Study on preparation of ultrafine NiFe_2O_4 particles by microemulsion method

摘要

Ultrafine NiFe_2O_4 particles with spinel structure were prepared in the system of water-in-oil microemulsion of water/Triton X-100-hexanol/cyclohexane. The effects of calcining temperature and the other operation conditions were systematically discussed based on the techniques of SEM, XRD, VSM and so on. The result showed that NiFe_2O_4 nanoparticles, with a narrow size distribution(30-70nm), could be obtained by microemulsion method. The crystal grain diameter of the ultrafine NiFe_2O_4 particles could be enhanced with the improvement of the calcining temperature, the molar ratio of water to surfactant (w=[H_2O]/ [surfactant]) and the concentration of Fe~(3+)(or Ni~(2+)), respectively. The VSM plots showed that the ferrimagnetic behavior was expected for this type of magnetic material. The XRD patterns and DTA-TG curves revealed that the optimal calcining temperature of NiFe_2O_4 sample was at around 500℃. The relation between the average particle size (D) and the value of w could be expressed as D=13.91 l+0.2628w. Moreover, it was indicated that low concentration of Fe~(3+)(or Ni~(2+)) was beneficial to the formation of small and regular NiFe_2O_4 particles.