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.
By dissolution of PVC and polyaniline in dimethylformamide, a series of blends PVC-polyaniline were produced which were studied
by scanning electron microscopy and thermogravimetry. Special attention is focused on the kinetic study of the thermal degradation
steps by using non-isothermal thermogravimetric data. The results show that the thermal stability of the synthesized blend
is decreased as the total amount of polyaniline is enhanced. Furthermore, the Brřnsted acid doped blend is more stable than
the corresponding undoped one. PVC and the PVC-polyaniline blends exhibit two mass loss steps which activation energy values
are in the range from 176 to 283 kJ mol-1 and 306 to 322 kJ mol-1, respectively.
Thermogravimetric data were used to calculate the number of acidic Brnsted sites in lamellar α-titanium (α-TiP), γ-titanium
(γ-TiP), α-zirconium (α-ZrP) and γ-zirconium (γ-ZrP) hydrogenphosphates. The numbers of acidic sites calculated for these
lamellar compounds were 7.81, 5.67, 6.33 and 5.56 for α-TiP, γ-TiP, α-ZrP and γ-ZrP, respectively. These values are in good
agreement with those found through potentiometric titration. The data obtained prove that thermogravimetric measurements can
be used as a reliable analytical tool to follow the ion-exchange capacity of this kind of crystalline lamellar compounds.
Infrared spectroscopy, thermogravimetry and differential scanning calorimetry techniques were used to study the metal-amino
acid interactions for adducts of the general formula CdCl2nL (n=1.0 or 1.5 and L=histidine or cysteine). After characterization the thermal degradation process was kinetically followed by a non-isothermal
method. The infrared data confirmed that the cation is coordinated the carboxylic oxygen atoms of the amino acid molecules.
The thermogravimetric results indicated that the main step of the thermal degradation of all amino acid adducts is connected
to the rupture of the metal-ligand bonds, to give the associated activation energies values of 77, 44, 55 and 41 kJ mol-1 for CdCl2nL, n=1.0 and 1.5, for histidine and cysteine, respectively.
Authors:A. Souza, M. Oliveira, I. Santos, M. Conceição, L. Nunes, and J. Machado
The kinetics of thermal decomposition of solid In(S2CNR2)3 complexes, (R=CH3, C2H5, n-C3H7,i-C3H7, n-C4H9 and i-C4H9), has been studied using isothermal and non-isothermal thermogravimetry. Superimposed TG/DTG/DSC curves show that thermal
decomposition reactions occur in the liquid phase, except for the In(S2CNMe2)3 and In(S2CNPri2)3 compounds.
Authors:D. R. Amancio, M. G. V. Nunes, O. N. Oliveira Jr., and L. da F. Costa
The number of citations received by authors in scientific journals has become a major parameter to assess individual researchers and the journals themselves through the impact factor. A fair assessment therefore requires that the criteria for selecting references in a given manuscript should be unbiased with regard to the authors or journals cited. In this paper, we assess approaches for citations considering two recommendations for authors to follow while preparing a manuscript: (i) consider similarity of contents with the topics investigated, lest related work should be reproduced or ignored; (ii) perform a systematic search over the network of citations including seminal or very related papers. We use formalisms of complex networks for two datasets of papers from the arXiv and the Web of Science repositories to show that neither of these two criteria is fulfilled in practice. By representing the texts as complex networks we estimated a similarity index between pieces of texts and found that the list of references did not contain the most similar papers in the dataset. This was quantified by calculating a consistency index, whose maximum value is one if the references in a given paper are the most similar in the dataset. For the areas of “complex networks” and “graphenes”, the consistency index was only 0.11–0.23 and 0.10–0.25, respectively. To simulate a systematic search in the citation network, we employed a traditional random walk search (i.e. diffusion) and a random walk whose probabilities of transition are proportional to the number of the ingoing edges of the neighbours. The frequency of visits to the nodes (papers) in the network had a very small correlation with either the actual list of references in the papers or with the number of downloads from the arXiv repository. Therefore, apparently the authors and users of the repository did not follow the criterion related to a systematic search over the network of citations. Based on these results, we propose an approach that we believe is fairer for evaluating and complementing citations of a given author, effectively leading to a virtual scientometry.
Authors:J. Botelho, A. Souza, L. Nunes, A. Chagas, I. Garcia dos Santos, M. da Conceição, and P. Dunstan
The standard molar enthalpies of formation of crystalline dialkyldithiocarbamates chelates, [Pd(S2CNR2)2], with R=C2H5, n-C3H7, n-C4H9 and i-C4H9, were determined through reaction-solution calorimetry in acetone, at 298.15 K. From the standard molar enthalpies of formation
of the gaseous chelates, the homolytic (172.43.8, 182.53.2,150.93.1 and 162.63.1 kJ mol−1) and heterolytic (745.03.8, 803.73.3,834.33.1 and 735.23.0 kJ mol−1) mean palladium-sulphur bond-dissociation enthalpies were calculated.
Authors:Paula Nunes, Marília Bezerra, L. Costa, Juliana Cardoso, R. Albuquerque, M. Rodrigues, Gabriela Barin, Francilene da Silva, and A. Araújo
The purpose of this study was to evaluate the physical–chemical properties of collagen (CL) and usnic acid/collagen-based
(UAC) films, using differential thermal analysis (DTA), thermogravimetry (TG/DTG), infrared spectroscopy (FTIR), and scanning
electron microscopy (SEM). Both films were prepared by casting process using polyethylene glycol 1500 (PEG 1500) as plasticizer.
In the spectrum of UAC, similar bands of the usnic acid are observed, indicating that the polymerization (film formation)
did not affect the stability of the drug. Distinctly, DTA curve of UAC did not show an endothermic peak at 201 °C, indicative
that the drug was incorporated into the polymeric system. These results were corroborated by the scanning electron microscopy
(SEM). The TG/DTG curves of UAC presented a different thermal decomposition profile compared to the individual compounds and
CL. These findings suggest the occurrence of molecular dispersion or solubilization of the drug in the collagen film.