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  • Author or Editor: A. Gouveia x
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Abstract  

The temporal and spatial distribution of the REEs was determined, by INAA, in sediment cores collected at Northern Iberian shelf along the area between the Finisterra Cape and the mouth of Minho river, to contribute to the understanding of the origin and sedimentation processes of sediments deposited at the Continental Shelf. The distribution pattern of the REEs were flat and similar to the shales. A negative Eu anomaly was found for all the sections of the analyzed cores. Significant positive correlations between the REE and Zr and Hf contents suggest that zircon is responsible for hosting both light and heavy REEs.

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Abstract  

A geochemical study was carried out in sediment cores along the Galician Continental Shelf and at the mouth of the Vigo and Pontevedra Rias. Multielemental analysis was performed by Instrumental Neutron Activation Analysis and Energy Dispersive X-ray Fluorescence Spectrometry. Sedimentological and geochemical characterisation (lithogenic, biogenic and anthropogenic elements) indicates different supplies for the fine-grained, deposited sediments. No significant heavy metal enrichment could be detected in coastal sediments despite the current sediment contamination in adjacent Rias. Variations in the accumulation rates suggest different factors controlling the sedimentation processes including sediment sources and geomorphology.

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Abstract  

Two sediment cores (~30 m long) were retrieved at the mouth of the Minho Estuary to assess its palaeoenvironmental evolution for the last millennia. Samples were characterized by Energy-Dispersive X-Ray Fluorescence Spectrometry and Instrumental Neutron Activation Analysis, complemented by sedimentological analyses. Provenance of major and trace element contents (lithogenic or biogenic, continental or marine) is assessed. The influence of grain size effect on total element concentration is discussed. Most of the samples present a negative Eu anomaly. Sedimentological and geochemical parameters allow differentiating four geological units––fluvial, marine, estuarine and sand barrier––which reflects the temporal evolution of the Minho Estuary.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Amorim, S. Eliziário, D. Gouveia, A. Simőes, J. Santos, M. Conceiçăo, A. Souza, and M. Trindade

Abstract  

The thermogravimetry (TG) is a technique used in the quality control of foods. In this work the moisture and ash contents in the rice and by-products (bran and husk), the thermal stability and the gelatinization process by conventional, thermogravimetric and calorimetric methods were studied. The moisture and ash contents obtained by TG and conventional methods did not present significant differences. The rice presented higher starch content, while the bran presented higher protein content. The thermogravimetric data presented the following thermal stability order: rice>bran>husk. The calorimetric curves indicated the gelatinization of the starch. The kinetic parameters were compatible.

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Abstract  

The thermal decomposition kinetics of the solid complexes Cd(S2 CNR2 )2 , where R =C2 H5 , n -C3 H7 , n -C4 H9 or iso -C4 H9 , was studied by using isothermal and non-isothermal thermogravimetry. The superimposed TG/DTG/DSC curves revealed that thermal decomposition reactions occur in the liquid phase. The kinetic model that best fitted the experimental isothermal TG data was the one-dimensional phase-boundary reaction-controlled process R1 . The thermal analysis data suggested the thermal stability sequence Cd(S2 CNBun 2 )2 >Cd(S2 CNPrn 2 )2 >Cd(S2 CNBui 2 )2 >Cd(S2 CNEt2 )2 , which accords with the sequence of stability of the apparent activation energies.

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Abstract  

With the aim of obtaining materials with applications in pigments, CoxZn7-xSb2O12 spinels were synthesized using the Pechini method. This method consists in the formation of a polymeric net, where the metallic cations are homogeneously distributed. In this work, two types of alcohol (ethyl glycol and ethylene glycol) were used for the synthesis of a zinc antimoniate spinel, CoxZn7-xSb2O12 (x=0-7). The materials were characterized by termogravimetry (TG) and differential thermal analysis (DTA). TG results indicated a decrease in total mass loss when cobalt was added to the solution substituting zinc, for samples prepared using the two different alcohols. Decomposition temperatures, obtained by TG and DTA, presented a decreasing behavior as cobalt was added to the material. In relation to the alcohols, all results indicated a better polymerization of the resin when ethylene glycol was used, being the most indicated one for cation immobilization. X-ray diffraction did not show differences between the two alcohols - both presented the spinel phase (Co, Zn)2.33Sb0.67O4. Samples with higher quantity of cobalt also presented ilmenite phase (Co, Zn)Sb2O6.

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Journal of Thermal Analysis and Calorimetry
Authors: D. Gouveia, A. Souza, M. de Maurera, C. da Costa, I. Santos, S. Prasad, J. de Lima, C. Paskocimas, and E. Longo

Abstract  

Using the Pechini method, pigments with spinel structure (Zn7Sb2O12)were synthesized by substitution of the cation Zn2+ by Co2+, in compounds with different concentrations of Sb2O3. The doping resulted in CoxZn(7–x)Sb2O12 phases(x=1–7) that were isomorphs to spinel, denominated as samples A and B. After thermal treatment at 400C for 1 h, the powders were characterized by thermogravimetry(TG) and differential thermal analysis (DTA). The results indicate a different behavior whena higher amount of Sb2O3 is used, due to the presence of a secondary phase (ilmenite).

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Journal of Radioanalytical and Nuclear Chemistry
Authors: J. D. T. Arruda-Neto, A. C. Cestari, C. B. Zamboni, M. Saiki, G. P. Nogueira, L. E. C. Fonseca, M. V. Manso-Guevara, A. Deppman, V. P. Likhachev, J. Mesa, O. A. M. Helene, S. A. C. Jorge, M. N. Martins, A. N. Gouveia, O. Rodriguez, F. Guzmán, and F. Garcia

Summary  

Neutron activation analysis has been used to study uranium incorporation in poultry bones as function of chow doped with: (a) uranium (20 ppm); (b) U-doped food (20 ppm) plus phytase (120 ppm) and (c) U-doped food (20 ppm) plus phytase (180 ppm). To investigate this situation experiments involving several groups of Cobb broilers was performed. Two animals per group were sacrificed weekly up to their adultness and uranium concentration in the tibia was measured. It was observed that the concentration of uranium (µg U/g bone) is decreasing all along the animal life spanning period of 14-42 days. This behavior suggests that the skeleton mass is growing faster than the corresponding accumulation of uranium. The administration of phytase seems not to alter this scenario.

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