368350 Oxidation of Mg Powders: Implications for Ignition and Aging

Friday, November 21, 2014: 9:45 AM
209 (Hilton Atlanta)
Hongqi Nie, NJIT, Newark, NJ, Edward Dreizin, New Jersey Institute of Technology, Newark, NJ and Mirko Schoenitz, Otto H. York Department of Chemical, Biological, and Pharmaceutical Engineering, New Jersey Institute of Technology, Newark, NJ

Magnesium is widely used in pyrotechnic formulations; it is also a component of reactive alloys, e.g., Al-Mg and B-Mg, which are potential fuels for explosives and propellants.   Despite its widespread applications, kinetics of oxidation of Mg powders are not well quantified.  As was recently shown for Al, such kinetics are of fundamental importance for the models aimed to describe thermally induced ignition of metal powders.  In addition, for Mg the issue of aging is important because its oxide, MgO, layer lacks protective properties typical of Al2O3.  In this work, mechanisms of the magnesium oxidation by both oxygen and steam were studied by thermo-gravimetric measurements for micron-sized spherical powders.  Two magnesium powders with different but overlapping particle size distributions were used.  The experimental results were interpreted taking into account the measured particle size distributions, and considering different assumptions for the location of the reaction interface.  When the reaction was assumed to occur at the metal-oxide interface, the best match between oxidation dynamics for particles of the same sizes but belonging to powders with different size distributions was achieved.  It was thus determined that the reaction occurs at the metal-oxide interface.   Kinetics of the low-temperature oxidation reactions for both oxidizing environments were quantified using thermo-analytical measurements and different data processing techniques.  Different stages of Mg oxidation were detected, characterized by different activation energies.  Simplified, diffusion-limited reaction models were developed for oxidation of magnesium in both oxygen and steam.  The models enable one to predict both low-temperature pre-ignition reactions occurring upon heating of Mg particles and the time of Mg powder aging when exposed to moisture or oxygen at different temperatures.

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See more of this Session: Exothermic Heterogeneous Processes
See more of this Group/Topical: Particle Technology Forum