Facile synthesis of micro-sized Ni-Al alloy powders through low-temperature chemical alloying

Micro-sized Ni-Al alloy powders were synthesized using different quantities of Ni and Al powders as well as AlCl3 as an activator in a quartz batch reactor at <= 773 K. This method, named low-temperature chemical alloying (LTCA), which allows Al atoms to diffuse into micro-sized nickel particles mediated by aluminum chloride (chemical promotor), is distinct from conventional processes, such as cast-and-crush, and gas atomization. As-synthesized Ni-Al alloys were characterized using different analytical techniques that included X-ray diffraction (XRD), particle size analysis, and field emission scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy (FESEM-EDS), to confirm the formation of alloy phases, such as Ni3Al, NiAl, Ni2Al3, and NiAl3. The analytical results showed that the crystalline phase compositions of the Ni-Al alloys were highly dependent upon the initial amounts of Ni and Al powders employed at the given alloying conditions (alloying temperature, 773 K; alloying time, 20 h; amount of AlCl3, 1.2 wt%). As a result of the thermal treatment of Ni-Al powder mixtures with the Al contents of (5, 15, 30, and 50) wt.% under continuous powder mixing by rotation, each powder was found to have (i) Ni solid solution + Ni3Al, (ii) Ni3Al, (iii) NiAl, and (iv) Ni2Al3 + NiAl3 phases, respectively, corresponding to the equilibrium states of the Ni-Al phase diagram. The cross-sectional analyses showed that the alloy structures of the heat-treated powders exist in a single-phase or core-shell form, depending on the number of crystalline phase compositions predicted from the phase diagram. In particular, the Ni-50 wt% Al powder has a unique Ni2Al3@NiAl3 core-shell structure. We further evaluate the performance of the as-developed Ni-Al alloy powders as oxidation-resistant materials and template materials for high-surface area (similar to 60 m(2)/g(cat)) nickel catalysts. (C) 2019 Elsevier B.V. All rights reserved.