(716a) Combustion Characteristics of Micron-Sized METAL and METAL-COMPOSITE PARTICLES IN Different Environments

Detailed metal particle, e.g. aluminum, combustion models are necessary for proper modeling and optimizing respective propellant and explosive formulations. Much work has been done for aluminum in describing the combustion characteristics for single particles ranging in diameter from 50-1000 μm. Currently, semi-phenomenological models are available for predicting burn times of such particles as a function of their diameter and oxidizing environment. However, such descriptions are poorly suited for particle sizes ranging from 1 to 50 μm, which are most commonly used in practical formulations. Respective experimental studies were largely limited to aerosols and cloud of fine powders, in which particle interaction effects and presence of particles of different sizes make it difficult to identify the rates of combustion of individual particles. Experiments characterizing single particle combustion for such fine micron-size powders are necessary to develop new and validate existing reaction models. In particular, a transition from the predominantly vapor-phase to surface reaction occurs in this particle size range and this transition should be adequately described in the respective models. A recent experiment has shown the feasibility of determining combustion times for 3 ? 15 µm size aluminum particles using a laser ignition setup. In that experiment, a particle jet crosses two laser beams. First, a low power laser is used to generate a scattered signal so that the particle size can be measured in real time. Second, a powerful CO2 laser beam is used to ignite particles, and their emission signatures are recorded to determine the burn times. In this work, the emission optical diagnostics is extended to enable time-resolved three-color optical pyrometry and tracing characteristic molecular emission of the species formed in the flame. A modified particle feeding mechanism is developed to study materials that are more sensitive than pure metal powders, including nanocomposite materials prepared using mechanical alloying and arrested reactive milling. Results for Al powders will be presented, including the burn times and particle temperature as a function of its size. Results for combustion of aluminum, Al-metal oxide, and Al-I2 composites will be presented and discussed.