The combination of Al nanoparticles (ANPs) as fuel and Hsub.2Osub.2 as oxidizer is a potential green space propellant. In this research, reactive force field molecular dynamics (ReaxFF-MD) ...simulations were used to study the influence of water addition on the combustion of Al/Hsub.2Osub.2. The MD results showed that as the percentage of Hsub.2O increased from 0 to 30%, the number of Al-O bonds on the ANPs decreased, the number of Al-H bonds increased, and the adiabatic flame temperature of the system decreased from 4612 K to 4380 K. Since the Al-O bond is more stable, as the simulation proceeds, the number of Al-O bonds will be significantly higher than that of Al-H and Al-OH bonds, and the Al oxides (AlOsub.x) will be transformed from low to high coordination. Subsequently, the combustion mechanism of the Al/Hsub.2Osub.2/Hsub.2O system was elaborated from an atomic perspective. Both Hsub.2Osub.2 and Hsub.2O were adsorbed and chemically activated on the surface of ANPs, resulting in molecular decomposition into free radicals, which were then captured by ANPs. Hsub.2 molecules could be released from the ANPs, while Osub.2 could not be released through this pathway. Finally, it was found that the coverage of the oxide layer reduced the rate of Hsub.2Osub.2 consumption and Hsub.2 production significantly, simultaneously preventing the deformation of the Al clusters’ morphology.
Nanothermites and high-energy explosives have significantly improved the performance of high-energy composites and have broad application prospects. Therefore, in this study, ...RDX/F2311/Fesub.2Osub.3/Al composite hollow microspheres were successfully prepared utilizing the electrospray method using F2311 as a binder between components. The results show that the combustion time of the composite hollow microspheres is shortened from 2400 ms to 950 ms, the combustion process is more stable, and the energy release is more concentrated. The H50 of the composite hollow microspheres increased from 14.49 cm to 24.57 cm, the explosion percentage decreased from 84% to 72%, and the sensitivity of the composite samples decreased significantly. This is mainly the result of the combination of homogeneous composition and synergistic reactions. The combustion results show that F2311 as a binder affects the tightness of the contact between the components. By adjusting its content, the combustion time and the intensity of the combustion of the composite microspheres can be adjusted, which provides a feasible direction for its practical application.
Concentration of PAHs, hopanes, and elements in PM.sub.10 aerosol samples was measured in two Nepalese urban centers, Tulsipur (725 m above sea level; 150,000 inhabitants) and Charikot (1,550 m above ...sea level; 23,000 inhabitants) in the monsoon period (August 2018) and pre-monsoon period (April-May 2019). The 24-h PM.sub.10 limit value of 50 microg m.sup.-3 for human health was significantly exceeded at all locations, and the Nepal concentration limit of 150 microg m.sup.-3 was exceeded at Tulsipur-bus station, Tulsipur-village, and Charikot-hospital in the pre-monsoon season. The average daily PM.sub.10 and PAHs concentrations showed seasonal variations, with lower concentrations in the monsoon season and the higher values in pre-monsoon season. The average daily PM.sub.10 and PAHs concentrations in the both sites were 133 mug m.sup.-3 and 23.8 ng m.sup.-3 in the pre-monsoon period and 49.6 mug m.sup.-3 and 2.30 ng m.sup.-3 in the monsoon period, respectively. The average daily hopane concentration during the pre-monsoon period was 1.40 ng m.sup.-3 in Tulsipur and 0.70 ng m.sup.-3 in Charikot. The IndP / (IndP + BghiP) ratio was higher than 0.5 during monsoon period, indicating combustion of biomass and charcoal burning. IndP / (IndP + BghiP) between 0.2 and 0.5 during pre-monsoon season indicates petroleum combustion. Fla / (Fla + Pyr) ratio between 0.3 and 0.5 during pre-monsoon and monsoon periods indicates high proportion of petroleum product combustion. The biomass burning associated with dense traffic in the center of the two cities was the main source of PAHs. The average daily element concentration was 6.80 ng m.sup.-3 in both locations during the monsoon period.
The char-CO.sub.2 reaction behaviour is important for oxy-fuel combustion of coal gangue and weathered coal or biomass. The thermal conversion characteristics of coal gangue, weathered coal, pine ...sawdust and their blends in CO.sub.2/N.sub.2 atmosphere were investigated using thermogravimetric analysis, focusing on the reaction behaviour of char and CO.sub.2. The results showed that the thermal conversion of coal gangue, weathered coal and pine sawdust all had two main stages, but pine sawdust had shorter time of thermal conversion. Mass loss of coal gangue/pine sawdust blends included two obvious stages with four overlapped peaks, which was different from coal gangue/weathered coal mixtures with two separated peaks. The addition of weathered coal or pine sawdust could improve the char-CO.sub.2 reactivity of coal gangue. However, the interactions were absent for all the coal gangue/weathered coal mixtures, and interaction between coal gangue and pine sawdust was obvious during the reaction of char and CO.sub.2, which was affected by the blending ratio of pine sawdust.
TiBsub.2-MgAlsub.2Osub.4 composites were fabricated by combustion synthesis involving metallothermic reduction reactions. Thermite reagents contained Al and Mg as dual reductants and TiOsub.2 or ...Bsub.2Osub.3 as the oxidant. The reactant mixtures also comprised elemental Ti and boron, as well as a small amount of Alsub.2Osub.3 or MgO to serve as the combustion moderator. Four reaction systems were conducted and all of them were exothermic enough to proceed in the mode of self-propagating high-temperature synthesis (SHS). The reaction based on Bsub.2Osub.3/Al/Mg thermite and diluted with MgO was the most exothermic, while that containing TiOsub.2/Al/Mg thermite and Alsub.2Osub.3 as the diluent was the least. Depending on different thermites and diluents, the combustion front temperatures in a range from 1320 to 1720 °C, and combustion wave velocity from 3.9 to 5.7 mm/s were measured. The XRD spectra confirmed in situ formation of TiBsub.2 and MgAlsub.2Osub.4. It is believed that MgAlsub.2Osub.4 was synthesized through a combination reaction between Alsub.2Osub.3 and MgO, both of which can be totally or partially produced from the metallothermic reduction of Bsub.2Osub.3 or TiOsub.2. The microstructure of the TiBsub.2-MgAlsub.2Osub.4 composite exhibited fine TiBsub.2 crystals surrounded by large densified MgAlsub.2Osub.4 grains. This study demonstrated an energy-saving and efficient route for fabricating MgAlsub.2Osub.4-containing composites.
Self-propagating high-temperature synthesis (SHS) is a good way to prepare ZrBsub.2-ZrC/metal cermet composites. In this work, ZrBsub.2-ZrC/Ni cermet composites with various Ni contents were ...successfully fabricated by SHS using the Ni-Zr-Bsub.4C system. The effects of Ni content and particle size of the Bsub.4C powder on the SHS reaction were investigated. The results indicated that with an increase in Ni content, the adiabatic temperature, maximum combustion temperature, ignition delay time, and ceramic particle size in the product all showed a gradually decreasing trend. The SHS products and the ignition of the SHS reactions were significantly dependent on the Bsub.4C particle size. The formation mechanism of ZrBsub.2 and ZrC during SHS from the Ni-Zr-Bsub.4C system was proposed based on the combustion wave quenching experiment.
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