| Recently, glass-ceramics attract much attention because of their excellently physical and chemical properties compared with glass and ceramic They have been widely-used in mechanical engineering, biomedical science, electromagnetism, electro-optics, astronomy, national defense and building adornment etc. Li2O-Al2O3-SiO2 glass-ceramics could be applied in manufacturing to cooktop panels, heat shield, heat-proof window cover, astronomical telescope and laser gyroscopes for its outstanding properties such as adjustable of near zero even negative low coefficient of expansion, high anti- shock, heat-resisting, corrode-resisting, high strength and good transparent property. In recent years, it widely-used in micro-electronics, optical instrument, navigational systems, modem science and technology national defense field and become one of the most useful new type of materials.The traditional state-reaction method has many weakness in preparation of glass-ceramics. Sol-gel method has more considerable advantages than state-reaction method. It has widely used to prepare glass and ceramic materials. Recently, It also used to prepare glass-ceramics.Based on the recent research progress of Li2O-Al2O3-SiO2 glass-ceramic, we first obtain the gel whose composition is CoO- Li2O-Al2O3-SiO2 by using alkoxide hydrolyzed method. We studied the relation of the heat-treated temperature and microstructure, properties. We also obtained lithium aluminate nanocrystallites (LiAlsO8and LiAlO2) by sol-gel method in low temperature for the first time. We studied the relation of the heat-treated temperature and microstructure, properties.The contents of the thesis are as follows:1 The preparation of monothlic CoO- Li2O- Al2O3-SiO2 gelWe first obtained the glass-ceramic material with the composition of CoO-Li2O-Al2O3-SiO2 by sol-gel method using lithium acetic acid, aliminum alkoxide (aluminum-iso-propoxide, Al(OPr~i)3), cobalt nitrates and tetraethyl silicate (TEOS) as starting materials. We studied the relation of the heat-treated temperature, microstructure and properties.CH3COOLi-2H2O, Co(NO3)2-6H2O, Al(OPr~i)3 and TEOS are used as raw materialsand nitric acid used as catalyzer. After AKOPr'^ and TEOS hydrolyzed, CH3COOLi-2H2O, Co(NO3)2-6H2O were added to the above solution, and we got the transparent sol. We obtained the monothlic transparent gel after the sol was dried at 45°C. Then the dried gels were heat-treated at different temperatures. We obtained monothlic CoO- Li20-Al20rSi02 glass-ceramic. The main results showed:(1) The colors of CoO- Li2O-Al2O3-SiO2 samples depended on the heat-treated temperature. CoO- Li2O-Al2O3-SiO2 gel presented a pink color but, when heat-treated at temperature higher than 300°C, acquired blue color.(2) Before heat-treated at 800°C, the materials with different composition are unformed. Above 850°C the compounds of Li, Al and Si are inspected in some samples. At 1170°C SiO2 separated out.(3) The broad absorption band in the wavelength range of 1200-1600nm of 0.2CoO-5Li2O-6Al2O3-89SiO2 sample in the range of 850-1000°C was observed, and the intensity of the absorption band increased with heat-treatment temperature. The broad absorption band in the NIR region is due to tetrahedral complex of [COO4].(4) Two emission bands at 520and 585nm and several small bands at 503,760 and 825nm are observed in the sample. This because of the luminescence of Co2+ in the glass-ceramic is very complex. Different sites are available for Co2+ in the glass-ceramic (glassy phase, interface between the crystal partials and the glassy phase, inside the nanocrystals). So the emission bands are more structured.2 -. Synthesis of LiAlsOg and Co2+: LiAlsOg nanocrystals by sol-gel methodUsing sol-gel method, we obtained LiAlsOg and Co2+: LiAlsOg nanocrystals. We studied the relation of the heat-treated temperature, microstructure and properties.CH3COOLi-2H2O, A1(NO3)3-9H^ Co(NO3)2-6H2O and tartaric acid were used as raw materials. We obtained LiAl5Ogand Co2+: LiAl5O8 nanocrystallites at 700 °C. The raw materials were dissolved in alcohol solution and stirred at 80°C for a while, and then the gel was obtained. The gel was heat-treated at different temperatures. In the range of heated temperatures, the size of LiAl5Og nanocrystals was 50-70nm. With the temperature the size of LiAlsOg nanocrystallites were increasing.CH3COOLi-2H2O^ A1(NO3)3-9H2O and citric acid were used as raw materials. Theraw materials were dissolved in distilled water and stirred at 80°C for a while, and then the gel was obtained. The gel was heat-treated at different temperatures. When the gel was heated to 700°C, LLAI5O8 nanocrystals with the of size 30-50 nm were formed. With the temperature increasing, the size of LLAI5O8 nanocrystallites was increasing.Al(OPr')3 and CH3COOLi-2H2O were used as raw materials with nitric acid used as catalyzer. The molar ratio of A1(OIV)3 and CH3COOLi-2H2O was 5:1. After AlCOPr^ was partly hydrolyzed in hot water (83°C), the CH3COOLi-2H2O was added to the former mixture. Then the clear sol was prepared from hot hydrolysis of Al(OPr')3 with nitric acid added. The sol was heat-treated at different temperatures. LiAlsOg nanocrystal was obtained at 900°C. The size of LiAlsOs nanocrystals were 5-10nm.The size of nanocrystal increased with the temperature increasing,3, Synthesis of y-LiA102 nanocrystal by sol-gel methodCH3COOLi-2H2Ck Al(NO3)3-9H2Oand tartaric acid were used as raw materials. We obtained y -LiA102 nanocrystallites at 700 °C . The raw materials were dissolved in alcohol solution and stirred at 80°C for a while, and then the gel was obtained. We studied the relation of the heat-treated temperature and microstructure, properties. In the range of heated temperatures, the size of Y -LiA102 nanocrystals were 40-60nm. With the temperature increasing, the size of Y -LiA102 nanocrystallites were increasing.Al(OPri)3 and CH3COOLi.2H2O were used as raw materials with nitric acid used as catalyzer. The molar ratio of Al(OPri)3 and CH3COOLi-2H2O was 1:1. After Al(OPr')3 was partly hydrolyzed in hot water(83°C), the CH3COOLi-2H2O was added to the former mixture. Then the clear sol was prepared from hot hydrolysis of Al(OPr')3 with nitric acid added. The sol was heat-treated at different temperatures. Y -LiA102 nanocrystal was obtained at 800°C. The size of Y -LiA102 nanocrystals were 10-20nm. The size of nanocrystal increased with the temperature increasing. |
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