HYSTERESIS AT THE GAS-LIQUID AND LIQUID-SOLID PHASE-TRANSITIONS OF CAPILLARY CONFINED CO2 - A POSITRONIUM ANNIHILATION STUDY

The hysteresis behaviour of capillary confined CO2 gas is studied thro ugh the positron/positronium annihilation technique. The arrangement o f the confining medium (VYCOR glass) allowed simultaneous measurement of the bulk and pore confined phase behaviour. Isobaric temperature cy cling showed marked hysteresis at the gas-liquid and liquid-solid phas e boundaries for the confined gas. Observations at the gas-liquid tran sition are in agreement with capillary condensation theories and simpl e ideas are proposed to explain the liquid-solid transition behaviour.