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  • Author or Editor: V. Balek x
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Abstract  

Diffusion of220Rn in ionic solids as affected by non-equilibrium defects, radiation damage, mechanical treatment and nonstoichiometry is discussed. Ferric oxide (alpha), zinc oxide and titanium dioxide (rutile) are used to demonstrate the application of the emanation thermal analysis for studying the respective effects.

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Abstract  

The emanation method and the method of surface labelling have been applied to study thermal processes. Using these methods, processes which are not connected with thermal effects can be analysed. In certain cases, for example in the study of poorly crystalline, or amorphous phases, these methods are even more sensitive than thermographic and X-ray techniques. The method of surface labelling is advantageous in cases when it is impossible to activate the samples by the parent isotope of the gas during the process of their preparation.

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Abstract  

Emanation thermal analysis, differential thermal analysis, thermogravimetry, X-ray diffraction, scanning electron microscopy (SEM) and surface area and porosity determination from nitrogen adsorption/desorption measurements were used to characterize the Mg-Al-CO3 LDH compound with the Mg:Al ratio 3:1 prepared by re-hydration of the Mg-Al mixed oxide. The mixed oxide was obtained after heating of the intial Mg-Al-CO3 LDH compound in air at 500°C for 2 h. The samples were re-hydrated by two ways namely in a distilled water at 20°C for 5 days or by moistening at 60°C in air with RH 80% during 10 days, respectively. The characteristics of the re-hydrated LDH samples were compared with the initial Mg-Al-CO3 compound. The influence of the re-hydration conditions on the microstructure, surface morphology and thermal stability of the regenerated Mg-Al-CO3 LDHs samples is discussed. It was demonstrated that the re-generation of the layered structure by the hydration of the mixed oxide in water or in air, respectively, took place via the dissolution-crystallization mechanism and that the layered double hydroxide with different surface area and thermal behavior were formed after re-hydration in water or humid air, respectively. The emanation thermal analysis revealed differences in the microstructure changes of the re-hydrated sample during heating. XRD patterns and results of the methods used supported the ETA results.

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Abstract  

In the Emanation Thermal Analysis the release of inert gas atoms previously incorporated in the sample is measured. Results of the statistical modelling of the inert gas release during thermal decomposition of solids are presented. The updated model supposing three components in the solid-state reaction system including the formation of an intermediate metastable component on the surface of the newly formed component was proposed for the modelling of the ETA curves. The release of inert gas atoms previously incorporated into the sample is used as a probe of microstructure changes. The random nucleation mechanism was considered in the modelling. The model can be used in modelling ETA curves of solid-solid, solid-gas and solid-liquid interactions where the existence of metastable intermediate component is supposed.

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Abstract  

New zinc acetate based complex compounds (of general formula Zn(CH3COO)2·1−2L·nH2O) containing one or two molecules of urea, thiourea, coffeine and phenazone were prepared namely: Zn(CH3COO)2·2.5H2O, Zn(CH3COO)2·2u·0.5H2O, Zn(CH3COO)2·tu·0.5H2O, Zn(CH3COO)2·2tu, Zn(CH3COO)2·cof·2.5H2O, Zn(CH3COO)2·2cof·3.5H2O, Zn(CH3COO)2·2phen·1.5H2O. The compounds were characterized by IR spectroscopy, chemical analysis and thermal analysis. Thermal analysis showed that no changes in crystallographic modifications of the compounds take place during (heating in nitrogen before) the thermal decompositions. The temperature interval of the stability of the prepared compounds were determined. It was found that the thermal decomposition of hydrated compounds starts by the release of water molecules. During the thermal decomposition of anhydrous compounds in nitrogen the release of organic ligands take place followed by the decomposition of the acetate anion. Zinc oxide and metallic zinc were found as final products of the thermal decomposition of the zinc acetate based complex compounds studied. Carbon dioxide and acetone were detected in the gaseous products of the decomposition of the compounds if ZnO is formed. Carbon monoxide and acetaldehyde were detected in the gaseous products of the decomposition, if metallic Zn is formed. It is supposed that ZnO and Zn resulting from Zn acetate complex compounds here studied, possess different degree of structural disorder. Annealing takes place by further heating above 600°C.

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