| Zirconia aerogels will be the ideal and preferred materials system,because of its high melting point(～2900 ℃)and low room temperature thermal conductivity(2.4 W/(m·K)),and it could be superior to the traditional SiO2 aerogel(limit temperature 1000℃).However,the preparation method of zirconia aerogels needs to be further improved.At present,metal alkoxide are used as zirconium source precursor to prepare zirconia aerogels.But metal alkoxides are expensive,easily hydrolyzed and the hydrolysis reaction is difficult to control.Most researches used epoxy compounds as gel accelerator to prepare zirconia aerogels.But the epoxy compounds are epoxides toxic,flammable and explosive.In addition,the thermal stability of zirconia aerogel at high temperature(1000 ℃)needs further improvement.This research aims to solve the above problems.In this paper,firstly,a variety of organic acids such as malic acid,tartaric acid and mercaptosuccinic acid are used as the gel accelerators to prepare zirconia aerogels.The gel mechanism is researched and the stability at high temperature of the zirconia aerogels prepared by this method is studied in detail.Secondly,the supercritical drying deposition process is also studied.In the supercritical drying process,silica is deposited on the zirconia to improve its high temperature resistance,and its microstructure and thermal stability are also studied.The main research contents can be summarized as below:1.Organic acids such as malic acid,tartaric acid,mercaptosuccinic acid and other organic acids are used as gel accelerators to prepare zirconia aerogels,and the mechanism of organic acids as a gel accelerator to prepare zirconia aerogels is studied.This method overcomes the defects of the toxicity of epoxide in conventional sol gel method.The zirconia aerogels prepared with malic acid as a gel accelerator have a specific surface area of up to 339 m2·g-1.2.Silica-modified zirconia aerogels were prepared by supercritical drying deposition.An appropriate amount of tetraethoxysilane(TEOS)is added to the solvent of absolute ethanol in the supercritical drying process.The deposition of Silica on the zirconia aerogel particles can effectively prevent the growth of crystal grains and the occurrence of phase transformation,and significantly improve the high temperature resistance of the aerogels material.The specific surface area of silica-modified zirconia aerogels is as high as 551 m2·g-1,and the linear shrinkage of samples after heat treatment at 1000℃ is reduced by～22%. |
