Preparation Of Silica Aerogel And Study On Its Heat Transfer Model

Silica dioxide aerogel is a porous material that constitutes a continuous three-dimensional network structure.This particular structure gives it unique properties such as ultra-high specific surface area,high porosity and very low thermal conductivity.With such unique structure and excellent properties,silica dioxide aerogel will have a good application prospect in many areas.Today,there are many problems in the industrial production of aerogels,such as high production costs,poor product stability,and insufficient mechanical properties of the finished product.Therefore,research on the optimal preparation method of silica dioxide aerogel and the analysis and verification of the heat conduction model of it are of great significance for the development of aerogel.The main contents of this paper are as follows:Silica dioxide aerogel samples were obtained by a series of processes such as sol-gel,aging,hydrophobic modification and CO2 supercritical drying with tetraethyl orthosilicate as the silicon source.A specific single factor experimental analysis was made on the gelling time during the experiment.The optimal molar ratio of Silica dioxide aerogel obtained by horizontal orthogonal experiment is:TEOS:EtOH:H2O:HCl:NH3·H2O=1:3:5:3×10-3:4.8×10-3,and a hydrophobic Silica dioxide aerogel with a porosity of up to 95.6%was obtained.To study the micro-structure,thermal conductivity,and thermal stability of silica dioxide aerogel,the optimal silica dioxide aerogel sample was scanned by scanning electron microscopy(SEM),and analyzed by specific surface area pore size analyzer(BET),thermal constant analyzer,TG thermogravimetric analyzer and Raman spectrometer.The results show that the aerogel sample prepared by this method has a complete skeleton,evenly distributed nanoparticles,uniform pore size and relatively developed pores,presenting a good three-dimensional network structure and strong thermal stability.According to the analysis,the aerogel sample has a specific surface area of 756.9 m2/g,a total pore volume of 1.5 1 cm 3/g,an average pore diameter of 16.22nm,a density of 96.8 kg/m2,and a thermal conductivity of 0.02W/(m·K).The gas phase thermal conductivity,solid phase thermal conductivity,radiation heat transfer coefficient and total thermal conductivity of the silica dioxide aerogel were analyzed by a rod-shaped cubic column structure model composed of small balls.A single factor experiment was conducted to study the effect of aging temperature on the thermal conductivity of silica dioxide aerogel,and the result shows that the thermal conductivity of aerogel increases slowly with the increase of aging temperature.The effects of specific surface area and density on the micro-structure of silica dioxide aerogel were analyzed by traditional heat conduction model and verified by experimental results.The gas phase thermal conductivity model was analyzed.The effects of specific surface area,density and ambient pressure on the gas phase thermal conductivity of silica dioxide aerogel were analyzed by gas phase thermal conductivity model.It was concluded and verified by experiment results that the gas-phase thermal conductivity of aerogel decreases with increasing specific surface area and density.And the gas-phase thermal conductivity of aerogel increases with the increase of pressure.When the ambient pressure P>106pa,the gas-phase thermal conductivity of the aerogel begins to approach that of the gas in free space.When the ambient pressure is P<104pa,the thermal conductivity of the gas phase approaches zero.