Principle of supercritical CO2 cleaning
Dry cleaning of medical devices by supercritical CO2

Like any pure body, CO₂ can be found in three different states of matter: the liquid, solid or gaseous state, depending on the thermodynamic parameters of pressure P, temperature T and volume V and quantity of matter n (mole). These parameters, known as variables of state, are not independent and are linked by an equation of state. A simple expression of this equation of state is the well-known perfect gas equation.

In figure 2 is given the phase diagram P = f (T ) of CO₂ . The lines represented on this diagram correspond, at a given pressure, to the melting, boiling and sublimation temperatures of CO₂ .