Ignition, combustion, and oxidation of mixtures of amorphous and crystalline boron powders

Ignition, combustion, and oxidation characteristics of mixtures of amorphous and crystalline boron powders are studied by using a laser ignition system and a thermogravimetric analyzer. Yellow, green, and white-glow flames are observed. When the weight ratio of the amorphous boron powder ( K ) is lower than 0.33, burning of the mixtures is found to be at the ignition stage, while the combustion stage gradually appears with increasing K . The emission spectrum intensity is weakened by 3/4 as K decreases from 1 to 0.75. No obvious emission spectrum is detected at K < 0.33. The ignition delay time is found to decrease significantly with increasing K , but it does not change much at K < 0.8. Mixtures with larger values of K have a lower peak temperature of differential thermal gravity and a greater weight gain and maximum reaction rate. The Satava-Sestak method is applied to study the kinetics of the oxidation reaction of the mixtures. The calculated apparent activation energy decreases from 297 to 191 kJ/mol as K increases from 0 to 1. For mixtures with K ranging from 0.23 to 0.75, the apparent activation energy mainly stays constant at a value of 280 kJ/mol.