| Yttrium aluminum garnet (YAG) crystals form in the cubic garnet structure, and belong to the isometric crystal system. Due to its homogeneous optical properties and lack of birefringence effects, Nd:YAG is widely used for lasers and luminescence materials. The YAG crystal has several disadvantages, however, it is hard to fabricate in a large size and with high neodymium concentrations. All these disadvantages have limited its application so as to exclude large-size solid-state lasers. Compared with the single crystal form, polycrystalline YAG ceramics have excellent possibilities for future application, because of their advantages, such as low cost, short preparation time, ease of mass production, etc. Moreover, YAG ceramics are potential advanced structural materials in view of their high creep and oxidation resistance ate high temperatures and their suitable heat conductivity. YAG powders doped with rare-earth metal elements can be used as ultra-short afterglow phosphors for cathode ray tubes and high-resolution displays. No matter to be used as powders directly or to be used to achieve high density and high transparency polycrystalline YAG ceramics, highly-dispersed ultra-fine YAG powder is necessary.In the present work, chemistry co-precipitation method was used to synthesize the YAG nanosized powders. The relations between the synthesis technology and the performance of the powders have been investigated systematically, through investigating the formation mechanism of YAG phase and the precursors by the terms DTA/TG, XRD, IR, TEM and so on, also the sinter-ability of the prepared powder was studied preliminarily.The results show that the precursors compose of metal hydroxides and nitrate using ammonia water as the precipitant. However, the precursors are mainly compound of carbonate when using ammonium hydrogen carbonate as precipitant. When ammonium hydrogen carbonate was used as the precipitating agent, pure phase YAG were obtained by calcining at 900°C for 2h without anyother intermediate phase with low metal ions concentration([Al3+] < 0.05mol/l), and the dispersion and sinter-ability of the powders is better than that synthesized by ammonia water; but pure phase YAG can not be synthesized with high metal ions concentration([Al3+] > 0.2mol/l), which need higher heat-treatment temperature more than 1000℃. This is caused by the segregation of the precipitation Al3+ and Y3+ in the precursors.In order to obtain high dispersed YAG nanosized powder, we controlled of process of washing, drying and the preparing of the prcursors through investigating the mechanism of the powder dispersion and agglomeration. The results show that the powder obtained from the precursor which was washed by low surface tension solvent and dried by the microwave oven has a good dispersion. Dring the preparation of precursor, different kinds of surfactants was used to improve the dispersion of the powders calcined under high temperature. In this experiment, highly crystalline, well-dispersed nano-sized YAG crystallites were obtained by calcining at 1000°C for 2h in the presence of the anionic surfactant OPS.In the end, the well dispersed nanosized YAG powder was used to prepare high density YAG ceramics, and different molding methods were chosed. In this experiment after the green body formed by uniaxial pressing sintered at 1550°C for 1h in vacuum, YAG ceramics with relative density of more than 97% were obtained. All in all, some of the results are creative and useful, and these will lay the foundation for the preparing of high transparent YAG ceramics in the future. |
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