A generalized reduced model of uniform and self-propagating reactions in reactive nanolaminates

摘要

A multiscale inference analysis is conducted in order to infer intermixing rates prevailing during different reaction regimes in Ni/Al nanolaminates. The analysis combines the results of molecular dynamics (MD) simulations, used in conjunction with a mixing measure theory to characterize intermixing rates under adiabatic conditions. When incorporated into reduced reaction models, however, information extracted from MD computations leads to front propagation velocities that conflict with experimental observations, and the discrepancies indicate that our MD simulations over-estimate the atomic intermixing rates. Thus, using only insights gained from MD computations, a generalized diffusivity law is developed that exhibits a sharp rise near the melting temperature of Al. By calibrating the intermixing rates at high temperatures from experimental observations of self-propagating fronts, and inferring the intermixing rates at low and intermediate temperatures from ignition and nanocalorimetry experiments, the dependence of the diffusivity on temperature is inferred in a suitably wide temperature range. Using this generalized diffusivity law, one obtains a generalized reduced model that, for the first time, enables us to reproduce measurements of low-temperature ignition, homogeneous reactions at intermediate temperatures, as well as the dependence of the velocity of self-propagating reaction fronts on microstructural parameters.