Commercial aluminum powders, part II: Energy release rates induced by rapid heating via pulsed laser excitation

Abstract

We used nanosecond laser pulses to excite various aluminum (Al) powders under an extremely fast heating rate (1013 K/s). Our interest lies in three timescales: early (1–10 μs), middle (10–500 μs), and late (tens of milliseconds). We used several spectroscopic methods to monitor AlO emission to track the Al oxidation on all timescales. The characteristic laser-induced air shock velocity determined relative energy release from each Al powder on the early timescale. We found that the Al nanopowders had higher laser-induced shock velocities than the micron-sized powders, indicating faster energy release. The AlO emission monitored in the early time regime correlated with the laser-induced shock velocities, confirming that the increases in laser-induced shock velocities observed resulted from earlier oxidation of the Al. The heterogeneous nature of the Al samples and the strong influence of their properties on fast energy release demonstrated the importance of well-characterized samples for interpreting detonation experiment results.