Preparation And Properties Of Silica Nanoporous Thermal Insulating Materials

Silica nanoporous thermal insulating materials with large surface area, low volume density, high porosity and low thermal conductivity were widely used in metallurgical chemical, aerospace industries and other fields. In this paper silica nanoporous thermal insulating materials were prepared by dry pressing method using microsilica powder and fumed silica as raw materials respectively, and infrared opacifiers, glass fibers and alumina as additives. The phase, microstructure, thermal insulating performance, mechanical behavior and thermal stability were studied by field emission scanning electron microscope (FESEM), X-ray diffraction analysis (XRD), specific surface area and porosity analysis, fourier transform infrared analysis (FT-IR), cold-side temperature analysis and coefficient of thermal conductivity analysis. The results show that:(1) The changes of processing such as the amount of bonding agent, forming pressure, calcination temperature and the compositon can influence the volume density and porosity of silica porous ceramics. It is found that fumed silica is more suitable for preparing silica nanoporous thermal insulating materials.(2) The effects of infrared opacifier are related to its type, particle size and its addition. It can effectively reflect and scatter part of the infrared radiation and then decrease the coefficient of thermal conductivity significantly under high temperature. When infrared opacifier is added, the coefficient of thermal conductivity of the samples decreases from 0.172 W/(m.K) to 0.045 W/(m.K) under 800℃.(3) Glass fibers can effectively improve the compression strength and decrease volume shrinkage of the samples under 1000℃, while it can also increase volume shrinkage of the samples under 800℃and decrease the thermal insulating performance. Nanometer alumina can obviously improve the thermal stability and reduce the volume shrinkage of the samples under 1000℃temperature.