Reactions leading to ignition in fully dense nanocomposite Al-oxide systems

Correlating ignition mechanisms of aluminum-based reactive materials with thermoanalytical measurements

“…29, and discussed above, a clear discrepancy between the observed reaction rates and predictions using a model relying on thermally activated diffusion was observed [154], even when the thickness of the initial oxide layer was assumed to be as small as 0.3 nm. The main issue was that the diffusion model failed to reproduce the shapes of the measured heat release curves for either constant heating rate or constant temperature experiments.…”

“…Minor adjustments for individual kinetic parameters, compared to those given in Table 1, enable one to reasonably describe the exothermic features observed for nano-composite thermites at temperatures above 600 K. Such adjustments are reasonable because the structures and stabilities of individual Al 2 O 3 polymorphs are expected to be affected by the presence of other oxides. However, lowtemperature reactions could not be successfully described considering this model despite any adjustments in the activation energy or pre-exponent for the first exothermic process, growth of an amorphous oxide layer [154]. The calculations would predict either a sharper than experimentally observed low-temperature peak or an incorrect effect of the heating rate.…”

“…Typical experimental data are illustrated in Fig. 30 [153,154]. For both materials, the heat release is well quantified and a strong function of temperature.…”

“…Although the mechanism of the generation of the Mott potential across an interface produced between two solid reactants remains subject of active research [156], CM model was applied to such an interface earlier [157]. Following that work, and modifying the CM equations for an interface produced around a spherical oxide inclusion in a metal matrix [158], the CM model was applied to describe an early reaction in nanocomposite thermites produced by ARM [144,145,147,153,154]. Effectively, the CM reaction describes growth of the Al 2 O 3 film thickness h, as:…”

“…Additional experimental studies focusing on the lowtemperature reactions exploited isothermal and scanning microcalorimetry using a TAM III calorimeter by TA Instruments [144,145,153,154]. Reaction rates were quantified at temperatures as low as 303 K for Al$MoO 3 and Al$CuO thermites.…”