Síntese e caracterização do sistema ZnO - FeO submetido à moagem de alta energia

Abstract

The (1-X).ZnO + X.FeO system was ball-milled in a high-energy planetary mill, varying X throughout the concentration range (i.e., for 0 ≤ X ≤ 1). The as-milled powders were characterized by X-ray diffraction, Mössbauer spectroscopy and vibrating sample magnetometry. Sintered pellets were also prepared for X ≤ 0.07, by further thermal annealing pressed milled samples, during 1h, at 1000 °C, in free atmosphere. These samples were additionally characterized by scanning electron microscopy and respectively to the electric transport properties. The results revealed that the high-energy milling induced, for every starting nominal concentration, an effective particle size reduction. For X ≤ 0.07, the asmilled samples showed the formation of a (Zn1-XFeX)O solid solution only, with a hexagonal compact structure. For 0.09 ≤ X ≤ 0.18, a saturation of the (Zn, Fe)O solid solution took place forming, additionally, the franklinite (ZnFe2O4). Three phases appeared for the X = 0.35 sample: ZnO, a (Fe, Zn)O solid solution and a Zn 1-δFe2-δO4 spinel-like phase. For the rest of the concentration range (i.e., 0.50 ≤ X ≤ 1) only the ZnO and (Fe, Zn)O phases were observed. All the as-milled samples presented magnetic hysteresis, which was attributed to contamination with metallic iron, originally present as impurity in the FeO precursor, or incorporated in the system by abrasion during the milling process; or, in the case of intermediary concentrations, also due to the Zn1-δFe2-δO4 spinel. The sintered samples revealed the segregation of the franklinite in a ZnO matrix, with a highly porous ceramic body and poor varistor behavior.