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Low-temperature adiabatic calorimeter with an automatic data-acquisition system for the temperature range 10 to 310 K the molar heat capacity of NH3(CH2)3NH3MnCl4

1985; Elsevier BV; Volume: 17; Issue: 4 Linguagem: Inglês

10.1016/0021-9614(85)90135-1

1096-3626

K. Chhor, J.F. Bocquet, C. Pommier,

thermodynamics and calorimetric analyses

A calorimeter of the adiabatic type has been constructed for measurements of the heat capacity between 10 and 310 K. An on-line microcomputer combined with an automatic data acquisition system controlled the calorimeter heating rate and computed the temperature and the heat capacity. The system allowed unattended operation for 15 h. The calorimeter with sample cell of 7 cm3 internal volume, used two miniature germanium and platinum sensors in the temperature ranges 10 to 30 K and 30 to 310 K, respectively. The resistance was converted into temperature (IPTS-68) by calibration tables stored in the microcomputer. The performance of the calorimeter assembly was tested by measurements on the heat capacity of NBS benzoic acid. The deviations of the smoothed values from those previously reported are better than 0.5 per cent between 100 and 300 K, increase to 1 per cent at 40 K, and are about 5 per cent below 20 K. The heat capacity of NH3(CH2)3NH3MnCl4 has been measured from 10 to 310 K. As previously reported by other methods, a structural phase transition occurs at 307.61 K associated with a molar enthalpy change of (735±20) J·mol−1. In addition a magnetic transition was observed in the temperature range 45 to 65 K. Finally, d.t.a. results between 100 to 350 K are reported and compared with those previously claimed by other authors.