Calorimetric study of calcium nitrate tetrahydrate and magnesium nitrate hexahydrate

• Published in: Journal of thermal analysis and calorimetry 2016-04, Vol.124 (1), p.539-546
• Main Authors: Sádovská, Galina, Honcová, Pavla, Pilař, Radim, Oravová, Lucie, Honc, Daniel
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Calcium nitrate; Chemistry; Chemistry and Materials Science; Enthalpy; Heating; Inorganic Chemistry; Magnesium; Mathematical models; Measurement Science and Instrumentation; Melting; Nitrates; Phase transformations; Physical Chemistry; Polymer Sciences
• ISSN: 1388-6150; 1588-2926; 1572-8943
• DOI: 10.1007/s10973-015-5159-y

The heat capacity and enthalpy of fusion of calcium nitrate tetrahydrate and magnesium nitrate hexahydrate were determined from 234.15 K to melting temperature by DSC. The modified stepwise method was used for heat capacity measurement, and enthalpy of fusion was determined from continuous heating by the rate of 10 K min −1 (Pilař et al. in J Therm Anal Calorim 118:485–491, 2014 ). Determined values were used for the calculation of entropy and Gibbs energy in the experimental temperature range. Melting point and enthalpy of fusion of calcium nitrate tetrahydrate are 317.1 ± 0.3 K and 36.6 ± 0.2 kJ mol −1 , and for the magnesium nitrate hexahydrate, the values are 362.9 ± 0.4 K and 40.8 ± 0.5 kJ mol −1 . One solid–solid phase transformation was observed for the magnesium salt at 345.7 ± 0.9 K with enthalpy of transition 3.1 ± 0.2 kJ mol −1 . The available accumulated energy composed of sensible (heating) and latent heat (phase transformations) is 43.4 and 63.8 kJ mol −1 for the hydrated calcium and magnesium nitrate, respectively. The kinetics of solid–solid phase transformation for magnesium salt was studied under non-isothermal conditions by DSC, and the process was described using autocatalytical model with parameters in the range of 0.50–0.85 for m and range of 2.58–1.48 for n , respectively.