Research On Preparation And Properties Of Ultralight Carbon Foam/SiO₂ Aerogel Composite

Aerogels have the advantages of low density and low thermal conductivity,but have low strength and high brittleness.Because of the translucent nature of aerogels,the radiation heat transfer is high and cannot be directly used.In this paper,carbon foam and SiO₂ aerogel are combined.The new lightweight insulation materials expand the application in building energy saving,cold chain transportation,industrial production and other fields.Firstly,the carbon foam pyrolyzed at different temperatures were characterized by thermogravimetric analysis and infrared spectral scanning test method,and the pyrolysis mechanism of melamine foam was analyzed.The effect of pyrolysis temperature on the microstructure,specific surface area and pore size characteristics,compressive strength and thermal conductivity of carbon foam was studied to obtain the best pyrolysis process for carbon foam.Secondly,focus on the sol-gel process and aging process of carbon foam/SiO₂ aerogel composites,and optimize the process parameters.According to the study of the influence of single factor on the gel time and density of carbon foam/SiO₂ aerogel composite,an orthogonal experiment was designed to discuss the content of anhydrous ethanol,deionized water,dilute hydrochloric acid and ammonia water on gel time and thermal conductivity.The effect is to obtain an optimal solution for the sol-gel process.The effects of three factors of aging liquid composition,aging temperature and aging time on the density and specific surface area of carbon foam/SiO₂ aerogel composites were designed to obtain the optimal solution for aging process.Finally,the carbon foam/SiO₂ wet gel prepared by the optimal process was immersed in a n-hexane solution with a trimethylchlorosilane content of 20%for surface modification,and dried under ambient pressure to obtain a carbon foam/SiO₂ aerogel.The results show that the hydroxyl groups on the surface of the carbon foam/SiO2 aerogel modified by trimethylchlorosilane are replaced by Si-CH₃ groups,which exhibit excellent hydrophobic properties.The carbon foam/SiO₂ aerogel composite is hydrophobic and the angle is 135°.The maximum compressive stress of the carbon foam/SiO₂ aerogel composite is about 1.0 MPa and the carbon foam serves as a skeleton support.At room temperature,the measured thermal conductivities of the CF and CF/SiO₂ aerogel composite were 0.035 W/m?K and 0.024 W/m?K,while at 300°C,it was reported to be 0.120 W/m K and0.057 W/m K.The aerogel filled in the carbon foam cells greatly reduces the thermal conductivity of the composite,and the carbon foam acts as an opacifier,greatly reducing the radiant thermal conductivity of the carbon foam/SiO₂ aerogel composite.