Preparation And Properties Of Sepiolite Nanofiber Enhanced Silica Aerogel

Silica aerogel is a solid nano-material with a three-dimensional network structure,which has the advantages of high porosity,low density,small pore size,and low thermal conductivity,making it have rich application value in many fields such as heat,optics,acoustics,and electronic equipment.However,due to the defects and poor continuity of the internal skeleton of silica aerogel,the mechanical strength of the material is low,brittle,and unstable,and irreversible structural collapse is easy to occur when subjected to small force,which limits the practical use of silica aerogel.To enhance the mechanical properties of aerogels,it is a better method to introduce fibers as reinforcing phases.In this thesis,high strength and low thermal conductivity fiber/silica aerogel composites were prepared by sol-gel method with sepiolite nanofibers as reinforcement,tetraethyl orthosilicate（TEOS）as silicon source precursor,and trimethylchlorosilane（TMCS）as the modifier.The effects of fibers on the mechanical properties of aerogel and the stability of the composites at high temperatures were studied.The main research results are as follows:（1）Purification and depolymerization of sepiolite fiber:The fiber size of sepiolite treated by pretreatment-acid treatment-freeze-thaw cycle has been stripped from micron to nanometer,and Mg2+in the structure has been successfully replaced by H+in acid,making its potential negative.Acid treatment changed the network structure of the fiber.Due to the shedding of magnesium,the magnesium-oxygen octahedron collapsed,and the upper and lower silicon-oxygen tetrahedrons were no longer restricted by it but peeled off into finer layers.（2）Preparation of sepiolite fiber/silica aerogel:Silica wet gel was prepared by sol-gel method,and pure silica aerogel and sepiolite/silica composite aerogel with different fiber content were prepared by atmospheric drying.With the increase of sepiolite fiber content,silica aerogels evolved from fragments,cracked solids,and non-cracked solids during drying.The effect of sepiolite fiber content on the structure and properties of aerogels was studied.（3）Main properties of sepiolite fiber/silica aerogel:In this thesis,the effects of Sepiolite Fiber as reinforcement on the mechanical properties,thermal insulation properties,and high-temperature characteristics of silica aerogel composites were further studied.It is found that the introduction of sepiolite fiber effectively enhances the mechanical properties of aerogels.Among them,the compressive strength of the composite aerogel with 25wt%SEP content is the largest,which is 1.2MPa.With the increase of the content of sepiolite fiber in aerogels,the thermal conductivity of aerogels first decreases and then increases,and the thermal conductivity ranges from 0.0140w/（m k）to 0.0228w/（m k）.The thermal conductivity of aerogel with 5wt%content is the lowest,which is 0.0128w/（m k）,far lower than that of air（0.0260w/（m k））.According to thermal analysis,the mass loss decreases with the increase in fiber content.At 1000℃,the Si O₂aerogel prepared with 25wt%sepiolite fiber has the best thermal stability and the least mass loss,only 7.29%.By testing the flame retardancy of the samples,SEP/Si O₂aerogels all showed excellent flame retardancy,in which the LOI value of SEP/Si O₂ aerogels was more than 80%and the UL-94 grade was V-0.SEP treated by 3MHCl hydrochloric acid and 20wt%oxalic acid was used as the reinforcing phase of Si O₂ aerogel.It is found that with the increase of fiber content,the mechanical properties of the composites are enhanced,the thermal stability is better,the thermal conductivity first decreases and then increases,and its high-temperature resistance and flame retardancy are enhanced.When the fiber content reaches 25wt%,SEP/Si O₂ composite aerogels show excellent mechanical properties,thermal stability,high-temperature resistance,and flame retardancy.The defects of pure Si O₂,such as brittleness,easy shrinkage,and cracking after drying,are solved,and the application temperature range of aerogel is expanded.