Atmospheric Preparation The Sio < Sub > 2 < / Sub > Aerogel Process And Its Performance Study

In this paper,Silica aerogels were prepared by two step (acid-base) sol-gel process using tetraethyl orthosilicate (TEOS) as precursor and ethanol (EtOH) as solvent,after post-treatment modification method or in-situ modification method respectively followed by ambient pressure drying and the preparation process of silica aerogels was continually optimized at the same time in order to overcome the disadvantage of supercritical drying method such as high energy consumption, expensive equipment, difficult to continually produce, in traditional preparation of silica aerogels.This paper made a systematic study of the effect of the factors(sol-gel process, surface modification as well as the ambient pressure drying) on the prepared silica aerogels. The silica aerogels was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform infrared spectroscopy (FT-IR),contact angle measurements, nitrogen adsorption/desorption tests, and differential-thermal gravimetric analysis (DSC-TG) to study the phase structure, morphology, surface groups, hydrophobicity, pore structure and thermal stability respectively.By orthogonal experiment and the control variable method,the experiments’ results showed as follows. Among the five orthogonal factors(ethanol consumption,water consumption,the reaction temperature, base consumption and surface modification agent),temperature has the greatest effect on the gelation time of silica aerogels prepared by by sol-gel method;surface hydrophobic modification has the greatest effect on silica aerogels’ density prepared by ambient pressure drying. Silica aerogels without hydrophobic modification had compact structure,bulky and uneven grain,smooth surface,density of0.542～0.814g/cm3,and almost lost nanoporous network structure of aerogels.At the same time hydrophobic modified silica aerogels had loose skeleton, relative uniformer and smaller grain (around20nm in size),density of0.099～0.427g/cm3. By continually optimizing the preparation process of silica aerogels,we found that excellent preparation condition is that material molar ratio of TEOS:of EtOH:H2O:NH3·H2O=1:(6-8):(5～6):(3～4.5)×10-3at room temperature (20～30℃) to conducat sol-gel reaction, hydrolysis pH at around3.5～4, using agent trimethylchlorosilane TMCS/TEOS molar ratio of1.8to2.4to conduct post-treatment modification through60℃,80℃,100℃,120℃,150℃classification warming dry.at atmospheric pressure.The Characterization of silica aerogels samples showed that:aerogels prepared by methyltrimethoxysilane (MTMS) in-situ modification had surface area of837.4m/g, average pore diameter of13.8nm,unit pore volume of2.83cm3/g.Aerogels prepared by the same amount of TMCS post-treatment modification in the same other conditions had surface area of973.4m2/g, average pore diameter of9.63nm,unit pore volume of2.96cm3/g. After heat treatment between300～700℃, the number of aerogels’ pore greatly reduced;the average pore diameter increased and maily concentrated between10～20nm;unit pore volume and specific surface areas reudced on the whole. From the thermal analysis,It was known that the hydrophobicity of the modified silica aerogels’can be retained in the air until they were heated at temperature of430℃～500℃,while in the nitrogen the maximum temperature is500～570℃.