Al and Ni nanoparticles as precursors for Ni aluminides

Abstract

Aluminides, intermetallic compounds of Al with at least one additional element, are promising materials particularly for high-temperature applications due to their physical and chemical properties. They are typically prepared starting from the elements using compacted, micrometer sized powders or multilayer systems, while the application of nanoparticles as precursors is much more uncommon although the high interface area can have advantages in the reactivity of the materials. We prepared Ni aluminides starting from submicron Al particles and Ni nanoparticles applying a self-propagating reaction. Upon applying separately prepared particles multiphase products containing Ni, Ni3Al, NiAl, Ni2Al3 as well as NiAl3 were observed depending on the sample size and heating rates. The preparation of single phase NiAl was possible applying particle mixtures synthesized by a two-step protocol. In a first step, submicron Al particles were synthesized via thermal decomposition of triisobutylaluminum. On the surface of the formed Al particles nanocrystalline Ni was deposited in a second step via thermal decomposition of bis(cycloocta-1,5-dien)nickel(0) resulting in the formation of well-mixed Ni–Al particle blends. Heating of powder compacts or loose powders under an atmosphere of Ar resulted in the formation of single phase NiAl at low as well as at high heating rates with no other intermetallic phases being present.