Laser ignition and combustion characteristics of micro- and nano-sized boron under different atmospheres and pressures

Boron (B) has potential applications in energetic materials as additive fuel. In order to understand the combustion mechanism of B with various scales, the ignition and combustion characteristics of micro- and nano-sized B under different pressures (0.4 MPa, 0.8 MPa and 1.2 MPa) and atmospheres (60% O2 + 40% N2, 80% O2 + 20% N2 and 100% O2) were studied by a laser ignition and combustion experimental system. The evolution images and specialized parameters of ignition and combustion under different conditions were obtained, and the effects of atmosphere and pressure on the ignition and combustion characteristics of micro- and nano-sized B were discussed. Meanwhile, the crystal structure and morphology of condensed combustion products were observed by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM), and then the compositions in micro-areas were analyzed by energy dispersive X-ray spectroscopy (EDX). The results show that, the burning of micro-sized B is relatively slow, while the burning of nano-sized B is intensified, and a deflagration-like phenomenon is observed for nano-sized B in pure oxygen with pressures of 0.8 and 1.2 MPa. The ignition delay time, combustion time and maximum flame temperature of nano-sized B are smaller than those of micro-sized B, while the maximum characteristic spectral intensity of nano-sized B is stronger. Besides, B2O3, B6O and BN exist in condensed combustion products of micro-sized B, but only B2O3 is detected for nano-sized B, and products agglomerating is observed for nano-sized B. In general, nano-sized B has significant advantages than micro-sized B in the ignition and combustion characteristics, especially under conditions of high oxygen concentrations and high pressures.