low-temperature solid-state reaction from MgH2and Sn. The thermoelectric performance showed that:All samples indicated n-type conduction within the whole temperature region, while specimens showed a tendency to be nearly p-type with increasing temperature.The Seebeck coefficient of Y-doped Mg2Sn has been enhanced at low temperature, and the figure of merit ZT was enhanced. The0.2%Y-doped Mg2Sn showed a maximum figure of merit ZT of0.032at340K, which is nearly3times of that in some literatures.The rapid densification of Mg2(Si, Sn) bulk materials were obtained by the low-temperature solid-state reaction from MgH2, Si and Sn followed by the Field-Activated and Pressure-Assisted Synthesis(FAPAS). The result showed that the Mg2(Si, Sn) solid solution wasn’t formed completely FAPAS process. Compared to pure Mg2Si and pure Mg2Sn, the thermal conductivity of Mg2(Si, Sn) solid solution has been greatly decreased.