Mechanical stimulation of gasless reaction in inorganic systems: A mini review

The investigation of shock compression in highly exothermic inorganic powder mixtures leading to reaction has been a subject of interest for several decades. In particular, understanding the processes occurring within the time scale of the high-pressure shock state, resulting in the formation of new materials and phases, has garnered significant attention. Chemical reactions in shock-compressed media are generally categorized based on their time scale: i) shock-induced chemical reactions occur in the shock front or shortly behind it (in the stress pulse) during the time scale of mechanical equilibration (<1 μs), and ii) shock-assisted chemical reactions occur on the longer time scale of bulk temperature equilibration (>10 μs) after the state of stress has been released. It is worth noting that a solid-state detonation wave involves a type of combustion with a supersonic exothermic front that accelerates through a medium, ultimately supporting the leading shock front. While extensive discussions have focused on shock-induced and shock-assisted reactions, as well as the solid-state detonation, certain questions regarding the possibility of i) shock-induced reactions occurring within the time scale of high-pressure shock state, and ii) chemical reactions occurring promptly enough after the shock wave to sustain a detonation wave (ultra-fast gasless reactions), remained unanswered. In this paper, we provide a brief review of shock compression of reactive heterogeneous media, with a particular emphasis on recent experimental studies. We critically address the chemical reactions occurring within these material systems and the underlying mechanisms, supported by in-situ and ex-situ experimental evidences. Specifically, our primary focus lies on the aluminum-nickel and the metal nitride-boron systems. Based on our analysis, we conclude that the shock-induced reactions can occur in the time scale of the propagated shock wave and can be explained by the mechanically induced thermal explosion phenomena. However, the observed phenomena so far cannot be attributed to solid-state detonation, since they cannot result in a self-sustained mode of shock wave propagation.