Preparation And Thermophysical Properties Of High Entropy Ceramic Fibers By Electrospinning

High entropy ceramic（HEC）materials are considered as promising thermal protection materials due to their low thermal conductivity caused by severe lattice distortion and enhanced phonon scattering.Moreover,introducing multi-elements will drastically increase the configurational entropy(ΔS_config),and resulting in better stability at high temperature due to lower Gibbs free energy(ΔG_mix=ΔH_mix-TΔS_config).Rare earth oxides（REO）have high melting point and are potential thermal protection materials for hypersonic vehicles.However,the unsatisfactory thermal conductivity coefficient hinders the practical application of REO at high temperature.In order to overcome these obstacles,high entropy rare earth oxides（HE RE₂O₃）were designed.REO have good mechanical properties and low thermal conductivity,which can be well-tuned by increase configuration entropy,improve stability,inhibit phase transformation and reduce thermal conductivity due to manufacturing HE solid solution.However,the high synthesis temperature becomes the bottleneck which hinders the large-scale production and practical application of HECs.It is very attractive to adopt a new method of low temperature synthesis of HECs.Therefore,in order to develop thermal protection materials with light weight,ultra-high temperature resistance,heat insulation,anti-sintering,strong stability and other excellent comprehensive performance,this paper adopts electrostatic spinning method to prepare single-phase cubic bixbyite structure HE RE₂O₃ ceramic fiber.Establish the internal relations of composition,structure and properties of HE RE₂O₃ ceramic fiber materials.Explore the influence law of different elements on its high temperature stability and thermal conductivity through the characterization analysis of laser thermal conductivity instrument.With the target element metal salt as the main raw material and polyvinylpyrrolidone（PVP,Mn1,300,000）as the adhesive,Two component(Y_0.5Yb_0.5)₂O₃,four component(Y_0.25Yb_0.25Sm_0.25Eu_0.25)₂O₃ ceramic solid solution fibers and HE(Y_0.2Yb_0.2Sm_0.2Eu_0.2RE_0.2)₂O₃（RE=Er、Dy、La）ceramic fiber are successfully prepared by electrospinning method.The study says:（1）Two component(Y_0.5Yb_0.5)₂O₃ and four component(Y_0.25Yb_0.25Sm_0.25Eu_0.25)₂O₃ ceramic solid solution fibers have a single structure of bixbyite,the fiber morphology is continuous and uniform,the diameter is less than 200 nm,and the surface is smooth.The thermal conductivity of ceramic solid solution fibers of two-component(Y_0.5Yb_0.5)₂O₃ and four-component(Y_0.25Yb_0.25Sm_0.25Eu_0.25)₂O₃ decreases significantly compared with that of Y₂O₃ materials,and is0.2482,0.1989 W·m^-1·K^-1 at room temperature.Respectively,the thermal conductivity of Y₂O₃ at room temperature is 1/85,1/106.However,the thermal conductivity of two and four-component ceramic solid solution fibers increases rapidly at high temperature,which needs further study.（2）HE(Y_0.2Yb_0.2Sm_0.2Eu_0.2Er_0.2)₂O₃ nanofibers have the same crystal structure as a single RE₂O₃ component（space group Ia^<sub>3）,and no other impurity phases exist.The characteristic peaks of（222）,（400）,（411）,（332）,（134）,（440）,（611）and（622）crystal surfaces are clearly visible and corresponded to the standard cards one by one,which proved that a good single-phase solid solution is formed,and the heat treatment temperature of 500℃significantly reduced the synthesis temperature of HEC.Fiber grain size is small（about 10 nm）,fiber continuous uniform,smooth surface,good crystallization,uniform distribution of elements,with good high temperature stability,after 1200℃high temperature heat treatment,fiber still has a good surface morphology and continuity,grain slightly grown,fiber structure stability,diameter shrinkage rate is less than 2%.HE(Y_0.2Yb_0.2Sm_0.2Eu_0.2Er_0.2)₂O₃ nanofibers have excellent low thermal conductivity of 0.24W·m^-1·K^-1 at room temperature and 0.48 W·m^-1·K^-1 even at 1473 K temperature.（3）The synthesized HE(Y_0.2Yb_0.2Sm_0.2Eu_0.2RE_0.2)₂O₃（RE=Er、Dy、La）nanofibers all have a single cubic bixbyite structure.The three nanofibers have uniform fibers,smooth surface,good crystallinity,and uniform distribution of elements.HE(Y_0.2Yb_0.2Sm_0.2Eu_0.2RE_0.2)₂O₃（RE=Er、Dy、La）have good low thermal conductivity,less than 0.6 W·m^-1·K^-1.Among them,HE(Y_0.2Yb_0.2Sm_0.2Eu_0.2La_0.2)₂O₃ has the best thermal conductivity,which is 0.1689 W·m^-1·K^-1 at room temperature and 0.3755 W·m^-1·K^-1 at 1473 K,which is supposed to potential thermal protection materials for hypersonic vehicles.Low thermal conductivity is related to the large atomic radius difference,atomic mass difference,lattice distortion caused by high entropy effect.