Synthesis, microstructure and oxidation of Co-MgAl2O4 and Ni-MgAl2O4 nanocomposite powders

Abstract

MgAl2O4-CoAl2O4 and MgAl2O4-NiAl2O4 solid solutions are synthesized by combustion in urea of the appropriate metal nitrates. The selective reduction in hydrogen of these oxides gives rise to a dispersion of nanometric Co or Ni particles in the spinel matrix. The reduction of the Co2+ and Ni2+ ions is complete at 900 and 1000 °C respectively. Owing to the homogeneity of the starting oxide solid solution, the size distribution of the metal particles is narrow and their average size is about 10 nm. During a thermal treatment in air, the nanometric metal particles located in the open porosity of the matrix are totally oxidized at temperatures lower than 700 °C, whereas those dispersed inside the matrix grains are stable up to 900 °C. These latter particles account for more than half of the total metal content.