Preparation And Properties Study Of SiO₂-Na₂O Binary System High Silica Glass Fiber

High silica glass fiber is a kind of special glass fiber with more than 95%SiO₂ content.It has excellent ablation resistance and heat insulation performance,and is widely used in the fields of national defense,aerospace,black and non-ferrous metal melt purification and filtration.At present,the domestic preparation of high silica glass fiber is mainly E-glass fiber multi-component method and SiO₂-B₂O₃-Na₂O ternary method,but the SiO₂-Na₂O binary method has greater advantages in cost,raw material utilization and so on.High silica glass fibers were prepared by acid leaching of SiO₂-Na₂O binary system.The fiber forming properties of SiO₂-Na₂O binary system glass and the effects of acid leaching and heat treatment on the fiber properties and structure were studied.The specific research contents are as follows:In the first part,the fiber forming properties and hygrothermal aging resistance of SiO₂-Na₂O binary system glasses with different Na₂O/SiO₂ ratios were studied.The viscosity of glass with different components and the strength of fibers with different diameters were measured by high temperature viscometer and single fiber dynamometer respectively.The results show that the viscosity range of the glass is 10^1.5-10² Pa.s.The tensile strength of the fiber is inversely proportional to the diameter of the fiber.The larger the diameter of the fiber is,the lower the strength is.In addition,the hygrothermal aging of the fibers with different aluminum content was studied by SEM and EDS.the results show that Na⁺in the fiber will precipitate to the surface of the fiber,forming a layer of alkaline Na₂CO₃ on the surface of the fiber,eroding the glass network structure,and rapidly reducing the mechanical properties of the fiber,However,increasing the content of Al₂O₃ can effectively improve the hygrothermal aging resistance of the fiber.In the second part,the effect of acid leaching on the structure and properties of high silica glass fiber was studied.The morphology and structure of precursor before and after acid leaching were characterized by scanning electron microscopy,infrared spectroscopy and micro Raman spectroscopy.The leaching process of Na⁺was characterized by ICP.The results show that the leaching rate of Na⁺in high silica fiber precursor is more than 85%after leaching in 3mol/L hydrochloric acid solution at 90?for 12 h.When the concentration of hydrochloric acid is 5 mol/L,the strength retention rate of the fiber after leaching is the highest.The analysis shows that Na⁺in the fiber is replaced with H⁺in the hydrochloric acid during the acid leaching process,and Si-OH is formed in the fiber.In the third part,the effect of heat treatment on the structure and properties of acid leached fiber was studied.The strength of the fiber after heat treatment was measured by single fiber dynamometer.The morphology and structure changes of the fiber during heat treatment were studied by scanning electron microscope,infrared spectrometer and micro Raman spectrometer.The results show that the optimum heat treatment temperature is 550-650?.The fiber strength increases by 45%after heat treatment at 550?for 35 min.In the process of heat treatment,Si-OH formed by acid leaching ion exchange condenses to form Si-O-Si and H₂O,which makes the structure of the fiber more compact,the network more complete and the strength of the fiber improved.In general,high silica glass fibers with more than 97%SiO₂ content were prepared by acid leaching with SiO₂-Na₂O binary method.The hygrothermal aging resistance of SiO₂-Na₂O glass fiber precursor can be improved by adding Al₂O₃.In the process of acid leaching,the concentration of hydrochloric acid should be controlled at 3 mol/L,and the temperature should be controlled at90?.The strength of the fiber after acid leaching can be effectively improved by heat treatment at550-650?.In addition,the mass production of high silica glass fiber prepared by binary acid leaching has been realized.The SiO₂ content of the mass production fiber has good high temperature resistance,but the strength of the fiber needs to be further improved.