Research On The Property Of SiO₂ Aerogels Modified And Dried At Ambient Pressure

SiO₂ aerogels,as a kind of controllable nanoporous amorphous materials,has been widely used based on its excellent performance such as high specific surface and low thermal conductivity etc..But as a kind of nanomaterials,on the one hand,SiO₂ aerogel materials is easy to absorb moisture in the air due to the poor hydrophobicity and lend to shorter service life;on the other hand,SiO₂ aerogel materials is easy to damaged under the influence of external dorces due to the poor mechanical properties.In this experiment,TEOS and TMOS were as silica source.SiO₂ aerogels were prepared with one-step catalytic method,sol-gel method,atmospheric pressure modification and atmospheric pressure dried method successively used.The main idea of the experiment is modification mainly devided into two aspects:different concentration of trimethylchlorosilane and n-hexane mixed solution were used as modification to improve the hydrophobic properties of the gel firstly.Different concentration of N3300 and acetone mix solution were used as modification to improve the mechanical properties secondly.The resulting samples were analyzed in many aspects such as micromorphology,thermal stability,hydrophobicity,and pore structure characterization etc.and discussed the effect of two different concentrations of modification on the structure and properties of aerogels.As the hydrophobic silica aerogels,the main conclusions are as follows:firstly,different concentrations of hydrophobic modification had significant effect on the hydrophobic properties of the samples and as the concentration increases,the hydrophobic angle of the sample increases,The largest hydrophobic angle?147°?were gained with TMCS:n-hexane=1:4.Secondly,the four groups of hydrophobically modified samples had good thermal stability and maintain good hydrophobicity at room temperature up to 400°C.And the changed modification concentration had little effect on thermal stability.Thirdly,the gained samples were sponge-like nanomaterial with inner pore size between 10 and 50 nm,the thermal conductivity of the four samples was close to 0.043 W/?mk?and the specific surface area was about 650 m²/g.As the mechanical properties enhanced silica aerogels,the main conclusions are as follows:firstly,the modification had a significant effect on the samples and after drying the complete columnar block sample were abtained.Secondly,as the concentration of the modification increases,the thermal stability of the sample becomed worse and worse.The samples weight losed up to 50%at 1000°C with the N3300:acetone=1:20.Thirdly,The changed concentration of the modification had a significant influence on the physical properties of silica aerogels such as the density and porosity of the sample.With the proportion of the modification redued,the density reduced and the porosity increased.Fourthly,the gained samples were sponge-like nanomaterial with inner pore size between 0²0 nm.As the concentration of the cross-linking modification increased,the internal skeleton of the sample exhibited a state of aggregation.