Abstract
Silica powders were obtained by decomposing tetraethoxysilane vapor thermally in an oxygen-containing gas at several stages of temperature between 400° and 1000°C, and mesurements of particle diameter, surface area, density, infrared spectrum, X-ray diffraction pattern and dispersibility in water, ethanol or n-hexane were carried out on them. The particle diameters, 0.07-1.9μm, of the silica powders decreased, and the BET surface area of them increased to 70m2/g at 733°C, with the rise of decomposing temperature. The powders obtained in the range from 544°C to 820°C exhibited densities of 2.18-2.07g/cm3. The surface areas estimated from the particle diameters and densities were about one third the BET surface areas. The internal hydroxyl group was contained in the powders obtained at temperatures below 650°C, and its concentration decreased with the rise of decomposing temperature. The powders were hydrophilic at decomposing temperature below 650°C, and the dispersibility of powders in water lowered with the rise of temperature above 650°C. The powders were amorphous. Silica was also obtained in a fibrous form, with diameters of 0.12-1.6μm, on the quartz plate surface on which a small amount of BaCl2, NiCl2 or SrCl2 was deposited from an aqueous solution.
