Atmospheric Pressure Drying Preparation Of Carbon Aerogel Composites Reinforced With Carbon Fibers

Carbon aerogels are composed of carbon nano particles,which are created by pyrolysis carbonization from organic aerogels.The carbon nano particles connected with each ather and formed the hree-dimensional network structure.Besides of lightweight and porous,carbon aerogels have excellent conductivity,which makes it can be widely used in catalysis,adsorption,hydrogen storage insulation and some other fields.The most important characteristic of carbon aerogels is that they can withstand the high temperature of 2000? or even 3000?after graphitization in inert or vacuum atmosphere.However,there are still many problems in the application of carbon aerogels,such as long preparation cycle,high cost,poor mechanical properties,large brittleness,and easy to be oxidized in aerobic environment.This paper adopts the targeted measures to solve these problems in practical application,which can provide a solution for the large-scale production and low application of carbon aerogels.Atmospheric pressure drying method was used to prepare the RF organic and carbon aerogels instead of supercritical drying,and using resorcinol and formaldehyde as raw materials.Different preparation parameters(precursor concentration,catalyst concentration,drying and carbonization process system)were changed to study the influence on morphology and structure of RF aerogel.The results show that when the concentration of precursor is 25%?40%and the concentration of R/C=500?2000,the bulk aerogel samples prepared have excellent structure and properties with low density and low shrinkage.When the precursor concentration is 25%,catalyst concentration is R/C=500,the density of RF sample is as low as 0.247g cm-3,and the carbonation shrinkage is 16%,which the pore diameter is near to 50 nm and the BET surface is 463m2 g-1.Refer to the atmospheric drying method of SiO2 aerogels,drying control additives was added to decrease the shrinkage of RF aerogels in atmospheric drying and improve the pore structure.In order to improve the mechanical properties of carbon aerogels,overcome the disadvantages of brittleness,this paper tries to use carbon fiber as reinforcement to be composited with RF aerogels by impregnating RF sol.The carbon aerogel composite materials producted have excellent strycture and properties with low shrinkage and special shape.According to the experiment results,the best preparation parameters are that the catalyst concentration is R/C=1000,the precursor concentration is 35%,the formamide content is F:R=0.5 and the best fit carbon fiber type is PAN carbon fiber felt.The prepared carbon fiber reinforced carbon aerogel composite material has high flexural strength(45MPa),and higher compressive strength in the 10%deformation(>5MPa),while the thermal conductivity is 0.15W m-1 k-1,these excellent performance can meet the needs at special environment.Finally,in order to solve the problem that the composite materials can be oxidized under aerobic environment at 350?.Silica-alumina sol with high purity and good stability was prepared using aluminum isopropoxide and TEOS as raw materials.Mullite sol was also be prepared by this way when the mole ratio of Al/Si is 3:2.Mullite sol was used to soak the caobon fiber reinforced carbon aerogels composite materials for preparing the antioxidant coatings,which can reach a certain antioxidant effect.