SiO2 aerogel has the characteristics of high porosity and high specific surface area. In order to explore the feasibility of using it as a new infrared functional additive for smoke composition, SiO2 aerogel was mixed with NaNO3 and NH4NO3 saturated solution respectively, and freeze-drying was introduced to make NaNO3 and NH4NO3 deposit in the pores or surface of SiO2 aerogel. So the powder-form infrared functional additive was prepared completely. The new powder not only reduces the frequency of the phenomenon of harden synthesized compound and improves its preparation process, but also guarantees the recovery of prefabricated particle size of SiO2 aerogel in the combustion process. The experimental results show that: when mixed with smoke composition, on the condition that the mixing ratio of additives is 20% and negative oxygen balance is 20, compared with the traditional smoke composition obscuring ratio, the smoke composition synthesized obscuring ratio can be increased by 72% and 47% in infrared band.
Combustion mechanism of magnesium has long been explored. It has been recently shown that spherical magnesium particles with highly active can be used to analyze combustion process in detail with the help of new methods and advanced instruments. This work is aimed at investigating the multiple diffusion reaction of single spherical magnesium particles in accordance with surface composition and combustion remains. Energy Dispersive Spectrometer (EDS), Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) were used to analyze the samples before and after reaction. In addition, combustion of magnesium particle was conducted in a microscope heating system. The results of the study show that an oxygen-rich layer formed on the particle surface before the particle was heated to burn. Dissolved oxygen was detected in this layer and its concentration is lower than that of stoichiometric MgO. The dissolution reaction of oxygen begins before the gas phase combustion and later on, after the gas phase combustion stops, becomes the dominated reaction. It is suggested that there are two sources of MgO formed during the oxidation process, Mg(s) → Mg(g) → MgO(s) and Mg(s) → oxygen-rich layer(s) → MgO(s). The latter is the dominated mechanism of surface heterogeneous reaction.
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