| Zr O2 aerogels have the unique properties. As its nanoscale-controlled structure,high specific surface areas, low density, high porosity and low coefficient of thermal conductivity characteristics, Zr O2 aerogels are widely used in many fields,especially in the field of heat insulation which has great potential application in the future. At present, to get complete blocks of aerogel materials are limited of the preparation method of the supercritical drying technology and the second phase of doping, because of the Zr O2 aerogel’s own friability, poor heat resistance. There are the problems of the high cost in the process of raw materials, the complex operation of the preparation of Zr O2 aerogels, the difficult shaping. It’s the right time to solve these problems for us.In this paper, we used Zr O(NO)3·2H2O as the raw material, FA as the agent to control the ambient drying, TEOS as the surface modification agent, based on the acid-base two-step catalytic method combined with atmospheric drying process compounded the Zr O2 aerogel powders with good microstructures. The we apply the Gel-casting method combined freeze-drying process to completed the preparation of Zr O2 porous materials with good shaping. In this study, we used SEM, XRD, FT-IR,DTA, TG and Nitrogen adsorption stripping to test the of Zr O2 aerogels composition,structure and thermal stability.The different process conditions on the microstructure of Zr O2 aerogels were studied and obtained the optimize parameters: the hydrolysis-condensation reaction temperature is 60 ℃, the volume ratio of alcohol to water is 3:1, the concentration of zirconium salt is 5 wt%, the acid/alkali catalytic p H is at 2/6, the molar ratio of FA to Zr is 0.5:1, the volume of TEOS in the alcohol solution is 15 vol %, the aging and drying temperature is 45 ℃. Then the mechanism of the sol-gel process in the preparation of wet gel is explored.The zirconia aerogel possess uniform distribution of particle size and pore size,and is characteristic of high specific surface area of 400.58 m2/g, with the pore volume size of 0.8 ~ 0.9 cm3/g, the average pore diameter is 8 ~10 nm. we can come to a conclusion that the Zr O2 aerogel in this study is lightweight mesoporous materials, made up of nano-sized particles which form the three-dimensional network structure. After the heat treatment process, the size of particles increases with the rise of the temperature. After 600 ℃ of heat treatment, zirconia aerogel are founded that it is mainly composed of Zr-O-Zr and Zr-O-Si, And TEOS as the surface modification agent are proved to be formed into bonds, and helpful to reduce the contraction of aerogel structure on atmospheric drying. After heated to 900 ℃,Zr O2 aerogels is began with crystallization,and the sizes of particles are up to 5 μm.The Gel-casting method, a near net-shape forming technique, combined freeze-drying technology is applyed to the preparation of Zr O2 materials in this study. There are two kinds of pores of their microstructure, the one is the because of the sublimation and evacuation process, leaving the lager pores with the size of 100μm~500 μm. Another is because of the crosslinking aerogel particles by the sintering process accumulated to form the smaller pores, with the size of 10 nm~10μm. After the heat treatment of 1000℃, the apparent density of Zr O2 porous material with the content of aerogels of 20 wt% is 0.7824 cm3/g, the open porosity of porous material is 70.43 %. The apparent density of Zr O2 porous materials increase with the increase of contents and sintering temperatures; the open porosity decrease with the increase of the apparent density and sintering temperature. |
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