Research On Specific Heat Of Undercooled Melt

Differential scanning calorimeter (DSC) combined with melt fluxing technique was used to realize undercooling of melt and its specific heat was measured at the same time, and its thermodynamics were calculated simultaneously and compared to four well-known models.Embedded in a flux of dehydrated B2O3, melts of Ge and Ag etc. were undercooled by repeatedly treatment of melting and solidifying with a DSC facility, with undercooling of 190 K and 146.9 K respectively for Ge and Ag. Influence of overheated temperature and cooling rates on the level of undercooling was analyzed respectively. At a given cooling rate, the degree of undercooling increases with increasing overheated temperature, and tends to be constant at last. It suggests that higher undercooling can be reached by increasing the overheated temperature in a stated range. At a given overheated temperature, the undercooling increases with cooling rates within the range of measurement.The specific heat of undercooled samples, such as Ge, Ag, etc. was measured. The specific heat on undercooled liquid state is linear with temperature, and it is the prolongation by extrapolating the curve of the specific heat on stable liquid to lower temperature. In the vicinity of the melting point, no uncontinuity is found.According to the measured specific heat difference between the undercooled liquid and the crystal state, as well as the measured melting enthalpy, thermodynamics of undercooled liquid in the process of solidification ,such as entropy difference and Gibbs free energy difference was calculated and compared to four well-known models. The result of analysis is that the calculated difference in Gibbs free energy has a good agreement with three models: Turnbull's, Singh and Holz's, Jones and Chadwick's. The calculated difference in entropy agrees well with the model of Singh and Holz.