Preparation And Properties Of Carbon Nanotubes/Al₂O₃-SiO₂ Aerogel Composite Heat Insulation Materials

In this study,Al₂O₃-SiO₂ aerogel composites doped with 0-1.0wt.%carbon nanotubes were prepared using Al₂O₃-SiO₂ aerogel as matrix and carbon nanotubes（CNTs）as reinforcement material to improve heat insulation and compressive properties.The microstructure,thermal insulation and compressive properties of the composites were analyzed by instruments of scanning electron microscope,nitrogen adsorption and desorption tester,Fourier transform infrared spectrometer,thermal conductivity tester and X-ray diffractometer.The effect of different content of carbon nanotubes on thermal insulation and compressive properties of Al₂O₃-SiO₂ aerogel was discussed,and the thermal insulation mechanism of composites was discussed by theoretical calculation.At the same time,the Abaqus software was used to simulate the temperature field of composite materials,and the simulation results were verified experimentally.The following results are obtained:（1）When the content of carbon nanotubes increases from 0 to 1.0wt.%,the pore size and specific surface area of Al₂O₃-SiO₂ composites containing 1.0 wt.%carbon nanotubes（AS/CNT-1.0）decrease by 8.36%and 17.3%,respectively,to 23nm and 446 cm²/g,and the density increases by 40%,to 0.21g/cm³.The decrease of pore size and specific surface is attributed to the dispersion distribution of carbon nanotubes,which restricts the growth of Al₂O₃-SiO₂ nanoparticles.（2）At 1000℃,the thermal conductivity of AS/CNT-0.5 and AS/CNT-1.0 composites decreased by 9.3%and 15%,respectively,to 0.189 W/m·K and 0.178W/m·K,compared with the original aerogel.This result is mainly due to the infrared shielding ability and uniform distribution of CNTs,which increases the multidirectional heat transfer path of composites.The compressive strength of AS/CNT-0.5 and AS/CNT-1.0 composites is increased by 16%and 84%,respectively,to 0.86 and 1.36 MPa,compared with the original aerogel,which is attributed to the high specific strength of carbon nanotubes and the anchoring effect on the aerogel matrix.（3）The theoretical thermal conductivity of composites at 25～1000℃is calculated by using a simplified cubic array structure model,and the error is within 8.5%with the experimental data.Based on the theoretical calculation results,it is speculated that the heat insulation mechanism of CNTs/Al₂O₃-SiO₂ composites is that carbon nanotubes inhibit radiation heat transfer and weaken solid heat transfer.（4）The cold surface temperature of carbon nanotubes/Al₂O₃-SiO₂composites was measured after heating at 1000℃for 1200 seconds.It was found that AS/CNT-0,AS/CNT-0.5 and AS/CNT-1.0 composites reduced to 768℃,753℃and 736℃respectively.Compared with experiment result,the error of AS/CNT-1.0 composite material simulating cold surface temperature is less than 5%,and the established model has certain reliability.（5）The temperature field distribution,heat flow state and cold surface temperature of 0-1.0 wt.%carbon nanotube doped Al₂O₃-SiO₂ aerogel composite were discussed.It was found that the maximum temperature area of the cold surface of the composite decreased significantly with the increase of carbon nanotube content.The temperature gradient increases gradually,and the temperature gradient of AS/CNT-1.0 is the largest,reaching 0.75.