The thermodynamic driving force for rapid crystallization of
liquid metals, i.e.the Gibbs free energy difference △G_(LS)
between undercooled liquid phase and product solid phase, is of essential importance for deepened investigations on rapid solidification such as the calculation of nucleation rate and the prediction of the formability of metastable phases as well as the feasibility of glass transition. An ultra-high-vacuum containerless processing technique by RF electromagnetic levitation melting was applied to undercoolliquid Fe and Ni by amounts up to 200 and 235 K. Specific heats of undercooled liquid Fe and Ni were measured by drop calorimetry and determined as. 48. 6 and 40. 5 J . mol￣(-1) . K￣(-1) respectively. On the basis of
Specific heat measurements, the △G_LS values of Fe and Ni were calculated according to its rigorous expression. Meanwhile, the theoretical models by Turnbull and Dubey-Ramachandrarao were also used to calculate the thermodynamic driving force approximately. It was found that Dubey-Ramachandrarao model usually showed smaller deviations but both models deviated significantly from the rigorous calculations provided that the undercooling exceeded 100 K. Since the deviation of approximated △G_(LS) value has a drastic influence on the calculation of nucleation rate in the undercooled
liquid metals, it is necessary to do rigorous calculations about the thermodynamic driving force for any quantitative research on rapid crystallization.