A Brief Review of Metallothermic Reduction Reactions for Materials Preparation

Abstract

Metallothermic reduction reactions (MRRs) are displacement reactions that use reactive metals to reduce compounds so that metals, alloys, nonmetal elementary substances, and composites are produced, often in a scalable manner. In recent years, nonmetal materials, mainly silicon and carbon, particularly in their nanostructured forms obtained using an MRR with magnesium as the reductant, have started to attract much attention. However, reactions using other metals as the reductant have not been widely investigated yet. Furthermore, the reaction mechanisms and their controlling factors remain unclear, and much more effort is needed to advance this emerging field. Here, MRR preparation methods for metals, alloys, nanoporous silicon, nanoporous carbon, and composites are discussed as an introduction for new researchers in this field.

A new approach to synthesize nano-yttrium boride particle through metallothermic reduction process

“…In fact, it has the lowest free energy among all the reductant metals and hence, it is considered as one of the best deoxidizing agents. The vapor pressure of calcium is adequately high, which permits a successful vapor stage calciothermic reduction of the reactants [37,38]. The utilization of magnesium is likewise feasible because of its lower oxygen affinity.…”

“…It is thermodynamically expected that the oxygen concentration under the Mg-MgO equilibrium will be higher than that of Ca-CaO. So, the calciothermic reduction of related oxides will be more favourable than magnesiothermic reduction [38,39]. The secondary reason for choosing Ca as reductant over Mg is the quantity of the used reductant.…”

Salt-mediated extraction of nanoscale Si building blocks: composite anode for Li-ion full battery with high energy density

“…The typical MTR uses vaporized metals for reducing silica into a porous structure above the melting point of metals (4650 1C). 21 However, without proper mediators, the generated exothermic heat aggressively destroys the initial morphology and incurs adverse agglomeration. 22 The heat scavengers (e.g., NaCl, KCl) partly dissipate the thermal energy to retain the structure and relieve the risk of an explosion.…”

Gas‐solid displacement reactions in the Ti–W–C system

“…34,35 Solid-state displacement reactions may be classified according to the state of matter of the displacing reagent (ie, solid-solid, liquid-solid, or gas-solid reactions), or according to the identity of the displacing reagent (ie, metallothermic, carbothermic, hydrogen reduction reactions, etc). 1,3,33 Further designations | 2377 DEMPSEY anD LIPKE may denote special reaction characteristics. For example, under certain conditions, partial or selective reactions with multicomponent compounds or solid solutions comprising at least one thermodynamically noble constituent can be variously termed in situ reactions, internal displacement reactions, or internal reduction reactions by analogy to nomenclature established in alloy oxidation literature.…”

“…Solid‐state displacement reactions—in which one or more constituents of a compound or solid solution are transferred to a product phase by chemical interaction with thermodynamically less noble reagents—are frequently encountered in high‐temperature materials processing, either by design as a means to prepare pure substances and composites, or inherently as a result of interface incompatibility between constituents in heterogeneous bodies . Solid‐state displacement reactions may be classified according to the state of matter of the displacing reagent (ie, solid‐solid, liquid‐solid, or gas‐solid reactions), or according to the identity of the displacing reagent (ie, metallothermic, carbothermic, hydrogen reduction reactions, etc) . Further designations may denote special reaction characteristics.…”