Effect of varying bilayer spacing distribution on reaction heat and velocity in reactive Al/Ni multilayers

Abstract

Self-propagating reactions in Al/Ni nanostructured multilayer foils are examined both experimentally and computationally to determine the impact of variations in reactant spacing on reaction properties. Heats of reaction and reaction velocities have been characterized as a function of average bilayer spacing for sputter-deposited, single-bilayer foils (having a uniform bilayer spacing) and for dual-bilayer foils (having two different bilayer spacings that are labeled thick and thin). In the latter case, the spatial distribution of the thick and thin bilayers is found to have a significant effect on reaction velocity, with coarse distributions leading to much higher reaction velocities than fine distributions. Numerical simulations of reaction velocity match experimental data well for most spatial distributions, with the exception of very coarse distributions or distributions containing very small bilayer spacings. A simple model based on thermal diffusivities and reaction velocities is proposed to predict when the spatial distribution of thick and thin bilayers becomes coarse enough to affect reaction velocity. This combination of experiment and simulation will allow for more effective design and prediction of reaction velocities in both sputter-deposited and mechanically processed reactive materials with variable reactant spacings.

Development of a reduced model of formation reactions in Zr-Al nanolaminates

“…Note that as expected, for a fixed value of the bilayer, the reaction velocity increases as the pre-exponent increases and the activation energy decreases. Also note that, consistent with earlier studies on reactive multilayered systems, [24][25][26]62 the reaction velocity generally increases as the bilayer decreases.…”

Quantifying transient states in materials with the dynamic transmission electron microscope

“…The two phases organize themselves into a structure reminiscent of eutectic reaction fronts that may be driven the same capillary forces. Modeling of the reaction had proceeded based on the assumption that the geometry was essentially planar and two-dimensional [44,[48][49][50][51]. This assumption clearly needs to be broadened to include three-dimensional structures.…”

“…The application of a localized source of heat initiates mixing and energy release that creates a selfpropagating reaction front that propagates throughout the material, releasing heat to the surroundings. RMLF have found application in material joining and other localized heat source applications [43][44][45][46][47][48]. One typical system that is used is alternating layers of Al and Ni that when heated will mix and form an intermetallic phase(s) that depends on the overall atomic composition.…”

Air blast characteristics of laminated al and NI-AL casings

“…Ni-Al reaction seems to be associated with bimetallic diffusion that largely depends on Al melting [3][4]. At the atmospheric condition, Al has a melting point of 933 K while the Ni melting point is 1726 K. To understand the heating behavior of Al, a 1D hydrocode (Chinook from Martec Ltd.) simulation was conducted for the early shock reverberating compression of Ni-Al laminated layers driven by the C4 detonation.…”

“…The heat of reaction for the NiAl product is 1.380 kJ/g; for the Ni 3 Al product, it is 0.4419 kJ/g in liquid phase and 0.7647 kJ/g in solid phase. Reaction of nanometric laminated Ni-Al can be found in a number of studies where ignition occurs at 450-900 K depending on the layer thickness/spacing [3][4]. This reaction threshold temperature is near the Al melting to facilitate diffusion mixing of Al and Ni.…”