Non-Contact AC Calorimetry on Undercooled Alloys

Abstract

A novel non-contact AC calorimetric technique based on inductive heating of a spherical metallic sample by a power-modulated radio frequency field under ultrahigh vacuum conditions has been developed. The sample’s external relaxation response (due to radiative heat loss) and internal relaxation response (due to finite thermal conductivity) can be measured pyrometrically, allowing calculation of both the sample’s heat capacity and thermal conductivity. The agreement between literature values (where available), predicted responses and measured data for (solid) Nb, Ni₆₀Nb₄₀, and Zr₇₆Ni₂₄ are excellent, demonstrating the feasibility and userfiilness of this technique. This method will be applied to Zr, Ni₆₀Nb₄₀, and Zr₇₆Ni₂₄ in the undercooled regime during the upcoming Second International Microgravity laboratory (IML-2) space shuttle flight in July, 1994. On Earth, the power required to overcome the force of gravity is so large that undercooling in UHV conditions is not possible with inductive levitation. In contrast, the microgravity enviroment of space allows decoupling of the inductive positioner and heater power requirements, thus enabling a sample to be processed in the deeply undercooled region. From the data taken during the mission, entropies and free energies will be calculated and compared to various theories of glass formation and metastability.