Low-Temperature Crystallization Of Mesporous SiO₂ And The Synthesis Of Zn₂SiO₄:Mn Phosphor In Molten Salts

Orderly mesoporous SiO₂ which processing ordered channel structure, large specific surface area and other features, could improved the contact area between reactants and the gibbs free energy greatly, so it can be as a kind of high reactivity of reactants. Research shows that crystalline SiO₂ structure has more excellent performance than the amorphous SiO₂, while the transformation of amorphous to crystalline still needs high temperature. In addition, the green commercial phosphor powder Zn₂SiO₄:Mn（abbreviate as ZSM）, as a kind of high crystallinity and high luminous efficiency, its preparation methods are mostly through high temperature solid state reaction that need high calcined temperature and long time of grinding, which making it difficult to produce. Therefore, to develop a low temperature method to crystallize the amorphous SiO₂ and synthesis ZSM luminescent material has a very important practical significance. And molten salt method is an effective method currently adopted to prepare the crystal under a low temperature, which can significantly reduce the temperature of the reaction to industrial production.In this thesis, to realize the crystallization of SiO₂ and the synthesis of green phosphor ZSM that mesoporous SBA-15 was mainly applied as the raw material and different molten salt system was adopted. The concrete research content is as follows:（1） SBA-15（contain P123） as silicon source, NaNO₃ as the molten salt, by changing the temperature to explore the lowest crystallization temperature of SiO₂, and explore the influence of other factors（such as heat holding time, mass ratio of SiO₂/NaNO₃） on the result of crystallization. Results suggested that the minimum crystallization temperature of SiO₂ was 460°C and the optimum conditions of the crystallization was that the mass ratio of SiO₂/NaNO₃ was 0.2g/10.0 g, the temperature was 500°Cwith the holding time 6 hours.（2） To confirm the role of P123 in the crystallization process, the crystallization was not appeared under the optimum condition when used SiO₂ spheres as the silicon source and NaNO₃ as the molten salt. However, the crystallization was happened when using SiO₂ spheres soaking in hydrochloric acid solution of P123 under the best conditions. The experimental results show that the organic materials P123 is an indispensable factor of crystallization process.（3） In addition, in order to further validate the content of P123 on the effect of the crystallization process, we used the calcined SBA-15（removed P123） as silicon source and NaNO₃ as the molten salt to explore the lowest crystallization temperature of SiO₂. The experimental results show that the lowest crystallization temperature was 490 °C higher than the lowest temperature using not calcined SBA-15 as silicon source, which can be concluded that the content of P123 has an impact on crystallization.（4） In NaCl-ZnCl₂ mixed molten salt, we synthesis ZSM green phosphor powder with different doping of Mn at 500°C with holding time for 2 hours using calcined SBA-15 as silicon source and analyze its fluorescence characteristics. Fluorescence properties results show that the optimal doping amountwas x=0.2, and the fluorescence lifetime was14.25 ms.