Study On The Technology Of Silica Aerogels Preparated By Water Glass

Silica Aerogels is a kind of nano lightweight porous materials which has a very high specific surface area, low density, low thermal conductivity and low velocity characteristics. Such as in adsorption, catalysis, heat insulation, and other fields, Silica Aerogels has a broad application prospect. Researchers have used poly-silanes, TMOS, TEOS and water glass as silica source prepared Silica Aerogels, but TMOS is toxic, TEOS is expensive, in recent years, Silicon Aerogels was prepared from water glass. The wet-gel strength is low, Gel cracking and crushing often occur in the process of atmospheric pressure, difficult to obtain a low density, high specific surface area of aerogels, and the process is not stable, the preparation period is longer, and the preparation process produces a large number of organic waste liquid. It is difficult to meet the demand of industrial production in this way, and no market competitive power. Silica Aerogels often is produced in the sol-gel process with supercritical ethanol more drying to the preparation, but which uses alcohol as inflammable, explosive, supercritical drying medium and high operating temperature, which make its industrial application by certain restrictions, so the research on CO2 as supercritical drying medium preparation technology has very important practical significance. This paper is to study the stability of the preparation of Silica Aerogels process optimization, and explore the optimum parameter which Silica Aerogels was prepared from water glass via CO2 supercritical drying process, at the same time combined with a variety of analysis methods of Silica Aerogels microstructure, phase structure, specific surface area and pore size distribution, hydrophobic properties, structural properties such as thermal insulation performance was tested.Low-density Silica Aerogels was prepared from water glass. This paper chooses three types of maturing process to carry the comparative experiments, shows the influence of Silica Aerogels preparation, and uses absolute ethyl ethanol to help aging avoid the thick network skeleton; meanwhile, absolute ethyl ethanol’s “locking watereffect” can replace the water in the wet gel pores, reduces the capillary forces. The tap density of the prepared Silica Aerogels is 0.0798g/cm3. After the surface modification, increasing the 3d solvent exchange can further reduce the tap density to 0.073 g/cm3. Using the aging process 2 in this paper to magnify the experiment 25 times can exactly-once steadily prepare the Silica Aerogels with a tap density of 0.0739g/cm3. The adsorption experiment has been proved that experimental prove Silica Aerogels’ s adsorption capacity on oil is 30 times to its quality. Using the double glass model to the relations between Silica Aerogels’ s ρ and λ, finding that when ρ>0.15g/cm3, λ will decline sharply with the decrease of ρ; when ρ<0.15g/cm3, its impact on λ will drop.Prepare Silica Aerogels by ambient drying and CO2 supercritical drying, design of the single-factor authentication test obtained the influence of various factors, by setting the drying temperature, CO2 emission rate, drying time and drying pressure ranges, design three factors and three levels orthogonal experiment, discuss the optimum parameter of CO2 supercritical drying. Research shows that when supercritical CO2 emission rate of 100 to 150 bubbles / min, the specific surface area of the sample reaches the maximum, density reaches the minimum; When the drying process the drying temperature is higher, the specific surface area of the sample is increased, the density increases; When the pressure in the drying process reaches 10 MPa, the specific surface area of the sample reaches the maximum, density reaches the minimum; The drying time has a small effect on the specific surface area and density of the sample, but will longer the drying time, higher the energy consumption. Synthetically considering supercritical drying method, the optimum parameter is that supercritical CO2 emission rate is 100 to 150 bubbles/min, drying temperature is 50 degrees, drying pressure is 10 MPa, drying time is 6 hour.By comparing the process and product performance of ambient pressure drying and CO2 supercritical drying, ambient drying process simplifies the process, and easy to implement industrial production, its sample compared with CO2 supercritical drying that tap density, average pore diameter and surface area are less than products by ambient pressure drying, However, it has a larger thermal conductivity. The morphology shows that Silica Aerogels consists of plenty of nanoscale particles, the result shows that Silica Aerogels’ holes is large, and the pore distribution is homogeneous. Because ambient pressure drying has greater shrink than CO2 supercritical drying, thinning the hole. However, silica aerogels prepared by ambient pressure drying is better on CO2 supercritical drying.