Imaging pyrometry of metal fragments initially generated during the supersonic impact of reactive metal projectiles

The early stage of the impact-initiated reaction of supersonic cylindrical reactive metal projectiles (magnesium, aluminum, titanium, and zirconium) with an inert aluminum oxide target is investigated experimentally with impact velocities from 1.1 to 1.3 km/s. A three-color imaging pyrometer is used to obtain temperature maps of the condensed fragments generated during the first few microseconds following contact between the projectile and the target. Experiments conducted in inert and oxidizing atmospheres confirm that chemical reactions initiate readily upon contact between the projectile and the target. In oxidizing atmospheres, the fragment temperatures measured for each metal are, on average, below but near the respective adiabatic temperature in air, except for Zr which produced temperatures significantly below expectations. Only the particles shed at the interface between the projectile and the target visibly react with the oxygen in the ambient atmosphere. At the impact velocities under study, only a small fraction, on the order of a few percent, of the mass of the projectile is finely fragmented during the initial impact event.