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Abstract  

Irradiation of α-Al2O3 (Corundum) was carried out in contact with acidic media and with different doses (100-to-2500 kGy) and dose-rates (0.9, 2.6 and 6.1 kGy·h−1) of γ-rays. Simultaneously parallel experiments were carried out using the same procedure, but preheated at 150°C for two days and then irradiated without acidic media. The solid thus obtained was used to determine the effect of γ-irradiation on the sorption capacities of microamounts of fission products from strongly alkaline aqueous solutions of uranium. The results revealed that the effect of γ-irradiation of α-Al2O3 and the acidic media in which it is immersed, is associated with a stable matrix resistant to significant changes in the composition of the surface layer; whilst it seems that the effect of γ-irradiation of preheated α-Al2O3, is connected with changes of surface-OH groups strongly affected by heat treatment and irradiation dose.

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Abstract  

The use of ionizing radiation to achieve some desired effect on silica gel, applicable to the adsorption of radionuclides has been investigated as a function of the dose-rate over a wide range of doses, in experiments with strongly alkaline aqueous solutions containing an excess of UO 2 2+ relative to trace concentrations of88Y,103Ru,134Cs and141Ce. The results obtained revealed that γ-irradiation of silica gel was reproduced with an uptake comparable to that measured for the unirradiated-silica gel. Radiation resistance is strongly influenced by the basic macromolecular structure, the presence of water, and the particular environmental exposure conditions.

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Abstract  

Ammonium uranate was precipitated from uranyl nitrate solution using gaseous ammonia, then filtered, washed with demineralized water and dried. The influence of pH and ammonia flow rate on their composition and structure were examined by X-ray diffraction analysis, making use of additional information obtained from infrared analysis.

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Abstract  

Thermal analysis of jute fibre reinforced vinylester resin with 30 vol% of fibre were performed by TG/DTG under dynamic conditions. The fibres were treated with alkaline solution at different temperatures and the final composition (cellulose, hemicellulose and lignin) of the fibre was determined by chemical analysis. Apparent activation energies were determined using a variety of conventional thermogravimetric methods. Two peaks were found in the composite differential curves: the first peak close to 327 and the second peak at 408°C. The apparent activation energy values for the second peak decreased when fibre were treated. The addition of the jute fibres produced a slightly decrease in the thermal stability of the composites.

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Abstract  

José Antonio Alzate dam mud sediment samples were collected from six sampling sites. The samples were analyzed by combining multielemental studies with structural details, including heating to very high temperatures. Characterization of mud sediment samples have been shown to have low concentrations of metals (Cr, Mn, Ni, Cu, Zn, Pb). No systematic trend was observed as a function of the sampling points.

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Abstract  

The aim of this study is to employ a thermogravimetric analyzer coupled to a mass spectrometer to research into the influence of heating rate and sample mass on the response of the detector. That response is examined by means of a particular efflorescence taken from an acid mine drainage environment. This mixture of weathered products is mainly composed by secondary sulfate minerals, which are formed in evaporation conditions, appearing as efflorescence salts. Thermogravimetry coupled to mass spectrometry has been used to analyze the three main loss steps that happen when this combination of minerals is heated from 30 to 1,100 °C. This inorganic material is based on a mixture of hexahydrite, zinc sulfate hexahydrate, apjonite, gypsum, plumbojarosite, calcite, quartz, and magnetite. While heating, three main effluent gases evolved from this efflorescence. At a standard heating rate of 10 °C/min, loss of water (dehydration) occurred over 30–500 °C in four major steps, loss of carbon dioxide (decarbonisation) occurred over 200–800 °C in three steps, and loss of sulfur trioxide (desulfation) occurred over 400–1,100 °C in three steps. According to the results, thermal analysis is an excellent technique for the study of decomposition in these systems.

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Abstract  

A great variety in retention properties occurs as a result of different methods of preparation of the sorbents. Specific surfaces and porosities, which are mostly connected with the sorption activities, may vary widely. The activation of Al2O3, SnO2 and silica gel, to produce highly active sorbents occurs only if the oxide is contacted with acid immediately after thermal treatment. The efficiency of the separation scheme has been tested using uranium and fission products under static conditions from strongly alkaline aqueous solutions.

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Journal of Thermal Analysis and Calorimetry
Authors:
I. Ruiz-Larrea
,
A. Fraile-Rodríguez
,
A. Arnáiz
, and
A. López-Echarri

Abstract  

New measurements of the (N(CH3 )4 )2 MnBr4 specific heat by adiabatic calorimetry around the ferro- paraelastic phase transition shown by the crystal around 276 K are compared with previous calorimetric studies on similar tetramethylammonium bromide compounds. The thermodynamic behaviour of the tribromides and tetrabromides derivatives together with the influence on the phase transition parameters of the cation and halogen molecular substitutions are examined. The thermal relaxation experiments permit to study the behaviour of the crystals thermal conduction as a function of the temperature. Finally, the Landau theory for second order phase transitions is used to describe the thermodynamic behaviour of some of these crystals.

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Abstract  

A calorimetric sensor has been developed to measure surface heat dissipations in the human body. An experimental prototype has been built in order to study its performance and a simple model that represents acceptably the experimental system has been proposed.

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