Reactive Bilayers by Self-activated Electroless Nickel-Phosphorous Deposition on Pure Aluminum

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Nickel-aluminum bilayers and multilayers are commonly used in reactive systems because of their high heat of mixing. Traditionally, the layers are sputter deposited, an expensive and time-consuming process. In this article, a chemical reduction technique, electroless nickel-phosphorous (EN) deposition, is used for formation of the Ni-Al bilayer using a pure Al substrate. Traditionally, EN deposition on Al requires surface activation due to the native oxide layer. Here, we tune the bath pH to dissolve this oxide layer, such that deposition can be obtained without surface activation. Deposition kinetics is measured by tracking the mass change with time and temperature, and we extracted the activation energies at two different pH values. At pH 7, the energy is 98.7 kJ/mol and reduces to 55 kJ/mol at a pH of 8. The process can also be extended to aluminum powders and flakes in order to form reactive core–shell structures.