Preparation And Magnetic Properties Of Mn-Zn Ferrite Fibres

Spinel type Mn-Zn ferrite fibres are a kind of novel ceramic fibrous materials. They have not only the characteristics of excellent refractory, corrosion resistant, antioxidization as other ferrite powder materials but also the predominance of a high anisotropy and low relative density. So that, these novel materials will have potential applications in the national defence and high-tech area.In this thesis, the organic complexation gel derived process has been developed and was used for the preparation of Mn-Zn ferrite fibers from the raw materials of citric acid and metal salts. Good spinnability gels were obtained by adjusting the proportion of raw materials and operational parameters. The gel precursors were characterized by FT-IR spectrum, X-ray diffraction (XRD) and thermo-analysis (TG/DSC). It is reasoned that these gel precuisors are formed by the carboxylic radiacl ligand reacting with metal ions in the aqueous solution throung a dual dentate model. These gel precursors with a linear type structure exhibited a very good spinnability.The gel fibre precursors have been investigated by thermo-gravimetric analysis and differential scanning calorimetry (TG-DSC) and the process consisted of dehydration, decomposition, cracking and the heat treatment procedure was determined subsequently. The morphologies of Mn-Zn ferrite fibres were characterized by scanning electron microscopy (SEM). Through the organic complexation gel derived process, spinel type ferrite fibres with a precise composition, fine diamater,high aspect ratio(length/diameter) were prepared. In particular, diameters of the Mn-Zn ferrite fibres could be thinner than 1μm, the lenth upto 80cm and the fibres composed of grains in a nanometer level. Magnetic properties of the Mn-Zn ferrite fibres were characterized by a vibrating sample magnetometry (VSM). Effects of heat treatment, Mn/Zn proportion and Mg, Ce, Co doping on the Mn-Zn ferrite fibre's magnetism were discussed. Appropriate Co doping can improve the coercive significantly and Ce doping has an effect on the increase of the saturation magnetization.