Adiabatic heat capacity measurements were made on
triphenylphosphite, molecular formula
C18H15O3P, between
140 and 335 K. The results confirm the existence of a phase which
is intermediate in stability between the
undercooled liquid and the crystal phase. This phase, called the
glacial phase, was recently reported for the
first time. At 227 K this phase disappears as the crystallization
starts. The melting temperature was found
to be 297.7 ± 0.2 K, the melting enthalpy 25090 ± 100 J
mol-1. The glass transition temperature
was 201.8
K, the ratio between the heat capacity of the undercooled liquid and
the glass at this temperature being 1.68.
T
0, the temperature at which the entropy of
the undercooled liquid equals that of the crystalline phase
was
calculated to be 169 K. A discontinuity in the specific heat of
the liquid phase was found close to the
melting point. This is related to the existence of a narrowly
avoided thermodynamic transition point.
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