Preparation And Properties Of SiO₂ Aerogel Monoliths Based On Tetraethoxysilane And Silica Sol

With its unique three-dimensional network structure,high porosity,high specific surface area and ultra-low thermal conductivity,silica aerogel has a broad application prospect in the field of building energy saving as a thermal insulation material.At present,the precursors for preparing SiO₂ aerogel include tetraethoxysilane?TEOS?,water glass?Na₂O·n SiO₂?,and silica sol?n SiO₂·H₂O?.However,the cost of preparing TEOS-based silica aerogel is relatively high,the preparation for water glass-based silica aerogel has a low energy efficiency and production efficiency,and silica sol-based silica aerogel has a higher density and higher thermal conductivity.In this paper,using TEOS and silica sol as precursors,the preparation and properties of SiO₂ aerogel monoliths were investigated.Using TEOS and silica sol as mixed silicon source,water and ethanol as solvents,hydrofluoric acid and ethylenediamine as acid and alkali catalysts,and ceramic fiber cotton as a reinforcement,a series of SiO₂ aerogel monoliths were obtained through sol-gel,aging,solvent replacement and modification of trimethylchlorosilane?TMCS?and ambient pressure drying.The effect of various factors such as the molar ratio of TEOS to SiO₂ in silica sol,the molar ratio of water to ethanol,the molar amount of total silicon source,the sol p H,and the molar ratio of TMCS to total silicon source,on the bulk density,thermal conductivity and the pore structure parameters of SiO₂ aerogel monoliths were discussed in detail.And the composition,microstructure,morphology and thermal stability of the obtained SiO₂ aerogel monoliths were characterized by XRD,FT-IR,SEM and TG,etc.In addition,three kinds of inorganic fiber substrates composited SiO₂ aerogel monoliths were prepared by impregnating ceramic fiber blanket,glass fiber felt,and glass fiber papers in the mixing SiO₂ sol with optimized ratio sol for aerogel preparation,and their thermal insulation and mechanical properties were preliminarily analyzed.The results showed that when the TEOS:SiO₂:H₂O:Et OH?mol?=1.25:0.75:30:10,the sol p H was 5,and the molar ratio of TMCS to total silicon source was 1.375,the obtained SiO₂aerogel monolith had the best performance.The obtained SiO₂ sol had a suitable gelation time?18 min?.The prepared SiO₂ aerogel monolith owned a strong hydrophobicity?contact angle of 139.7°to water?,amorphous phase structure and a complete crack-free appearance.It had a high specific surface area?574.7 m²/g?,low density?0.1423 g/cm³?and low thermal conductivity?0.0273 W/?m·K??,as well as a good thermal stability.In addition,three kinds of obtained inorganic fiber substrates composited SiO₂ aerogel monoliths had good integrity and excellent thermal insulation and mechanical performance.SiO₂ aerogel particles were well dispersed in glass fiber felt,ceramic fiber blanket and glass fiber paper.The thermal conductivities of prepared composite monoliths were 0.0346 W/?m·K?,0.0337 W/?m·K?and0.0359 W/?m·K?and their compressive strengths?50%strain?were 4.38 MPa,1.63 MPa and1.45 MPa,respectively.This paper provides a guidance for the preparation of low-cost,high-performance SiO₂ aerogel monolithic insulation materials.