Hm. Fretwell et al., ANOMALOUS FREEZING AND MELTING BEHAVIOR OF CAPILLARY CONFINED CO2, Journal of radioanalytical and nuclear chemistry, 210(2), 1996, pp. 575-582
In this paper we present our recent positron annihilation study of the
liquid<->solid phase boundary for CO2 confined in nanometer pores of
VYCOR glass. We find that CO2 remains liquid in the pores far below th
e bulk freezing temperature and there is pronounced hysteresis between
freezing and melting compared to that seen at the gas-liquid boundary
in the pores. On freezing we see evidence of open space created in th
e pores. This leads to complex melting behaviour possibly involving th
e formation of gas-liquid interfaces. We see that frezing in the pores
is totally irreversible, so that any solid which forms (no matter how
small) remains stable up to the higher melting temperature. In contra
st melting is more reversible (possibly indicating nucleation centres
which permit immediate re-freezing). Finally, the pre-frozen state in
the pores is different to the post-melted state.