Effect of initial oxide layer on ignition and combustion of boron powder

Only few data exist for experimental studies on ignition and combustion of boron particles with initial oxide thickness. The oxidation, ignition and combustion characteristics including the onset temperatures, weight gain, apparent activation energy, emission spectra during combustion, and ignition delay time of crystalline boron powders with different initial oxide thickness (x₀) were studied by a laser ignition and thermogravimetric (TG) analyses. Simulations of the kinetics of oxide layer during boron ignition were conducted using a common model. The results indicated that the onset temperature was approximately 775°C, independent of x₀. The total weight gain decreased with increasing x_0, whereas the weight gain at 775°C did not change. The apparent activation energy was found to be insensitive to x₀ and had a constant value of about 210 kJmol ^-1. The intensity of the emission spectra gradually decreased while the ignition delay time increased with increasing x₀. Numerical simulation showed that the removal rate of oxide layer enhanced with increasing x₀. The experimental results revealed that the oxidation of boron powder was no diffusion-controlled process at low temperatures. But the diffusion of oxygen could become important to the oxidation reaction at high temperatures