A tetramethylorthosilicate(TMOS)/ethanol solution was gelled together with BaTiO 3 nanoparticles or carbon nanoparticles. The wet gel was dried in supercritical carbon dioxide, resulting in aerogel nanocomposites with compositions in the range of BaTiO 3 / SiO 2 = 1/100 to 20/100 and C/SiO 2 = 20/100 to 80/100. The bulk density of the aerogel obtained was in the range of 0.1 to 0.2 g/cm 3 , the porosity was about 95%, and the specific surface area was in the range of 400 to 700 m 2 /g. These values represent the characteristics of the aerogel. The relative permittivity and dielectric loss were respectively approximately 2 and 5 © 10 ¹3 for the BaTiO 3 -silica aerogel nanocomposite, and in the range of 5 to 10 and 0.012 to 0.4 for the carbon-silica aerogel nanocomposite.

The ferrite-silica aerogel nanocomposite prepared by a solgel process and a supercritical drying process was investigated from the point of view of new composite material. The ferrite nanoparticles were prepared by a coprecipitation method and added to tetramethylorthosilicate (TMOS) in the range of 0 to 20 mol %. The ferrite-silica wet gel was prepared from TMOS containing ferrite nanoparticles, ethanol, deionized water and NH 3 aq. as a catalyst, and replaced the liquid phase and aged in the ethanol. Then, a hydrophobing treatment was performed in hexamethyldisilazane toluene solution. Finally, the ferrite-silica wet gel was dried in the supercritical carbon dioxide fluid. The obtained ferrite-silica aerogel nanocomposite was evaluated by bulk density, porosity, specific surface area, pore size distribution, SEM and TEM observation, EDS analysis and magnetization measurement by VSM. As a result, even if it added the ferrite, the characteristics of aerogel was held and the magnetic property of the ferrite remained unchanged in the aerogel.

A Au nanoparticle-silica aerogel nanocomposite was prepared by the gelling of a tetramethyl orthosilicate (TMOS)/ethanol solution together with Au nanoparticles and drying the wet gel in supercritical carbon dioxide. The aerogel nanocomposite contained Au nanoparticles at a concentration of 0.268 ppm. The bulk density, porosity, and specific surface area of the obtained nanocomposite were 0.126 g/cm 3 , 94%, and 890 m 2 /g, respectively. The nanocomposite was reddish-violet in color and transparent, and had a relative permittivity of approximately 6 with a dielectric loss of ca. 1 × 10 −3 in the range of 10 MHz to 1 GHz.

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