Authors:M. Batista, M. Ginani, D. Melo, and A. Oliveira
ZnS(1-x)MSx(x=0.01 and M=Mn2+, Cu2+ and Eu2+) compounds have been obtained by precipitation from homogeneous solutions of zinc, copper, manganese and europium salts,
with S2- as the precipitating anion, formed by the decomposition of thioacetamide. The thermal study of the milled zinc acetate, thioacetamide,
copper acetate, manganese acetate and europium nitrate, respectively, was studied for thermal analyis TG/DSC. XRD respect
exhibits a zinc blend crystal structure.
Authors:M. Santos, A. Azeredo, D. Melo, and L. Julião
The decay products of uranium and thorium natural series are widely distributed in all the terrestrial crust. Their concentrations are considerable in the phosphates utilized as fertilizer in the Brazilian agriculture. In this work analysis was performed on238U,234U,232Th,238Th,226Ra and210Po in 22 Brazilian tobacco samples. The results showed238U and234U are in isotopic activity equilibrium (0.5±0.2 mBq/g). The equilibrium was not reached in the case of thorium isotopes: the228/232Th ratio was about 6.4. The average values obtained were 34.3 mBq/g for228Th and 5.4 mBq/g for232Th. The226Ra values were higher than its radioactive precursor,238U. This can be explained by the high affinity of radium to tobacco plant and the uranium removal during physical and chemical processes. The high concentration of210Po (20 mBq/g) in tobacco samples may be due to radon daughter products being electrically charged and then attaching themselves to inert dusts, which then become attached to tiny hairs on tobacco leaves. The results of this work are consistent with values presented in specialized literature.
Authors:A. Azeredo, L. Julião, M. Santos, D. Melo, and J. Lipsztein
Internal contamination with radioactive materials of mining workers is a common problem in Brazil. This is caused by the presence of uranium, thorium, and their natural decay series associated with the mined ore. The clear examples are the workers at the niobium mine located in the state of Goiás. The niobium is associated with considerable quantities of uranium and thorium, but the mine is not legally subject to radiation protection requirements.Twenty mine workers were evaluated using in vitro bioassay techniques (urine and feces). The fecal samples were analyzed by alpha spectrometry using the method developed in the Bioassay Laboratory of the Instituto de Radioproteção e Dosimetria/CNEN which evaluates thorium and uranium isotopes simultaneously. Minor modifications were introduced to measure a higher level of activity, around 1 Bq of uranium per sample. The urine samples were analyzed by alpha spectrometry for thorium and by fluorimetry for uranium. The results obtained show that a control of the occupationally-exposed workers is necessary.
Authors:A. M. Garrido Pedrosa, M. J. B. Souza, D. M. A. Melo, and A. S. Araujo
The thermo-programmed reduction study of Pt/WOx–ZrO2 materials prepared with different tungsten loading were performed by thermogravimetry. The samples were synthesized by impregnation method and calcined at 600, 700 and 800°C. The characterizations of both un-calcined and calcined materials were carried out using different techniques: thermal analysis (TG and DTA), X-ray diffraction (XRD) and thermo-programmed reduction (TPR). TG and DTA analysis of un-calcined were used to determination of calcination temperatures of the samples. XRD diffractograms were useful to help us in the determination of phase presents. TPR profiles showed between three and four events at different temperatures attributed to platinum reduction and the different stages of tungsten specie reduction.
Authors:F. M. Aquino, D. M. A. Melo, R. C. Santiago, M. A. F. Melo, A. E. Martinelli, J. C. O. Freitas, and L. C. B. Araújo
Thermogravimetric data using the non-isothermal kinetic models of Flynn and Wall and “Model-free Kinetics” were used to determine the activation energy to study the decomposition kinetics of the ligand groups with system’s metallic ions that takes part in the synthesis of PrMO3 (M = Ni or Co). This activation energy was determined for the stage of highest decomposition of the organic matter to establish parameters in synthesis condition optimization and application of the proposed material.
Authors:A. Souza, M. Tavares, D. Melo, M. Conceição, J. Espinola, and C. Airoldi
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).
Authors:L. Julião, A. Azeredo, M. Santos, D. Melo, B. Dantas, and J. Lipsztein
This study is a comparison between bioassay data of thorium-exposed workers from two different facilities. The first of these facilities is a monazite sand extraction plant. Isotopic equilibrium between232Th and228Th was not observed in excreta samples of these workers. The second facility is a gas mantle factory. An isotopic equilibrium between232Th and228Th was observed in excreta samples. Whole body counter measurements have indicated a very low intake of thorium through inhalation. As the concentration of thorium in feces was very high we concluded that the main pathway of entrance of the nuclide was ingestion, mainly via contamination through dirty hands.The comparison between the bioassay results of workers from the two facilities shows that the lack of Th isotopic equilibrium observed in the excretion from the workers at the monazite sand plant possibly occurred due to an additional Th intake by ingestion of contaminated fresh food. This is presumably because228Ra is more efficiently taken up from the soil by plants, in comparison to228Th or232Th, and subsequently,228Th grows in from its immediate parent,228Ra.
Authors:D. Melo, G. Vicentini, L. Zinner, K. Zinner, H. de Souza, M. Batista, A. Garrido Pedrosa, and R. Bezerra
Complexes of neodymium and europium with amides and aminoxides were synthesized and characterized by complexometric analyses
with EDTA, CHN microanalytical procedures, IR absorption spectra, absorption spectra of neodymium complexes, emission spectrum
of europium compounds at 77 K, thermogravimetric analyses in N2 and differential scanning calorimetry (DSC) in N2. Infrared
spectroscopy results revealed that the nitrate molecules are bound to the central ions as bidentate. Thermogravimetric plots
indicated that the decomposition of the complexes occurs in the range 363-1163 K and resulted in the formation of Ln2O3 residues.
Authors:A. Garrido Pedrosa, M. Câmara, F. Borges, H. de Souza, H. Scatena Jr, D. Melo, and L. Zinner
Complexes of rare earth trifluoroacetates (TFA) with 4-methylmorpholine-N-oxide (MMNO) of composition Ln(TFA)33MMNO (Ln=Eu, Dy, Ho, Er, Yb and Y) were synthesized and characterized by elemental analysis data, complexometric titration with EDTA,
IR absorption spectra, thermogravimetric analyses and differential scanning calorimetry (DSC) in N2 atmosphere. Infrared spectroscopy data revealed that the MMNO molecules are bound to the central ion through the oxygen of
NO groups. These data suggest that the trifluoracetate groups are also coordinated. Thermogravimetric curves indicate that
the decomposition of MMNO begins at approximately 350 K and results in Ln2O3 residue at around 1170 K. A theoretical kinetic study was carried out using a QBASIC program with the TG input data for the