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Journal of Thermal Analysis and Calorimetry
Authors: Crislene Morais, C. Gameiro, P. Santa-Cruz, S. Alves Jr, L. Soledade, and A. Souza

Abstract  

The complexes of general formula Ln(btfa)3L, where Ln=Eu or Tb, btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione, L=1,10-phenanthroline (phen) or 2,2-bipyridine (bipy), were synthesized by reacting the corresponding metal chloride with the proper β-diketone and the other ligand. The complexes were obtained in the powder form and were characterized by photoluminescence and TG. Their thermal decomposition was studied by non-isothermal thermogravimetric techniques. The Eu(btfa)3bipy complex presented the highest thermal stability and it melts before being decomposed. The complex Eu(btfa)3phen presented the largest activation energy for a heating rate of 5C min–1.

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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  

The high-density polyethylene, thermoplastic widely-used in the production of industrial domestic utilities, was collected in two situations: virgin high-density polyethylene (JV 060) and post-consumption high-density polyethylene (with features of low-density polyethylene). After collecting the samples, they were submitted to natural aging with the quantification of the incident solar radiation for 180 days. The samples were characterized by melt flow index, differential scanning calorimetry, tensile strength, rupture load, elongation at break and infrared. The results showed that after 180 days of exposure the virgin high-density polyethylene presented physical properties similar to the post-consumption polyethylene.

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Abstract  

The application of Mössbauer spectroscopy, X-ray diffractometry, thermogravimetric analysis and PIXE in the characterization of the particulate matter in atmospheric aerosols in Metropolitan Region of Vitória (MRV), Brazil have been investigated. The main sources of particulate matter, natural, industrial and antropogenic from human activities, have been studied to identify its contribution in the atmospheric particles. During the years 1995 to 1999 samples of total suspended particles (TSP, Ø 100 m) were collected from four points within MRV. The inhalable particles (PM10 Ø 10 m) and sedimented particles (SP) were also collected from the same region. A receptor modeling was used for the identification of the source of particulate matter in the collected urban aerosol.

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Journal of Thermal Analysis and Calorimetry
Authors: R. Macêdo, J. Barbosa-Filho, E. da Costa, and A. de Souza

Abstract  

The terpenoids acetyl sitosterol, lupeol, acetyl diosgenin and stigmasterol were studied. Comparison of the thermogravimetric curves and the activation energies of the terpenoids suggested the following sequence of thermal stability: acetyl sitosterol < acetyl diosgenin < lupeol < stigmasterol. The DSC curves allowed determination of the melting points and the degrees of purity. Comparison of the TG and DSC curves revealed the presence of phase transitions without mass loss that were attributed to rearrangements in the terpenoid molecules.

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Abstract  

The crystallization behavior of Co75-xFexGe15B10 (x=3.0, 4.6 and 6.0) amorphous alloys was monitored by differential thermal analysis and thermo-mechanical analysis. The crystallization process of the melt spun ribbons was interrupted at 450, 525, 650, 800 and 900C and their microstructures were investigated by X-ray diffractometry. It was observed that the crystallization occurs in a sequential mode attributed to the formation of different types of precipitates. It was shown that the crystallization products change as a function of Fe content. After full crystallization, GeFe, Co3B, FeGe2 and Co2Ge compounds were found as well as a Co rich solid solution.

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Journal of Thermal Analysis and Calorimetry
Authors: H. Ouriques, M. Trindade, M. Conceiçăo, S Prasad, P. Filho, and A. Souza

Abstract  

The thermogravimetric curves of di-n-propylammonium, di-iso-propylammonium, di-n-butylammonium and di-iso-butylammonium chlorides showed similar profiles, characterized by mass loss in only one stage, corresponding to decomposition of compounds. The following thermal stability order was obtained: [Bu2 nNH2]Cl>[Pr2 nNH2]Cl>[Pr2 iNH2]Cl>[Bu2 iNH2]Cl. The values of activation energy for non-isothermal data obtained by Ozawa and Coats-Redfern integral methods were in agreement and stability order obtained by thermogravimetry were reproduced in both methods. The decomposition reactions of [Pr2 nNH2]Cl, [Pr2 iNH2]Cl and [Bu2 iNH2]Cl were better described by A3 model and [Bu2 nNH2]Cl by A2 model.

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Journal of Thermal Analysis and Calorimetry
Authors: C. Xavier, C. Costa, S. Crispim, M. Bernardi, M. Maurera, M. Conceiçăo, E. Longo, and A. Souza

Abstract  

The pigments used in ceramic applications are of nature predominantly inorganic and they should be thermally stable, insoluble in glazing, resistant to the chemical and physical agents' attacks. This work aimed at the synthesis by the polymeric precursor method of ZrO2-based inorganic pigments, doped with Fe, Ni, Co, Cr and Cu cations. The fired pigments were characterized by thermogravimetry (TG), differential thermal analysis (DTA) and X-ray diffraction (XRD). Among the metals used to zirconium-doping, the best result was achieved with the cations Cu, which presented the monophase pigment, even as 20 mol% of dopant. Up to the temperature of 1000C the pigments presented a good thermal stability.

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Journal of Thermal Analysis and Calorimetry
Authors: Ana Santos, I. Basílio, F. de Souza, A. Medeiros, Márcia Pinto, D. de Santana, and R. Macêdo

Abstract  

Thermal analysis is an essential analytical tool in development of new formulations as well as to study the interaction between drugs and excipients. This work aims to investigate the possible interactions between metformin and excipients as microcrystalline cellulose (Microcel MC101®), starch sodium glycolate (Explosol®), sodium croscarmellose (Explosel®), PVP K30, magnesium stearate, starch and lactose, usually employed in pharmaceutical products. TG, DSC and DTA techniques were used for the thermal characterization to track if the thermal properties of the drug substance were modified in the mixture. Disregard of the starch and lactose systems, no changes in thermal behavior of mixtures were found. Thermogravimetric studies (TG) of metformin and its binary mixtures showed different thermal behavior.

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Journal of Thermal Analysis and Calorimetry
Authors: Adney Luís A. da Silva, Guilherme G. G. Castro, and Mariana M. V. M. Souza

Abstract

Lanthanum strontium chromite (LSC) powders were synthesized by the combustion method, using five different fuels (urea, glycine, ethylene glycol, α-alanine, and citric acid). The ignition of the reagent mixture with urea takes a longer time, and more gases are released by combustion. A calcination step is essential for a good crystallization of the perovskite phase. X-ray diffraction patterns showed formation of perovskite phase and a small amount of SrCrO4 for the sample synthesized with urea after calcination. The crystallite sizes are in the range of 23–33 nm. Scanning electron microscopy revealed the porosity of the powders and the presence of agglomerates, formed by fine particles of different shapes. Thermogravimetric analysis showed a large mass loss for the sample synthesized with citric acid, probably caused by the absence of ignition, with primary polymerization of the precursor reagents.

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