(605c) Thermal Initiation of Consolidated Reactive Nanocomposite Materials

Reactive nanocomposite powders prepared by arrested reactive milling are consolidated into cylindrical pellets of diameter 0.635 cm by uniaxial die compaction to up to 95% of theoretical maximum density. These pellets are placed in an enclosed chamber and ignited by a CO2 laser. The ignition delay and combustion pressures are measured. Temperature at the back of the laser heated pellet is also measured in selected experiments. Different thermite compositions are characterized. Ignition delays are measured as a function of laser power and material composition. In addition, the effect of pellet density on the ignition delay is identified for the same material and a fixed laser power. A heat transfer model describing laser heating of a cylindrical pellet is implemented into a numerical code. The pellet thermal diffusivity required for calculations is found from separate experiments using the flash method. The exothermic chemical reaction leading to ignition is represented by a zero-order Arrhenius reaction term with the activation energy identified from earlier experiments with non-consolidated nanocomposite thermite powders. Initial calculations disregarding the chemical reaction are performed to validate the match of the temperature measured at the back surface of the laser heated pellets and that predicted by the model. The reaction term is added to the model and the value of the pre-exponent is adjusted to match a single data point for the measured ignition delay. The model parameters are then fixed and the correlation between predicted and measured ignition delays is analyzed for a range of the laser powers and pellet densities. The calculations are in good agreement with the measurements suggesting that the proposed ignition model describes accurately the thermal initiation of the consolidated reactive samples.