Research On Modified Preparation And Properties Of Silica Aerogels

Silica aerogels have excellent properties such as low density,high porosity,high specific surface area,low thermal conductivity,and low refractive index due to its unique threedimensional network structure.So that they have considerable research value and application prospects in aerospace,medicine,building materials,adsorption catalysis and other fields.However,pure silica aerogels often have defects of strong hygroscopicity and poor mechanical properties,which limits its large-scale use.According to the defects existing in the pure silica aerogels,based on improving the mechanical properties of silica aerogels,the surface modification and the enhancement of the skeleton structure of silica aerogels are carried out.On the base of optimizing the experimental modification method of silica aerogels,the effects of hydrophobic modification and polymer enhanced modification on the structure and performance of silica aerogels were studied,and silica aerogels with enhanced hydrophobic mechanical properties were prepared and dried at atmospheric pressure.The main research contents and corresponding conclusions of this article are as follows:(1)Taking commercial water glass with a modulus of 3.1 as the precursor,and after solgel reaction,trimethylchlorosilane(TMCS)is selected as the surface hydrophobic modifier,and the method of naming groups in MQ silicone resin is adopted.The concept of M/Q was introduced as a quantitative basis for the surface hydrophobic modification of silica aerogels.The amount of different TMCS corresponding to different M/Q values was calculated by calculation.Performance analysis of silica aerogels with different properties.It was found that different M/Q values influenced the structure and properties of the silica aerogels prepared.When M/Q is controlled at 3.5,the prepared hydrophobic silica aerogels had the best modification effect and the highest thermal stability.It exhibits a three-dimensional network structure at the microscopic level,and the pore volume,maximum diameter,and average pore diameter are the largest.This result can provide a reference for surface hydrophobic modifier TMCS added in the experiments in this paper.(2)Orthosilicic acid solution obtained from cation exchange resin of commercial water glass with a modulus of 3.1 and tetraethyl orthosilicate(TEOS)were used as composite silicon source,mixed at different ratios,and subjected to a sol-gel process and TMCS was selected for surface hydrophobic modification,and silica aerogels were prepared by atmospheric pressure drying,and the structure and performance of the samples were analyzed.The test results showed that when the volume ratio of TEOS to the solution of orthosilicic acid was 1:3 and 1:4,the samples were all able to form into blocks,with better thermal performance,increased microporous structure and significantly thickened silicon skeleton.Considering the principle of economy,the volume ratio between TEOS in the mixed silicon source and the solution of orthosilicate acid was 1:3 in the later experiment.(3)Use the orthosilicate solution obtained by commercial water glass with modulus 3.1 through cation exchange resin and ethyl orthosilicate(TEOS)as the composite silicon source,and the silane coupling agent KH-570 is used as a reinforcing phase and mixed with it to produce gel.The surface of the gel was modified by TMCS,and then KH-570 reinforced modified silica aerogels were obtained by drying under atmospheric pressure.The structure and properties of reinforced modified silica aerogels were studied by adding different amounts of KH-570.The related tests of the prepared silica aerogels found that the thermal stability of KH-570 reinforced modified silica aerogels was maintained at about 300 °C,and the total heat loss was about 25-34%.With the use of KH-570,the silicon skeleton of silica aerogels could be significantly thickened and enlarged.In addition,with the increase of the amount of KH-570,the large clusters in the grid structure of silica aerogels increased,the particle diameter inside the samples became larger,the connecting area between them increased,and the densification degree of the structure increased.When the addition amount of KH-570 was large,the silica aerogels presented a mesoporous structure.When the addition amount of KH-570 was small,the double-pore structure of the silica aerogels was preserved to a certain extent.The results showed that the addition of KH-570 could improve the mechanical properties of silica aerogels to some extent.(4)Blending the MQ silicone resin as a reinforcing phase with a solution of orthosilicic acid obtained from water glass with a modulus of 3.1 through a cation exchange resin and a solution of tetraethyl orthosilicate(TEOS)as the composite silicon source through a sol-gel process,using TMCS as a surface hydrophobic modifier,MQ silicone resin-reinforced silica aerogels were obtained by drying at atmospheric pressure.The effects of different amounts of MQ silicone resin on the structure and properties of reinforced modified silica aerogels were discussed.The relevant results showed that the addition of MQ silicone resin kept the thermal stability of the final samples at about 290 °C and the total heat loss was 9-16%.The addition of MQ silicone resin could increase the clusters between nano-SiO2 particles.The aerogel skeleton was enlarged and thickened,and at the same time,the pore structure of the silica aerogels was retained.Increasing the amount of MQ silicone resin would lead to an increase in the density of the samples and an increase in heat loss.The clusters between SiO2 particles in its nanoskeleton structure would increase,and the flaky and bulk structures would become more and more obvious.The wider "neck" ink bottle structure was transformed into a mesoporous structure with slits.