Isenthalpic Solidification and the Specific Heat of Supercooled Liquid Phosphorus

Abstract

Isenthalpic solidification of a unary (one‐component) supercooled liquid results in either two‐phase invariant equilibrium or in single‐phase univariant equilibrium, depending on the degree of supercooling prior to solidification. When postsolidification univariant equilibrium obtains, a determination of the specific heat at constant pressure, C_p^l, of the supercooled phase relative to the stable, solid phase can be made by measuring the adiabatic temperature rise during recalescence. Values of C_p^l for highly supercooled phosphorus over the temperature range −1° to +18°C have been determined with this method. No evidence for the changes in molecular association deduced from earlier viscosity data on supercooled phosphorus was found in the temperature variation of the specific‐heat function. The enthalpy and specific‐heat values determined for supercooled liquid phosphorus agree with published values for the stable liquid above the normal melting point, T_e=44°C.