Shock Loading of Granular Ni/Al Composites. Part 2: Shock-Induced Chemistry
MJ Cherukara and TC Germann and EM Kober and A Strachan, JOURNAL OF PHYSICAL CHEMISTRY C, 120, 6804-6813 (2016).
We use molecular dynamics simulations to characterize the chemical processes resulting from the shock compaction of a loosely packed granular reactive composite of Ni and Al. For all of the impact strengths studied (with piston velocities up in the range 0.5-2.5 km/s), we find that reactions initiate in the vicinity of the collapsed pores. For the lowest impact velocities (u(p) <= 0.75 km/s), the reactions that initiate at the collapsed pores subsequently slow down as thermal transport dissipates the initial temperature excursion and outpaces the exothermic energy release rate. At intermediate impact velocities (u(p) approximate to 1.0 km/s), the localization of thermal kinetic energy is sufficient to establish a reaction rate that is self-sustaining in exothermic energy release, and the sample reacts within a few nanoseconds. At the highest impact velocities (u(p) >= 1.5 km/s), the localization of translational kinetic energy as well as thermal energy following pore collapse drives the rapid propagation of the reaction from the collapsed pores.
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