Supercritical drying of porous materials
     Generally, the porous material include: aerogels, xerogels, frozen gel, polymer foam, prefabricated ceramic, porous glass and bio foam. As a family, a porous material --- airgel (especially SiOz airgel) is a new lightweight three-dimensional disordered porous amorphous solid material level, with a continuous network structure, and its unique open holes network skeleton structure and composition are nanometer particle diameter (1-100nm). Up to 99.8% porosity, high surface area of ​​1400 m2 / g, the density can be controlled at 3-500 kg per square meter. It has a low refractive index (about 1.02), a small Young's modulus, low dielectric constant (about 1.1), low thermal conductivity [about 0.012W / (m · K)], the low sound propagation velocity (approximately l00m / s) and strong gas adsorption capacity of a special nature. These special properties of nanoscale almost from its porous structure. Aerogels have been used Qielun Markov detectors, acoustic impedance pot composite materials, catalysts or catalyst carriers, adsorbents, filter materials, high-temperature insulation materials and preparation, etc. Efficient charging him.
Aerogels are usually prepared by the sol - gel process and supercritical drying process composition, that is, first by the sol - gel process the wet gel, and then using microporous structure without changing its supercritical drying method to remove the wet gel holes in the liquid solvent. In a conventional evaporation drying process, causing the collapse of the gel structure of the porous network, the main factor damage capillary pressure (i.e. surface tension). Experimental results show that when the fluid reaches the critical temperature and critical pressure, the gas - liquid interface that line disappears, the surface tension is zero. Therefore, the use of supercritical drying in the drying process can be eliminated nanoporous materials capillary pressure generated within the pores, thereby maintaining the original material state nanoporous structure.

 

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