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  • Author or Editor: J. Šubrt x
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A trial was performed to study the thermal decomposition of sodium hydride with DTA within the temperature range of 500 to 800 K. The best description of this process is provided by the Avrami equation . The activation energy of this processE a=115 kJ/mole and the frequency factorZ=2·107 sec−1 were determined.

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Emanation Thermal Analysis (ETA) was used to characterize microstructure changes of hydrous ruthenia and hydrous ruthenia-titania as precursors for preparation of RuO2 and (RuO2)0.9-(TiO2)0.l by heating in the temperature range of 20–600C in argon. A good agreement was found between ETA, TG and DTA results, X-ray diffraction patterns and surface area measurements of intermediate products of the thermal treatment.

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Emanation thermal analysis was used to characterize the thermal behaviour of alumina coatings as deposited on EUROFER 97 steel surface by filtered vacuum arc technique. Temperature ranges of the healing of cracks and structure irregularities observed by SEM were determined from the ETA results. Transport properties of the alumina coatings were assessed from the ETA results by the evaluation of radon diffusion parameters in the temperature range from 50 to 300°C. Healing microstructure irregularities of the alumina coatings can be expected in the range 300–700°C as indicated by the decrease of the radon release rate. From the ETA results it followed that the onset of healing the cracks observed by the SEM on the surface of one alumina coating sample can be expected at 430°C.

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Emanation thermal analysis (ETA) was used for characterization of the thermal behaviour of a borosilicate glass, designed for the vitrification of hazardous waste. Changes of release rate of radon atoms from the glass sample were measured continuously during heating in an air flow from 20 to 1000C. Annealing of surface roughness, cracks and technological defects was indicated in the temperature range of 275–400C by a decrease of radon release rate. A decrease of viscosity of the glass sample (in the proximity of the glass transition temperature, T g) was indicated by the increase of the radon release rate starting at 430C, whereas the decrease in the radon release rate starting, at 600C, corresponded to the glass softening. Mathematical modelling was used for the description of the kinetics of radon release from the labelled glass sample and for the simulation of the ETA curve. Good agreement between the experimental data and the results of mathematical modelling of the ETA curve was found.

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The paper reviews the actual state of the development and use of emanation thermal analysis (ETA). Examples of its recent applications are presented. The advantages of ETA in the microstructure characterization of materials under in situ conditions of their heat treatment are outlined.

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Brannerite based ceramics, designed as a matrix for immobilization of high level radioactive waste (HLW), was investigated from the viewpoint of microstructure changes and atomic transport properties caused by leaching of the ceramics at pH 2 and 11, respectively. Scanning electron microscopy (SEM) and emanation thermal analysis (ETA) techniques were used for this purpose. Surface morphology, microstructure changes and transport properties of both ‘as-leached’ and ‘as-prepared’ samples were compared and the effect of leaching on the thermal behavior of the ceramics samples heated in the temperature range from 20 to 1250°C was characterized. The mobility of radon in the brannerite ceramics was evaluated by mathematical modeling from ETA results. The thermal behavior of the non-leached brannerite ceramics sample and its natural analogue brannerite mineral was compared using the ETA.

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Thermal behaviour of N-doped titania powders prepared by heat treatment of anatase in gaseous ammonia at 550 and 575°C, respectively, was characterized by emanation thermal analysis (ETA). The ETA results were used to assess transport properties of the samples subsurface using the mobility data of radon atoms previously incorporated into the samples to the depth of 60 nm. It was demonstrated that the radon permeability of anatase in the temperature range 50–500°C was enhanced for the N-doped titania as compared to the non-doped titania powder. Microstructure changes accompanying the anatase-rutile transition were pointed out from the decrease of the radon release rate in the temperature range 850–1000°C. The results of surface area and porosity measurements, DTA results as well XRD patterns supported the ETA results.

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Emanation thermal analysis (ETA) was used to characterize the thermal reactivity of amorphous brannerite mineral of general formula U1–xTi2+xO6 (locality El Cabril, near Cordoba, Spain). It was demonstrated that on sample heating up to 880C microstructure changes taking place in the sample were accompanied by the formation of new radon diffusion paths, followed by their closing up during the final transformation of amorphous to crystalline brannerite in the range 900–1020 C. Relative changes in structure irregularities that served as radon diffusion paths during heating and subsequent cooling of the sample to temperatures of 300, 550, 750, 880, 1020 and 1130C, respectively, were determined from the ETA results. Mass losses in temperature ranges of 230–315, 570–760 and 840–1040C were observed by thermogravimetry. Mass spectrometry indicated the release of CO2 mainly due to the decomposition of minor carbon amount in the brannerite mineral sample.

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