Thermal Conductivity and Heat Capacity of Adamantane and Hexamethylenetetramine Under Pressure

Abstract

We have used the transient hot-wire technique to measure simultaneously the thermal conductivity and the heat capacity per unit volume of solid adamantane and hexamethylenetetramine. Data were obtained over the temperature range 115 K. to 445 K, and at pressures up to 2.5 GPa. The thermal conductivity of plastic crystalline adamantane is much less temperature dependent than those of normal crystalline adamantane and hexamethylenetetramine. The volume dependence of the thermal conductivity of plastic crystalline adamantane is considerably smaller than those of the normal crystalline phases, and thus more similar to that of a liquid. The molar heat capacities for the different phases and substances were found to change very little with pressure. We discuss the temperature and volume dependences of the thermal properties in relation to available theoretical models.