A redox reaction model for self-heating and aging prediction of Al/CuO multilayers

Abstract

Sputter-deposited Al/CuO multilayers capable of highly energetic reactions have been the subject of intense studies for tunable initiation and actuation. Designing high performance Al/CuO-based initiator devices definitively requires reliable prediction of their ignition and reaction kinetics including self-heating or aging as a function of heating rate and environmental conditions. The paper proposes a heterogeneous reaction model integrating an ensemble of basic mechanisms (oxygen diffusion, structural transformations, polymorphic phase changes) that have been collected from recent experimental investigations. The reaction model assumes that the rate of reaction is limited by the transport of oxygen across the growing layer of Al2O3 separating Al and CuO. Importantly, we show that the model predicts reasonably all exotherms through a wide range of temperature (ambient -1000 °C), all resulting from a pure diffusion process as experimentally observed for such Al/CuO multilayers. The model shows how the temperature ramp affects the structure of the multilayer and especially the growth of alumina-based interfacial regions. It highlights the importance of the interfacial chemistry evolution such as the native mixture of AlxCuyOz transformation into a thin amorphous alumina, and the polymorphic phase transformation of this latter. The first one occurring at ~350 °C results in a loss of continuity of the interface leading to the accelerated redox 2 reaction whereas the second one occurring between 500 and 600 °C produces a denser barrier to oxygen diffusion leading to the stop of redox reaction. We finally use the model to simulate thermal annealing as usually performed in accelerated aging experiments. We theoretically observe and experimentally validate that a two weeks exposure of the multilayers at 200 °C starts degrading the multilayers thermal properties whereas when the temperature remains below 200 °C, the material keeps its entire integrity.

Unexpected enhanced reactivity of aluminized nanothermites by accelerated aging

“…(1 α), limited to independent reactions occurring successively after each other, within specific temperature ranges. However, the thermite reactions, which combines chemical oxido-reduction reactions with mass transport through barrier layers [35][36][37][38] that have dynamical changes in their structures over temperature cannot rigorously be reduced to a single Arrhenius law activation. Thus, we opted for the use of a differential isoconversional method based on the Friedmann method.…”

“…Thus, we opted for the use of a differential isoconversional method based on the Friedmann method. [35,[39][40][41] In contrast to Kissinger, this methodology states that the reaction rate is only a function of temperature at constant reaction progress. This can be easily demonstrated by taking the logarithmic derivative of the reaction rate equation (Eq.…”

How Thermal Aging Affects Ignition and Combustion Properties of Reactive Al/CuO Nanolaminates: A Joint Theoretical/Experimental Study

“… is the source term representing the exothermal Al oxidation, with corresponding to the value of the redox reaction 2Al + 3CuO → Al 2 O 3 + 3Cu given in [ 28 ]. For more details about the model implementation, see [ 26 ]. Table 1 summarizes the main model parameters used in the following aging study.…”

“…Along this line, a very recent and thorough experimental study showed that under slow heating rates, the release of gaseous oxygen from the CuO occurring well below reaction onset (i.e., at ~250 °C) initiates the Al oxidation process at the vicinity of native interfaces until a proper Al 2 O 3 is formed at ~400 °C [ 25 ]. Based on these findings, Lahiner et al proposed a redox reaction model suitable for investigating slow heating rates and low temperature experiments [ 26 ]. The model permits describing the kinetics of the reactant and product layer thicknesses (including Al, CuO, Cu 2 O, Al 2 O 3 ) of reacting sputter-deposited Al/CuO nanolaminates upon annealing at low temperature (ambient to 500 °C) [ 26 ].…”

“…Based on these findings, Lahiner et al proposed a redox reaction model suitable for investigating slow heating rates and low temperature experiments [ 26 ]. The model permits describing the kinetics of the reactant and product layer thicknesses (including Al, CuO, Cu 2 O, Al 2 O 3 ) of reacting sputter-deposited Al/CuO nanolaminates upon annealing at low temperature (ambient to 500 °C) [ 26 ]. This preceding work offers a unique opportunity to investigate Al/CuO nanolaminates aging in an original manner, allowing for efficient in silico screening of structures modification and ensuing performances alteration when the Al/CuO thermite nanolaminates are subject to long-term storage at the ambient temperature and upon annealing as well.…”