Fabrication of Metal Powders for Energy-Intensive Combustible Compositions Using Mechanochemical Treatment: 2. Structure and Reactivity of Mechanically Activated Al–Modifier–SiO2 Mixtures

Abstract

The results of studying the particles of the aluminum–modifier–quartz composites after mechanochemical treatment (MCT) in a planetary centrifugal mill by various physicochemical methods are presented. Graphite (C), polyvinyl alcohol (PVA), and stearic acid (SA) are used as modifiers. To increase the dispersive ability of plastic metallic powders (metal–modifier), MCT was performed in the presence of quartz, the weight fraction of which in the composite varies from 5 to 20%. The largest grinding of aluminum particles is observed with an increase in the graphite content from 5 to 20% and SiO₂ content from 5 to 10% in the composition of aluminum–modifier–quartz composites. The particle decreases, while that of crystallites increases with the MCT of the Al–SA–SiO₂ system with an increased quartz content in the composite. The maximal imperfection of aluminum after MCT is characteristic of the Al–SA–5%SiO₂ samples. An increase in the particle size and, correspondingly, a decrease in the specific surface with rather small crystallite sizes are observed after MCT for the Al–PVA–SiO₂ composition. It is shown that the imperfection of the crystalline structure of aluminum particles increases with an increase in the quartz content in the system. The synthesized powder material is a composite formation of aluminum and quartz particles bound by polymer formed based on polyvinyl alcohol in this case. The MCT of the Al–modifier–SiO₂ mixtures results in an increase in the powder activity both due to the accumulation and redistribution of defects in aluminum particles and due to the change of the surface structure due to the incorporation of modifying additives into the destructed oxide layer. The conceptual model of transformation of the surface layer and subgrain structure of aluminum particles during MCT is presented.