Synthesis of needle-like nickel nanoparticles in water-in-oil microemulsion

Needle-like nickel nanoparticles with a diameter of 6–18 nm and a length of 100 nm have been prepared in the cationic w/o microemulsion of water/CTAB, n-butanol/n-octane by reduction of nickel chloride with hydrazine hydrate. X-ray diffraction (XRD) and transmission electron microscope (TEM) characterizations indicated that these nickel nanocrystallites were needle-shaped with a face-centered cubic structure. The effect of the ratios of surfactant to n-octane on the formation of the needles was discussed. It was found that the average size of nickel nanoparticles was affected mainly by the size of microemulsion droplets, and the appropriate ratios of surfactant to water were in the range of 4.6–33.0 in this paper. The magnetic measurement for a typical sample showed that the coercivity was 264 Oe, different from that of bulk nickel and spherical nanoparticles (5 nm).