Research On Li₂O-ZnO-Al₂O₃-SiO₂Glass-ceramics Prepared By Sol-gel Process

Li2O-ZnO-Al2O3-SiO2(LZAS) glass-ceramics have adjustable thermal expansion coefficients(TECs). At the same time, they own good thermal and chemical stability, strength, a higher softening deformation temperature and a lower crystallization temperature. If coating the sol precursor on some material surface, it can improve the material life or expand the application field. Preparation by sol-gel method has advantages like good uniformity, high reactivity, low preparation temperature and obtained composition completely according to original formula and stoichiometric amounts, which can overcome some existing problems.This paper prepared the glass-ceramics and the sol by sol-gel method, and studies the effects of pH value, temperature, the addition of water and ethanol and DMF on the sol formation and properties by measuring the sol viscosity and gelatin time, successfully obtains24Li2O-8Al2O3-17ZnO-51SiO2stable, transparent sol and glass-ceramic as well as more reasonable technological process and process parameters. We addressed the effects of heat treatment, aluminum sources and composition change on the crystallization and microscopic structure with differential scanning calorimeters, X-ray diffraction, infrared spectrum and scanning electronic microscope.The results show that the appropriate ratio of prehydrolysis of TEOS ratio is n (TEOS):n (C2H6O):n (H2O):n (HNO3)=1:3:1:0.03, and the reaction should run at room temperature for one hour, which can prepare the sol with moderate viscosity for subsequent reaction. In the preparation of boehmite, we choose HNO3as peptizer, the raw material ratio is n(H2O)/n(Al(C3H7O)3)=100, the temperature is keeping around85℃, pH value is adjusted between3.5-4.1, after the precipitate is peptized, through aging for12h under90℃, we can obtain stable sol during a shorter time. When the sol is mixed, we choose HNO3to adjust the pH value, the viscosity of the sol first reduces then increases as pH value rises. Relatively appropriate pH value is1.1, at this time gelatin time is the longest, sol stability is the best. We should keep the reaction at room temperature because raising the temperature cause the viscosity to increase largely. The addition of DMF may cause the sol to gelatinize.Along with the heat treatment temperature rises the crystalline degree is increasing and the average particle size shows a tendency of increasing; the crystallization is not greatly influenced when using different aluminum sources, the main phases have no changes, as the temperature rises, β-quartz solid-solution turns into (3-spodumene solid-solution gradually, at the same time βⅡ-LZS turns intoyo-LZS, while preparation by A1(NO3)3is more likely to crystallize. Types of crystalline and the crystalline degree are different due to different compositions, and with similar composition the crystallization is similar too. Increasing of the content of lithium helps form β-quartz solid-solution and β-spodumene solid-solution; with less lithium, the main phase is Zn2SiO4along with trace amounts of ZnAlO4and SiO2, increasing of the content of aluminum helps form ZnAl2O4, while increasing of the content of zinc helps form SiO2.