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- Author or Editor: A. De Oliveira x
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Abstract
Membranes of latex extracted of the seringueira tree (Hevea brasiliensis), genetically improved by selection and statistics methods, were prepared by air drying a 10 mL suspension of the ammonia in latex 10% (v/v). TG-DTG and DSC curves were used to characterize the membranes. Thermal stability and thermal decomposition of these compounds were analyzed. The results obtained show no differences among latex from different clones.
Abstract
The standard molar enthalpy of formation of crystalline di-isobutyldithiocarbamate complexes of P, As, Sb and Bi(III) has been derived by solution calorimetry at 298.15 K. The corresponding standard molar enthalpies of sublimation were estimated by means of differential scanning calorimetry. From the standard molar enthalpies of formation of the gaseous chelates the homolytic and heterolytic mean metal-sulphur bond-dissociation enthalpies were calculated.
Abstract
Dosimetric gel is used in several measurements due to its linearity, low cost, and possibility for 3D measurements. This work brings a new possibility to apply the Fricke Xylenol Gel recipe in the diagnostic measurements region. The Fricke Xilenol Gel (FXG) dosimeter is associated with the Fe(II) to Fe(III) oxidation, when irradiated, being the final ion concentration proportional to the absorbed dose. To achieve the scope, the former dosimeter was modified through the benzoic acid addition in the original recipe forming a new dosimeter, the Benzoic Xylenol Gel (BFXG). The results obtained with this new dosimeter demonstrated a higher sensibility for low absorbed dose values, bringing down the absorbed dose inferior limit from 0.1 to 0.006 Gy, that is more adequate for radiodiagnostic absorbed dose measurements. This result shows the possibly of BFXG dosimeter to be used for measurements in the radiodiagnostic region, as for tomography and mammography techniques.
Abstract
In this work, the synthesis of Nd-doped SrSnO3 by the polymeric precursor method, with calcination between 250 and 700 °C is reported. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After heat treatment, the material was characterized by XRD and infrared spectroscopy. Ester and carbonate amounts were strictly related to Nd-doping. According to XRD patterns, the orthorhombic perovskite was obtained at 700 °C for SrSnO3 and SrSn0.99Nd0.01O3. For Sr0.99Nd0.01SnO3, the kinetics displayed an important hole in the crystallization process, as no peak was observed in HTXRD up to 700 °C, while a XRD patterns showed a crystalline material after calcination at 250 °C.
Abstract
The composite montmorillonite-8-hydroxyquinoline (Swy-1-8-HQ) was prepared by two different processes and studied by using thermogravimetric analysis (TG/DTG and DSC), as well as helpful techniques as fluorescence in the UV-visible region and X-ray diffraction. The composites developed fluorescent appearance, however with quantum poor efficiency and they exhibited distinct TG and DSC thermal behavior. The fluorescence data of spectra associated to the TG/DT curves allowed to suggest that the 8-HQ was present in the composites in two different circumstances: 1 - intercalated in the interlayer spaces (Swy-1-8-HQ2), rigidly associated to the substrate feasible as a monolayer with the aromatic rings parallel to the silica layer; and/or, 2 - adsorbed on the surface (Swy-1-8-HQ1), either as a bilayer formation or tilting of the molecules to the silicate layer sheet. All results confirmed above are in agreement with X-ray diffraction patterns, once the interlayer space increases when 8-HQ is incorporated. The experimental results confirm the formation of the composites in agreement with the method used in the preparation.
Abstract
Sediments from the Admiralty Bay, King George Island, Antarctica, were investigated by 57Fe Mössbauer spectroscopy, X-ray diffractometry, and radiometry. Quartz, feldspar, chlorite, calcite, dolomite, mica, kaolinite, hematite and magnetite were identified as constituent minerals in the sediment samples. The phase composition and the iron distribution among the crystallographic sites of iron-bearing minerals (silicates, magnetite and hematite) of samples from different location have been derived from the complex Mössbauer spectra. At different locations sediments had significant characteristic differences in the mineral composition, in the iron distribution among the crystallographic site of silicates, and in the specific radioactivity of Cs radionuclides. These results indicate differences in the rock formation and alteration by the sediments in this maritime part of Antarctica. There is a much higher amount of iron oxides in the sediments from south part of the geological fault across the Admiralty Bay than in the north part. This can be associated with much more alteration in the rocks in the south part compared to the northern one. This finding can contribute to the question of the history of the formation and alteration of volcanic rocks in the border of Antarctica.
Abstract
NiWO4 and ZnWO4 were synthesized by the polymeric precursor method at low temperatures with zinc or nickel carbonate as secondary phase. The materials were characterized by thermal analysis (TG/DTA), infrared spectroscopy, UV–Vis spectroscopy and X-ray diffraction. NiWO4 was crystalline after calcination at 350 °C/12 h while ZnWO4 only crystallized after calcination at 400 °C for 2 h. Thermal decomposition of the powder precursor of NiWO4 heat treated for 12 h had one exothermic transition, while the precursor heat treated for 24 h had one more step between 600 and 800 °C with a small mass gain. Powder precursor of ZnWO4 presented three exothermic transitions, with peak temperatures and mass losses higher than NiWO4 has indicating that nickel made carbon elimination easier.
Abstract
Sulfated molecular sieves were synthesized and characterized by XRD, FTIR, chemical analyses, acidity measurements and N2 adsorption–desorption isotherms. Sulfatation led to structural changes in the solid framework by increasing the acidity and accessibility of the acid sites. Br⊘nsted and Lewis acid sites of mild to high strength improved the conversion of alcohols, but the selectivity was modest over sulfated FAU type Y, ZSM-5 and γ-Al2O3 solids at temperatures lower than 200 °C. The characteristics of the sulfated AlSBA-15 molecular sieve in terms of acidity, textural properties and accessibility possibly make this solid useful for catalytic reactions involving bulky organic compounds.
Abstract
57Fe and 151Eu Mössbauer spectroscopy as well as RF susceptibility measurements were applied to study the effects of Pr substitution either into the rare earth or into the Ba site in Eu1–x
Pr
x
Ba2Cu3O7–
and EuBa2–x
Pr
x
Cu3O7–
, respectively. Site mixing of Pr between the rare earth and Ba sites could be excluded by the utilization of 57Fe Mössbauer spectroscopy. It was found that there exists a correlation between the 151Eu isomer shift and the onset temperature of the superconducting transition independent of the location of Pr. RF susceptibility measurements provide an evidence for a difference in the magnetic moment of Pr substituted for the Eu or Ba sites. The obtained results can be explained by hole filling as the dominant effect of Pr substitution.
Abstract
Copper monoxide (CuO) was successfully obtained by microwave-assisted hydrothermal method, using different conditions—in a solution without base, in a solution alkalinized with NaOH or with NH4OH. The powders were analyzed by thermal analysis (TG/DTA), X-ray diffraction (XRD), infrared spectroscopy, UV–Visible spectroscopy, and scanning electronic microscopy. XRD results showed that CuO was obtained with monoclinic structure and without secondary phases. Thermal analysis and infrared spectra indicated the presence of acetate groups on the powder surface. TG curves also showed a mass gain assigned to the Cu(I) oxidation indicating that a reduction possibly occurred during synthesis. The high and broad absorption band in the UV–Vis spectroscopy from 250 to 750 nm indicated the coexistence of Cu(II) and Cu(I), confirming the Cu(II) reduction, inside the CuO lattice. It was also possible to confirm the Cu(II) reduction by a displacement of the Me–O vibration bands observed in the IR spectra at around 500 cm−1.
