Research On The Performance And Component Processing Techniques Of Transparent Magnesium Aluminate Spinel Ceramics

Transparent ceramics are functional materials with excellent mechanical, electronic, magnetic, and/or thermal properties. They have wide application prospects and are one of the focuses for the research in concurrent material science and technology. Magnesium aluminate spinel, or MgAl2O4, ceramics are transparent over a wide range of wavelength, chemically inert, remain high strength at high temperatures, and therefore are the important infrared or transparent armor material for the defense industries. They have an infinite potential in civil applications as well.Currently the research on the preparation of ultra-fine powders, the forming of the greens, and the sintering techniques of MgAl2O4 ceramics has made considerable progresses. Transparent MgAl2O4 ceramics have been prepared successfully in China. The work is still on its research and development stage, nevertheless, and there is much to do with regard to the densification behavior when sintering in the presence of sintering aid, the technical parameters for repeated production of highly qualified ceramics, and the suitable techniques for processing large and non-planar spinel components. Spinel's ever increasing applications in defense industries are asking urgently for higher performance, larger components, and steady procurement of the material. Therefore, further investigation into the technology of the preparation of ceramics and of the fabrication of components is necessary.This dissertation aimed at meeting the demands of practical application, conducted the research on the preparation, performance and component processing techniques of transparent MgAl2O4 ceramics. By probing into the densification behavior of the spinel powders, key thermodynamic data were obtained or calculated, and the working mechanism of LiF was investigated. Optical processing techniques were experimented and evaluated. Qualified domes up to SR100mm were made and transferred.The influences of LiF on the microstructure and optical performances were examined. It shows that LiF densifies the ceramics by promotes grain growth and pore removal. Ceramics with 1.0wt%～1.5wt% LiF achieves optimal optical transmittance, which is close to the theoretical limit in the range of infrared band. For the first time, the amount of residual Li in the ceramics was detected. It demonstrates that, different from the viewpoint of fellow researchers, Li+ failed to get out of the ceramics in large amount when sintering. The state of being of Li+, and the behavior of F-, which are crucial to a better understand of the densification mechanism of LiF doped spinel, need further investigation.The densification process of spinel under hot pressing was investigated. Densification curves of spinel ceramics were outlined against the data from a number of sintering runs. The densification activation energy of spinel powders were figured out. The machinability characteristics of spinel ceramics were introduced. It is the earliest reported domestic study dedicated to the fine processing techniques of ceramic spinel. The ceramics achieved excellent surface roughness of 0.5～0.8nm(Ra) after processing. Large spinel ceramic components were prepared in order to satisfy the specific need.The application of transparent spinel ceramics to the packing of LED was explored for its early stage, which may lead to a the prosperous field for MgAl2O4 ceramics'application in the future.