Prof. Hendrik J. Viljoen will study heterogenous chemical reactions under mechanic excitation. New macroscopic models will be developed to account for non-equilibrium energy distribution within shock and reaction zones, considering energy distribution among translational, rotation, and vibrational modes, mixing, and supersonic transitions. Molecular dynamics will be used to simulate atomistic behavior in the reaction zone, and distributed continuum dynamics equations will incorporate the atomic model into the macroscopic behavior. These atomistic-macroscopic models may find applications in the description of cryochemical self-propagating reactions; mechanical alloying and sonochemistry as techniques to reduce ignition temperatures and activation energies for reaction; shock-induced reactions of solids, in which chemical reaction energy must be transformed into translational energy in order to sustain the shock wave. The authors will investigate by molecular dynamics the ultrafast reaction between sulfur and aluminum microcrystallites subjected to a shock wave. To develop the continuum model, they will simulate high pressures above the Hugoniot elastic limit, and add equations describing pore collapse and solid compaction to the classical conservation equations. Finally, the molecular dynamics and continuum models will be matched by identifying the critical energy exchange modes and integrating over the characteristic times for the exchange modes. This grant is being funded by the Kinetics and Catalysis and the Process and Reaction Engineering programs.
