Systematic evaluation of inorganic salts as a heat sink for the magnesiothermic reduction of silica

Abstract

In this study, the effectivity of a series of inorganic salts, sodium chloride, calcium chloride, magnesium chloride, potassium chloride, and sodium bromide as heat sinks during magnesiothermic reduction of silica to porous silicon was investigated. The salts were chosen based on cost, thermal stability, ability to remain chemically inert during the reduction process, and ease of removal after the reaction. The structural integrity of the spherical porous silicon nanoparticles was observed using scanning electron microscopy, the surface area was determined via nitrogen adsorption experiments, and the crystallite size was determined using powder X-ray diffraction analysis; together, these were used to determine the efficacy of each salt. The ability of a salt to act as an effective heat sink was found to be highly correlated and principally dependent on the heat capacity of the salt. Calcium chloride was found to be the most effective heat sink overall among the five heat sinks investigated here.

Crystallinity‐controlled SiO x anode material prepared through a salt‐assisted magnesiothermic reduction for lithium‐ion batteries

“…27 Various inorganic salts, such as NaCl, KCl, CaCl, and MgCl 2 , are generally used as heat absorbents that collect the excess heat from exothermic reactions. [28][29][30] Therefore, the choice of heat absorbent is crucial for controlling the exothermic reaction of the magnesiothermic reduction, as they are critical in determining the morphology and microstructure of SiO x .…”

“…As a result, microstructural changes in SiO x , such as the formation of secondary phases (eg, Mg 2 Si and Mg 2 SiO 4 ) and abnormal growth of Si crystals, are induced 27 . Various inorganic salts, such as NaCl, KCl, CaCl, and MgCl 2 , are generally used as heat absorbents that collect the excess heat from exothermic reactions 28‐30 . Therefore, the choice of heat absorbent is crucial for controlling the exothermic reaction of the magnesiothermic reduction, as they are critical in determining the morphology and microstructure of SiO x .…”

High Surface Area Mesoporous Silicon Nanoparticles Prepared via Two-Step Magnesiothermic Reduction for Stoichiometric CO2 to CH3OH Conversion

“…However, it has recently been demonstrated that due to the exothermic nature of the reaction, carrying out the entirety of the reaction at 650 °C results in significant morphological damage and lowering of surface area of mp-Si formed . A demonstrated method to circumvent this issue involves the addition of various inorganic salts to the reaction as a heat sink to minimize the sintering of Si nanoparticles, , but this has not been shown to produce porosity at the same level that can be achieved by using methods that involve reduction of SiCl 4 precursor in the presence of inorganic salt templates . Furthermore, addition of an extra reagent to the process can increase the overall cost of the reaction as well as the amount of solvent required to remove the heat sink, rendering such methodologies undesirable for large-scale production.…”