Authors:P. Melnikov, R. V. Gonçalves, and H. Wender
Sb(VO3)3 has been synthesized by interaction between NH4VO3 and Sb2O3. The compound crystallizes in monoclinic system with lattice parameters: a = 17.150; b = 15.940; c = 14.600 Å and angle β = 90.50°. The scanning electronic microscopy shows thin flat plates measuring ~20 μm along with detritus material. The synthesis was simulated by thermal analysis and the final product identified by X-ray diffraction. Thermal analyses of the ternary system xNH4VO3 + (1 − x)(NH4)2HPO4 + Sb2O3 lead to the formation of Sb(VO3)3 and SbPO4 at 500 °C. At high temperature (900 °C), SbVO4, SbOPO4, VO and SbP5O14 are formed. The data of thermal analysis match with the composition of intermediate and final products. No solid solutions containing simultaneously PO4−3 and VO4−3 ions have been found.
Authors:P. S. Epaminondas, K. L. G. V. Araújo, J. A. Nascimento, M. C. D. Silva, R. Rosenhaim, L. E. B. Soledade, N. Queiroz, A. L. Souza, I. M. G. Santos, and A. G. Souza
Physico-chemical properties, spectroscopy, and thermal analyses were used aiming at evaluating the influence of toasting and of the flaxseed variety on thermo-oxidative behavior of flaxseed oils. Thermogravimetry (TG) and differential scanning calorimetry (DSC) were associated to gas chromatography, infrared spectroscopy and UV–Vis spectroscopy, as well as to physico-chemical analyses to characterize the oils obtained from raw and toasted flaxseeds. No meaningful differences in the thermal and oxidative stabilities were noticed comparing oils obtained from the brown and the golden flaxseeds. Nevertheless, the UV–Vis spectra indicated that both flaxseed oils were at the beginning of the oxidation process. The previous toasting of the seeds led to a higher oxidation for both varieties being harmful to the flaxseed oil quality.
Grewia gum is a naturally occurring polysaccharide which has potential as a pharmaceutical excipient. Differential scanning calorimetry and Fourier transform infrared (FT-IR) spectroscopy techniques were used to examine the thermal and molecular behaviours, respectively, of mixtures of grewia gum with cimetidine, ibuprofen or standard excipients, to assess potential interactions. No disappearance or broadening of the melting endotherm was seen with cimetidine or ibuprofen. Similarly, there was no interaction between grewia gum and the standard excipients tested. The results obtained using thermal analyses were supported by FT-IR analysis of the material mixtures. Grewia gum is an inert natural polymer which can be used alone or in combination with other excipients in the formulation of pharmaceutical dosage forms.
A free-base tetraphenyl porphyrin (TPP) and its corresponding metalloporphyrins (MTPP) where M = Co, Fe and Sn were synthesized
and characterized by UV–visible spectroscopy, FTIR and 1Hnmr spectroscopy. Thermal studies of these porphyrins were carried out in synthetic air from room temperature to 800 °C using
thermal analyser. The residues of MTPP after thermal treatment were qualitatively analysed, which showed the presence of corresponding
metal oxides. Further, the above MTPP were subjected to thermogravimetry–evolved gas and mass spectrometry (TG–EGA–MS) analysis
for the detailed information about evolved gases at their corresponding decomposition temperatures. This information may be
used to predict the probable mechanism for ring opening of the macromolecular porphyrins.
Heat capacities (Cp) of solid benzene, biphenyl,p-terphenyl,p-quaterphenyl, and poly-p-phenylene were analyzed using the ATHAS Scheme of computation. The calculated heat capacities based on approximate vibrational
spectra of solid benzene and the series of oligomers containing additional phenylene groups were compared to experimental
data newly measured and from the literature to identify possible additional large-amplitude motion. The skeletal heat capacity
was fitted to the Tarasov equation to obtain the one- and three-dimensional vibration frequencies Θ1 and Θ3 using a new optimization approach. Their relationship to the number of phenylene groupsn is: Θ1=426.0−150.3/n; and Θ3=55.4+81.8/n. Except for benzene, the quantitative thermal analyses do not show significant contributions from large-amplitude
motion below the melting temperatures.
Authors:K. L. G. V. Araújo, P. S. Epaminondas, M. C. D. Silva, A. E. A. de Lima, R. Rosenhaim, A. S. Maia, L. E. B. Soledade, A. L. Souza, I. M. G. Santos, A. G. Souza, and N. Queiroz
Physicochemical and thermal analyses were undertaken to evaluate the influence of the temperature on the oxidation of sea fish oil once its polyunsaturated fatty acids deteriorate rapidly. Fish oil displayed four decomposition steps in synthetic air atmosphere and only one step in nitrogen atmosphere. The first step started at 189 and 222 °C for oxidizing and inert atmospheres, respectively. An OIT value of 53 min was measured at 100 °C. After the degradation process the peroxide index and the iodine index reduced from 35.38 to 9.85 meq × 1000 g−1 and from 139.79 to 120.19 gI2 × 100 g−1, respectively. An increase of the free fatty acids amount from 0.07 to 0.17% was observed while viscosity increased from 57.2 to 58.0 cP. Absorption at 272 nm also increased. The thermogravimetric and spectroscopic techniques are reproducible and versatile being an option for characterization of edible oil oxidation.
M2UO2(C2O4)2⋅nH2O compounds (M=K, Rb and Cs)have been prepared and characterized by chemical and thermal analyses as well as by X-ray diffraction and infrared
spectroscopy. X-ray powder data show that the compounds belong to an orthorhombic system. Thermal and infrared studies show
that the compounds decompose to M2UO4 through the formation of alkali metal carbonate and UO2 as intermediates. K2UO2(C2O4)2⋅3H2O, and Rb2UO2(C2O4)2⋅2H2O gave K2UO4, Rb2UO4 at 700 and 600C respectively, while in the case of Cs2UO2(C2O4)2⋅2H2O, the intermediate products of decomposition reacted to yield Cs2U4O13 at 1000C.
The thermal decomposition of the polypropylene and liquid paraffin mixtures with inorganic additives was studied in dynamic
conditions. Thus, typical thermal analyses were carried out and thermal decomposition of samples in a specially designed apparatus
was also processed. One can observe for samples of sufficiently low mass that thermal analysis allows clear distinction of
samples that contain and do not contain liquid paraffin, respectively. Moreover, it is possible to separate two stages of
the decomposition process. The relationship between the logarithm of conversion degree and temperature (so called three-parameter
model) was used for the description of these processes. Relations between coefficients in three-parameter equation in micro-scale,
and characteristic temperatures of thermal decomposition in laboratory scale were observed in spite of meaningful differences
in the course of the processes.
Authors:P. S. Epaminondas, K. L. G. V. Araújo, A. Lima de Souza, M. C. D. Silva, N. Queiroz, A. L. Souza, L. E. B. Soledade, I. M. G. Santos, and A. G. Souza
Chemical and thermal analyses of golden and brown flaxseeds were carried out for raw and toasted seeds aiming at evaluating their nutritional and thermo-oxidative properties. Moisture, lipids, protein, soluble carbohydrates, and ash contents were quantified. Concerning lipids and proteins, in average, no meaningful differences were observed for the two varieties, being also equivalent to the literature data. The golden variety had a lower amount of fibers and a higher amount of soluble carbohydrates than the brown variety. The techniques of thermogravimetry and differential scanning calorimetry were applied for elucidating the thermal degradation process of the seeds. The toasted gold and brown seeds were more stable to thermal decomposition than the raw seeds, under oxidative conditions. Golden seeds seem to be more susceptible to oxidation than brown seeds, under toasting conditions. Finally, no meaningful advantages were observed for the golden seeds in comparison to the brown ones.
Authors:Murat Turkyilmaz, Alper Onder, and Yakup Baran
Four polydentate azomehines and their mono- and binuclear Pt(II), Cu(II), and Ni(II) complexes were synthesized and characterized. The resulting complexes were characterized by FTIR, magnetic measurements, elemental analysis, conductivity measurements, and thermal analysis. Electronic spectra and magnetic susceptibility measurements sustain the proposed distorted square-planar structures for the copper complexes. The electronic spectra display the characteristic pattern of square-planar stereochemistry for the other complexes. The thermal analyses have evidenced the thermal intervals of stability and also the thermodynamic effects that accompany them. Azomethine complexes have a similar thermal behavior for the selected metal ions. The decomposition processes as water elimination, chloride anion removal as well as degradation of the organic ligands were observed.