A small sample-size automated adiabatic calorimeter from 70 to 580 K

Abstract

An automatic adiabatic calorimeter for measuring heat capacities in the temperature range 70-580 K, equipped with a small sample cell of 7.4 cm3 in the internal volume has been developed. In order to obtain a good adiabatic condition of the calorimeter at high temperature, the calorimeter was surrounded in sequence by two adiabatic shields, three radiation shields and an auxiliary temperature-controlled sheath. The main body of the cell made of copper and the lid made of brass are silver-soldered and the cell is sealed with a copper screw cap. A sealing gasket made of Pb-Sn alloy is put between the cap and the lid to ensure a high vacuum sealing of the cell in the whole experimental temperature range. All the leads are insulated and fixed with W30-11 varnish, thus a good electric insulation is obtained at high temperature. All the experimental data, including those for energy and temperature are collected and automatically with a personal computer using a predetermined program. To verify the accuracy of the calorimeter, the heat capacities of α-Al2O3 of the calorimetric standard reference material is measured. The standard deviations of experimental heat capacity values from the smoothed values are within ± 0.28%, while the inaccuracy is within ±0.4% compared with those of the National Bureau of Standards over the entire working temperature range.