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CRTA for the thermoanalytical screening of volatile compounds

1. Calibration of standard Q-derivatograph sample holders vs. vapor partial pressures during quasi-isobaric quasi-isothermal heating

Journal of Thermal Analysis and Calorimetry
Authors: V. Logvinenko, G. Gavrilova, I. Karpova, and P. Stabnikov

Abstract  

Quasi-equilibrium thermogravimetry (variant of CRTA) is utilized as a thermoanalytical screening method for volatile compounds, standard Q-derivatograph sample holders (platelike holder, open crucible, crucible with lid, and conical holder) were calibrated against the partial pressures of metal β-diketonate vapor (in sublimation and evaporation processes) in the range 0.0006–0.11 atm. The mathematical relationship between the vapor partial pressure, the holder construction, the vapor molecular mass, and the mutual diffusion coefficient of the gas was derived and considered. It is possible to obtain a roughp-T relationship for volatile compounds by using stabilized temperatures of sublimation (evaporation) processes in four pressure-calibrated sample holders.

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Abstract

The kinetic curves at infinite temperature for the solid-state reactions of the interface shrinkage type were drawn theoretically by taking account the particle size distribution in the sample mixture. The CRTA curves for the reactions with the particle size distribution can be drawn by utilizing the universal kinetic curves at infinite temperature. The proper kinetic treatment for the CRTA curves with the particle size distribution is discussed in connection with the property of the kinetic equation with respect to the particle size distribution. The present kinetic consideration is taken as a simulation for the reactions with a certain distribution in α among the reactant particles, produced preferably by the mass and heat transfer phenomena during the thermoanalytical measurements. The merit of the rate jump method by a single cyclic CRTA curve is also discussed on the basis of the present results.

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Abstract  

Thermodesorption is here considered for its possibility of giving access to the microporosity of adsorbents. The requirements of this application (good separation of successive desorption steps, good control of the desorption pressure and temperature throughout the sample, possibility of a safe kinetic analysis of each step) are here fulfilled by carrying out the thermodesorption in the Controlled transformation Rate Thermal Analysis (CRTA) mode. The method is applied to 4 zeolites (3A, 4A, 5A and 13X) and a well characterized charcoal, from −25 to 325°C, after pre-adsorption of water.

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Abstract  

Quasi-equilibrium thermogravimetry (variant of CRTA) is put to use as an express method of thermoanalytical screening for volatile compounds. During the experiments for PT relationship calculations (running with several calibrated standard sample holders) the non-volatile (polymerized) residue is formed (and is decomposed with further temperature rising). Thermogravimetric data are used for the calculation of the kinetic parameters for the polymerization reaction, taking place (concurrently with the evaporation) in the melt of the studied volatile compound.

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Abstract

We used CRTA for the study of both the elaboration and characterization of several polyphosphate glasses. We show that controlled transformation rate thermal analysis is able to remove a systematic error present in classical thermal analysis, in the study of the precursor of the phosphate glass. We show too that in CRTA, water release in the phosphate glasses can take place by diffusion phenomena at low temperature and that it is not due to the crystallization. These two examples illustrate some interests of this inverse method in the study of the decomposition of inorganic compounds with water release.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Fulconis, F. Morato, F. Rouquerol, R. Fourcade, A. Feugier, and J. Rouquerol

Abstract  

The reduction of UO2F2 by dry H2 was studied by Controlled Rate EGA, with a special set-up operating under a gas flow under atmospheric pressure. At the constant transformation rate selected, this reduction apparently takes place in one main step, around 450C (for a total duration of 100 h), followed by a small exothermic step. The final product is a stoichiometric, well crystallized UO2. XRD analysis shows the occurrence of two successive intermediates of which one has a structure close to that of UO2, but with interstitial fluorine atoms.

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Table 1 Mass loss and temperature data of halotrichite under dynamic conditions and under CRTA conditions Decomposition process

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