A high-speed electrothermography approach is applied to investigate the mechanism and kinetics for nanostructured Al/Ni foils. Application of the Kolmogorov−Johnson−Mehl−Avrami and adiabatic thermal explosion models reveal that the activation energy for nucleation appears to be much higher than that for the reaction. It is shown that formation of intermetallic nuclei is the limiting step that defines the ignition characteristics of the foils at temperatures below 500 K, while the process is reaction-limited at higher temperatures. Nucleation is also shown to play an important role during rapid (∼10 m/s) propagation of the combustion (reaction) wave along the Al/Ni foils. These findings suggest new approaches for controlling the ignition and combustion processes for nanostructured reactive materials.

In this paper, the authors overview previous publications and present novel results related to self-sustained solid-state reactions: the solid flame. Due to recent advances in the fabrication of nano-structured reactive media, this phenomenon, which is first reported fifty years ago, has found a new perspective for a wide variety of exothermic systems. These fundamental findings permit novel routes for synthesis of advanced engineering materials with controlled microstructure, as well as for design of high-energy density systems with tuned parameters for energy release.

Reactive nanocomposites (RNCs), which are comprised of stochastically layered metals, were fabricated using short-term high-energy ball milling of nickel and aluminum powders. By varying the milling conditions, the internal nanostructure of the RNCs can be controlled. Utilizing the slice and view methodology by use of a dual beam scanning electron/ion microscope, 3D reconstruction of the RNC particles was accomplished and their nanostructures were quantitatively and statistically analyzed. The reactivity, including ignition and combustion parameters, as well as microstructure of the combustion wave, for different RNCs was analyzed using high-speed infrared imaging and high-speed micro video recording. The direct relationships between the 3D structural characteristics and reactivity parameters have been determined. A comparison with existing theoretical models allows us to conclude that, for specially designed RNCs, the reaction can be initiated and self-propagates solely due to solid-state mechanisms, i.e., in the solid flame mode. In addition, a novel nano quasi-homogeneous reaction regime was discovered. It was directly demonstrated that, by understanding the fundamental quantitative relationship between the structure and properties of RNCs, unprecedented control over the reaction can be achieved.

A single-step method for the preparation of metastable ε-Fe3N nanoparticles by combustion of reactive gels containing iron nitrate (Fe­(NO3)3) and hexamethylenetetramine (C6H12N4) in an inert atmosphere is reported. The results of Fourier transform infrared spectroscopy (FTIR) and thermal analysis coupled with dynamic mass spectrometry revealed that the exothermic decomposition of a coordination complex formed between Fe­(NO3)3 and HMTA is responsible for the formation of ε-Fe3N nanoscale particles with sizes of 5–15 nm. The magnetic properties between 5 and 350 K are characterized using a superconducting quantum interference device (SQUID) magnetometer, revealing a ferromagnetic behavior with a low-temperature magnetic moment of 1.09 μB/Fe, high room temperature saturation magnetization (∼80 emu/g), and low remanent magnetization (∼15 emu/g). The obtained value for the Curie temperature of ∼522 K is close to that (∼575 K) for bulk ε-Fe3N reported in the literature.

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