Thermogravimetric data were used to calculate the kinetics of isothermal degradation of layered tetratitanate intercalated
with n-alkyldiamines H2N(CH2)nNH2 (n=2, 3, 4, 6 or 8). The hydrous matrix showed two mass loss steps from the thermogravimetric curve, corresponding to the release
of physisorbed and lattice water molecules. For the intercalated matrices a third mass loss was observed due to the release
of organic moiety. From these values, the amine intercalated matrices can be ordered in the following sequence of thermal
stability; C4>C2>C3≅C6>C8. Kinetic studies were carried out to the release of lattice water molecules. The kinetic model that
best adjusted the experimental isothermal TG data was the diffusion mechanism controlling process.
Seismic coda Qattenuation (Qc) in the frequency range from 6 to 20 Hz of two distinct Scoda windows (early and later portions) are compared to analyse the effects of both coda windows on crustal seismic attenuation estimates around Samambaia fault (João CâmaraNortheastern Brazil). Qcvalues associated with the later portion are systematically higher than those related to the early portion. These values follow a frequency (f) function given by Qc(f) = Q0f, where Q0= 11739 and= 1.000.06. In general, Q0estimate is less sensitive to site effects and stabler than that obtained from the early portion of S coda waves, while its corresponding frequency dependence is similar to that obtained from the early portion of S coda waves. It suggests thatparameter does not depend on coda window's location along the seismic signal. A comparative analysis of both Q0andvalues with those found recently shows that there is no difference in using early or later portion of S coda waves in the stations located on Pre-Cambrian basement in the João Câmara area. This comparison also shows that the major variations in Q0values were observed at seismic stations installed on sedimentary terrain. Differences in the seismic attenuation, in both sides of the Samambaia fault, were also observed in this study, and it is in agreement with the hypothesis that Samambaia fault is a kind of boundary between two seismic attenuation zones.
Authors:M. Souza, Marta Conceição, M. Silva, L. Soledade, and A. Souza
Statins are a group of lipoproteins that
are used in medicine to treat the high cholesterol level. The effectiveness
of statins in reducing the cholesterol level is significant and in long time
scale the reduction of the cholesterol level helps to avoid the incidence
of degenerative diseases. Simvastatin and lovastatin are belonging to the
‘statins’ family, one of the pharmacologic groups used in the
control of dislipidemy. The objective of this work is the thermal stability
and kinetic study of the active forms of simvastatin and lovastatin.
Thermal data indicated that lovastatin and simvastatin are stable up
to 190 and 170°C in air and up to 205 and 203°C in nitrogen, respectively.
For melting temperatures DSC curves showed good correlation with the literature
data. Comparing the activation energies of the statins at heating rate of
10°C min–1, lovastatin is more stable
than simvastatin under the applied experimental conditions.
Authors:G. A. A. Teixeira, A. S. Maia, I. M. G. Santos, A. L. Souza, A. G. Souza, and N. Queiroz
Cloud point (CP), cold filter plugging point (CFPP), and pour point (PP) of biodiesel samples obtained from blends containing different amounts of beef tallow, babassu oil, and soybean oil were investigated by the corresponding conventional techniques and by temperature modulated differential scanning calorimetry (TMDSC). The CP and CFPP values correlate well with the crystallization temperature (Tonset) obtained from the TMDSC curves, being the highest for the biodiesel sample containing the highest amount of methyl stearate. A correspondence between PP and the peak temperature was also noticed, pointing out that pouring ceases after the crystallization of the heavier fatty acid ester. Among the samples of biodiesel, Bio-3 (highest amount of babassu oil) and Bio-4 (highest amount of soybean oil) showed better cold-flow properties, or in other words, lower values of CP, CFPP, and PP. Independently of the composition, the cold-flow properties of all biodiesel samples meet the requirements from the Brazilian National Agency of Petroleum, Natural Gas, and Biofuels (ANP).
Authors:E. Medeiros, R. Tocchetto, L. Carvalho, M. Conceição, and A. Souza
In this work, the influence of attapulgite concentration on the nucleating efficiency of isotactic polypropylene (iPP) and
on the kinetics of non-isothermal crystallization were ascertained.The study was conducted by DSC. The nucleating efficiency
was determined according to the procedure described by Fillon and the kinetics of non-isothermal crystallization was determined
using Ozawa's method using cooling rates of 2, 5 and 10C min−1.Our results indicate that both the relative crystallinity and the crystallization temperature increase with filler content
and that a maximum occurs at 2% mass/mass filler content. Both parameters decrease with increasing cooling rates. The Ozawa's
exponent tended to increase with temperature and filler content.
Authors:J. Souza, A. Santos, L. Polese, Marisa Crespi, and C. Ribeiro
Poly(3-hydroxybutyrate), PHB has been structurally
modified through reaction with maleic anhydride, MA. Transesterification reaction
was carried out fixing the PHB and MA and besides time and temperature the
concentration of the triethylamine (used as catalyst) was changed. Glass transition,
melting and crystallization temperature obtained from DSC curves and thermal
degradation temperatures obtained from TG traces were used to evaluate the
influence of the reaction conditions on the modification of PHB according
to factorial design. On the base of the results the optimum conditions are
to perform the PHB modification reaction with MA reaction at 110C for
1 h with 5% v/v triethylamine.
Authors:J. Santos, L. Lima, Iêda Santos, and A. Souza
The thermal degradation process of mineral base lubricating oils was
studied in this work by means of thermal, spectroscopic and rheologic analysis.
The lubricating oils were degraded at temperatures varying from 150 to 210C,
and for degradation times from 1 to 48 h. After the degradation, the lubricating
oils were characterized by X-ray fluorescence, IR and NMR spectroscopies,
rheological properties and thermal analyses (TG/DSC). The spectroscopic analyses
determined the oxidation reaction products. TG curves indicate that the thermal
stability of lubricating oils is below 161C. TG curves in air present
three mass loss stages, whereas in nitrogen there are only two mass loss steps.
DSC analyses in air indicate two highly exothermic peaks related to hydrocarbon
oxidation and combustion processes, while in nitrogen only two endothermic
peaks were observed. The decrease in the degradation temperature led to a
decrease of the lubricant viscosity.
Authors:R. Candeia, J. Freitas, M. Souza, Marta Conceição, Iêda Santos, L. Soledade, and A. Souza
The most feasible alternative among fuels derived from biomass seems
to be the biodiesel, having the required characteristics for a total or partial
substitution of diesel oil. Therefore, the aim of this work is to evaluate
the thermal and rheological behavior of the blends of diesel with the methanol
biodiesel obtained from soybean oil, using B5, B15 and B25 blends. All thermogravimetric
curves exhibited one overlapping mass loss step in the 35–280C
temperature range at air atmosphere and one step between 37–265C
in nitrogen. The rheological study showed a Newtonian behavior (n=1) for all blends.
Authors:E. F. S. M. Ramalho, I. M. G. Santos, A. S. Maia, A. L. Souza, and A. G. Souza
Chemical composition of oils and fats used in the biodiesel synthesis can influence in processing and storage conditions, due to the presence of unsaturated fatty acids. An important point is the study of the biodiesel thermal stability to evaluate its quality using thermal analysis methods. In this study the thermal stabilities of the poultry fat and of their ethyl (BEF) and methyl (BMF) biodiesels were determined with the use of thermogravimetry (TG/DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC), in different atmospheres. The TG/DTG curves of the poultry fat in synthetic air presented three decomposition steps while only one step was observed in nitrogen (N2) atmosphere. The DSC results indicated four exothermic enthalpic transitions in synthetic air and an endothermic transitions in N2 atmosphere attributed to the combustion process and to the volatilization and/or decomposition of the fatty acids, respectively. For both biodiesels the TG/DTG curves in air indicated two mass loss steps. In the DSC curves four exothermic transitions were observed in synthetic air besides an endothermic one in N2 atmosphere.
Authors:F. Vieira, Soraia Souza, A. Oliveira, S. Lima, E. Longo, C. Paskocimas, L. Soledade, A. Souza, and Iêda Santos
In this study undoped and Cr, Sb or Mo doped TiO2 were synthesized by polymeric precursor method and characterized by X-ray diffraction, UV–VIS spectroscopy, infrared spectroscopy
and thermogravimetry (TG). The TG curves showed a continuous mass loss assigned to the hydroxyl elimination and Cr6+ reduction. Doped TiO2 samples showed a higher mass loss assigned to water and gas elimination at lower temperatures. In these doped materials a
decrease in the anatase–rutile phase transition temperature was observed. After calcination at 1,000 °C, rutile was obtained
as a single phase material without the presence of Cr6+.