The asymptotic limit of a successful initiation process in an ideal solid high explosive (HE) is a steady-state detonation wave; the elements of which are described in a number of textbooks.[1] A shock will compress and heat the HE, providing the activation energy to trigger chemical reactions.  These reactions transform the solid HE into gaseous products at very high pressure and temperature. The chemical energy released thereby supports the propagation of the shock front, which is defined as a successful “Shock to Detonation Transition” process.  Modeling and simulation tools define the extent of chemical energy release as a single parameter (λ) in reactive flow models, e.g. Lee-Tarver Ignition and Growth Reactive Burn.[2]  To date, these tools have not been predictive outside of experimental conditions they have been fit to.  A possible solution toward predictive capability is the generation of a more descriptive parameter for the extent of chemical reactions. This project focuses on solving this gap using measured chemical products from shocked HE.

The ultimate goal of the Chemical Diagnostics project is to improve upon the single parameter (λ) in theories and models of HE initiation and detonation propagation.  This may be accomplished by simply incorporating more realistic descriptions of the relevant chemical energy release rates to govern/bound the λ parameter.  To achieve this goal a benchtop apparatus capable of monitoring the chemical identities and molecular velocities of gaseous products from small HE samples reacting in vacuum will be utilized.  The rapid expansion into vacuum quenches the chemistry and preserves the gaseous species for interrogation.  The apparatus employs laser-driven shock initiation of ~ mg scale HE samples and Time-Of-Flight Mass Spectrometry (TOFMS) as the main chemical diagnostic.[3] Preliminary results from a small number of thin-film physical-vapor-deposited pentaerythritol tetranitrate (PETN) samples have shown promise in the technique. Those results are consistent with a simple qualitative interpretation whereby:  (1) weak shock inputs result in HE sample deflagration, yielding reaction intermediates (e.g. NO2) with relatively slow molecular velocities, and (2) strong shock inputs lead to “detonation-like” chemistry, producing thermodynamically stable products (e.g. CO, N2) with hyperthermal molecular velocities. Mentees will have the opportunity to become familiar with a wide variety of topics including; sample preparation, laser driven shock techniques, chemical diagnostics and data analysis techniques.

 1) Fickett, W. and Davis, W.C., Detonation, U. California Press, Berkeley, CA, 1979.

 2) Lee, E.L. and Tarver, C.M., Phenomenological model of shock initiation in heterogeneous explosives. Physics of Fluids, 1980. 23(12): p. 2362.

      3) Fossum, E.C., et al., Benchtop energetics: Hyperthermal species detection. Propellants, Explos., Pyrotech., 2012. 37(4): p. 445.

Explosives; Energetic Materials; Shock Initiation; Detonation; Deflagration; Chemical Dynamics; Laser Driven Shocks

citizenship

Open to U.S. citizens

level

Open to Postdoctoral and Senior applicants

Additional Benefits

relocation

Awardees who reside more than 50 miles from their host laboratory and remain on tenure for at least six months are eligible for paid relocation to within the vicinity of their host laboratory.

health insurance

A group health insurance program is available to awardees and their qualifying dependents in the United States.