CONSTRUCTION OF AN ADIABATIC CALORIMETER IN THE TEMPERATURE-RANGE BETWEEN 13 AND 505 K, AND THERMODYNAMIC STUDY OF 1-CHLOROADAMANTANE

An adiabatic calorimeter working in the temperature range between 13 a nd 505 K was constructed. The calorimeter was designed so as to minimi ze the temperature drift in each adiabatic shield and to achieve highl y stable temperature around the calorimeter cell. The imprecision in t he thermometry was found to be 10(-5) K. The imprecision in the heat c apacity measurement was found to be less than +/- 0.04%,and the inaccu racy to be less than +/- 0.4% between 13 and 50 K and less than +/- 0. 2% above 50 K, respectively. Heat capacities of 1-chloroadamantane wer e measured between 13 and 445 K with this calorimeter, and the standar d thermodynamic functions were evaluated. The temperature, enthalpy, a nd entropy of fusion were determined to be (439.7 +/- 0.1)K, (5.53 +/- 0.01) kJ mol(-1) and (12.6 +/- 0.1) J K-1 mol(-1), respectively. The temperature and enthalpy of crystalline phase transition were determin ed to be (248.6 +/- 0.1)K and (4.30 +/- 0.02) kJ mol(-1) respectively, and the corresponding entropy was (17.3 +/- 0.1) J K-1 mol(-1). The m agnitude of entropy is discussed in connection with the restricted dis order of molecular orientations in the plastically crystalline phase. Heat capacity anomaly of a kind of Schottky type was observed around 3 10 K in the plastically crystalline phase, and its potential molecular mechanism is considered. (C) 1998 Elsevier Science Ltd. All rights re served.