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Abstract  

A characterization of principal congruences of the subvariety C of semi-DeMorgan algebras is given. This characterization is applied to determine the subdirectly irreducible algebras of the variety C and to describe a poset such that the lattice of its order ideals is isomorphic to the lattice of subvarieties of C.

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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  

Instrumental neutron activation analysis (INAA), have been used for the definition of compositional groups of potteries from Justino site, Brazil, according to the chemical similarities of ceramic paste. The outliers were identified by means of robust Mahalanobis distance. The temper effect in the ceramic paste was studied by means of modified Mahalanobis filter. The results were interpreted by means of cluster, principal components, and discriminant analyses. This work provides contributions for the reconstruction of the prehistory of baixo São Francisco region, and for the reconstitution of the Brazilian Northeast ceramist population of general frame.

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Abstract  

The standard (p 0=0.1 MPa) molar enthalpies of formation, Δf H m 0, for crystalline phthalimides: phthalimide, N-ethylphthalimide and N-propylphthalimide were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry, as, respectively, – (318.01.7), – (350.12.7) and – (377.32.2) kJ mol–1. The standard molar enthalpies of sublimation, Δcr g H m 0, at T=298.15 K were derived by the Clausius-Clapeyron equation, from the temperature dependence of the vapour pressures for phthalimide, as (106.91.2) kJ mol–1 and from high temperature Calvet microcalorimetry for phthalimide, N-ethylphthalimide and N-propylphthalimide as, respectively, (106.31.3), (91.01.2) and (98.21.4) kJ mol–1. The derived standard molar enthalpies of formation, in the gaseous state, are analysed in terms of enthalpic increments and interpreted in terms of molecular structure.

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Abstract  

The recycling of soft drink bottles poly(ethylene terephthalate) (PET) has been used as an additive in varnish containing alkyd resin. The PET, called to recycled PET (PET-R), was added to the varnish in increasing amounts. Samples of varnish containing PET-R (VPET-R) were used as a film onto slides and its thermal properties were evaluated using thermogravimetry (TG). Throughout the visual analysis and thermal behavior of VPET-R it is possible to identify that the maximum amount of PET-R added to the varnish without changing in the film properties was 2%. The kinetic parameters, such as activation energy (E) and the pre-exponential factor (A) were calculated by the isoconversional Flynn-Wall-Ozawa method for the samples containing 0.5 to 2.0% PET-R. A decrease in the values of E was verified for lower amounts of PET-R for the thermal decomposition reaction. A kinetic compensation effect (KCE) represented by the lnA=−13.42+0.23E equation was observed for all samples. The most suitable kinetic model to describe this decomposition process is the autocatalytic Šesták-Berggren, being the model applied to heterogeneous systems.

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Abstract  

The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(α)) could be calculated. Hence, the kinetic triplet (E±SD, logA±SD and f(α)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152±4 kJ mol−1, logA=14.1±0.2 s−1 for the kinetic model, and the autocatalytic model function was: f(α)=αm(1−α)n0.42(1−α)0.56.

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Titanium(IV)–EDTA complex

Kinetics of thermal decomposition by non-isothermal procedures

Journal of Thermal Analysis and Calorimetry
Authors: Luciana Guinesi, C. Ribeiro, Marisa Crespi, A. Santos, and Marisa Capela

Abstract  

This work aims the evaluation of the kinetic triplets corresponding to the two successive steps of thermal decomposition of Ti(IV)–ethylenediaminetetraacetate complex. Applying the isoconversional Wall–Flynn–Ozawa method on the DSC curves, average activation energy: E=172.49.7 and 205.312.8 kJ mol–1, and pre-exponential factor: logA=16.380.84 and 18.961.21 min–1 at 95% confidence interval could be obtained, regarding the partial formation of anhydride and subsequent thermal decomposition of uncoordinated carboxylate groups, respectively. From E and logA values, Dollimore and Mlek methods could be applied suggesting PT (Prout–Tompkins) and R3 (contracting volume) as the kinetic model to the partial formation of anhydride and thermal decomposition of the carboxylate groups, respectively.

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Abstract  

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.

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The question addressed in this paper is whether plant traits and plant functional types related to forage selection by grazers are also related to those expressing short-term community response after grazing. Vegetation of natural campos grassland in south Brazil was examined for species composition and locally described for seven morphological traits before and after a controlled grazing period by bovine cattle. An optimization algorithm was used for the identification of plant functional effect types (PF ef T) and plant functional response types (PF ef T)-in this case, groups of plants similar in a given set of traits (assessed before and after one grazing short period, respectively) and in their association to grazing intensity. The results have shown that plant traits optimally defining plant types related to forage selection (PF ef Ts) were the same traits optimally defining short-term community response to grazing (PF re Ts); also similar trends of plant morphological variation were observed among populations before and after grazing, based on the traits’ correlation structure. However, at the community level the correlation vanished, since similar communities described by the performances of PF ef Ts were not as similar when described by PF re Ts. Hence, whether plant functional types related to forage selection (effect types) are also related to community response to grazing may depend on the level of organization considered. The paper advances on the operational definition of possible overlaps between effect and response plant functional types.

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Summary  

The axial and radial distribution of the catalyst concentration, in the riser of an EMC - experimental cold model of a fluid catalytic cracking type unit, was measured by gamma-absorption. The solid concentration in the circulating fluidized bed was determined by measurements with a 241Am gamma-source and a NaI(Tl) detector. The operation, instrumental measurements and data acquisition system of the cold unit were automated. The catalyst concentration measurements were carried out in static experiments and in the circulating fluidized bed. A calibration of the distribution concentration was made with experimental data from gas velocity and pressure drop along the riser that gave the best multi-regression model. A spatial resolution of 5.0 . 10-3 m by scanning the riser and a catalyst density resolution of 5.0±0.8 kg/m3 were obtained. The axial catalyst concentration distribution, in the 5-13 kg/m 3  interval, showed a predicted pattern according to the literature. The radial distribution was in an annular configuration for this diluted catalyst concentration.

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