Investigation on the effect of microencapsulation with some organic coating agents on surface morphology and thermal property of magnesium particles

摘要

Magnesium powder is one of the most important components of many energetic materials because of its good burning and illuminating properties. However, magnesium is very active, and it also has a high affinity with oxygen, nitrogen and water. The formation of magnesium compounds deteriorates many of the desirable properties of ground magnesium, e.g., the reduction or even elimination of its pyrotechnic properties and hence severely limits its applications. In this research, microencapsulation technique based on a solventon-solvent method has been used to enhance the nitration/oxidation resistance of magnesium powder with nitrocellulose and viton as alternative coating agents. The coating quality and the mechanism of the nitration/oxidation reactions of pure and coated samples were studied by means of scanning electron microscopy (SEM), thermogravimetry analysis (TCA) and X-ray diffraction (XRD) methods. Thermogravimetry analysis (TGA) of pure sample exhibited two successive phenomenons in the wide range of temperature (at about 500-1200 °C) which related to nitration and oxidation processes respectively. However because of greater thermodynamic stability, at elevated temperatures, any nitride formed is eventually converted to the corresponding magnesium oxide (MgO) compound. Also, these results confirm by XRD and SEM data of Mg particles that heated at different temperatures. Finally, the results of this investigation showed that Mg microparticle could be effectively coated with viton through a solventon-solvent experiment at optimum conditions in which the oxidation reaction occurs at 20°C higher than that of the uncoated particles and overall nitration/oxidation reaction completed under 1000 °C, with 66% mass gain. The result confirms that by coating of Mg particles by proper coating agents, the efficiency of the magnesium based pyrotechnic system can be increased.