Non-isothermal kinetic applied to thermal decomposition of commercial alkyd varnish

Samples of commercial alkyd resin varnish were spread in a film form on slides, dried at room temperature and exposed to solar radiation from one day up to seven months.Thermogravimetric measurements have been done. Based on the TG data, the Flynn-Wall isoconversional method was applied. The activation energy varied between 176-154 kJ mol(-1) and logA was between 15.5-12.9 min(-1) for A, B and C samples at 95% confidence level.

Thermal study of cyclopalladated complexes of the type [Pd-2(dmba)(2)X-2(bpe)] - (X=NO3-, Cl-, N-3(-), NCO-, NCS-; bpe=trans-1,2-bis(4-pyridyl)ethylene)

The synthesis, characterization and thermal analysis of the novel cyclometallated compounds [Pd-2(dmba)(2)Cl-2(mu-bpe)] (1), [Pd-2(dmba)(2)(N-3)(2)(mu-bpe)] (2), [Pd-2(dmba)(2)(NCO)(2)(mu-bpe)] (3), [Pd-2(dmba)(2)(SCN)(2)(mu-bpe)] (4), [Pd-2(dmba)(2)(NO3)(2)(mu-bpe)] (5) (bpe=trans-1,2-bis(4-pyridyl)ethylene; dmba=N,N-dimethylbenzylamine) are described. The thermal stability of [Pd-2(dmba)(2)X-2(mu-bpe)] complexes varies in the sequence 1 > 4 > 3 > 2 > 5. The final residues of the thermal decompositions were characterized as metallic palladium by X-ray powder diffraction.

Structural and spectroscopic analysis of gamma-Al2O3 to alpha-Al2O3-CoAl2O4 phase transition

Co-doped alumina powders were synthesized by means of the polymeric precursor method to obtain ceramic pigments. The effect of different contents of Co2+ on phase transition gamma to alpha-Al2O3 and appearing of CoAl2O4 spinel were studied by means of X-ray diffraction. A partial phase diagram of the system CoAl2O3 was proposed from these data by means of determination of the percentages of these phases according to the calcining temperature. Critical particle size to phase transition was determined by means of calculations of crystallite size and determination of superficial area through the BET method. UV-vis spectroscopy of the samples allow to compare the band shift with the phase transition. Besides, a study of thermal stability and intensity of the blue coloration of the synthesized powders with the presence of cobalt in relation to the calcining temperature was accomplished and compared to the phase transition. The results show that the higher blue color intensity was obtained for the powders with Co-doped gamma-Al2O3 closest of phase transition to alpha-Al2O3 + CoAl2O4. (c) 2005 Elsevier B.V. All rights reserved.

Thermal degradation of a composite solid propellant examined by DSC - Kinetic study

The thermal decomposition of ammonium perchlorate (AP)/hydroxyl-terminated-polybutadiene (HTPB), the AP/HTPB solid propellant, was studied at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in non-isothermal conditions. The Arrhenius Parameters were estimated according to the Ozawa method. The calculated activation energy was 134.5 W mol(-1), the pre-exponential factor, A, was 2.04.10(10) min(-1) and the reaction order for the global composite decomposition was estimated in 0.7 by the kinetic Shimadzu software based on the Ozawa method. The Kissinger method for obtaining the activation energy value was also used for comparison. These results are discussed here.

Solid-state compounds of 4-methoxybenzylidenepyruvate and cinnamylidenepyruvates with thorium (IV) - Preparation and thermal studies

By close control of experimental variables affecting precipitation, solid-state compounds of the type Th(OH)(m)L4-m.nH(2)O, where L stands for 4-methoxy-benzylidenepyruvate, cinnamylidenepyruvate or 4-dimethylaminocinnamylidene-pyruvate; m=0 to 3 and n=0.5-3 were isolated. Chemical analysis, TG, DTG, DSC and X-ray powder diffractometry have been employed to characterize and to study the thermal behavior of these compounds in dynamic air atmosphere. In all cases, hydration water is slowly lost between 30 and 160degreesC; a continuous, slow rate, mass loss is observed thereafter and beyond 280-400degreesC the rate of decomposition/oxidation increased rapidly, to give ThO2 as the final product, beginning at 412-510degreesC. The results associated with the hydroxo-compounds indicate that the loss of constitution water (OH ions) and the decomposition / oxidation of the organic moieties occur as simultaneous process.

Composting of urban solid residues (USR) by different dispositions - Kinetics of thermal decomposition

The thermal behavior and non-isothermal kinetics of thermal decomposition of three different kinds of composting of the USR like: stack with drilled PVC tubes (ST), revolved stack (SR) and stack with material of structure (SM), from the usine of composing of Araraquara city, São Paulo state, Brazil, within a period of 132 days of composting were studied.Results from TG, DTG and DSC curves obtained on inert atmosphere indicated that the cellulosic fraction present, despite the slow degradation during the composting process, is thermally less stable than other substances originated from that process. Due to that behavior, the cellulosic fraction decomposition could be kinetically evaluated through non-isothermal methods of analysis.The values obtained were: average activation energy, E-a=248, 257 and 259 kJ mol(-1) and pre-exponential factor, logA=21.4, 22.5, 22.7 min(-1), to the ST, SR and SM, respectively.From E-a and logA values and DSC curves, Malek procedure could be applied, suggesting that the SB (Sestak-Berggren) kinetic model is the appropriated one to the first thermal decomposition step.

An investigation of the thermal behavior of heterobimetallic species containing copper(II) and tetracyanopalladate(II)

Synthesis, characterization and thermal behavior of four compounds that have the general formula [Cu{Pd(CN)(4)}(L)(x)](n), in which en = 1,2-diaminoethane and pn = 1,3-diaminopropane (L = en, x = 1 (I); L = pn, x = 1 (II); L = en, x = 2 (III); L = pn, x = 2 (IV)) were described in this work. The complexes were studied by elemental analysis, infrared spectroscopy (IR), differential thermal analysis (DTA) and thermogravimetry (TG) and the residues of the thermal decomposition were characterized by X-ray powder diffraction and found as a mixture of CuO and PdO. The stoichiometry of the compounds was established via thermogravimetric and elemental analyses and their structures were proposed as coordination polymers based on their infrared spectra. The following thermal stability sequence was found: IV < I=II < III.

Solid-state compounds of 2-chlorobenzylidenepyruvate with some bivalent metal ions - Synthesis, characterization and thermal behaviour

Solid-state M-2-Cl-BP, where M stands for Mn, Fe, Co, Ni, Cu, Zn and Pb and 2-Cl-BP is 2-chlorobenzylidenepyruvate, have been synthesized. Thermogravimetry and derivative thermogravimetry (TG/DTG), simultaneous thermogravimetry and differential thermal analysis (TG-DTA), X-ray powder diffractometry, infrared spectroscopy, elemental analysis, and complexometry were used to characterize and to study the thermal behaviour of these compounds. The results led to information about the composition, dehydration, thermal stability and thermal decomposition of the isolated compounds.

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(beta-dik)(3)L (where Ln=Tb(+3), beta-dik=4,4,4-trifluoro-1-phenyl-1,3butanedione(btfa) and L=1,10-fenantroline(phen) or 2,2-bipiridine(bipy). The powders were characterized by melting point, FTIR spectroscopy, LTV-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 degrees C.min(-1) heating rate. The CHN elemental analysis of the Tb(btfa)(3)bipy and Tb(btfa)(3)phen 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)(3)phen < Tb(btfa)(3)bipy.

Thermal degradation of geomembranes after exposure to heat

HDPE and PVC geomembranes are sensitive to changes in their properties when in contact with high temperatures. The effects of hot temperature on polymeric geomembranes are assessed by the ASTM D794 and ASTM D5721.This paper brings an analysis of degradation of the Poly Vinyl Chloride (PVC) and High Density Poly Ethylene (HDPE) geomembranes when exposed to conventional and air oven after specific periods.. Mechanical and physical properties were evaluated. OIT tests were also performanced to evaluate the level of oxidation degradation occurred on the HDPE geomembranes. Geomembranes of two thicknesses were tested: 1.0, 2.0 nun (PVC) and 0.8, 2.5 mm, (HDPE). The results obtained show, for example, that after the last period of exposure, the PVC geomembranes (1.0, 2.0 mm) were more rigid and stiffer than fresh samples. The HDPE geomembranes, on the other hand, when exposed to heat presented increases in deformation. OIT tests showed efficient to detect some level of degradation on the HDPE geomembranes.

Thermal behavior of the maleic anhydride modified poly(3-hydroxybutyrate)

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 110 degrees C for 1 h with 5% v/v triethylamine.

Structural carbon/epoxy prepregs properties comparison by thermal and rheological analyses

Two different carbon/epoxy prepreg materials were characterized and compared using thermal (DSC, TGA, and DMA) and rheological analyses. A prepreg system (carbon fiber preimpregnated with epoxy resin F584) that is currently used in the commercial airplane industry was compared with a prepreg system that is a prospective candidate for the same applications (carbon fiber prepreg/epoxy resin 8552). The differences in the curing kinetics mechanisms of both prepreg systems were identified through the DSC, TGA, DMA, and rheological analyses. Based on these thermal analysis techniques, it was verified that the curing of both epoxy resin systems follow a cure kinetic of n order. Even though their reaction heats were found to be slightly different, the kinetics of these systems were nevertheless very similar. The activation energies for both prepreg systems were determined by DSC analysis, using Arrhenius's method, and were found to be quite similar. DMA measurements of the cured prepregs demonstrated that they exhibited similar degrees of cure and different glass transition temperatures. Furthermore, the use of the rheological analysis revealed small differences in the gel temperatures of the two prepreg systems that were examined.

Synthesis, characterization and thermal behaviour of solid-state compounds of yttrium and lanthanide benzoates

Solid-state Ln(Bz)(3)center dot H(2)O compounds where Ln stands for trivalent yttrium or lanthanides and Bz is benzoate have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffractometry, infrared spectroscopy and chemical analysis were used to characterize and to study the thermal behaviour of these compounds. The results led to information about the composition, dehydration, thermal stability and thermal decomposition of the isolated compounds.

Preparation and thermal decomposition of solid state compounds of 4-methoxybenzylidenepyruvate with alkali earth metals, except beryllium and radium

Solid compounds of general formula ML(2) . nH(2)O [where M is Mg, Ca, Sr or Ba; L=4 methoxybenzylidenepyruvate (4-MeO-BP); n = 4, 1 or 0] have been synthetized. Thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), x-ray diffraction powder patterns and elemental analysis have been used to characterize the compounds. The thermal stability of these compounds as well as that of the decomposition products were studied using Pt or Al2O3 crucibles in an air or a CO2 atmosphere.

Influence of silver additions on the thermal behavior of the Cu-8 mass% Al alloy

The influence of additions of 2, 4, 6, 8, 10 and 12 mass% Ag on the thermal behavior of the Cu-8 mass% Al alloy was studied using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicate that the presence of silver introduces new thermal events, due to the formation of a silver-rich phase and, for additions of 10 and 12 mass% Ag, it is possible to verify the formation of the gamma (1) phase (Cu9Al4) and the metastable transitions which are only observed in alloys with a minimum of 9 mass% Al.