Figure 2

X-ray diffraction data collected during the cooling ramp from room temperature down to − 180 °C. (a) Clathrate and solid CO2 diffraction effects are detected below − 30 °C and − 100 °C, respectively. (b) Low-temperature phase diagram for the H2O–CO2 system redrawn after10; the experimental cooling ramp is shown by a red arrow. (c) Representative X-ray diffraction patterns collected at − 10 °C, − 60 °C and − 150 °C; the Rietveld refinement of the − 150 °C pattern yields 10 ± 3 wt% CO2(solid) and 1.7 ± 0.8 wt% clathrate (a 100 wt% closure is imposed on the sum of CO2(solid) + clathrate + graphite).