Abstract
The metal-oxide materials prepared in this study included nanoporous SiO2 aerogel (have multiple applications in thermal insulation systems) and nanopartilce Y2O3 (red-emitting nanophosphor Y2O3:Eu). High porosity, low density and low thermal conductivity hydrophobic SiO2 aerogel synthesis consist of a two-step synthesis, surface modification by esterification and supercritical drying with supercritical carbon dioxide. Wet gel is produced from waterglass under basic condition by adding water and NH4OH. Wet gel is extracted with liquid CO2 followed by supercritical drying. Silica aerogel densities of 0.1∼0.2 g/cm3 and porosities of 90∼95 % are produced. The silica aerogel is obtained with low solid thermal conductivity (less than 0.025 W/mK) in air and less than 0.010 W/mK upon evacuation to below 10-4 torr. It has 3 to 6 times better insulation properties (polyurethane=0.030 W/mK, glass fiber=0.042 W/mK, foam glass=0.060 W/mK). The nanophosphor Y2O3:Eu is synthesized by mixing two water-in-CO2 microemulsion with one containing Y3+ and Eu3+ ions and the other containing OH- ions in the water core. The nanoparticles are studied by X-ray diffraction, transmission electron microscopy and photoluminescence. Nanometer Y2O3:Eu phosphor can be synthesized by the process, and the size is in the range 10∼30 nm. Emission intensity of the phosphor obtained by the process is higher than that prepared by solid-state reaction method. It is fine enough for application without grinding or milling.
