Hysteresis at the gas-liquid and liquid-solid phase transitions of capillary confined CO2: a positronium annihilation study

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Abstract
The hysteresis behaviour of capillary confined CO2 gas is studied through the positron/positronium annihilation technique. The arrangement of the confining medium (VYCOR glass) allowed simultaneous measurement of the bulk and pore confined phase behaviour. Isobaric temperature cycling showed marked hysteresis at the gas-liquid and liquid-solid phase boundaries for the confined gas. Observations at the gas-liquid transition are in agreement with capillary condensation theories and simple ideas are proposed to explain the liquid-solid transition behaviour.