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334 results on '"Matos, Jivaldo"'

23. A thermal degradation study of Y and La methanesulfonates

Author

de Moura de Maria F.V., Matos Jivaldo DO.R., and de Farias Robson F.

Subjects
methanesulfonates, thermal degradation, rare earths, Chemistry, QD1-999
Abstract

The synthesis, characterization and thermal degradation of yttrium and lanthanum methanesulfonates is reported. The prepared salts were characterized by elemental analysis and infrared spectroscopy. The thermal degradation study was performed using thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC).Using the thermogravimetric data, a kinetic study of the dehydration ofY and Lamethanesulfonates was performed employing the Coats-Redfern and Zsakómethods. It was verified that under heating, yttrium and lanthanum methanesulfonates undergo three main processes: dehydration, thermal degradation and oxide formation. Furthermore, depending on the nature of the atmosphere, i.e., inert or oxidant, the thermal degradation process could be endothermic (N2) or exothermic (air).

Published
2006
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24. Optimization of mobile phase for separation of carbohydrates in honey by high performance liquid chromatography using a mixture design

Author

Cano Cristiane B., Felsner Maria L., Bruns Roy E., Matos Jivaldo R., and Almeida-Muradian Lígia B.

Subjects
mobile phase optimization, HPLC, carbohydrates, mixture design, honey, Chemistry, QD1-999
Abstract

A mixture design was used to optimize the mobile phase composition for separation of carbohydrates in honey by High Performance Liquid Chromatography. Nine ternary acetronitrile, water and ethyl acetate mobile phases corresponding to a simplex centroid design with axial points were test to separate those carbohydrates most frequently encountered in honey samples. The results suggest that a special cubic model accurately describes changes in the proportions of these solvents in the mobile phase close to the region of optimal peak separation. The addition of a third solvent, ethyl acetate, to binary mobile phase of water and acetonitrile permitted a significant improvement in carbohydrate separation that can be applied to the quantitative analysis of these compounds in honey.

Published
2006

26. Synthesis, characterization and a thermal (TG-DSC) study of gadolinium and lutetium methanesulfonate coordination compounds with pyridine-N-oxide and 2-, 3- and 4-picoline-N-oxides

Author

de Moura Maria F.V., de Matos Jivaldo R., and de Farias Robson F.

Subjects
gadolinium, lutetium, coordination compounds, thermogravimetry, Chemistry, QD1-999
Abstract

The synthesis, characterization and a thermal (TG and DSC) study of the coordination compounds Gd(MS)3.(py-NO)2, Gd(MS)3.(2-picNO)2, Gd(MS)3 .(3-picNO)2, Gd(MS)3.(4-picNO)2, Lu(MS)3.(py-NO)2.2H2O, Lu(MS)3 (2-picNO)1.5.H2O, Lu(MS)3. (3-picNO) and Lu(MS)3.(4-picNO)2 are reported (MS = methanesulfonate, py-NO = pyridine-N-oxide, 2-picNO, 3-picNo and 4-picNO are 2-, 3- and 4-picoline-N-oxides, respectively). The observed thermal stability trend is: 2-picNO < py-NO < 4-picNO < 3-picNO for Gd and 2-picNO < 4-picNO < 3-picNO < py-NO for Lu. It was shown that the release of ligand molecules (endothermic) is followed by the thermal degradation of the ligands (exothermic).

Published
2005
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43. Ilustração da influência da razão de aquecimento nos resultados de termogravimetria

Author

Matos Jivaldo do Rosário, Miyano Miriam Hisami, Siqueira Lilian, Moura Maria de Fátima Vitória de, and Luiz José Marques

Subjects
heating rate, thermogravimetry, stoichiometry determination, Chemistry, QD1-999
Abstract

The effects of the heating rate on a TG curve of a sample have been widely discussed in the literature. This paper shows the influence of heating rate (beta) in thermogravimetry results when stoichiometry determinations are studied. For this purpose the compound Sm(CH3SO3)3.2(3-picNO) was considered beta of 2,5; 5; 10; 20 and 40degreesC min-1 in dynamic air atmosphere were obtained. The results are in agreement with proposed stoichiometry for beta equal to 2,5 and 5degreesC min-1. However, using a higher beta the same results were not obtained resulting in false stoichiometry determinations.

Published
2000

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