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Pulsed bed calorimetry

A jump in speed and sensitivity

Journal of Thermal Analysis and Calorimetry
Authors: S. Walter, A. Hadj Mebarek, and S. Diyani

Abstract  

Conventional calorimetry has always the difficulty of choosing between near to equilibrium working conditions and high thermal ramp rates. Thus, either the transport phenomena and sample homogeneities are good but the signals become weak due to thermal losses, or the signals are sharp, but strong gradients across the sample lead to chemical and thermal heterogeneities. The described pulsed fluidized bed technique, by strongly stirring the sample, allows good sample homogeneities even at high ramp rates. Moreover, the permanently regenerated cover gas allows as well a good heat transfer towards the thermocouples as a constant atmosphere composition leading to very precise onset temperatures.

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Abstract

Pure alkali metal preparation is a complex problem: in most available commercial samples, all of them are simultaneously present. Conventional separation techniques are not always effective enough to reach parts per million total impurity levels. However, near the melting point, superficial segregation occurs. A zone melting derived technique coupled with a specifically developed solvent extraction process allows the total impurity content of sodium to be lowered below a few parts per million. The described thermal process, although using chemical reactions, is purely physically steered: it purifies as well potassium containing sodium as sodium containing potassium. 4 alkali metals are considered: Li, Na; K, and Cs.

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Water assisted thermal segregation

A new way for high purity material preparation

Journal of Thermal Analysis and Calorimetry
Authors: S. Diyani, S. Walter, and A. Hadj Mebarek

Abstract

Solid state purification generally requires efficient diffusion mechanisms in order to allow impurity migration towards the sample surface, from which it can be removed by a suitable mean. Since solid state diffusion just becomes efficient near the melting point, generally high working temperatures are required, resulting in expensive, energy consuming processes. The addition of small amounts of a common liquid solvent of both matrix and impurity results, even at low temperatures, in effective diffusion mechanisms the thermodynamical aspects of which are discussed in this work. Thermal cycling enhances the efficiency of the described process. Its concerns industrial and analytical applications.

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