Meta-structural Ceramic Fibrous Aerogels Fabrication And Thermal Insulating Properties

Thermal control under extreme conditions in the aerospace and military fields requires thermal insulation materials that can withstand complex mechanical stress,severe thermal shock and long-term high-temperature environments.Ceramic fiber aerogel has received much attention because of its light weight,low thermal conductivity,fire and corrosion resistance,and mechanical flexibility,but still suffers from shortcomings such as insufficient deformation capacity,poor thermal stability,and low heat insulation performance at high temperatures.To overcome the complex preparation method of traditional ceramic aerogels,insufficient mechanical and thermal stability,and the high thermal conductivity at high temperature,this paper proposed a far-field electrospinning method,and prepared three kinds of ceramic fibrous aerogels with excellent mechanical and thermal properties.At the same time,the mechanism of multi-scale structure design to enhance the mechanical and thermal integration was systematically studied.In addition,in view of the poor thermal insulation performance of ceramic fibrous aerogels at high temperature,the method of absorbing or reflecting thermal radiation to reduce the thermal conductivity at high temperature is proposed.The main contents are as follows:Far-field electrostatic spinning and turbulence-assisted electrostatic spinning methods are proposed.Traditional electrostatic spinning tends to form two-dimensional film.To overcome this inherent defect,the far-field electrostatic spinning method is proposed to reduce the electrostatic field force and increase the degree of fiber entanglement by multi-physic field coupling.Hence,the precursor fibers formed by electrostatic spinning can form a three-dimensional fluffy structure and realize the one-step preparation of large-scale three-dimensional fiber aerogels.The composition design and grain boundaries improvement by amorphous phase,and the force-thermal integrated enhancement mechanism of hypocrystalline ceramic fibrous aerogels（ZAG）are proposed.The near-zero Poisson’s ratio and near-zero thermal expansion coefficient are achieved through the multi-scale structural design.And provide a new solution for enhancing the thermomechanical stability of ceramic fibrous aerogels.ZAG exhibit excellent mechanical flexibility and has the highest elastic compression deformation capacity with strains as high as 95%among ceramic aerogels at present,and show excellent fatigue resistance and tensile and bending deformation capacity.ZAG exhibit excellent thermal stability,including excellent thermal shock resistance and high temperature elastic deformation capacity.Moreover,ZAG has excellent thermal insulation properties and exhibits ultra-low thermal conductivity at room temperature.The mechanism of carbon thermal stability at high temperature and absorption of thermal radiation to reduce high temperature thermal conductivity of carbon rich ceramic fibrous aerogels（CCAG）are proposed.With excellent force-thermal performance of the aerogels,the amorphous carbon in ceramic matrix exhibits excellent stability at high-temperature through the design of the two phasic ceramic composition and the grain pining effect.The amorphous carbon can absorb thermal radiation at high temperatures efficiently,thus significantly reducing the high-temperature thermal conductivity.This research makes up for the shortcomings of the ceramic aerogel in terms of high-temperature thermal insulation.The mechanism of the force thermal stability enhancement and reduction in high-temperature thermal conductivity by reflecting thermal radiation due to medium entropy effect of medium entropy ceramic fibrous aerogel（MECA）are proposed.The nucleation potential barrier is increased and the grain growth is inhibited through the design of the medium entropy ceramic composition.Therefore,the grain sizes of MECA are effectively reduced,enabling MECA to exhibit excellent mechanical flexibility and thermal stability.Moreover,the Ti O₂ in medium entropy ceramic composition can effectively reflect thermal radiation,thus significantly reducing the thermal conductivity at high-temperature.