Preparation, Structure And Properties Of Nano-crystalline Composite NiZn Ferrite

With the development of the miniaturization of micro-electronic devices and magneto-electronic devices, which are being widely used in the field of modern, information technology, and the correspondingly demand for miniaturization and low profile, the electro-magnetic properties of ferrite devices are also expected to satisfy the high permeability, high frequency, wide frequency range and low power loss. Ni-Zn ferrite with spinel structure (AB₂O₄) is a polynary metal oxide sintered substance, which has been playing an important role in the application of high frequency in field of magneto-electronic devices. The power loss of this kind of materials has always been an object of study to many researchers, especially under the circumstances of increasing demand for the miniaturization, integration, and modularization of products used in electronics and information industry. Apart from the demands for the high permeability and wide frequency ranges, new requirement is also needed in the preparation of materials, and device combination and assembly process, where materials need firing at low temperatures. Therefore, it is of great significance to develop a new Ni-Zn ferrite material with high permeability, high saturation magnetization, high cut-off frequency and low sintering temperature, which will surely promote the development of micro-electronic manufacturing industry. In this thesis we introduce the nano-technique into Ni-Zn ferrite preparation. Starting with raw material fabrication, this thesis presents systematically the forming mechanism of Ni-Zn ferrite nano-crystallites; the sintering mechanism of nano-crystalline-built Ni-Zn ferrite, their microstructure and magnetic performances and their magnetic spectrum and power loss characteristics at high frequencies, in order to furnish some important basic findings for the manufacturing of micro-electronic devices, which can work at high frequency with low loss, compact size and integration, and can be used for the applications with high frequency, low power loss devices. This thesis consists of seven chapters. The main contents are as follows:The first chapter summarizes the current development of ferrite magnetic material researches, by paying special attention to the application of nano-technology in the magnetic material researches, analyses the present status of various ferrite manufacturing processing methods, on the bases of which, a new processing using gel-auto-combustion in the preparation of ferrite nano-crystallite and ferrite precursor is put forward against the weaknesses of traditional ferrite preparation process.The second chapter systematically reveals the nanocrystalline NiZn ferrite synthesis process by gel-auto-combustion method, the influences of manufacturing conditions on nanocrystalline ferrite formation, the characterisations of nanocrystalline ferrite's structure and magnetic properties, and extracts the physical mechanism of synthesizing nanocrystalline NiZn ferrite.The third and fourth chapters present the nanocrystalline re-synthesis method, that is, making grains, packing and sintering directly to form polycrystalline ferrite by using nanocrystalline ferrite method, investigating the process of doping in the sol to prepare doped nanocrystalline ferrite and then making grains, packing and sintering to , sythesis polycrystalline NiZn ferrite, and also study the microstructures of doping or nanocrystalline-synthesized NiZn ferrites at different sintering temperatures; explain its sintering mechanism by ball model hypothesis, focusing on the effects of sintering temperatures, the doping substances, the doping quantities on the ferrite microstructures, and the relationships between microstructure and magnetic properties or, power loss at high frequencies.Chapter five deals with the Nano-micro-crystalline composite sintering Ni-Zn ferrite process; the power loss at high frequencies and magnetic spectrums of the materials sintered at low temperature, which has laid a solid foundation for further application of different sizes of nanocrystalline, for the designing and manufacturing different nano-micro-crystalline composites materials, and for the preparation of materials with special structure, function or composite structure.Chapter six gives a new way to manufacture Ni-Zn ferrite nanocrystalline by...