A shock tube technique has been developed to allow the separation of heatup from ignition delay time for a metal particle. An analytical model was formulated to predict the position, velocity and temperature of a boron particle in the shock tube as a function of time. The model was used to determine ignition delay time and particle temperature at ignition. Ignition delay times were measured for boron particles of nominally one micron diameter. Particle size and shape diagnostics were conducted by means of scanning electron microscope and floatation tests. Shock tube experiments were conducted using mixtures of ten, twenty, and fifty percent oxygen in argon. Particle ignition occurred over a range of 2200K to 3600K and 100 to 400 psia. Ignition delay was shown to vary directly with particle diameter and inversely with gas temperature and oxidizer pressure. The data were used to calculate an activation energy for the boron ignition reaction. Particle temperature at ignition was calculated. (Modified author abstract).

A shock tube study was conducted to determine the ignition limit of clouds of boron particles. The ignition limit is an experimentally determined curve, plotted on temperature-pressure coordinates, separating the ignition and no ignition zones. A 3-inch inside diameter constant area shock tube employing a helium/air gas system was used for igniting the boron particles. The particles were ignited in the high temperature region behind the reflected shock wave. The boron samples used were 30-50 micron diameter agglomerates (1-2 micron primary particles) and 0.015 micron diameter particles. Ignition delay time of 0.015 micron particles was also obtained. (Author).