Preparation of silica Aerogel
S. Kistler named Aerogel. S. Kistler was the first to name Aerogel. silica aerogel He defined aerogel by supercritical method as the material that is obtained by supercritically dry wet gel. Aerogels were defined in the mid-to late 1990s with the advent and development of atmospheric dry technology. The aerogel structure is a cylindrical Nano porous network with a three-position network. This structure has high permeability, extreme porosity and low density. The bulk density of aerogel is adjustable between 0.003-0.500g/cm-3. (The density is 0.00129g/cm-3).
In most cases, the preparation of aerogel involves a sol gel process and a process of supercritical drying. Sol-gel is a process that involves controlling the conditions of hydrolysis and polycondensation in the solution. This allows for nanoclusters to be formed and then adhere to one another to form gel. To prevent damage to material structures caused by surface tension within the micropores, the gel is treated with the supercritical process. It is then placed in a vessel under pressure and heated to increase temperature, causing the liquid to phase change to supercritical fluid. Surface tension is no longer present. The supercritical liquid is then released from the pressure vessel to produce a low-density porous gas with a continuous nano-scale network structure. Material gel.
As a thermal insulation material
The nano-network structure in silicon aerogel is so thin that it effectively limits local thermal excitation. In addition, its thermal conductivity at solid state is 2 to 3 orders of magnitude less than glassy materials. Nano-pores prevent gas molecules from contributing to heat conduction. The silicone aerogel’s refractive indices is very close to one, and its annihilation factor for both infrared and visual light is greater than 100. It transmits sunlight well and blocks infrared radiation, making it a great transparent thermal insulation. It is used in the solar energy usage and energy-saving of buildings. The radiant heat conduction in silicon aerogel is further reduced by doping. At room temperature and under pressure, the thermal conductivity for carbon-doped aerospace gel can be as low a 0.013 w/m K. This is the solid with the lowest conductivity. As a replacement for polyurethane, it is expected that this material will be used to insulate refrigerators. Silicon aerogel, when combined with titanium dioxide, can become a new high-temperature thermal insulating material. The thermal conductivity of the material at 800K only is 0.03w/mK. This new material will be used for military applications.
The low sound speed of the sonic wave is one of its main characteristics. silicon aerogel The material is ideal for acoustic delay and high temperature sound insulation. It has a wide acoustic-impedance range (103 – 107 kg/m2 s) and is a good acoustic resistance material for ultrasonic detection. As an example, the most commonly used acoustic turns Zp = 1 is a good example. It is possible to use ultrasonic detectors or generators that are 5 x L07 kg/m2 * S, but the air’s acoustic resistant is only 400kg/m2 * S. A silicon aerogel coupling between air and piezoelectric materials is made of a thin layer of silicon aerogel of 1/4 wavelength. It can improve sound wave transmission efficiency and reduce signal-to noise ratio in device application. Experimental results indicate that using silica with a 300 kg/m3 density as a coupling medium can increase sound intensities by 30 dB. Silica aerogels with a gradient of density will increase sound intensity.
In the chemical and environmental industries. Aerogels with nanostructures can be used to filter gas in a different way. The material is unique in that it has a uniform distribution of pore sizes and high porosity. It is an efficient gas filter material. It is a material that is much larger than a table. Aerogels have a wide range of applications as new catalysts and catalyst carriers.
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