솔 - 젤법에 의한 석영유리의 제조 2 . 초임계 건조 및 소결 = Manufacture of Silica Glass by Sol - Gel Process 2 . Supercritical Drying and Sintering

다국어 초록 (Multilingual Abstract)

Aerogels were manufactured by supercritical drying of the wet gel which was made using 2-step sonogel process and silica glass was obtained by sintering of these aerogels. Effect of the microstructure of aerogels on process variables was investigated. Ethanol was chosen as a supercritical drying solvent, and the operating condition was set to 300℃ and 1500 psi. Sintering was performed with isothermal stages at 150℃, 300℃, 400℃, 600℃, 900℃ and 1100℃, and gaseous atmosphere was changed from nitrogen(<300℃) to oxygen(300-600℃) and helium(>600℃). It took about 8 hours in supercritical drying, and 17 hours in sintering. Supercritical drying with ethanol made the surface of aerogels hydrophobic, resulting in minimum adsorption of water on the surface. Since reduction of particles occurred due to high temperature during supercritical drying, optimum supercritical drying temperature must exist. Long isothermal stage at 150℃ eliminated bloating of sintered sample. The volume of aerogels reduced slowly up to 1070℃, but the pores were closed suddenly at 1100℃. Incomplete supercritical drying and low gelation pH produced crystals in sintering. The structure of wet gel had strong effect on the sintering conditions.