Supercritical drying (red arrow) goes beyond the critical point of the working fluid in order to avoid the direct liquid-gas transition seen in ordinary drying (green arrow).

Supercritical drying is a process to remove liquid in a precisely controlled way, similar to freeze drying. It is useful in the production of MEMS and the drying of spices, and is commonly used in the production of aerogel. Image File history File links Drying. ... Image File history File links Drying. ... In chemistry and condensed matter physics, a critical point specifies the conditions (temperature, pressure) at which the liquid state of the matter ceases to exist. ... Freeze drying (also known as Lyophilization) is a dehydration process typically used to preserve a perishable material, or to make the material more convenient for transport. ... Micro Electro-Mechanical Systems (MEMS) is the technology of the very small, and merges at the nanoscale into Nano Electro-Mechanical Systems (NEMS) and Nanotechnology. ... Screen shot of Spice OPUS, a fork of Berkeley SPICE SPICE (Simulation Program with Integrated Circuits Emphasis) is a general purpose analog circuit simulator. ... A 2. ...

As a substance crosses the boundary from liquid to gas (see phase diagram), the size of the liquid decreases. As this happens, surface tension at the solid-liquid interface pulls against any structures that the liquid is attached to. Delicate structures, like cell walls, the dendrites in silica gel, and the tiny machinery of MEMS devices, tend to be broken apart by this surface tension as the interface moves by. A liquid will assume the shape of its container. ... A gas is one of the phases of matter. ... In physics, surface tension is an effect within the surface layer of a liquid that causes the layer to behave as an elastic sheet. ... A cell wall is a more or less solid layer surrounding a cell. ... Some examples of silica gel sachets Silica gel is a granular, porous form of silica made synthetically from sodium silicate. ...

To avoid this, the sample should be brought from the liquid phase to the gas phase without crossing the liquid-gas boundary on the phase diagram; in freeze-drying, this means going around to the left (low temperature, low pressure). However, some structures are disrupted even by the solid-liquid boundary. Supercritical drying, on the other hand, goes around the line to the right, on the high-temperature, high-pressure side. This route from liquid to gas does not cross any phase boundary, instead passing through the supercritical region, where the distinction between gas and liquid ceases to apply. In chemistry and condensed matter physics, a critical point specifies the conditions (temperature, pressure) at which the liquid state of the matter ceases to exist. ...

Fluids suitable for supercritical drying include carbon dioxide (critical point 31.1 degrees Celsius 1072 psi) and freon (25 to 30 C, 500-600 psi) . Nitrous oxide has similar physical behavior to carbon dioxide, but is a powerful oxidizer in its supercritical state. Supercritical water is also a powerful oxidizer, partly because its critical point occurs at such a high temperature (374 C) and pressure (3212 psi)[1]. Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. ... The degree Celsius (°C or ℃ (Unicode 0x2103)) is a unit of temperature named after the Swedish astronomer Anders Celsius (1701–1744), who first proposed a similar system in 1742. ... Pounds-force per square inch (lbf/in²) is a non-SI unit of pressure. ... Freon is a trade name for a group of chlorofluorocarbons used primarily as a refrigerant. ... Nitrous oxide, also known as dinitrogen oxide or dinitrogen monoxide, is a chemical compound with chemical formula N2O. Under room conditions it is a colourless non-flammable gas, with a pleasant, slightly sweet odor. ... Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ... Water (from the Old English word wæter; c. ...

Phase diagram showing the supercritical region (yellow) of carbon dioxide.

In most such processes, acetone is first used to wash away all water, exploiting the complete miscibility of these two fluids. The acetone is then washed away with high pressure carbon dioxide, the industry standard now that freon is unavailable. Again, acetone and liquid carbon dioxide are completely miscible. The carbon dioxide is then heated until its pressure goes beyond the critical point, at which time the pressure can be gradually released, allowing the gas to escape and leaving a dried product. Image File history File links Download high resolution version (4919x3519, 434 KB)Graph of phase change temperatures and pressures of carbon dioxide. ... Image File history File links Download high resolution version (4919x3519, 434 KB)Graph of phase change temperatures and pressures of carbon dioxide. ... In physical chemistry and materials science, a phase diagram is a type of graph used to show the equilibrium conditions between the thermodynamically-distinct phases. ... Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. ... For an alternate use of acetone, see Acetone (music). ... Miscibility is the ability of two or more substances to mix, and form a single homogeneous phase. ...