Study On Preparation Of High Strength And Super Elastic Lamellar Structured Silica Nanofibrous Aerogels For Thermal Insulation

Currently,with the proposal of the goal of peak carbon dioxide emissions and carbon neutrality in China,an urgent task in priority is to reduce energy waste and raise energy efficiency.In various fields such as building insulation,industrial production,pipeline conveyance,chemical,metallurgy,high-temperature catalysis,etc.,the thermal insulation materials can effectively cut down ineffective dissipation of heat energy,and improve energy utilization.Therefore,the development of thermal insulation materials has always been a central issue in industry and academia.Among the existing thermal insulation materials,ceramic aerogel materials with their porous structure,low thermal conductivity,and temperature resistance have shown great potential.However,traditional ceramic aerogels have poor mechanical properties and are easy to break due to their discontinuous pearl necklace-like granular skeleton,which severely limits their practical applications.By contrast,ceramic fibrous aerogels reveal excellent mechanical properties,strong structural stability and low thermal conductivity,making them a hot spot for current research.In all various kinds of fabrication method of ceramic fibrous aerogels,electrospinning is one of the most potential methods because of its wide range of raw material sources,simple device,convenient operation,controllable process and efficient preparation.In this work,two polymer templates of polyvinyl alcohol(PVA)and polyvinyl butyral(PVB)were added separately to silica sol to obtain a uniform and stable spinning solution.The flexible silica nanofiber membranes(SNFMs)was prepared via electrospinning and subsequent calcination treatment.The discrepancy of two polymer templates in spinning process were investigated.While using PVA as polymer template,the prepared SNFMs exhibited outstanding properties with smooth surface,relatively uniform diameter and excellent mechanical properties.After calcination at 800°C,the tensile strength is up to 1.5MPa,much higher than the corresponding SNFMs obtained from PVB with only about 0.6MPa.Based on this,the SNFMs obtained from PVA with outstanding mechanical properties is used as the construction element,and bonding aluminum borosilicate sol(Al BSi sol)is introduced into it.Afterwards,the lamellar structured silica nanofibrous aerogels(SNFAs)were assembled by the method of soak-stacking,freeze-drying and then calcination.The influence of the concentration of the Al BSi sol as immersion solution on the micro morphology,mechanical properties and thermal insulation properties of the material was studied.By adjusting the concentration of Al BSi sol to 1wt%,the obtained SNFAs has the best mechanical properties,which demonstrated compressive strength as high as 160 k Pa at 60%recoverable strain,shear strength as high as 21 k Pa at 20%recoverable strain with thermal conductivity only 0.0389 W m^-1 K^-1.After that,the compression resilience performance was further studied,showing excellent fatigue resistance for 500 cyclic compressions at 60%strain with no obvious plastic deformation(0.32%),and good dynamic viscoelasticity with small damping ratio(only?0.03).In addition,the shear performance of the material was further studied,demonstrating superior fatigue resistance for 100 cycles of shearing with 20%strain and indicating that the layered structure is stable.Finally,the performance of compressive resilience of SNFAs in high and low temperature(500°C and-100°C)was studied,revealing that the plastic deformation after500 cycles was only 2.1%and 6.4%at-100°C and 500°C,respectively.And more than 85%of the initial maximum stress was retained after 500 cycles,exhibiting excellent high temperature resistance.In summary,SNFMs obtained from PVA polymer template were used as the basic building unit.By adding Al BSi sol as binder and combining electrospinning,sol impregnation-layer stacking method and subsequent processing,lamellar structured SNFAs was prepared,which exhibited fascinating mechanical properties(high strength,super elastic),low thermal conductivity(0.0389 W m^-1 K^-1)and outstanding temperature resistance(up to 1100°C).The synergy of their great mechanical properties and thermal insulation properties further compensates for the shortcomings of existing ceramic fibrous aerogels,which greatly expands their further application and provide new ideas for the subsequent design and development of new ceramic fibrous aerogels for thermal insulation.