An efficient approach that combines short-term (minutes) highenergy dry ball milling and wet grinding to tailor the nano-and microstructure of Ni +Al composite reactive particles is reported. Varying the ball-milling conditions allows control of the volume fraction of two distinct milling-induced microstructures, that is, coarse and nanolaminated. It is found that increasing the fraction of nanolaminated structure present in the composite particles leads to a decrease in their ignition temperature (T ig ) from 700 and 500 K. Material with nanolaminated microstructure is also found to be more sensitive to impact ignition when compared with particles with a coarse microstructure. It is shown that kinetic energy (W cr ) thresholds for impact ignition, obtained for an optimized nanolaminated microstructure, is only 100 J. High-speed imaging showed that the impact-induced ignition occurs through formation of hot spots caused by impact. Molecular dynamic simulations of a model system suggest that impact-induced localized plastic deformation raises the local temperatures to ∼600 K, enough to initiate exothermic reactions. Analysis of the kinetics and reaction mechanism shows that the reason for low T ig and W cr for nanolaminated microstructure is the rapid solid-state dissolution of nickel in aluminum lattices.

High temperature (>1000 K) reaction kinetics in the stoichiometric (1:1 by molar ratio) Al-Ni system was investigated by using the, so-called, electrothermal analysis (ETA) method. ETA is the only technique that allows studying kinetics of a heterogeneous gasless reaction at temperatures above the melting points of the precursors. Special attention was focused on methodological aspects of the ETA method. Two different reaction systems were studied: (i) initial Al/Ni clad particles; (ii) the same powders but after 15 min of high energy ball milling. Analysis of the obtained results leads to the conclusion that such mechanical treatment decreases the apparent activation energies of the reaction in the Ni-Al system, from 47 +/- 7 kcal/mol for the initial powder to 25 +/- 3 kcal/mol after ball milling. Comparison of these data with those reported previously was also made.

Direct synthesis of silicon carbide (SiC) nanopowders (size 50–200 nm, BET ~20 m2/g) in Si–C system is conducted in an inert atmosphere (argon) using a self‐propagating high‐temperature synthesis (SHS) approach. A preliminary short‐term (e.g., minutes) high‐energy ball milling (HEBM) of the initial mixture, which involves pure Si and C powders, is used to enhance system reactivity. Two conditions of HEBM with different force fields (17G and 90G) are applied and the results are compared. The influence of HEBM's conditions on the microstructure of mechanically treated mixtures and combustion products is also investigated and discussed. Obtained results suggest that by changing the intensity of mechanical treatment one may prepare a completely amorphous reactive mixture containing carbon and silicon, or gradually change the ratio of (Si/C)–SiC phases and finally produce pure silicon carbide powder during the milling process. The influence of HEBM on the combustibility of the Si/C mixture possesses a critical character: the self‐sustained reaction becomes feasible only after a critical time of ball milling (i.e., 10 min for 90G; 30 min for 17G). Comparison of the microstructures for as‐milled and as‐synthesized powders reveals that for all investigated conditions the morphologies of the as‐milled reactive Si/C media are essentially the same as that for SiC combustion products. The mechanism for direct synthesis of SiC by combustion reaction is also proposed.

The influence of short-term (≤10 min) high energy ball milling (HEBM) on the microstructure and reactivity of a titanium-carbon powder mixture is reported. It is proved that the mechanism of microstructural transformation in a Ti-C mixture during HEBM defines the reaction mechanism in the produced Ti/C structural energetic materials. More specifically, it is shown that after the first two minutes of dry milling (DM) in an inert (argon) atmosphere the initially crystalline graphite flakes were almost completely amorphized and uniformly distributed on the surface of the deformed titanium particles. A subsequent “cold-welding” leads to formation of Ti-(C-rich/Ti)-Ti agglomerates. TEM studies reveal that the (C-rich/Ti) composite layers consist of nano-size (20 nm) Ti particles distributed in the matrix of the amorphous carbon and thus are characterized by extremely high surface area contacts between the reagents. A rapid self-ignition of the material during DM occurs just after 9.5 min of mechanical treatment, resulting in formation of pure cubic TiC. Wet grinding (WG) of a Ti-C mixture in hexane, under otherwise identical parameters, provides more “soft” conditions, which do not allow the rapid amorphization of carbon during the first stage of grinding. As a result graphite and titanium form sandwich-like Ti/C composite particles, in which the reagents contact primarily along the boundaries of the layers. Such particles gradually transform to the TiC phase without a spontaneous reaction during the HEBM process. The reactivity, i.e., self-ignition temperature and ignition delay time, of different milling-induced microstructures, were also studied. It was found that the ignition temperature in Ti-C structural energetic material prepared under optimized HEBM conditions is ∼600 K, which is more than three times lower than that of the initial reaction mixture (Tig ∼ 1900 K). A significant decrease of the effective activation energy for interaction in the Ti-C system is observed (from 95 kcal/mol to ∼56 kcal/mol). It is explained by the fact that solely solid-state reactions are responsible for the ignition phenomenon in the produced structural energetic materials, whereas the dissolution of carbon in a melt is responsible for the reaction in non-mechanically treated mixtures. Analysis of the milling-induced microstructures and reaction kinetics of the Ti/C composite particles suggests that a combination of several factors is responsible for enhancement of their reactivity, with the carbon amophization on the first stage of HEBM playing a key role through formation of layers that provide intimate high surface area contacts between the reagents.