Tailored Reactivity of Ni+Al Nanocomposites: Microstructural Correlations

KV Manukyan and BA Mason and LJ Groven and YC Lin and M Cherukara and SF Son and A Strachan and AS Mukasyan, JOURNAL OF PHYSICAL CHEMISTRY C, 116, 21027-21038 (2012).

DOI: 10.1021/jp303407e

An efficient approach that combines short-term (minutes) high-energy 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 similar 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.

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