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A variant on this process involves the direct injection of supercritical carbon dioxide into the pressure vessel containing the aerogel. The result of either process exchanges the initial liquid from the gel with carbon dioxide, without allowing the gel structure to collapse or lose volume. [24]
Jets of liquid carbon dioxide. Liquid carbon dioxide is the liquid state of carbon dioxide (CO 2), which cannot occur under atmospheric pressure.It can only exist at a pressure above 5.1 atm (5.2 bar; 75 psi), under 31.1 °C (88.0 °F) (temperature of critical point) and above −56.6 °C (−69.9 °F) (temperature of triple point). [1]
Supercritical carbon dioxide is used in the production of silica, carbon and metal based aerogels. For example, silicon dioxide gel is formed and then exposed to s CO 2. When the CO 2 goes supercritical, all surface tension is removed, allowing the liquid to leave the aerogel and produce nanometer sized pores. [34]
An upturned vial of hair gel Silica gel. A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. [1] [2] Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady state, although the liquid phase may still diffuse through this system.
Carbon dioxide (CO 2) is usually pumped as a liquid, usually below 5 °C (41 °F) and a pressure of about 50 bar. The solvent is pumped as a liquid as it is then almost incompressible; if it were pumped as a supercritical fluid, much of the pump stroke would be "used up" in compressing the fluid, rather than pumping it.
When chilled by dry ice, liquid carbon dioxide or liquid nitrogen, the thermoplastics can be finely ground to powders suitable for electrostatic spraying and other powder processes. [1] Cryogenic grinding of plant and animal tissue is a technique used by microbiologists .
Glassy carbon is also an example of a non-graphitizing carbon material. The precursors for graphitizing carbons pass through a fluid stage during pyrolysis (carbonization). This fluidity facilitates the molecular mobility of the aromatic molecules, resulting in intermolecular dehydrogenative polymerization reactions to create aromatic, lamellar ...
Many gases can be put into a liquid state at normal atmospheric pressure by simple cooling; a few, such as carbon dioxide, require pressurization as well. Liquefaction is used for analyzing the fundamental properties of gas molecules (intermolecular forces), or for the storage of gases, for example: LPG , and in refrigeration and air conditioning .