Ni/NiO powdered nanoparticles with average sizes 10–30 nm were prepared by a levitation-jet method involving the condensation of Ni metal vapour in a mixture of helium with various amounts of air or oxygen. The process was undertaken with the application of a DC electric field up to 6.5 kV cm⁻¹. The particles were characterized by X-Ray diffraction, transmission electron microscopy, BET adsorption and vibrating sample magnetometry. It was found that the intensity of the applied electric field and partial oxygen pressure correlated with the main structural and magnetic parameters of the nanoparticles, such as average particle size, residual ratio of nickel, coercivity and maximum magnetisation. The specific surface area of the particles correlated with the magnitude of the external electric field. Room-temperature hysteresis loops of weakly oxidized nanoparticles show ferromagnetic-like behaviour, whereas the strongly oxidized ones exhibit a low-field ferromagnetic feature superimposed to a paramagnetic signal, regardless of the particle size. Magnetic measurements allowed for the estimation of the residual metal Ni content in the powdered nanoparticles, which can be as low as 0.04 at.% depending on oxygen partial pressure and external electric field strength.

Spherical oxidized nickel particles 15 to 200 nm in average size have been produced by a crucibleless aerosol method involving metal vapor condensation in an inert gas flow and oxidation processes. The particles have been characterized by scanning electron microscopy, X-ray microanalysis, X-ray diffraction, BET surface area measurements, and vibrating-sample magnetometry. The process parameters have been optimized for the preparation of particles with tailored size, specific surface area, and saturation magnetization. A dc electric field applied to the condensation zone during the oxidation process reduces the size and increases the extent of oxidation of the particles. We have studied low-temperature oxidation of carbon monoxide and propane on nickel nanopowders differing in particle size and extent of oxidation. The nanoparticles with optimized characteristics have been shown to have a marked catalytic effect on these processes.