There has been a great deal of speculation that the state of an explosive at the shock front might involve transient metallization. When the energetic molecules are compressed to a state of high density, the electron confinement increases, causing the electron kinetic energies to increase. This is a purely quantum mechanical effect described in its simplest form by the well-known “particle in a box” model. Metallization means that a portion of the bonding electrons are driven into the conduction band. The covalent bonds weaken, or even vanish, leaving all the nuclei free to drift away from their original locations while creating delocalized electrons.
Theorists have done quantum calculations on nitromethane ( E. J. Reed, M. R. Manaa, L. E. Fried, K. R. Glaesemann, and J. D. Joannopoulos, A transient semimetallic layer in detonating nitromethane Nat. Phys. 4, 72-76 (2008)). and TATB (C. J. Wu, L. H. Yang, L. E. Fried, J. Quenneville, and T. J. Martinez, Electronic structure of solid TATB under uniaxial compression: On the possible role of pressure induced metallization in energetic materials, Phys. Rev. B. 67, 235101-235107 (2003)) and have concluded that the density and temperature at the detonation front is a bit short of metallization. Others claim that metallization can occur in solid explosives that have defect sites (M. M. Kuklja and A. B. Kunz, Modeling of shock compression of RDX with defects, AIP Conf. Proc. 505, (2000)). It is difficult to produce shock waves strong enough to metallize materials. A recent paper used a giant laser facility to produce a metallizating shock in liquid ammonia (A. Ravasio, M. Bethkenhagen, J. A. Hernandez, A. Benuzzi-Mounaix, F. Datchi, M. French, M. Guarguaglini, F. Lefevre, S. Ninet, R. Redmer et al., Metallization of Shock-Compressed Liquid Ammonia, Physical Review Letters 126, 025003 (2021)). We are developing a new laser launcher that can produce much greater pressures that will allow us to produce metallized states on a tabletop with high throughput and study them in much greater detail than ever before.
When a plastic-bonded explosive metallizes, there is no longer any distinction between the atoms from the explosive, from the binder and from any other additives. This can lead to unique extreme chemical processes we wish to study. The figure below shows how we would produce metallized states in a transparent medium such as nitromethane. We will be able to reflect the beam from our velocimeter (PDV = photon Doppler velocimeter) off both the shock front and the piston that drives the shock, allowing us to map out the metallized Hugoniot. We can use our other probing methods to understand these novel chemistries and to better understand detonations at the extreme limit.