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  • Author or Editor: Z. Málek x
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For experimental investigation of the temperature-dependences of specific heat and thermal conductivity in the range 4–300 K a continuous-flow helium cryostat has been developed. Its adaptation for low-temperature calorimetry and its use for measurement of the temperature-dependences of the specific heats of bulk samples of metals and insulators are described in this note. The phase transition from the normal to the superconductive state has been measured on NbTi and its critical temperature determined. Two methods of determination of the temperature-dependences of the specific heats of metals and insulators have been developed. The inaccuracy of specific heat determination did not exceed 2 % with metal materials and 5 % with insulating materials.

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Abstract  

Emanation Thermal Analysis (ETA), based on the measurement of the release of radon from previously labelled samples, has been used for 'in-situ’ characterisation of the morphology changes of intercalated montmorillonitic clay. The thermal behaviour of hydroxyaluminium intercalated montmorillonite was monitored in course of the preparation of alumina pillared montmorillonite, making possible to determine optimal temperature for the isothermal treatment of the intermediate product. Moreover, the thermal stability of alumina pillared montmorillonite porous structure was determined from the ETA data. A good agreement of ETA data and surface area, XRD patterns. DTA, and TG resulted was found.

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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 dehydration and dehydroxylation of the smectites, beidellite and montmorillonite (dioctahedral) and saponite and laponite (trioctahedral), were investigated by ETA, DTA, TG and X-ray diffractions. There are differences between the behaviors of di- and trioctahedral clays which are due to the differences in the ability of the exchangeable cations to migrate into hexagonal holes of the SiO4 network and due to the fact that the dehydroxylation and recrystallization of dehydroxylated trioctahedral smectites occur simultaneously, whereas there is a temperature gap of about 300°C between the dehydroxylation and the recrystallization of dioctahedral smectites.

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The silica waste originating from a geothermal power plant in Mexico was investigated with the aim of finding its applicability as a raw secondary material for ceramics production. The thermal behaviour of the original silica waste (containing NaCl and KCl from marine brine) and of the purified silica was characterized by means of DTA/TG, emanation thermal analysis (ETA) and thermodilatometry (TD). The reactivity of the purified silica waste mixed with CaCO3 (1.8 mass%) was characterized by means of ETA, DTA and TG. The microstructures and phase compositions of the final products prepared by heating in air were tested by means of X-ray diffraction and of scanning electron microscopy coupled with electron probe X-ray microanalysis. The thermal analysis methods allowed determination of the optimal conditions for thermal treatment of the silica waste in order to obtain partly sintered porous materials for use as refractory bricks.

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The second step of the international comparative experiment SROK, the determination of the concentration of the burnup monitors is discussed.

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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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Iron(III) hydroxide and oxide-hydroxide samples prepared by precipitation of 0.2M iron(III) nitrate solution by 5M NaOH and subsequently aged at pH 12 for times of up to 50 h have been characterized. The sorption properties towards Sr2+ were characterized by radiotracer method using85Sr, morphology of the samples was characterized by Transmission Electron Microscopy and Emanation Thermal Analysis. X-ray diffraction patterns characterized the crystallinity of the samples aged for various times. The maximum (100%) sorption capacity for85Sr corresponding to amorphous iron(III) hydroxide decreased to 75% with the time of precipitate ageing (up to 40 h). This finding corresponds to the development in crystallinity and morphology of the sorbent.

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