One-step low temperature reactive consolidation of high purity nanocrystalline Mg2Si

Abstract

Bulk Nanocrystalline Mg 2 Si thermoelectric materials were synthesized and consolidated in a one-step process through a solid-state reaction between magnesium hydride and silicon, using the spark plasma sintering (SPS) method. The hydrogen produced in the process alleviates the problem of the oxidation of Mg. The samples were reactively sintered at temperatures in the range 723-823K and under a uniaxial pressure in the range of 71-164 MPa in 5 min. Powder X-ray diffraction (XRD) analysis showed the products to be pure Mg 2 Si. The grain size of the consolidated samples was less than 500 nm, as determined by transmission electron spectroscopy (TEM). Residual nano-pores were observed by scanning electron microscopy at grain boundaries; their presence is believed to be the consequence of hydrogen evolution during the reactive sintering. The effect of synthesis temperature and pressure on crystallite size, density, and transport properties was determined. The results showed that use of MgH 2 instead of Mg in the one-step method prevents the formation of MgO. The addition of 1 at.% Bi as a dopant improved the power factor significantly.Samples with 1 at.% Bi had a ZT of 0.6 at 775 K.

Thermoelectric performance of n-type Mg2Ge

“…This method was previously used to avoid the long, high temperature traditional methods in the synthesis of Mg 2 Si 19 , with the objective of reducing the volatilization and oxidation of Mg. The electronic transport properties are compared with those of an Sb-doped sample and previous reports on Sb-doped Mg 2 Ge samples fabricated by melting techniques followed by hot-pressing 12, 17 .…”

Gas‐Phase Plasma Synthesis of Free‐Standing Silicon Nanoparticles for Future Energy Applications

“…Already at the beginning of the research, it was understood that having a reduced thermal conductivity is not only enough, but improving the electrical conductivity of Si is a requirement to achieve high ZT values, at least around 1. For achieving higher electronic conductivity, doping and surface functionalization became important steps to reach higher ZT values using Si‐based nanostructures. One of the most studied system is SiGe alloy with improved ZT values of up to 1.3 (at 1775 K) for n‐type Si 0.8 Ge 0.2 .…”

Effects of Complex Modification by Sr–Sb on the Microstructures and Mechanical Properties of Al–18 wt % Mg2Si–4.5Cu Alloys

“…It was proved that Mg 2 Si reinforced Al composites have improved mechanical properties at a wide range of temperatures [3,4] and high wear resistance [5]. It is also attractive in materials because of the abundance and nontoxicity of its constituent elements [6]. Owing to the excellent combination of physical and mechanical properties, Mg 2 Si has been widely used as a reinforced phase to prepare Mg 2 Si/Al alloys, which are attractive candidate material for aerospace, automotive, and other applications such as drilling pipes in deep and ultra-deep wells for gas and oil [7,8,9,10].…”