Aluminum metal combustion in water revealed by high speed microphotography.

摘要

In high explosives designed for air blast, cratering, fragmentation, and underwater applications, metallic additives chemically react with the oxidizer and are used to tailor the rate of energy delivery by the expansion medium. Although the specific mechanism for sustained metal combustion in the dense detonation medium remains in question, it is generally accepted that the fragmentation of the molten particle and disruption of its oxide layer are a necessity. In this study, we use high speed microphotography to examine the ignition of small 25--76 (mu)m diameter and 23 mm long aluminum wires, rapidly heated by a capacitor discharge system, in water. Streak and framing photographs detailing the combustion phenomenon and the fragmentation of the molten aluminum were obtained over periods of 100 nsec--100 (mu)sec with a spatial resolution of 2 (mu)m. The wire temperature was determined as a function of time by integrating the circuit equation together with the energy equation for an adiabatic wire, and incorporating known aluminum electrical resistivity and temperature functions of energy density in the integration. In order for the aluminum to sustain a rapid chemical reaction with the water, we found that the wire temperature has to be raised above the melting temperature of aluminum oxide. The triggering mechanism for this rapid reaction appears to be the fragmentation of the molten aluminum from the collapse of a vapor blanket about the wire during its first oscillation. 14 refs., 9 figs.