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Abstract  

A method for the dissolution of sintered UO2 samples and the determination of ammonium ions in the solution by spectrophotometry for the chemical quality control of UO2 fuel for nitrogen is described. The acid mixture used simplifies the problem of recovery of uranium from the waste generated during the analysis of nitrogen. Nitrogen content in ppm in the sintered UO2 samples is determined within an RSD of 10%.

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calcium sulfoaluminate (yeelimite), anhydrite and calcium oxide, produced by heating at various temperatures in the range 1150–1250 °C. The raw mixture to be sintered was proportioned (approximately) to give the ettringite phase; the additives were mixed

Open access
Journal of Thermal Analysis and Calorimetry
Authors:
M. Perraki
,
T. Perraki
,
K. Kolovos
,
S. Tsivilis
, and
G. Kakali

Abstract  

The sintering and hydration processes of a modified cement raw mix were examined using thermal analysis techniques. One reference and four modified mixtures, prepared by mixing the reference sample with 0.5, 1.0, 1.5 and 2.0 % w/w of a wolframite-stibnite mineral were studied. The clinkering reactions were recorded and the total enthalpy change during the sintering was determined by means of a differential scanning calorimetry. The combined water and the Ca(OH)2 content in samples hydrated for 1 to 28 days were determined, using thermogravimetry. As it is concluded, the effect of the added mineral on the sintering and hydration reactions can be fully recorded and evaluated using thermal analysis.

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Abstract  

Heat capacity measurements were carried out on Pb1-xLaxWO4+x/2 (x=0.2) and Pb1-xLa2x/3WO4 (x=0.2, 0.5) solid solutions prepared by sintering and mechanical alloying (MA) methods. For all the solid solutions, sintered samples showed slightly larger heat capacity around 100 K in comparison with MA samples, which was presumably caused by the excitation of mobile oxide ion motion. For sintered scheelite-type structured PbWO4s, high-temperature synthesis introduced oxide ion interstitials even for the Pb1-xLa2x/3WO4 system, which resulted in the excess heat capacity at low temperature for excitation. On the other hand, for the samples prepared by room-temperature MA technique, oxide ion seemed to occupy the regular sites rather than interstitial ones and excess heat capacities were not observed.

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Journal of Thermal Analysis and Calorimetry
Authors:
W. Kucza
,
J. Obłąkowski
,
R. Gajerski
,
S. Łabuś
,
M. Danielewski
,
A. Małecki
,
J. Morgiel
, and
A. Michalski

Abstract  

The ultrasonic spray pyrolysis (USP) technique was used for synthesis of alumina- and zirconia-based powders. The starting agents were aqueous solutions, atomized by the ultrasonic spray generator and pyrolized in the furnace under the open-air conditions. The powders prepared by USP were in the form of solid and hollow aggregates (spheres) consisted of nanosize amorphous grains as determined by the microscopy and the X-ray diffraction techniques. The alumina-based powders were consolidated by the pulse plasma sintering resulting in single-phase materials. Different behavior of solid and hollow particles during the isostatic sintering is found; a higher degree of deformation of spheres is observed in the second case.

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Abstract  

Naturally occurring opals from three different regions in Australia were studied for their thermal characteristics. All the opals showed initial expansion followed by contraction in thermomechanical analysis (TMA) although the temperature at which the change from expansion to contraction occurred depended on their provenance. Thermogravimetric analysis (TG) revealed different rates and temperatures of dehydration for these opals. A general correlation between the temperature at which there was a zero thermal expansion and that of the maximum rate of dehydration was observed. A dehydration–sintering mechanism is proposed with the effect of sintering being more pronounced following total dehydration.

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Journal of Thermal Analysis and Calorimetry
Authors:
F. Albuquerque
,
B. Parente
,
S. Lima
,
C. Paskocimas
,
E. Longo
,
A. Souza
,
I. Santos
, and
V. Fernandes

Abstract  

The use of clays for ceramic filter processing may reduce its cost, leading to different applications, as water treatment. In this work, a low cost tile clay mixed with kaolin, for use in ceramic filters, were evaluated. Mineralogical and thermal changes occurring during sintering were characterized by differential thermal analysis, thermogravimetry, thermomechanical analysis and X-ray diffraction. An increase in the initial melting temperature of samples due to kaolin addition was observed. Mullite formation in kaolin was observed by DTA and in other samples by XRD. TMA analysis permitted the observation of pre-sintering step, around 850C. This step is difficult to observe in other types of analysis.

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Preparations were characterized by specific surface area, thermogravimetry, and X-ray diffractometry. Thermal effects observed were (a) sulfur loss, (b) sintering, (c) crystallization and transformation of the crystalline phase(s). Thermoanalytical curves indicate that decomposition of the sulfate occurs in two distinct steps. Decrease of surface area due to (b) and (c) is concomitant to decomposition of sulfate. Sulfate was found to hinder sintering, crystallization and phase transformations of ZrO2 and TiO2. In low-titania and -zirconia sulfated TiO2-ZrO2 the minor component enhances the effect of sulfate. In equimolar TiO2-ZrO2 sulfate decomposition is accompanied by rapid formation of crystalline TiZrO4.

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Abstract  

Photodissolution tests of UO2 sintered pellets were carried out in 3M nitric acid solution and at about 50 °C under UV irradiation. The light source was a Hg-lamp emitting a light of 254nm wavelength. In the products, chemicals such as H2O2 and NO2 ion were detected during photodissolution of the UO2 sintered pellets. Based on this result, a new dissolution mechanism of UO2 in nitric acid solution by photochemical reaction was suggested in this study.

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Abstract  

The high T C superconducting phase Bi2Sr2Ca2Cu3Ox (2223) in the Pb-BSCCO system has been produced by EDTA-gel processing using nitrate solutions. The precursor has heated in two stages, at 300 and 800C each for 2 h, to avoid the burning of the important species involved in the final product. The effects of time (6 to 48 h) and temperature (845 and 855C) on the formation of the 2223 phase have been studied by sintering the samples in air. Thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and a vibrating sample magnetometer (VSM) have been employed to investigate the powder produced at different stages of decomposition, oxidation and formation of sintered materials from the powders. The volume-fraction of the 2223 phase at 845C increases with time, the maximum value of the 2223 phase was obtained at 120 h. It has been observed that the formation of the high T C phase is remarkably enhanced at the temperature of the endothermic peak of the DTA curve. The best result has been obtained in the sample sintered for 24 h at the temperature 855C (endothermic peak). This also indicated that at 855C, the large volume-fraction of 2223 phase with T C 113 K grew in short time and as the sintering time increased, it decomposed into the Bi2Sr2CaCu2Ox (2212) phase and other phases.

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