A. G. de Souza

Comparative studies on some analytical methods : Thermal decomposition of powder milk

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.

Thermochemical parameters of complexes of di-isobutyldithiocarbamate with phosphorus-group elements

The standard molar enthalpy of formation of crystalline di-isobutyldithiocarbamate complexes of P, As, Sb and Bi(III) has been derived by solution calorimetry at 298.15 K. The corresponding standard molar enthalpies of sublimation were estimated by means of differential scanning calorimetry. From the standard molar enthalpies of formation of the gaseous chelates the homolytic and heterolytic mean metal-sulphur bond-dissociation enthalpies were calculated.

Thermal Behaviour of Some Terpenoids

The terpenoids acetyl sitosterol, lupeol, acetyl diosgenin and stigmasterol were studied. Comparison of the thermogravimetric curves and the activation energies of the terpenoids suggested the following sequence of thermal stability: acetyl sitosterol < acetyl diosgenin < lupeol < stigmasterol. The DSC curves allowed determination of the melting points and the degrees of purity. Comparison of the TG and DSC curves revealed the presence of phase transitions without mass loss that were attributed to rearrangements in the terpenoid molecules.

Synthesis and kinetic study by ozawa method of the thermal decomposition of complexes Ln(thd)3phen

Recently, highly luminescent lanthanide complexes with mixed ligands such as and β-diketone and two herobiaryl ligands have been synthesized and suggested as promising light-conversion molecular devices as described by several authors. The synthesis, luminescence, quantum yields, spectroscopic characteristics, structure, among others properties of these complexes, including the possibility of production thin film films from these materials have been discussed, but little is known about their thermal decomposition kinetics. In this work we report the determination of kinetic parameters of thermal decomposition of the complexes Gd(thd)3phen and Er(thd)3phen (thd=2,2,6,6-tetramethyl-3,5- heptanodione; phen=1,10-phenantroline) using the method proposed by Ozawa (1965). The kinetic parameters obtained for activation energy were: 90 and 87 kJ.mol-1, the values of frequency factor were: 2.3x107 and 2.0x107 s-1 for Gd(thd)3phen and Er(thd)3phen, respectively. On the kinetic energy of the complexes, we notice the following order in thermal stability: Gd(thd)3phen < Er(thd)3phen.

Synthesis and determination of the kinetic parameters for non-isothermal decomposition of complexes Ln(thd)3phen

In this work the kinetics of the thermal decomposition of two ß-diketone lanthanide complexes of the general formula Ln(thd)3phen (where Ln = Nd+3 or Tm+3, thd = 2,2,6,6- tetramethyl-3,5-heptanodione and phen = 1,10-phenantroline) has been studied. The powders were characterized by several techniques. Thermal decomposition of the complexes was studied by non-isothermal thermogravimetry techniques. The kinetic model that best describes the process of the thermal decomposition of the complexes it was determined through the method proposed by Coats-Redfern. The average values the activation energy obtained were 136 and 114 kJ.mol-1 for the complexes Nd(thd)3phen and Tm(thd)3phen, respectively. The kinetic models that best described the thermal decomposition reaction the both complexes were R2. The model R2 indicating that the mechanism is controlled by phase-boundary reaction (cylindrical symmetry) and is defined by the function g(α) = 2[1-(1-a)1/2], indicating a mean reaction order. The values of activation energy suggests the following decreasing order of stability: Nd(thd)3phen > Tm(thd)3phen.

Natural clay applied to the clarification of used automotive lubricating oil

Clarification process using clays is widely used in the used lubricating oils re-refining industry, mainly because of its adsorbent capacity to retain impurities. This study aimed to the determination of optimal conditions for used lubricating oil clarification process, using natural clays as well as its recovery to be re-used to the process. The re-refining process of used lubricating oil was optimized from experimental design. Recovered clays showed no significant changes in their original structures, according to the X-ray diffraction, infrared spectroscopy, and thermogravimetric analyzes. The results of used lubricating oil characterizations were in accordance to the ANP resolution no 130, which regulates its commercialization in the country. All solvents were recovered by vacuum distillation.

Synthesis and Thermal Characterization of Luminescent Powers of Terbium (III) with Mixed Ligands

This work deals with the synthesis and thermal decomposition of complexes of general formula: Ln(ß-dik)3L (where Ln=Tb+3, ß-dik=4,4,4-trifluoro-1-phenyl-1,3- butanedione(btfa) and L=1,10-fenantroline(phen) or 2,2-bipiridine(bipy). The powders were characterized by melting point, FTIR spectroscopy, UV-visible, elemental analysis, scanning differential calorimeter(DSC) and thermogravimetry(TG). The TG/DSC curves were obtained simultaneously in a system DSC-TGA, under nitrogen atmosphere. The experimental conditions were: 0.83 ml.s-1 carrier gas flow, 2.0±0.5 mg samples and 10°C.min-1 heating rate. The CHN elemental analysis of the Tb(btfa)3bipy and Tb(btfa)3phen complexes, are in good agreement with the expected values. The IR spectra evinced that the metal ion is coordinated to the ligands via C=O and C-N groups. The TG/DTG/DSC curves of the complexes show that they decompose before melting. The profiles of the thermal decomposition of the Tb(btfa)3phen and Tb(btfa)3bipy showed six and five decomposition stages, respectively. Our data suggests that the thermal stability of the complexes under investigation followed the order: Tb(btfa)3phen < Tb(btfa)3bipy.