Research On The Heat Insulation Performance Of The Multi-scale Mullite Whiskers/fibers Reinforced SiO₂ Aerogels

As the world’s energy crisis continues to be intensified,it has become the consensus of the world that we need to adopt new technology and develop efficient thermal-insulation material.In our study,we synthesized a multi-scale mullite whiskers/fiber enhanced material inspired by pine branches.This material is used to replace traditional one dimensional fibers and combine with SiO₂ aerogels,which will benefit to improving the mechanical strength and reduce the brittleness of SiO₂aerogels.The microstructure,compression rebound performance and heat insulation properties of composite materials are studied systematically in this paper.Firstly,multi-scale mullite whiskers/fiber enhanced body was made through vacuum impregnation and freeze drying.The research showed that there are two reactions in this process.One of it is that aluminum silicate fiber transformed into mullite fiber,and the other one is that mullite whiskers were formed on the surface of fibers by gas-solid reaction.The optimum process parameters to in situ synthesize mullite whiskers were 0.16 mol/L silica sol,0.5 mol/L Al（NO₃）₃ solution,2.0 mol/L NH₄F solution,the holding time of 2 h and the sintering temperature of 1200°C.Secondly,SiO₂ sol was added into mullite whiskers/fibers by sol-gel method and vacuum impregnation.Finally,multi-scale mullite whiskers/fibers reinforced SiO₂aerogels（MF/MW/SiO₂ aerogels）was synthesizing by supercritical drying and ambient pressure drying.The results showed compression stress of MF/MW/SiO₂aerogels synthesizing by supercritical drying showed good compression stress.At the compressive strain of 10%,the compression stress of MF/MW/SiO₂ aerogels was0.105 MPa,much higher than that of MF/MW enhanced body（0.019 MPa）.Meanwhile,this kind of material showed good compression resilience performance（92.8%）and low thermal conductivity（0.028 W/（m·K））.The strength of SiO₂ aerogel was enhanced by the multi-scale synergistic effect of mullite whiskers/fibers,while SiO₂ aerogels effectively cushioned the damage to the whiskers and fibers.