Preparation of ultrafine nickel ferrite powders using mixed Ni and Fe tartrates

Ultrafine nickel ferrite powders of 10 nm in particle size were prepared by the calcination of gel powders of coprecipitated Ni- and Fe-containing tartates at 250 degrees to 400 degrees C/2 h. The gel powder was a mixture of Ni and Fe tartrates exhibiting characteristics of the individual salts. The mixing homogeneity of the two salts strongly influenced the history of thermal reaction and the characteristics of the powder thus obtained. Both the formation temperature and the particle size increased with the retrograde of the mixing state, which initiated the increase in crystallite sizes of the intermediates, gamma-Fe2O3 and NiO or Ni metal phases. Defect nickel ferrite spinel was formed if the oxygen fugacity was lower. Defect ferrites, especially those obtained at lower calcination temperatures, were highly susceptible to thermal decomposition at higher temperatures. (C) 1999 Academic Press.