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  • Author or Editor: M. Tavares x
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Abstract  

The properties of polymeric blends originate from the synergistic association of their components. In this investigation, phenolic resins obtained by the reaction of cashew-nut shell liquid (CNSL) and aldehyde are used in several applications. Mixtures of CNSL with industrial reject ethylene-co-vinyl acetate (EVA reject) were prepared with an EVA reject content up to 70%. The thermal compatibility and stability were evaluated by means of thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). For blends containing a high percentage of EVA reject, the TG curves clearly show two decomposition stages, one at 350‡C and the other at 450‡C (onset 467‡C). The DIG curves of the blend containing 70% CNSL exhibit decomposition at 240‡C. The DSC curves show that the samples containing a high percentage of EVA reject are incompatible, withT g values around −30‡C.

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Abstract  

Concentrations of uranium in several brands of di-calcium phosphate commercialized in Brazil were measured by means of a recently developed electrofission/SSNTD technique. These results, plus the alimentary habits of brazilian consumers, allowed to estimate the radiation exposure. Calculations of internally localized doses (hot spots) were worked out and some aspects of radiobiological effects and risks were addressed.

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Abstract  

Instrumental neutron activation, atomic absorption spectroscopy and conventional methods of analysis were used on eight different silicate rocks and two minerals. Trace elements and major constituents were determined. It was considered that the methods should be regarded as complementary analytical techniques.

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Abstract  

The present study determined the organic and inorganic composition of human enamel and dentin. The instrumental neutron activation analysis, inductively-coupled plasma spectrometer, thermogravimetric and differential thermal analysis and X-ray diffraction analysis applied were and performed in the Nuclear Technology Development Centre (CDTN) and Elemental Analysis in the Department of Chemistry of the Federal University of Pernambuco, Brazil. The coronal dentin and enamel were separated from dentin mechanically (1) and by wear (2). The analyses were effective and led to the identification of the main elements present in enamel and dentin: Ca, Na, Cl, Zn, P, Mg, N, C, H, O. There was no contamination of samples of enamel or dentin in either separation technique; however, with separation technique 1, lower percentages of mainly Ca (7.25%) and O (15.16%) components were detected in dentin compared with technique 2.

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Abstract  

The thermal decomposition reactions of crystalline chelates of general formula Ln(thd)3 (Ln=La,Pr, Nd, Sm and Gd; thd=2,2,6,6-tetramethyl-3,5-heptanedione) have been studied by isothermal thermogravimetry. Several models were proposed initially to calculate the kinetic parameters by isothermal method, thus the time reduced method was used to define the best kinetic models. The Avrami–Erofeev (Am=2, 3 and 4) and R1 and R2 models presented good agreement with experimental data, as well as, linear correlation coefficient (r) and standard deviation (s).

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Journal of Thermal Analysis and Calorimetry
Authors: Rogério L. Pagano, Verônica M. A. Calado, Frederico W. Tavares and Evaristo C. Biscaia

Abstract

In the present contribution, a procedure to estimate parameters using non-isothermal data was applied. The estimation procedure is based on the use of an energy balance in DSC furnace. The approach found all kinetic parameters of autocatalytic model (E 1, E 2, A 1, A 2, m, n) besides the ultimate reaction heat and their confidence regions by using deterministic and heuristic algorithms. The application of this approach to isothermal data was done in a previous work and similar results were obtained. The results show that the use of an energy balance is a good methodology to estimate cure kinetic parameters of non-isothermal experiments.

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Summary  

Sediment cores from Catingueiro, Barrinha and Rio das Pedras marginal lagoons of the Moji-Guaçu River basin were analyzed for rare earth elements (REEs), Fe, Ta and Th by instrumental neutron activation analysis (k 0-INAA). Data indicated similarities between Catingueiro and Barrinha lagoons, while a distinct scenario was seen for Rio das Pedras likely due to changes of sedimentation rate in 1950's. By using Fe, Sc, Ta and Th as conservative elements, double normalization technique was performed in order to assess the distribution pattern of Ce, Eu, La, Sm and Tb for each core. In all cases, it was evident a depletion of lighter REE elements in the Rio das Pedras lagoon.

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Sunflower biodiesel

Use of P-DSC in the evaluation of antioxidant efficiency

Journal of Thermal Analysis and Calorimetry
Authors: M. L. A. Tavares, N. Queiroz, I. M. G. Santos, A. L. Souza, E. H. S. Cavalcanti, A. K. D. Barros, R. Rosenhaim, L. E. B. Soledade and A. G. Souza

Abstract

The higher is the degree of unsaturation in ester chain of a biodiesel, the smaller is its oxidation stability. Sunflower biodiesel obtained by the ethyl route possesses a high amount of unsaturated fatty acids, mainly oleic acid (C18:1) and linoleic acid (C18:2), thus being more prone to the oxidation process. In Brazil, with the purpose of meeting the specifications of the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP), antioxidant additives, from synthetic and natural origins, have been added to the biofuel. Antioxidants are an alternative to prevent the oxidative deterioration of the fatty acid derivatives, as they are substances able to reduce the oxidation rate. In this study, the oxidative stability of sunflower biodiesel, obtained by the ethyl route and additivated with different concentrations of the antioxidants butylated hydroxytoluene (BHT) and t-butylhydroquinone (TBHQ), was evaluated by means of Pressure differential scanning calorimetry (P-DSC) and the Accelerated oxidative stability test (Rancimat, Method EN 14112). The results obtained by the two techniques showed the same oxidation tendency. Thus, P-DSC can be used as an alternative to determine the oxidative stability of biodiesel. The antioxidant TBHQ, added to biodiesel at the concentrations of 2000 and 2500 mg kg−1, raised the oxidation induction time to a value higher than 6 h, the limit established by the Resolution ANP number 7/2008, thus being the best alternative among the studied antioxidants.

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