Preparation And Thermal Properties Research Of Aluminum Doped SiO₂ Aerogel

With the rapid development of economy,the traditional thermal insulation materials cannot meet the needs of human beings.As a kind of nano-porous material,aerogel has the characteristics of light weight,low thermal conductivity and high surface area.It has broad application prospects in the field of architecture,engineering,medicine and so on.However,the traditional raw material of aerogel is expensive,and the high energy consumption of the drying process limits the rapid development of aerogel.This paper,in order to reduce the preparation cost of aerogels,kaolin is used as raw material.By reacting with acid,the mixed solution of silicon and aluminum is obtained.The SiO₂ aerogels and Al doped SiO₂ aerogels are prepared by different ion impurity removal methods.XRD,TEM,BET,TG-DSC,FTIR and other techniques are used to characterize the microstructure and thermal properties of SiO₂ aerogels with the presence of aluminum.Finally,the aerogel coating with low thermal conductivity is prepared by mixing the self-made aerogel with the film forming agent.The thermal performance of the coating is characterized by measuring the time lag factor.The main conclusions are as follows:1)There is a large amount of silicon and aluminum in the kaolin.Kaolin can be reacted with hydrochloric acid to obtain a mixed solution of silicon and aluminum.The metal impurity ions are removed by cation exchange resin.The SiO₂ aerogel is obtained under the catalysis of ammonia.The structure and properties are investigated by XRD,TEM,and FTIR.The influence of the presence of sodium ions on the structure of aerogels is also investigated.2)1,2 propylene oxide is used to adjust the pH value of the solution slowly through the ring opening reaction and promote the co-gel of silicon aluminum.The influence of different factors on the sol to gel is also discussed.The gelation time can be controlled by adjusting the amount of the gel assistant and the amount of the drying control agent.3)The content of aluminum in the SiO₂ aerogel product is controlled by the dosage of 1,2-PO,setting of aging time,process of ion impurity removal and choice of modifier.The SiO₂ aerogel with high aluminum content can be obtained.4)The thermal properties of SiO₂ aerogels doped with alumina are investigated by calcination treatment.Aluminum can enter the Si-O-Si network skeleton,the presence of Al can inhibit the crystal transformation of amorphous SiO₂ under high temperature treatment.The higher the content of aluminum,the greater the density of aerogel,but the smaller the volume change rate.5)The volume of aluminum doped SiO₂ aerogel has the phenomenon of“spring back”during the calcination treatment.The thermal conductivity decreases with the increase of the volume.The thermal insulation property of aerogel can be improved.The content of aluminum is higher,the influence of heat treatment on the thermal properties of aerogels is greater.6)The coating with low thermal conductivity at room temperature is obtained by mixing self-made aerogel with different film forming additives.The time lag factor is used to characterize the thermal insulation property of the coating.The time delay factor is used to characterize the thermal insulation performance of the coating and good thermal insulation property of aerogel coating is obtained.