Fabrication Of Transparent Ceramics And Fibers Via Glass Crystallization

The development of laser technologies have set new demands on the requirement for inorganic transparent materials with high quality.Transparent ceramics have been widely studied because of their excellent optical and robust mechanical properties.Despite of substantial progress in ceramic technology,it still remains a long-standing challenge for fabrication of transparent ceramics under mild conditions.This thesis focuses on the fabrication of transparent ceramics via glass crystallization.Through regulation of crystallization process of glass system,the transparent ceramics with high crystallinity can be successfully prepared.The mechanical and optical properties of the transparent ceramics have been studied.The related results of the work are summarized as follows:1.In the glass system of TeO₂-Bi₂O₃-Nb₂O₅,the role of Bi/Nb in glass forming as well as the influence on the crystallization processes of glass have been studied.It is found that the stability of glass decreases and the crystallization tendency can be tuned by introducing Bi₂O₃to replace Nb₂O₅.As a typical heavy metal with large size,the introduction of Bi may produce strong steric hindrance effect,which is supposed to lead the slow crystal growth process.As a result,the transparent nanoceramics can be prepared and the size of crystal grains spanning three orders of length scales from?15?m to?20 nm by raising the nucleation curve and simultaneously suppressing the growth one.The obtained transparent nanoceramics exhibit interesting mechanical properties.The mechanical properties can be improved compared with the parent glass.The nanoceramics also show enhanced optical properties,including the dynamic optical filtering ability and efficient radiative transition in the near-/mid-infrared wavebands.2.The microstructures of the BaO-Al₂O₃-LaF₃-Si O₂oxyfluoride system have been studied.It is found that the fluoride and oxide network structure are locally separated and can easily form the oxide-and fluoride-rich phase.The energy requirement for the breaking of chemical bonds,ionic diffusion and structural relaxation is lower in fluoride network structure,leading to the crystallization of LaF₃ nanostructure at first.During nanocrstyallization,[Al O_xF_y]structure present at the interface between oxide and fluoride phase,which can suppress the further growth of LaF₃.Then the oxide crystal phase?BaAl₂Si₂O₈?starts to form in the meantime and it can warp the LaF₃ nanophase.As a result,transparent multiphasic ceramics,which are consisted of LaF₃ and BaAl₂Si₂O₈ phases,can be achieved.The optical properties of the prepared materials have been investigated.The result indicates that the luminescence of Eu can be promoted by the multiscale structure provided by LaF₃and BaAl₂Si₂O₈.3.Transparent ceramics have been fabricated.First,the precursor fibers are fabricated based on the fiber-drawing method.Second,the crystallization process of the precursor fibers are tuned via carefully control of the heat-treatment duration and temperature.Importantly,transparent nanoceramic fiber and multiphase ceramic fiber can be successfully achieved by the pressureless crystallization process.The microstructure,light guiding and luminescence properties of the ceramic fibers have been characterized.It is found that the microstructures of ceramic fibers are similar to the bulk ceramics.Besides,the transparent ceramics exhibit excellent light propagation and luminescence properties.