Supercritical CO2 [WORDS ON SCREEN] - On the density of carbon dioxide. This video is part of an exhibition about CCS (Carbon Capture and Storage) at ETH Zurich. Introduction to the behavior of CO2. This video visualizes the densities of liquid, gaseous and supercritical CO2. Below the critical point, in the two phase region, on the isotherm of 28 degrees celsius, the liquid and gas phase coexist. Above the critical point, the supercritical phase occurs. The experiment follows a vertical line through the critical point between the orange and the green dot. At the initial condition the liquid and vapor phase coexist. To visualize the density of the different states of CO2, two floaters with different densities are placed into the view cell. Both floaters swim on the liquid phase, due to their lower density. To reach the supercritical state, the view cell is heated up. The two phases slowly merge to form the supercritical phase. The supercritical phase of CO2 has a density between the liquid and vapor phase... therefore, the lighter green floater swims on the supercritical phase, while the heavier red floater sinks to the bottom. When cooling down the CO2 to the initial condition... the supercritical phase will immediately separate into the two phases, liquid and gaseous CO2, when the critical point is reached. During the separation, some of the newly formed liquid droplets have a size similar to the wavelength of light, therefore, the CO2 appears opaque. This effect is called the critical opalescence.