ISGR is a reaction between molten metal and a gas bubbled through it to produce solid reinforcement particles. Small initial bubble size as well as turbulence in the melt, for example from a rotating impeller, controls how large these particles grow. Nanocomposites have been previously produced in this way, with aluminum nitride reinforcement in an aluminum matrix using nitrogen gas, and titanium carbide reinforcement in an aluminum/titanium melt using methane gas.
SHS is a combustion-like exothermic reaction which has been extensively developed to produce a variety solid compounds by externally igniting a pellet of compacted powders, then allowing the reaction to self-propagate as the heat of the reaction ignites the remaining reactants. More recently, this process has been adapted to produce titanium carbide nanoparticle reinforcements in metal alloys, including aluminum. This is possible both ex-situ, where the reacted pellet containing titanium carbide and aluminum is melted and dispersed into the metal, as well as in-situ, where the molten metal is the ignition source for the reaction.