Preparation And Properties Of Co Precursor SiO₂ Aerogels And Composites At Ambient Pressure

Silica aerogels have been widely applied in various fields such as thermal insulation,adsorption,catalysis,acoustics,optics and electricity fileds due to low density,high porosity,high specific surface area,high transmittance and low thermal conductivity.However,silica aerogels were greatly hamper commercial applications because of the high manufacture costs and poor mechanical properties.Therefore,reducing production costs,improving mechanical properties and promoting the application of silica aerogels are of great research and economic significance.This paper mainly includes the following three parts:?1?Low-cost MTMS based silica aerogel was synthesized by sol-gel process based on atmospheric drying process by using water as the only solvent and MTMS as silicon precursor,and the production cycle was shortened to 2 days.The optimum synthesis parameters were as follows:precursor:water:CTAB:DMF=1:50:8.23×10^-5:0.5?molar ratio?,acid-base catalyst 1.0 ml and 0.5 ml respectively,and 20 vol%TMCS ethanol solution was used for hydrophobic modification.The Silica aerogels with low density(0.042 to 0.21 g?cm^-3),high porosity?88.78%to 97.77%?,broad specific surface area(135.4 to 553.6 m²?g^-1),high contact angle?139.51°?,has a maximum adsorption rate of 11 for organic liquids.?2?MTMS based Silica aerogels have the problems of smaller specific surface area and larger pore size distribution.Therefore,MTMS/TEOS co-precursor silica aerogels are synthesized combined with the advantages of MTMM and TEOS.The density of co-precursor Silica aerogels is 0.08018 to 0.3499 g?cm^-3,porosity is 95.80%to 81.60%,and the specific surface area is 123 to 913 m²?g^-1,the contact angle is 127°;when MTMS:TEOS=7:3,the aerogels can maintain a complete macroscopic appearance,excessive TEOS makes the aerogels more pact and broken into small pieces.The maximum adsorption rate is 12 when MTMS:TEOS=9:1,but the maximum adsorption rate is only 3.23 at MTMS:TEOS=6:4;the thermal stability is 280.34 to 331.31?,The specific surface area of MTMS:TEOS=7:3 samples increased from 241 to 322 m²?g^-1 after heat treatment at 600?for 1 h.At this time,silica aerogel from hydrophobic to hydrophilic because-CH₃ was oxidized.?3?Glass fiber reinforced co-precursor Silica aerogel composites were synthesized by using co-precursor aerogel as matrix and modified short glass fiber as reinforcement.The density of composite material is 0.0959 to 0.126 g?cm^-3,corresponding porosity is 85.60%to 80.68%.The addition of glass fiber reduces the most probable pore size from 91 to 85 nm,and the specific surface area is 331 to 353m²?g^-1;contact angle is 127°with good hydrophobicity,the adsorption ratio of organic liquid decreases with the increase of glass fiber content;the chemical bond formed between fiber improve the mechanical property of the composite,the maximum compressive strength is 23.15 kPa.