Study On Hydrothermal Synthesis Of Boehmite Nanorods And The Fabiration And Properties Of Boehmite Nanorods Aerogels

Thermal insulation material is a kind of functional one with low density,low thermal conductivity and certain heat resistance ability,and can prevent heat flow transfer.Traditionally,fibrous thermal insulation material is comprised of micronsized fibers overlapped with each other and presents lots of micron-sized pores among fibers.Due to the entanglement and overlapping among fibers,fibrous thermal insulating material usually possesses good mechanical properties and can be used in a wide temperature range.If the scale of the fiber is reduced from micronsized to nano-sized,it will further increase the complexity of the solid phase heat transfer pathway among the fibers,reduce the pore size and decrease the gas phase heat transfer,which is beneficial to increase its thermal insulation property.In this paper,the one-dimensional boehmite nanorods were prepared by the hydrothermal methods.Based on them,boehmite nanorods aerogels were constructed via entangling and overlapping among the nanorods,which changed and improved the traditional structures of particle-packing aerogels.To some extent,it breaks through traditional structures formation of aerogels and is provided with theoretical and experimental significances.In the experiments,aluminum tri-sec-butoxide(ASB)was chosen as alumina precursor.Boehmite nanorods were fabricated via sol-gel process and hydrothermal method.In order to understand the influences for boehmite nanorods during the course of preparation,some of pivotal parameters,such as hydrothermal temperature,time,the contents of acetic acid and alcohol and the stirring conditions,were discussed,and the growing regularity of nanorods in one-dimensional direction was explored.The results show that the hydrothermal temperature and the contents of acetic acid play an important part in the promotion of the one-dimensional growth for nanorods.However,the hydrothermal time and the contents of alcohol have little effects for the growth of nanorods.After the analysis of dissipative particle dynamics(DPD),one-dimensional growth of beohmite nanorods tends to increase with the increase of stirring rate in the influences of mutual repulsion between solvent and sol particles and shear action.Based on the two kinds of boehmite nanorods,boehmite nanorods aerogels with the different micromorphologies were synthesized via sol-gel process and freeze drying technology under the help of chitosan.Their microstructues and properties of were characterized and analyzed.The results show that the soft and long nanorods were stuck onto chitosan skeletons,whereas the rigid and short ones stacked each other.The crystalline structure of boehmite does not change after composed chitosan into aerogels and the crystal of chitosan can be prevented.Owing to the constructional difference of nanorods,the aerogels have different porous structures.The sample of CHI-160 has higher specific surface area and lower pore diameter compared with CHI-200.However,CHI-200 has better thermal stability.With the content increase of chitosan,the compressive property of compose aerogels increases and the thermal conductivity reduces.Compared with CHI-200,CHI-160 shows higher compressive strength and modulus,and lower thermal conductivity.