The influence of heating conditions of the samples of nickel nanopowders on the modes of their interactions with the air

In the present work, compact samples of pyrophoric nickel nanopowders with an average particle size of 55 nm obtained by the method of chemical metallurgy were investigated. The possibility of passivation of compact samples 3 mm in diameter made of nickel pyrophoric nanopowders in the air is experimentally shown for the first time. The time of complete passivation is only 3–5 s for a relative sample density 0.4–0.5. According to X-ray phase analysis, only Ni phase was observed in passivated samples. It was found that passivated samples maintain thermal stability in the air at slow (< 10 °C/s) heating to ~ 200 °C; it is an important parameter for fire safety at handling of nanopowders. The analysis of passivated samples by the SEM method showed no traces of sintering of nickel nanoparticles, even after testing for thermal stability. The uniform distribution of oxygen within passivated samples according to energy dispersive X-ray analysis data indicates the volumic nature of the interaction of samples with the air during passivation. For the passivated samples, critical heating conditions were determined, under which self-ignition occurs.