Heterogeneous decomposition and oxidation during combustion of magnesium diboride particles

Abstract

Magnesium diboride (MgB2) is a potential substitute of amorphous boron (B) as high energy density fuel. The heterogeneous decomposition and oxidation mechanisms during combustion of MgB2 were studied using a laser ignition testing system, an X-ray diffractometer, and a thermogravimetric differential scanning calorimetry combined thermal analysis system. B and magnesium (Mg) were also tested in the laser ignition experiments as control groups. The combustion process of MgB2 contained two stages: an explosion stage and a stable combustion stage. During the explosion stage, a great number of sparks were created and burst out from the sample stack. The color of combustion flame was white at first, and then turned into yellow before the stable combustion stage started. Compare with B and Mg, MgB2 had shorter ignition delay time (8 ms) and longer stable combustion stage time (891 ms), which indicated its outstanding energy release properties. Characteristic emission spectra of MgB2 showed MgO, BO2, and gaseous Mg were the major gaseous intermediate products during combustion. Moreover, decomposition and oxidation products of MgB2 were both found in the condensed combustion products. The thermal oxidation process of MgB2 contains three exothermic peaks: melt and oxidation of Mg impurity (∼650 °C), start of MgB2 decomposition (∼850 °C), and oxidation of Mg-B compounds (∼900 °C).