Reversibility of melting and crystallization of indium as a function of the heat conduction path

The melting and crystallization behavior of indium has been investigated by temperature-modulated, differential scanning calorimetry as a function of thermal resistance between the heater/sensor and the sample, and as a function of the modulation parameters using a heater-controlled, heat-flux calorimeter. The thermal resistance between the heater/sensor and the indium sample was varied by placing the indium above polymer layers of different thickness. This results in apparent shifts of the onset of melting to higher temperatures and a striking reduction of the apparent degree of reversibility of melting with increasing thermal resistance. The apparent degree of reversibility is judged by an integral analysis of the modulated and total heat-flow rate, not the reversing, complex heat capacity, which is ill suited for the description of the melting process. The modulation frequency and amplitude have larger effects on the total and reversing heat-flow rate if the thermal resistance is low. A change in thermal resistance can transform a known reversible process that is coupled with a large latent heat, to an apparently non-reversing one.