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The adsorption mechanism of oleic acid(OA) on the surface of aluminum(Al) nanoparticle was studied using ReaxFF molecular dynamics simulation. A surface-oxidized Al nanoparticle was constructed to simulate the single-molecule and multi-molecule adsorption processes of OA on the surface of Al nanoparticle. It was found that single OA molecule adsorbed on the surface of the Al nanoparticles through its –COOH group to form a carboxylate structure, thereby forming a chemical adsorption monolayer on the surface of Al nanoparticle. During the multi-molecule adsorption process, the chemical adsorption layer will become denser with the increase of initial density of OA in the system. When the initial density is large enough, excess OA molecules were adsorbed outside the chemical adsorption layer by physical adsorption and form a chemical-physical bilayer adsorption structure on the surface of the particles. The simulation results were verified by the adsorption layer thickness determined with XPS and the bonding structure detected with FTIR. The adsorption mechanism of OA on the surface of Al nanoparticle was found to changes from a chemical monolayer adsorption to a chemical-physical bilayer adsorption with the increase of OA concentration.

A comprehensive ignition model for single boron particles in an oxygenated environment containing O2 and H2O is developed. Microcharacteristics of the boron oxide layer on the surface of boron particles at elevated temperatures are studied. Two typical distributions of species inside the surface oxide layer are detected. One is composed of three layers [B2O3, (BO)n, and B2O3], while the other is composed of two layers [(BO)n and B2O3], both according to the order from the internal to external side of the layer. In the model development, two submodels, submodel I and submodel II, are developed with regard to two different observed species distributions in the surface oxide layer. For submodel I, it is assumed that both (BO)n and O2 are the governing species diffusing into the liquid oxide layer. For submodel II, only (BO)n is the governing species. These two submodels are combined into a new bi-directional model consisting of four key kinetic processes: evaporation of the liquid oxide layer, global surface reaction between oxygen from the environment and boron, reaction between the inner boron core and oxygen, and global reaction of boron with water vapor. The ignition time predicted by the model is in good agreement with previous experimental data.