Preparation And Properties Of Boehmite Fiber Doped Silica Aerogel

Silica aerogel is one of the solid nanomaterials filled with air in their structural pore.Its porosity is as high as 80⁹9.8%,the typical size of the pore structure is2¹00 nm,and the thermal conductivity is as low as 0.013⁰.03 W·m^-1·k^-1.It has a wide range application prospects in thermal,acoustic,optical and particle detection,especially in the field of thermal insulation.The preparation of silica aerogel often adopts supercritical drying method,which has high energy and resource consumption and has certain dangers.At present,researchers have begun to study the ambient pressure drying process,but the prepared aerogel is mostly in the form of fragments.Fiber doping is used to improve the mechanical strength of aerogel.The commonly used fibers are glass fiber and carbon fiber.These fiber has poor high temperature stability and larger fiber diameter damage the pore structure of aerogel.Silica aerogels are easily sintered at high temperatures and lose their thermal insulation properties.Therefore,it is necessary to develop a silica aerogel with high strength and complete bulk and high stability at high temperature.This paper explores the effect of the modification process in the ambient drying process on the preparation of intact bulk silica aerogel.It was found that the modification mode and modifier concentration affect the modification rate and modification degree of hydroxyl groups on the surface of aerogel,thus affecting the integrity of the obtained aerogel.The silica aerogel obtained was the best when directly modified and the modifier trimethylchlorosilane concentration was 10%?volume fraction?.In this paper,boehmite fiber was selected as the reinforcing phase to enhance the mechanical strength of silica aerogel.The length and diameter of the boehmite fiber are small;it is rich in hydroxyl groups and has good compatibility with the sol;it is converted into alumina fiber at high temperature,and the high temperature stability is good.The effect of doping content of boehmite fiber on the thermal conductivity and mechanical strength of aerogel was investigated.It is found that the diameter of the fiber is nanometer,which is consistent with the pore diameter of the aerogel.The doping has no significant effect on the aerogel structure and maintains its excellent thermal insulation performance.When the fiber doping content is 5 wt%,the aerogel thermal conductivity is 0.0198 W·m^-1·k^-1,which is lower than 0.026 W·m^-1·k^-1 of static air,the mechanical strength of the aerogel increases from 0.401 MPa to 1.496MPa,an increase of 2.73 times.Compared with pure silica aerogel,boehmite fiber doped silica composite aerogel has a broader application prospect in the field of thermal insulation.This paper further studied the effect of boehmite fiber doping on the high temperature properties of silica aerogel.It has been found that fiber doping effectively increases the aerogel use temperature.At 1000°C,the pure silica aerogel is sintered with a pore volume of only 0.96 cm³/g.The composite aerogel maintains a pore size structure with a pore volume of 2.67 cm³/g,which is higher than the pore volume?2.22 cm³/g?of a pure silica aerogel at 900°C.This is due to the fact that on the one hand the addition of fibers inhibits the sintering of the silica particles;on the other hand,the boehmite fibers have a certain supporting effect.