Thermal Stability of Compact Pyrophoric Nickel Nanopowder Samples after Passivation

The use of nanopowders implies the ability to safely store them without changes in their physicochemical parameters ensured by passivation. In this work, we have determined the thermal stability range in air for compact samples of different diameters prepared from pyrophoric nickel nanopowders and then passivated. The results demonstrate that compact samples prepared from nickel nanopowder can be safely stored in air at temperatures of up to about 200°C without additional oxidation, which points to their high thermal stability. The lack of a noticeable heat release during slow heating to 200°C and the presence of only Ni in both the passivated and heat-treated samples according to X-ray diffraction data suggest that the oxide layer is very thin or that there are noncrystalline oxide phases. The observed uniform oxygen and nickel distributions over fracture surfaces of samples after heating suggests that their interaction with air during both the passivation process and heating to temperatures on the order of 200°C is a bulk process.