Combustion reaction in multilayered nickel and aluminum foils

Ni/Al (3/1) multilayer reaction piles were heated in a vacuum furnace and the temperature (100 readings per s for a precision of 0.2°C) of the reaction pile was measured continuously during the combustion reaction. The ignition temperature (at which the combustion starts) is almost the same independent of heating rate and the thickness of the foils. This temperature corresponds to the melting of Al which triggers the reaction. For thin Ni foils, less than 25 μm thick, the maximum temperature shows a plateau with time, close to the adiabatic reaction temperature or the eutectic temperature close to Ni3Al. For thicker Ni foils, the maximum temperature decreases with the increase of foil thickness and the combustion is incomplete. The reaction time between the ignition temperature and the maximum temperature (or the beginning of the plateau temperature) increases from 8 s for a 12.5 μm Ni foil to 125 s for a 150 μm Ni foil and the relation is almost linear. For Ni foils less than 25 μm thick, the final microstructure is homogeneous with a grain size approximately equal to the combined initial Ni and Al foil thicknesses. In the range used, 1–100°C min−1, the heating rate has very little effect on the combustion reaction. From the temperature-time profile and microstructure analysis, there are evidences of melting of Al, decomposition of Al3Ni and Al3Ni2, and the formation of NiAl and Ni3Al.