CALORIMETRIC MEASUREMENTS ON SOME UNDERCOOLED METALS AND ALLOYS

Undercooling was achieved directly in the cell of a high temperature c alorimeter (Setaram HTDSC) for Ni, Fe, Cu, Pd and several alloys, usin g cooling rates between 1 and 15 K min(-1). The samples were immersed in alumina powder inside a standard alumina crucible under flowing hel ium. Ag, Au and Al were not undercooled significantly. The reproducibi lity of the measurements was within 1.5%. The heat of solidification o f Ni at an undercooling of Delta T = 220 K was -17.5 +/- 0.2 kJ mol(-1 ), which is the same absolute value of the heat of fusion at the equil ibrium melting point T-m. This implies that the specific heat of the u ndercooled liquid is very close to that of the crystalline solid in th is temperature range. Fe appears to display a similar behavior at Delt a T = 220 K. The difference between the heat of fusion at T-m and the heat of solidification at an average value of Delta T = 95 K is signif icant for a Pd77.5Cu6Si16.5 glass-forming alloy. From these data, we c alculated an average specific heat difference between the liquid and c rystal phases of 7 +/- 5 J mol(-1) K-1. The enthalpy data for Pd82Si18 comply with those of the ternary Pd-Cu-Si.