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Abstract  

Equilibrium adiabatic heat-capacity measurements have been made on zone refined samples of CeB6 and PrB6. Companion measurements made on LaB6, NdB6, and GdB6 have been reported elsewhere. These show cooperative lambda-type anomalies associated with antiferro-magnetic ordering. Except for lanthanum hexaboride, Schottky internal crystal field levels result in significant contributions to the thermodynamic functions. The gross thermodynamic properties at 298.15 K heat capacity (Cp/R), entropy increment (ΔT 0,m S 0/R), and Gibbs energy function are correlated with the nature of the lanthanide. For LaB6, CeB6, PrB6, NdB6, and GdB6 the three properties are, respectively: {11.654, 12.014, 11.997, 11.916, 11.695} Cp/R; {10.001, 11.803, 12.430, 12.558, 13.982} S0/R, and finally {4.379, 5.912, 6.232, 6.451, 7.905}Φ0 m/R.

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Summary  

This contribution deals with the calibration of a DSC apparatus between −100 and 0°C using compounds with well-known temperature and heat of transition. Only a few suitable substances are mentioned in literature. For that reason another compound, adamantane, is proposed with a solid-solid transition at −64.56°C and a heat of reaction being 24.78 J/g.

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Use of subambient DSC for liquid and semi solid dosage forms

Pharmaceutical product development and quality control

Journal of Thermal Analysis and Calorimetry
Authors: E. Schwarz and S. Pfeffer

Examples of the use of subambient DSC for characterizing excipients which have the melting range within ambient or subambient temperatures as well as liquid and semiliquid dosage forms are presented in the following paper.

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Journal of Thermal Analysis and Calorimetry
Authors: Jiří Kučerík, Petra Bursáková, Alena Průšová, Lucie Grebíková, and Gabriele Ellen Schaumann

Abstract

Qualitative and quantitative aspects of hydration of four humic acids (HA) and three fulvic acids (FA) originating from different sources were investigated. DSC experiments at subambient temperatures were carried out in order to monitor differences in ice behavior originating from freezable water surrounding humic molecules. It was found that kinetic effects play a significant role in hydration processes of both HA and FA. In fact, the hydration took part over 21 days which was detected as a progressive decrease in ice melting enthalpy. Simultaneously, the peak shapes and positions changed indicating structural changes in the physical structure of the humic substances. In case of FA, the dependency of melting enthalpy on water concentration showed a linear trend resembling a complete hydration previously observed for water-soluble hydrophilic polymers. In contrast, the melting enthalpy of some HA increased in a step-like way with increasing water content, suggesting preservation of original hydrophobic scaffold during the hydration. The differences between the rather young FA and the rather old HA lead to the conclusion that water can play a significant role in processes of humification. We assume that separation of hydrophobic and hydrophilic domains and thus increase in nanoscale heterogeneity represents an important physical contribution to the overall humification process. It was also demonstrated that the higher content of oxygen in humic molecules is not the only indicator of higher water holding capacity. Instead the porosity of humic matrix seems to contribute as additional parameter into these processes.

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7) operated using subambient temperature cooling with an Intracooler 2P so that heat-cool program response would be more precise. About 2–3 mg of polymer was accurately weighed using a Mettler UMX5 microbalance for each scan, sealed in 10 μL

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