Preparation And Properties Research Of SiO₂ Aerogels And Their Composites

SiO2 aerogels are three dimensional continuous porous nano solid materials,which are widely used in catalysis,heat insulation,sound insulation and adsorption.However,due to its complex production process,high cost and low strength of material,it is not conducive to its industrial production and practical application.The purpose of this project is to explore a cheaper preparation method,simplify the preparation process of SiO2 aerogels,and improve the performance of the composites by using the composite materials,and expand its application in real life.The research includes the following three parts:(1)The preparation process of hydrophobic SiO2 aerogel with low cost and simple technological process was explored.A cheap solution of sodium silicate was used as a silicon source and hydrochloric acid as an acid catalyst.Only a mixture of n-hexane,isopropanol and silylated modifier(TMCS and HMDZ)was used to exchange the silane.Hydrophobic SiO2 aerogels were obtained by ambient pressure drying under normal tension.The density,functional groups,microstructure,specific surface area and hydrophobicity of the aerogels were tested.The results showed that the performance of the aerogels obtained from the precursor solution of 6wt%SiO2 concentration using three methyl silicane was the best,with a density of 0.0987g/cm3.The results show that the porosity is 95.51%,the specific surface area is 681.34m2/g,the pore volume is 3.37cm3/g,the average pore diameter is 12.42nm,and the water contact angle is 151.1°.(2)The preparation process of SiO2 polyester fiber aerogel felt doped with TiO2 has been explored.Polyester fiber was used to enhance the SiO2 polyester fiber aerogel felt and reduce the thermal conductivity of aerogel felt by adding different rutile TiO2 as infrared shading agent.The functional groups,specific surface area,microstructure and hydrophobicity of SiO2 polyester fiber were characterized by doping different TiO2 content.The influence of precursor solution doped with different TiO2 content on the thermal conductivity of manufactured goods was discussed.The results showed that when the TiO2 doped 4%TiO2 aerogel felt,the thermal insulation property of aerogel felt was the best,and the thermal conductivity was 0.0242W/(m·K)。(3)The preparation process of SiO2 composite aerogels with high mechanical strength was explored.The SiO2 aerogel particles falling from the fiber felt were common problems of traditional SiO2 aerogel felt,because the strength of the fiber reinforced was not guaranteed for a long time,and the application of SiO2 aerogels was limited.The combination of phenolic resin and SiO2 aerogel can greatly improve the mechanical strength of SiO2 aerogels,and the use of m cresol as raw material of phenolic resin makes the phenolic resin network hydrophobic,and improves the performance of composite aerogels after atmospheric drying.In this paper,sodium silicate solution was used as silicon source,and cresol and Formaldehyde Solution were added into the reactor to heat up the composite gel.After drying at atmospheric pressure,phenolic resin SiO2 composite aerogels were obtained.The influence of different SiO2 content on the thermal conductivity and mechanical strength of phenolic resin SiO2 composite aerogels was explored.The results showed that the increase of SiO2 content could improve the mechanical properties of phenolic composite SiO2 aerogels,and the compressive strength of SiO2 composite was 20% 0.28MPa.