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

摘要

Boron (B) has potential applications in energetic materials as additive fuel. In order to understand thecombustion mechanism of B with various scales, the ignition and combustion characteristics of microandnano-sized B under different pressures (0.4 MPa, 0.8 MPa and 1.2 MPa) and atmospheres (60O_2 + 40 N_2 , 80 O_2 + 20 N_2 and 100 O_2 ) were studied by a laser ignition and combustion experimentalsystem. The evolution images and specialized parameters of ignition and combustion underdifferent conditions were obtained, and the effects of atmosphere and pressure on the ignition and combustioncharacteristics of micro- and nano-sized B were discussed. Meanwhile, the crystal structure andmorphology of condensed combustion products were observed by X-ray diffraction (XRD) and field emissionscanning electron microscope (FE-SEM), and then the compositions in micro-areas were analyzedby energy dispersive X-ray spectroscopy (EDX). The results show that, the burning of micro-sized B isrelatively slow, while the burning of nano-sized B is intensified, and a deflagration-like phenomenonis 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-sizedB, while the maximum characteristic spectral intensity of nano-sized B is stronger. Besides, B_2O_3 , B_6O andBN exist in condensed combustion products of micro-sized B, but only B_2O_3 is detected for nano-sizedB, and products agglomerating is observed for nano-sized B. In general, nano-sized B has significant advantagesthan micro-sized B in the ignition and combustion characteristics, especially under conditionsof high oxygen concentrations and high pressures.