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- Author or Editor: F. Ramírez x
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Abstract
Natural non-pretreated polycrystalline lithium nitrate was irradiated by gamma-rays of60Co with total radiation doses from 10 to 100 Mrad, at room temperature. No color centers were observed in samples irradiated in this range. X-ray and infrared studies evidenced the distortion of the lattice planes. In general, the following species were detected NO2, NO3 radicals, and NO2 2−, NO3 2−, O2 − ionic radicals.
Abstract
The use of18F radionuclide in the preparation of 2-[18F]-FDG is reported.
Abstract
For samples of irradiated natural and enriched (95%) Li2CO3, normal distillation to dryness of the alumina column eluates permits recuperation of approximately 80% of the tritium. The distilled samples were concentrated by electrolysis and a subsequent vacuum distillation resulted in a tritium enrichment of the order of 30%. The enriched samples were used to prepare sealed, calibrated sources, with different levels of tritium radioactivity, to be used as standards for the determination of tritium in unknown samples using liquid scintillation.
Abstract
The35S products formed in irradiated CCl4, CHCl3 and C2HCl3 were analysed. In CCl4 no trace of C35SCl2 was found whereas35SO2 was identified. In CHCl3, CCl3 35SCl was an important product and after saturation with oxygen CCl3 35SO2Cl became a major product. In C2HCl3,35S product appeared as compound of low volatility.
Abstract
This study presents an evaluation of the decomposition kinetic of low-grade nickeliferous laterite by thermogravimetric analysis. Kinetic parameters were calculated using the Ozawa and the iso-conversional Friedman methods. Simplified kinetics models like those based on the reaction order were also applied for the simulations. Two-dimensional shrinkage models of the reaction interface mechanism were adopted as describing the thermal transformation process from non-isothermal kinetic analysis. The iso-conversional method (model-free kinetics) reveals that the decomposition of low-grade nickeliferous laterite does not follow a single mechanism because the determined activation energies and pre-exponential factor are not constant during the course of the reaction.
Abstract
Although the product resulting from the nitrosation of 1,1,3-trimethylurea is a carcinogenic agent, there have been no kinetic studies reported on such a reaction. This work determines the kinetic parameters and the corresponding reaction mechanism.
Abstract
The nitrosation of 1,3-dialkylureas was carried out in the presence of carboxylic acids and halides in an aqueous perchloric medium. The aim of this work was to validate the proposed mechanism for the nitrosation of such substrates. In accordance with the rate limiting step of the proposed mechanism, the protonic transfer to the solvent, basic catalysis and an absence of catalysis by halides should be observed. The Br⊘nsted parameters were determined by basic general catalysis.
Abstract
In this work, a synthetic hydroxyapatite, Bio-gel HTP, marketed by BIO-RAD®, has been studied in order to propose a method to remove the excess fluoride present in drinking water. The removal of fluoride ions by this adsorbent has been studied as a function of solution pH, and fluoride ion concentration. Experiments of fluoride ions sorption have been carried out with the use of 18F radiotracer in solutions of NaF at several concentrations with an ion selective electrode used for fluoride analysis. The adsorption isotherms show that the best fluoride adsorption on hydroxyapatite occurs at a pH range of 7.0–7.5. At this pH value the solid presents an important capacity of subtraction of fluoride, of around of 100 mmol/100 g.
Abstract
Using differential scanning calorimetry (DSC) we have studied the physical aging of an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) modified by two different contents of an acrylonitrile-butadiene-styrene (ABS) and cured with 1,3-bisaminomethylcyclohexane (1,3-BAC). Samples fully cured were annealed at temperature of 125C for periods of time of 72 and 120 h, to determine the process of physical aging. The apparent activation energy for the enthalpy relaxation, Dh*, is determined as the sample is heated at 10C min-1 following cooling at various rates through the glass transition region. DSC studies suggested that the presence of thermoplastic inhibits the process of relaxation.
