Vakuum očuvanje superkritično fluid has many special properties

When the temperature and pressure of the fluid are above its critical point, the interface between the gas and the liquid phase nestajes, and the properties of the system become uniform, and it is no longer divided into gas and liquid. The shaded region fluid above the critical temperature and critical pressure is called supercritical fluid (SCF for short). Viscosity, lower surface tension and higher diffusivity are similar to gases. Due to the special transfer properties and surface properties of supercritical fluids, it has a great effect in chemical separation processes such as extraction, crystallization, chromatography, drying, and certain chemical reaction processes. Broad application prospects.

Vakuum konzerviranje sol-gel metoda

Nanoparticles and preparation method thereof Nanoparticles generally refer to particles with a size of 1-100 nm. Due to the quantum effects, small size effects and surface effects of such particles, as well as electrical, thermal and catalytic properties that are quite different from ordinary particles, nanomaterials have been promoted and applied in many fields such as miniature biological devices, electronic functional materials, coatings and catalysts. application. At present, the methods for preparing nanoparticles include: mechanical grinding, hydrogen arc plasma, supersonic expansion, laser evaporation, sputtering, thermal decomposition, chemical vapor deposition, and sol-gel method. Among them, the sol-gel method has attracted the attention of the majority of chemists because of its simple method, mild conditions, and easy control of particle size. The sol-gel method was originally a technique for the preparation of glass and ceramic materials, and has been increasingly used in the preparation of nanoparticles in recent years. The homogeneous solution of precursors, reagents and catalysts is converted into polymers by hydrolysis and polymerization or condensation of hydrolyzed products, and then the organic components and solvents are removed by drying and roasting of the gel to obtain nanomaterials. The precursors of the sol-gel method are generally metal or non-metal alkoxy compounds or inorganic salts. The unitary or multi-component metal oxide ultrafine particles prepared by the sol-gel method have the advantages of uniform particle composition, high purity, small particle size and narrow distribution. Not only can be used to prepare nanoparticles, but also can be used to prepare three-dimensional infinite polymer solids and nanostructured solid aerogels. In the sol-gel method, the drying process of the gel is an important process. In the conventional drying process, the surface tension of the liquid causes the shrinkage of the gel to be very large, so that sometimes only large particles can be obtained. The supercritical drying technology developed in recent years can overcome this shortcoming.

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