A substance can have three states (solid, liquid and air) in general but a substance can be a supercritical fluid when it reaches above its critical point (Tc, Pc). This has the characteristics of both air (high diffusion) and liquid (melting ability). These unique characteristics can be used in the pharmaceutical and food industry, as a substitute of organic solvents which have a high burden on the environment. Also in the semiconductor and MEMS field, it is useful for cleaning ultrafine products and for being a drying solvent. This environmental-friendly new technology is attracting many interests.

Characteristics of supercritical liquid

No surface tension

Compared with organic solvent, it has low surface tension and viscosity of carbon dioxide which enables it to spread and dry into ultrafine areas. In addition, there are no damages caused by drying because it can remove carbon dioxide without the presence of surfactant of air and liquid.

Viscosity of carbon dioxide

Surface tension of carbon dioxide

Melting and diffusion

Supercritical fluid has the characteristics of liquid (melting) and air (diffusion). Its physical property value reaches the middle point of liquid and air. Each molecule of carbon dioxide in particular has small interaction to one another, thus it can spread into superfine places and by increasing its density it can obtain more melting ability. For this reason, it had been applied as an extractant for a long time. In addition, it converts its melting ability significantly by controlling temperature and pressure which enables the extracted ingredients to be separated easily.

Physical property value of air, liquid and supercritical liquid
  Air Supercritical Fluid Liquid
Density [kg/m3] 0.6~1.0 200~900 1000
Viscosity [Pa・s] 10-5 10-5~10-4 10-4
Diffusion coefficient [m2/s] 10-5 10-7~10-8 <10-9

Environment friendly

Carbon dioxide is safe as it is not poisonous, toxic nor flammable. The carbon dioxide used is the same as those that occur at thermal power stations, as they are gathered and refined. This technology can lead to immobilizing discharged carbon dioxide.

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