An On-line Automated Adiabatic Calorimeter in the 13–300 K. Heat Capacity of Cyclohexanol

Abstract

Abstract A computerized adiabatic calorimeter system operating in the temperature range 13–300 K is described. A digital voltmeter is used for energy measurement and the duration of energy input is determined by a program unit operated by 1 Hz pulse. Temperatures of the calorimeter are measured by a 25 Ω platinum resistance thermometer and an automated ac double bridge. The measured resistance is converted into temperature (IPTS-68) by a calibration table stored in a mini-computer. Criterion for the realization of thermal equilibration is that a temperature drift calculated from the latest six data becomes smaller than a preset value, usually 7×10−8 Ω s−1. The system is able to measure the heat capacity of solid and liquid in an intermittent heating mode and gives the computed results during measurement. Some examples of the test runs on cyclohexanol crystal are shown and the results are compared with those obtained by manual measurements by use of dc Müller bridge. A relaxational heat capacity anomaly observed in glassy crystalline state of cyclohexanol is discussed in correlation with a secondary relaxation observed by previous dielectric measurement.