Figure 3

Schematic representation of X-ray diffraction microtomography of the experimental capsule (left) and the phase transitions observed in the H₂O–CO₂ fluid upon cooling (right). The inset shows the microtomogram collected at − 180 °C, i.e., when the fluid is converted into solid crystalline clathrate and CO_2(s): red, green and blue channels have been attributed to the characteristic peaks of solid CO₂, clathrate and graphite, respectively, and combined into an RGB image after background removal (left) or clustering (right); the estimated mass percentages of solid CO₂ and clathrate are reported.