Ignition of an exothermal reaction by collision between Al and Ni crystals

Classical molecular dynamics methods have been used to investigate the atomic-scale dynamics of collisions between two Al and Ni crystals with rough surfaces. The crystals were approached along the direction perpendicular to the surfaces and simultaneously displaced along the direction parallel to them at relative velocities in the range between 1 and 10 nm ns(-1). The mechanical stresses operating at collision determine a local deformation of Al and Ni lattices, accompanied by a significant temperature rise. As the Al melting point is reached, the Al crystal partially melts and Ni atoms start dissolving into the molten phase. The significant heat of mixing liberated further promotes the Al melting and the Ni dissolution processes. In the absence of neighboring Al-Ni interfaces, the heat dissipation processes and the limited rate of Ni dissolution gradually lead to the extinction of the reactive behavior. Conversely, the presence of Al-Ni interfaces in the vicinity of the Al-Ni one formed by collision permits the propagation of the high-temperature chemical reaction. It is shown that the ignition and propagation of the self-sustaining reaction is sensitive to the distance between Al-Ni interfaces and to their degree of chemical mixing