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Abstract  

The temperature dependence of heat capacity of a natural zinc silicate, hemimorphite Zn4Si2O7(OH)2·H2O, over the temperature range 5–320 K has been investigated by the method of low-temperature adiabatic calorimetry. On the basis of the experimental data on heat capacity over the whole temperature interval, its thermodynamic functions C p(T), S(T) and H(T) − H(0) have been calculated. The existence of a phase transition in the area of 90–105 K determined on the basis of vibrational spectra has been confirmed, and changes of entropy ΔS tr. and enthalpy ΔH tr. of the phase transition have been calculated. Hemimorphite heat capacity has also been determined by the calculation methods according to the valence force field model in LADY program. The values of force constants of valence bonds and angles have been calculated by semi-empirical method PM5. The calculated IR and Raman spectra concordant with the experimental spectra have been obtained. The heat capacity values calculated according to the found vibrational states satisfactorily agree with those experimentally obtained with an accuracy of ±1.7% in the area of 120–200 K, and not more than ±0.8% for the interval of 200–300 K. This fact testifies that the calculation of thermodynamic characteristics is correct.

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Abstract  

Polyimide BTDA-ODA sample was prepared by polycondensation or step-growth polymerization method. Its low temperature heat capacities were measured by an adiabatic calorimeter in the temperature range between 80 and 400 K. No thermal anomaly was found in this temperature range. A DSC experiment was conducted in the temperature region from 373 to 673 K. There was not phase change or decomposition phenomena in this temperature range. However two glass transitions were found at 420.16 and 564.38 K. Corresponding heat capacity increments were 0.068 and 0.824 J g–1 K–1, respectively. To study the decomposition characteristics of BTDA-ODA, a TG experiment was carried out and it was found that this polyimide started to decompose at ca 673 K.

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Journal of Thermal Analysis and Calorimetry
Authors: Ljubiša Balanović, Dragana Živković, Aleksandra Mitovski, Dragan Manasijević, and Živan Živković

10973-010-0785-x . 29. Bissengaliyeva , MR , Bekturganov , NS , Gogol , DB . Researches by the method of low-temperature adiabatic calorimetry and quantum chemical computation of

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Journal of Thermal Analysis and Calorimetry
Authors: Igor E. Paukov, Yulia A. Kovalevskaya, Alexei E. Arzamastcev, Natalia A. Pankrushina, and Elena V. Boldyreva

characteristics of a natural zinc silicate hemimorphite researches by the method of low-temperature adiabatic calorimetry and quantum chemical computation of vibrational states . J Therm Anal Calorim . 2010 ; 101 : 49 – 58 . 10.1007/s10973

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