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.
Thermogravimetric data and the kinetic interpretation of the curves of mass loss for ferrocene, ferrocenecarboxylic and ferrocenedicarboxylic
acids and a series of ferrocene-containing polyamides are presented. The results indicate that the degradation process occurred
with more than one stage of thermal degradation. The apparent activation energy values and the FTIR spectra of the degradation
products suggest that the degradation mechanism occurred by either scission of weak links or by random scission of the chain.
Apparently, the N-vicinal methylene group was the primary site of attack of oxygen on the polymer chain.
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.
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:A. Garrido Pedrosa, M. Souza, S. Lima, Dulce Melo, A. Souza, and A. Araújo
bifunctional catalysts were synthesized using impregnation and polymeric precursor
methods. After the synthesis process the samples were calcined at 600, 700
and 800C and characterized by X-ray diffraction, nitrogen adsorption
and temperature programmed reduction study by thermogravimetry. DTG-TPR profiles
showed between three and five reduction events at different temperatures attributed
to platinum reduction and to different stages of tungsten species reduction.
A comparative study of the synthesis method influence on the DTG-TPR curves
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:R. Macêdo, O. de Moura, A. de Souza, and A. Macêdo
This work present comparative results on powder milk storage quality, obtained from analytical methods. Protein content was
determined conventional (Kjeldahl) and colorimetric with biuret reagent at 540 nm and integral quality by thermogravimetric
and biological methods. A method was developed for the protein separation of powder milk. Powder milk was submitted to degradation
processes at 45, 60 and 80°C for 20 days. The results indicated that protein content values were inconsistent if determinations
by Kjeldahl and colorimetric methods and biological tests were compared. There is evidence of thermal decomposition of powder
milk as detected by biological and thermogravimetric methods.
Authors:A. Silva, M. Souza, J. Aquino, V. Fernandes, and A. Araújo
The coke removal of HZSM-12 zeolite deactivated in the reaction of n-heptane cracking was studied by thermogravimetry using
two multiple heating rate integral kinetics models proposed by Ozawa-Flynn-Wall and Vyazovkin to obtain the activation energy
of process of thermoxidation of coke. The results obtained by both models presented excellent accordance with the related