Research On Preparation And Properties Of Zirconia-based Flexible Ceramic Fibers

High-temperature insulation materials are essential parts of national defense,military and high precision manufacturing.Especially with the rapid development of hypersonic equipment in space or in the field of thermal weapons,the structural research and preparation technology of thermal protection materials has become a major difficulty in the development of hypersonic equipment.The use of thermally insulating materials to prevent the diffusion of external heat flow to the interior is important to ensure the safe and normal operation of structural/non-structural components in high temperature environments.According to the future demand for optimization of high-end thermal insulation materials,the trend is to develop lightweight,flexible,high-strength and stable performance high-temperature insulation materials.Ceramic fiber materials are the first choice for thermal insulation materials because of their higher thermal stability and corrosion resistance than traditional insulation materials.However,their inherent brittleness limits the wider application.Based on the above background,in this paper,two flexible ceramic fibers were prepared and their properties were investigated using zirconia fibers as the main components.（1）The precursor sols with spinnability were prepared and electrostatically spun to form gel fibers with submicron fineness using silane and butyl zirconate as raw materials and acetic acid as complexing agent,varying the zirconium source to acetic acid ratio.The changes in composition,structure and morphology of the Zr O₂/Si-C-O ceramic fibers with increasing heat treatment temperature and the effects on their mechanical properties were studied in focus.The results show that the increase of temperature leads to the increase of fiber diameter and grain size,as well as the transformation of Zr O₂ phase.At a heat treatment temperature of 800°C,the ceramic fibers maintain a tetragonal crystalline phase with a diameter of about 480 nm and a grain size of 8.5 nm after refinement by the amorphous Si-C-O phase,with a maximum tensile stress of 1.67 MPa,and exhibit excellent thermal stability at 1300°C.（2）The precursor sol was prepared by condensation of siloxane as a silicon source with butyl zirconate,which existed in the system in the form of Si-O-Zr and was finally retained in the ceramic fibers.By adjusting a series of parameters to explore the relationship between the raw material ratio and the sol conductivity,viscosity and morphology of the formed fibers,the optimal spinning sol ratio was obtained as follows:10 wt.%polyvinylpyrrolidone/ethanol solution added at 5.0 g,acetic acid added at 4.2 g,and the viscosity of the system was around400 c P,at which time the electrospun gel fibers had good morphology.The Zr-Si-O-C ceramic fibers calcined under argon atmosphere can still maintain a single tetragonal zirconia crystalline phase at 1200°C,and a multiphase structure of amorphous phases Si O₂,Si CO₃ and free carbon exist simultaneously,and the grain size is less than 15.2 nm,and the fiber film has good flexibility.The effect of calcination atmosphere on Zr-Si-O-C ceramic fibers was also compared,and the results showed that the Zr-Si-O-C ceramic fibers calcined in argon gas at 1000°C had higher content of amorphous components,smoother and flatter fiber surface as well as smaller grain size than those in air.In addition,the fibers have good mechanical properties,with a maximum tensile stress of 2.32 MPa;they have a certain degree of acid and alkali resistance,and are still flexible after 48 hours of treatment with strong acids or bases;their thermal conductivity is0.042 W/（m·K）at room temperature in air;and their multiphase structure and the presence of infrared shielding agents bring good infrared shielding ability to reduce heat transfer at high temperatures.In addition,the three-dimensional Zr-Si-O-C ceramic fiber mats with certain thickness were assembled by stacking and freeze-drying methods,and the material exhibited lightweight and thermal insulation properties,extending a new idea for the application of ceramic fibers.