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Journal of Thermal Analysis and Calorimetry
Authors: K. L. G. V. Araújo, P. S. Epaminondas, M. C. D. Silva, A. E. A. de Lima, R. Rosenhaim, A. S. Maia, L. E. B. Soledade, A. L. Souza, I. M. G. Santos, A. G. Souza, and N. Queiroz

Abstract

Physicochemical and thermal analyses were undertaken to evaluate the influence of the temperature on the oxidation of sea fish oil once its polyunsaturated fatty acids deteriorate rapidly. Fish oil displayed four decomposition steps in synthetic air atmosphere and only one step in nitrogen atmosphere. The first step started at 189 and 222 °C for oxidizing and inert atmospheres, respectively. An OIT value of 53 min was measured at 100 °C. After the degradation process the peroxide index and the iodine index reduced from 35.38 to 9.85 meq × 1000 g−1 and from 139.79 to 120.19 gI2 × 100 g−1, respectively. An increase of the free fatty acids amount from 0.07 to 0.17% was observed while viscosity increased from 57.2 to 58.0 cP. Absorption at 272 nm also increased. The thermogravimetric and spectroscopic techniques are reproducible and versatile being an option for characterization of edible oil oxidation.

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Journal of Thermal Analysis and Calorimetry
Authors: P. S. Epaminondas, K. L. G. V. Araújo, J. A. Nascimento, M. C. D. Silva, R. Rosenhaim, L. E. B. Soledade, N. Queiroz, A. L. Souza, I. M. G. Santos, and A. G. Souza

Abstract

Physico-chemical properties, spectroscopy, and thermal analyses were used aiming at evaluating the influence of toasting and of the flaxseed variety on thermo-oxidative behavior of flaxseed oils. Thermogravimetry (TG) and differential scanning calorimetry (DSC) were associated to gas chromatography, infrared spectroscopy and UV–Vis spectroscopy, as well as to physico-chemical analyses to characterize the oils obtained from raw and toasted flaxseeds. No meaningful differences in the thermal and oxidative stabilities were noticed comparing oils obtained from the brown and the golden flaxseeds. Nevertheless, the UV–Vis spectra indicated that both flaxseed oils were at the beginning of the oxidation process. The previous toasting of the seeds led to a higher oxidation for both varieties being harmful to the flaxseed oil quality.

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Journal of Thermal Analysis and Calorimetry
Authors: D. Melo, G. Vicentini, L. Zinner, K. Zinner, H. de Souza, M. Batista, A. Garrido Pedrosa, and R. Bezerra

Abstract  

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.

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Journal of Thermal Analysis and Calorimetry
Authors: A. Garrido Pedrosa, M. Câmara, F. Borges, H. de Souza, H. Scatena Jr, D. Melo, and L. Zinner

Abstract  

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 Dy complex.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Botelho, A. Souza, L. Nunes, A. Chagas, I. Garcia dos Santos, M. da Conceição, and P. Dunstan

Abstract  

The standard molar enthalpies of formation of crystalline dialkyldithiocarbamates chelates, [Pd(S2CNR2)2], with R=C2H5, n-C3H7, n-C4H9 and i-C4H9, were determined through reaction-solution calorimetry in acetone, at 298.15 K. From the standard molar enthalpies of formation of the gaseous chelates, the homolytic (172.43.8, 182.53.2,150.93.1 and 162.63.1 kJ mol−1) and heterolytic (745.03.8, 803.73.3,834.33.1 and 735.23.0 kJ mol−1) mean palladium-sulphur bond-dissociation enthalpies were calculated.

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Abstract

Biodiesel has the advantage of being renewable and clean and for these reasons has been studied recently both academically and in industry. Research in this area is focused on developing new synthetic routes to obtain a purer product or to find new alternative sources of food to replace conventional oils. Papaya biodiesel is obtained from oily residues with a fatty acid composition similar to olive oil. It is generally discarded by the ton, considering that Brazil is the world’s largest producer of papaya with an annual output of 1,811 million tons, productivity of 52 t/hectare and domestic consumption at 86.5%. This study was designed by means of thermal analysis (TG, DSC, P-DSC, and MT-DSC), to verify the possibility of achieving high quality biodiesel, with oxidative stability and flow properties previously indicated by composition analysis of its fatty esters, physical–chemical properties (including oxidative stability) using classical methodology, recommended by ASTM D 6756.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Dantas, A. Almeida, Marta Conceição, V. Fernandes Jr, Iêda Santos, F. Silva, L. Soledade, and A. Souza

Abstract  

This work presents the characterization and the kinetic compensation effect of corn biodiesel obtained by the methanol and ethanol routes. The biodiesel was characterized by physico-chemical analyses, gas chromatography, nuclear magnetic resonance and thermal analysis. The physico-chemical properties indicated that the biodiesel samples meet the specifications of the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP) standards. The analyses by IR and 1H NMR spectroscopy indicated the ester formation. Gas chromatography indicated that biodiesel was obtained with an ester content above 97%. The kinetic parameters were determined with three different heating rates, and it was observed that both the methanol and ethanol biodiesel obeyed the kinetic compensation effect.

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Journal of Thermal Analysis and Calorimetry
Authors: C. Santos, B. Capistrano, F. Vieira, M. Santos, S. Lima, E. Longo, C. Paskocimas, A. Souza, L. Soledade, and I. Santos

Abstract  

In this work, spinels with the general formula Zn2−xCoxTiO4 were synthesized by the polymeric precursor method and thermally treated at 1,000 °C. The powder precursors were characterized by TG/DTA. A decrease in the DTA peak temperature with the amount of zinc was observed. After the thermal treatment, the characterizations were performed by XRD, IR, colorimetry and UV/VIS spectroscopy. The XRD patterns of all the samples showed the presence of the spinel phase. Infrared spectroscopy showed the presence of ester complexes for Zn2TiO4 after thermal treatment at 500 °C, which disappeared after cobalt addition, indicating that organic material elimination was favored.

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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: Camila Xavier, R. Candeia, M. Bernardi, S. Lima, E. Longo, C. Paskocimas, L. Soledade, A. Souza, and Iêda Santos

Abstract  

Magnesium and zinc ferrites have been prepared by the polymeric precursor method. The organic material decomposition was studied by thermogravimetry (TG) and differential thermal analysis (DTA). The variation of crystalline phases and particle morphology with calcination temperature were investigated using X-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. The colors of the ferrites were evaluated using colorimetry. Magnesium ferrite crystallizes above 800°C, presenting a yellow- orange color with a reflectance peak at the 600–650 nm range, while zinc ferrite crystallizes at 600°C, with a reflectance peak between 650–700 nm, corresponding to the red-brick color.

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