Nickel nanoparticles were synthesized via liquid-phase reduction of NiCl2·6H2O with N2H4·H2O. The efficacy of different dispersing agents in preventing agglomeration was systematically compared, establishing a clear processing-dispersion correlation. Four different types of dispersants were selected to compare their effects on the microstructure and dispersibility of nano nickel powder. Among them, Ni nanoparticles prepared using sodium dodecyl sulfate (SDS) as dispersants exhibit superior microscopic morphology and dispersion. And then, the mass ratio between the precursor and dispersant was systematically optimized, resulting in spherical nickel nanoparticles with controllable particle size and favorable physical properties. When the mass ratio of SDS to Ni salt reached 150%, the prepared spherical Ni nanoparticles had the optimal dispersion and a minimum average particle size of 79 ± 12 nm. By estimating Nv, the concentration of nickel nanoparticles is about 2.15 × 1017 particles cm−3 at this ratio. After thermal treatment, the quality of the samples became stable beyond 415 °C with a maximum weight reduction of 6.75% at 150% SDS/Ni-salt ratio, and no residual surface sulfur was detected. The saturation magnetization of Ni nanopowders gently decreased with decreasing dispersant content from 35.3 emu·g−1 to 31.6 emu·g−1 at 300 K, while soft ferromagnetic behavior was maintained, which is more beneficial for the stability of multilayer ceramic capacitor performance.
Yuan et al. (Tue,) studied this question.