| Traditional polymer-based thermal insulation building material has the disadvantages of moisture absorption and poor heat resistance because of the high porosity,which affects its performance greatly.As a novel amorphous state lightweight porous material,aerogel has good thermal insulating and heat resisting property,it is super-hydrophobic after surface modification,can be used as heat insulation material.However,the raw materials and processing requirements for the preparation of aerogel are more stringent,making it is expensive and difficult to widely be used in construction industry.Extending material scope of preparation and reducing the production cost are thus significant for application in the construction industry.Kaolin is used as raw material for preparing super hydrophobic insulation SiO2-Al2O3 aerogel in this thesis,by using sol-gel and atmospheric pressure drying process."two steps"and"one step"methods are proposed to prepare super hydrophobic insulation SiO2-Al2O3 aerogel.Furthermore,parameters of the preparation process and properties of aerogel are investigated.The main research work and conclusions of the research work are summarized as following.?1?The optimal technical process and parameters of preparing aerogel with kaolin is proposed based on experiments.The optimum reaction temperature,reaction time and the optimal mass ratio of kaolin to Na2CO3 sintering reaction is determined,and the technical steps of calcination,dissolution in acid solution,aging,solvent exchange,dispersion,surface modification and drying are established.The aerogel powder obtained in the experiments has uniform particle size,low density,large specific surface area,large pore volume and stability.The microstructure of the aerogel is analyzed.The results show that the kaolin is a proper low cost raw material for preparing SiO2-Al2O3 aerogel.?2?A two-step method for preparing SiO2-Al2O3 aerogel with kaolin as silica source and AlCl3·6H2O as alumina source is proposed.Factors including the concentration of HCl solution,proportioning of raw materials are investigated and optimized.?3?A one-step method for preparing SiO2-Al2O3 aerogel with kaolin as the raw material is proposed and experimentally validated.The one-step method can fully use the silica and alumina in kaolin,and can increase the raw material efficiency,simplify the production procedure and lower the cost of aerogel.?4?The thermal stability of SiO2-Al2O3 aerogel is investigated.The density,superhydrophobic property,thermal conductivity,volumetric stability is analyzed and studied.The results show that the structure and physical properties of the aerogel is greatly affected by the temperature.The density is reduced and thermal insulation capacities of the aerogel are enhanced if the aerogel is heated below 300oC,and aerogel keep super hydrophobic.So,by the 300oC heating,maintaining the property of super hydrophobic,the aerogel has the lowest density,thermal conductivity,thermal diffusivity and good volumetric stability. |
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