Study On Preparation Of Alumina Fiber By Sol-gel Method

With the rapid development of modern science and technology, there is an urgent requirement for the research and development of high-temperature and high-strength materials. Meanwhile, the use of the fiber is gradually increasing. This paper introduces the current utilization status of oxides-based fibers, summarizes the various preparation methods of alumina fibers, and determines the synthetic process of alumina fibers by sol-gel method with sodium aluminate and sodium silicate as the source material. The experimental conditions and features of sol-gel method are studied by using XRD, SEM, XRF, and TG-DTA et al. techniques. Moreover, the spinning process parameters and heat treatment parameters are determined.The main research content and conclusion in this paper are as followed:(1) The preparation process of alumina sol and silica sol are investigated through orthogonal experiment and single-factor experiment respectively. In addition, synthetic process of polymeric aluminum chloride gel is also studied. The results show that:a certain amount of NaCl crystal exists in the polymeric aluminum chloride gel formed by sodium aluminate and hydrochloric acid, which can be removed through the wash in the generation phase of Al(OH)3. The order of affecting importance in gel preparation through the orthogonal experiment result is PVA addition>reaction temperature>reaction time. Based on the above results, the influence rules of gel spinnability are determined:5 wt% of the acetic acid amount and 0.06 wt% polyvinyl alcohol, stirring in a water bath at 80℃ for 7h. The initial stirring speed is 500r/min, and it decreases to 100r/min when spinnability occures.(2) The spinning technology is studied. Spinning temperature between 20 and 40℃ is the best, and humidity is between 60% and 80%. The choice of appropriate stretching rate depends on the viscosity.(3) The effect of drying condition for apparent morphology and content of gel is investigated. Moreover, gel decomposition process kinetic is studied using non-isothermal kinetics. The results show that:the activation energy of thermal decomposition reduces from 43.713kJ·mol-1 to 40.68kJ·mor’by adding SiO2 into gel. Heating mechanism is determined. Firstly, the temperature increases to 450℃after 4h and then kept for 30min. And then, the temperature increases to 1200 ℃ after 2h and then kept for another 2h.(4) The thermal decomposition product characterization of hydrogel fibre is studied. The results show that:The fiber phase transforms into γ-Al2O3 crystal form from uncrystallized and then transforms into α-AI2O3. The crystalline of alumina fiber rise sharply ranging form 800℃ to 1000℃ when addition of SiO2 is 2% and 4%, and become constant afterwards. Moreover, the average particle size of the primitive decreases with the addition of SiO2. Finally, the final fiber product has a smooth surface, diameter is about 10μm and length-to-diameter ratio can reach about 30000.