Study On Preparation Of Porous Mullite Nanofiber-based Thermal Insulation Materials

With the increase of global energy consumption and carbon emissions,the contradiction between the rapid growth of human demand for energy and the decreasing energy stock has become more and more prominent.Energy conservation and improvement of energy utilization are urgent.In the fields of building insulation,smelting,and pipeline transportation,the use of insulation materials can reduce energy loss and improve energy utilization efficiency.At the same time,technological advance is constantly challenging the performance of existing insulation materials.The military,aerospace,and high-temperature catalysis are all raise higher requirements for the performance of insulation materials.As a result,the development of high-performance insulation materials has become a hot topic in the materials research community.Among the existing thermal insulation materials,mullite nanofiber-based thermal insulation material has abundant pore structure,excellent high-temperature resistance,high temperature creep resistance,thermal shock resistance,etc.So,it is a highly promising thermal insulation material.However,the current mullite nanofiber-based materials tend to have low thickness and limited thermal insulation performance,which limits the application scenarios of mullite nanofiber-based thermal insulation materials.How to further improve its thermal insulation capacity is one of the hot spots in the research of mullite nanofiber-based materials.The sol-gel method has advantages in raw material mixing uniformity,safety,energy consumption,and operation difficulty;electrospinning has the advantages of easy steps,simple equipment,low cost,convenient adjustment of process parameters,and controllable spinning process,etc.The combination of the two methods has become one of the most promising approaches for the preparation of mullite nanofibers.In this project,aluminum chloride hexahydrate,aluminum isopropoxide,and ethyl orthosilicate are used as raw materials to configure the precursor solution.Polyethylene oxide is used as a spinning auxiliary to prepare the spinning sol,which is combined with electrospinning to prepare mullite nanofiber-based thermal insulation material.The mullite nanofiber-based insulation material with a thickness of 150 mm and a bulk density of 6 mg/cm~3 is finally prepared,which is a significant increase in thickness compared with the conventional film-like mullite fiber material.In addition,pore structure with pore size ranging from 1 to 32 nm is introduced on single mullite nanofiber,so that the thermal conductivity of the mullite nanofiber material reaches 0.024 W m^-1 K^-1 at room temperature,compared with 0.030 W m^-1 K^-1 at room temperature for the solid mullite nanofiber material.The thermal insulation capacity of the mullite nanofiber-based insulation material is significantly improved by both increasing the material thickness and the introduction of the pore structure.In the 400°C hot bench test,the 25 mm thick sample can achieve a temperature reduction of 288°C with excellent thermal insulation performance.The crystalline transformation pattern,mechanical properties,and high-temperature resistance of porous mullite nanofiber-based thermal insulation materials during calcination are further investigated.It is found that during calcination,the precursor fibers show the transition from crystal-free structure toδ-Al₂O₃ crystals at 900°C,and reach complete crystallization at 1300°C.The porous mullite nanofiber-based insulation material is able to withstand a tensile stress of 13 k Pa and compressive stress of 1.98 k Pa.After 50 cycles of flexure and 500 cycles of compression,there is no significant decay of stress,showing that the material has good flexibility and durability.At the same time,the material can still keep its own properties unchanged at a high temperature of 1300℃,showing good high-temperature resistance,which greatly broadens the application scenarios of mullite thermal insulation materials in the field of high-temperature thermal insulation.By combining the above factors,the porous mullite nanofiber-based thermal insulation material prepared in this project has significantly lower thermal conductivity(as low as 0.024 W m^-1 K^-1)and significantly higher thickness（up to 150 mm）than the conventional mullite nanofiber thermal insulation material.At the same time,the material shows excellent thermal insulation performance,as well as good temperature resistance（it can be used at temperatures up to 1300°C）and mechanical properties.The material shows great advantages and application prospects in the field of high-temperature thermal insulation,and provides new ideas for the development of future thermal insulation materials.