Search Results

You are looking at 1 - 10 of 13 items for :

  • Author or Editor: M. C. D. Silva x
  • Chemistry and Chemical Engineering x
  • All content x
Clear All Modify Search

Abstract  

Ground tire rubber (GTR) was treated by microwaves at the same power and at different times of exposure, in order to improve their recycling characteristics. The resulting materials were characterized by thermogravimetric analysis (TG/DTG) and differential scanning calorimetry (DSC). DSC analysis showed that the microwaves treatment, specially for longer exposure times, changes the thermal behavior at low temperatures, that is to say, changing its glass transition (T g), probably due to the modification in the chemical structure of the rubber. The TG/DTG analysis showed that the thermo-oxidation behavior of the sample after the microwaves treatment is different from the sample before the treatment. The thermo-oxidation temperature of the devulcanized rubber is shifted to lower temperatures, even for the rubber treated in short times.

Restricted access

Abstract  

Fluoride glasses have been extensively studied due to their high transparency in the infrared wavelength. The crystallization kinetics of these systems has been studied using DTA and DSC techniques. Most of the experimental data is frequently investigated in terms of the Johnson-Mehl-Avrami (JMA) model in order to obtain kinetic parameters. In this work, DSC technique has been used to study the crystallization of fluorozirconate glass under non-isothermal conditions. It was found that JMA model was not fit to be applied directly to these systems, therefore, the method proposed by Mlek has been applied and the Šestk-Berggren (SB) model seems to be adequate to describe the crystallization process.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: M. C. D. Silva, L. M. da Silva, N. A. Santos, M. M. Conceição, A. G. Souza, and A. O. dos Santos

Abstract

Nowadays the growing fuel deficit requires the development of alternative fuel sources. Biodiesel is a good substitute to the conventional diesel because it is quite similar to the fossil fuel in its main characteristics. However, there are some obstacles, as the properties of cold-flow, to the development of a more useful alternative fuel. In this work we use the X-ray diffraction and differential calorimetry scanning to study low temperature properties of ethylic Babassu biodiesel. Our results show that the nucleation of crystals starts below −8 °C and the crystallization temperature does not change significantly when the sample was submitted to a winterization process. The higher concentrations of ethyl esters from saturated fat acid are probably responsible for this characteristic. The X-ray diffraction, combined with DSC measurements, was efficiently employed in the characterization of cold-flow biodiesel properties, showing to be very helpful techniques.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Marta M. Conceição, V. J. Fernandes Jr., F. S. M. Sinfrônio, J. C. O. Santos, M. C. D. Silva, V. M. Fonseca, and A. G. Souza
Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Rosiane M. C. Farias, Marta M. Conceição, Roberlúcia A. Candeia, Marta C. D. Silva, Valter J. Fernandes Jr., and Antonio G. Souza

Abstract

The diversity of raw materials and technological routes employed in the biodiesel production has resulted in products with different chemical properties. This non-uniformity in the biodiesel composition may influence to the fuel quality. The aim of this study was to evaluate biodiesel blends of passion fruit and castor oil in different proportions and their thermal stability. Biodiesel blends of passion fruit and castor oil presented parameters in the standards of the Petroleum, Natural Gas and Biofuels National Agency. The TG curves indicated that castor oil biodiesel was more stable. Passion fruit biodiesel has a high content of oleic and linoleic acids, which are more susceptible to oxidation. Biodiesel blend of passion fruit and castor oil 1:1 increased the thermal stability in relation to passion fruit biodiesel. Biodiesel blend of passion fruit and castor oil 1:2 presented higher thermal stability, because castor oil has a high content of ricinoleic acid.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Romulo D. A. Andrade, Elaine A. Faria, Amaury M. Silva, Wandallas C. Araujo, Gustavo C. Jaime, Kenia P. Costa, and Alexandre G. S. Prado

Abstract

The Brazilian government has presented a biofuel program, which aims the addition of 2% of biofuel in fossil diesel in 2008 and 5% up to 2013. Thus, the knowledge of heat of combustion of biofuel/diesel blends is necessary. The biodiesel was produced by transesterification of soybean oil with a yield of 87%. The diesel-like was obtained by pyrolysis of soybean oil. This biofuel presented all parameters according to ANP. The obtained heats of combustion were 41.36 ± 0.17; 38.70 ± 0.16; and 36.71 ± 0.17 MJ/kg for diesel, diesel-like and biodiesel, respectively. The results show that the heats of combustion of biofuels are approximately 17% smaller than fossil diesel. The obtained data also show that the heats of combustion depend on the methodology used for the biofuel production. Addition of biofuels to traditional diesel fuel results in a linear decreasing of the heat of combustion with the amount of the alternative fuel added to the diesel.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: C. M. Silva, R. S. Amaral, A. Amaral, J. A. Santos Júnior, D. C. Santos, L. E. Lima, and S. V. Silveira

Summary  

Studies performed by the Brazilian Nuclear Corporation (NUCLEBRAS), in collaboration with the Geological Survey Company of Brazil (CPRM), identified high levels of natural uranium in the districts of Pedra and Venturosa, in the rural region of the state of Pernambuco (PE) - Brazil, where the maximum value found in rocks was 22,000 mg.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Marta C. D. Silva, J. R. Botelho, Marta M. Conceiçăo, B. F. Lira, Monyque A. Coutinho, A. F. Dias, A. G. Souza, and P. F. A. Filho
Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: M. A. S. Silva, R. G. Kelmann, T. Foppa, A. P. Cruz, C. D. Bertol, T. Sartori, A. Granada, F. Carmignan, and F. S. Murakami

Abstract

The thermal behaviour of fluoxetine hydrochloride and five capsules available in Florianópolis, Brazil was investigated. The raw material’s purity, kinetic parameters, thermal behaviour and melting characteristics were determined by differential scanning calorimetry and thermogravimetric analysis, as well as the thermal study of the capsules. The purity was 99.12±0.15%. The thermal decomposition followed a zero order kinetic, activation energy of 88.67 kJ mol−1 and frequency factor of 3.539·107 min−1. DSC curves obtained from the capsules suggest compatibility between the drug and excipient.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: D. Hoffman, R. Henderson, K. Gregorich, D. Bennett, R. Chasteler, C. Gannett, H. Hall, D. Lee, M. Nurmia, S. Cai, R. Agarwal, A. Charlop, Y. Chu, G. Seaborg, and R. Silva

Abstract  

The isotope260Lr, produced in reactions of18O with249Bk, was used to perform chemical experiments on lawrencium to learn more about its chemical properties. These experiments involved extractions with thenoyl trifluoroacetate, elutions from cation exchange resin columns with ammonium alpha-hydroxyisobutyrate, and reverse-phase chromatography using hydrogen di(2-ethylhexyl) orthophosphoric acid to investigate the chemical properties of Lr. The results from the elutions gave information about the ionic radius of Lr(III) which was found to elute very close to Er. An attempt to reduce Lr(III) with hydroxylamine hydrochloride was unsuccessful.

Restricted access