From sol–gel prepared porous silica to monolithic porous Mg2Si/MgO composite materials

Abstract

Mg 2 Si is apart from its conductivity properties expected to be a promising candidate for thermoelectric applications due to its low toxicity, low costs, and the high abundance of its precursor chemicals. Through the addition of a homogeneous distribution of nanoparticles (e.g. MgO) and by reducing the size of Mg 2 Si to the nanometer regime, it is possible to decrease the thermal conductivity by increasing phonon-interface scattering and, as a result, improve the thermoelectric properties. However, classical approaches do not allow for the synthesis of nanocomposites from Mg 2 Si and MgO. In this work, a straightforward route is presented towards homogeneously mixed Mg 2 Si/MgO via a two-step magnesiothermic reduction process starting from sol-gel derived hierarchically organized porous silica. Monolithic materials composed of Mg 2 Si and MgO in variable molar ratios are built up from a macroporous network of Mg 2 Si with homogeneously distributed MgO particles exhibiting a crystallite size in the range of 24-37 nm. Highlights •We present a new and versatile method to prepare macroporous Mg 2 Si/MgO composites.• Both components, Mg 2 Si and MgO, are homogeneously distributed in the final composite.• Our approach can easily be extended to other highly porous silica templates.• The Mg 2 Si/MgO network comprises nanosized MgO particles in a 3D interconnected Mg 2 Si network.

Highly Porous Magnesium Silicide Honeycombs Prepared by Magnesium Vapor Annealing of Silica-Coated Polymer Honeycomb Films toward Ultralightweight Thermoelectric Materials

“…11 In addition, Elsaesser and co-workers reported that porous Mg 2 Si can be prepared by Mg vapor annealing of a silica monolith comprising rod-like silica particles. 12,13 These reports indicate that porous Mg 2 Si can be synthesized by forming porous silica followed by Mg vapor treatment. However, granular composites exhibit reduced conductivity because of the contact resistance between particles.…”

Synthesis, structural and photoluminescence properties of Mg2Si/Si nanocomposites consisting of Si nanosheet bundles and Mg2Si deposits

“…3) Mg 2 Si-based composites were also investigated for thermoelectric applications. [4][5][6][7][8][9] The Mg 2 Si/Si composites for thermoelectric applications were investigated due to their decreasing thermal conductivity by effective phonon scattering at the grain boundaries. [10][11][12] In addition, the Mg 2 Si/Si composite is also expected to be an anode material in Li ion batteries and its high capacity characteristics were reported.…”