| Li2O-Al2O3-SiO2(LAS) system transparent glass-ceramics have excellent properties such as low thermal expansion coefficient, high visible light transmittance and high mechanical strength. They have been extensively applied in electronic packaging, fireproof doors and windows, optical elements, radar antenna cover etc. In this thesis, LAS transparent glass-ceramics were prepared by the melting-crystallization technique. The influence of components, forming procedures and thermal treatment conditions on the the structure and optical properties of transparent LAS glass-ceramics were investigated in detail. In addition, LAS glass-ceramics doped with transition metal ions and rare earth ions were examined with respect to their transparency and fluorescent properties.ANSYS analysis indicated that a temperature gradient field was formed during the melting process, with higher temperature around the crucible wall and lower temperature in the medium. The mass convection caused by the temperature difference was beneficial to the uniformity and clarification of glass melt. In the melt-forming process the surface temperature of thick glass was lower, while the internal temperature was higher than that of nucleation in glass (>700℃). As a result, the glass interior was prone to form primary crystal nuclei. The melt forming experiments showed that, with low cooling rates the primary crystal nuclei were generated in the glass interior, leading to the abnormal growth of crystal nuclei in the following cystallization process. Hence, the glass interior turns opalescent after the thermal treatment. Thermal stability investigation demonstrates that LAS glass-ceramics with a β-quartz solid solution phase showed excellent long-term stability below900℃. However, above900℃the crystalline phase was converted into an opalescent β-spodumene phase.In the preparation of glass-ceramics MgF2plays dual roles as both a nucleating agent and a fusing agent. Using ZrO2/TiO2as a complex nucleating agent, a certain amount of MgF2was added into LAS glass-ceramics. With the content of MgF2increasing, the glass crystallization temperature was decreased, and the crystallite size firstly decreased and then increased. The crystallization activation energy was intended to increase, and the crystallization index first increased and then decreased. With the content less than0.5wt%, MgF2could promote nucleation by the phase separation, leading to grain refinement of LAS glass-ceramics. Otherwise, it reduced the thermal stability of the glass-ceramics, resulting in the devitrification of LAS glass-ceramics because of the crystallite abnormal growth.LAS glass-ceramics were doped with rare earth ions and transition metal ions. Structural analysis showed that the pinning effect of Ce4+and Nd3+ions improved the structural stability of glass-ceramics, suppressing the phase transition from β-quartz solid solution to β-spodumene solid solution. These two types of ion doping made the grain refinement of crystalline phases, but the visible light transmittance of parent glass and glass-ceramics was decreased. Since the valence change and the color complement and twice coloration of ion co-doping occurred after the thermal treatment, LAS glass-ceramics exhibited diverse colors, making controlled coloring of glass-ceramics possible.Fluorescent analysis of rare earth doped LAS glass-ceramics showed that, when the Sm3+and Ce4+ions were co-doped, the excited energy could be efficiently transferred from Ce3+ions to Sm3+ions, and the fluorescent intensity of Sm3+ion doped glass-ceramics was enhanced. However, with the Ce3+ions concentration increasing, the fluorescent intensity of LAS glass ceramics was decreased due to the weakening interaction and the reduced efficiency of energy transfer between Ce3+ions and Sm3+ions.The above results give some theoretical insight into the preparation of high transparent, grain refinement, coloring and high luminous LAS glass-ceramics, implying practical significance in the production of high performance glass-ceramics. |
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