The thermal decompositions of ammonium metavanadate, molybdic acid and ammonium phosphomolybdate supported on carborundum
or silica were subjected to non-isothermal kinetic study. The compensation effect is discussed in connection with the quantitative
estimation of the support effect.
Summary Many years ago, thermal analysis earned its place as a current instrumentation technique in assisting/solving the analytical problems of pharmaceuticals. A relative new trend is the study of the thermal stability of food additives in connection with the molecular structure. The studied compounds were: natrium and potassium glutamate, respectively natrium, potassium and calcium benzoate. The thermogravimetric data (TG) were obtained in dynamic nitrogen atmosphere, with open Pt crucible and heating rates of 5, 7, 10 and 12 K min-1, using a Perkin-Elmer TGA7 equipment. In order to estimate the non-isothermal kinetic parameters, the Friedman's differential-isoconversional method and the method suggested by Budrugeac and Segal (based on the compensation effect) were used. A variation of the activation energy vs. conversion was observed by using Friedman's method. The discrimination between the different reaction steps was performed by the non-parametric kinetic method, suggested by Sempere, Nomen and Serra. This is due to a complex process. The thermal stability data are very important for avoiding a possible misuse by processing of the studied food additives.
This paper describes the influences of some parameters relevant to biomass pyrolysis on the numerical solutions of the nonisothermal
nth-order distributed activation energy model (DAEM) involved the Weibull distribution. Investigated parameters are the integral
upper limit, the frequency factor, heating rate, the reaction order and the shape, scale and location parameters of the Weibull
distribution. Those influences can be used for the determination of the kinetic parameters of the nonisothermal nth-order Weibull DAEM from thermoanalytical data of biomass pyrolysis.
A new method of the multiple rate iso-temperature was used to define the most probable mechanism g(α) of a reaction; the iterative iso-conversional procedure has been employed to estimate apparent activation energy Ea, the pre-exponential factor A was obtained on the basis of Ea and g(α). In this new method, the thermal analysis kinetics triplet of dehydration of calcium oxalate monohydrate is determined,
which apparent activation energy Ea is 82.83 kJ mol-1, pre-exponential factor A is 1.142105-1.235105 s-1, the most probable mechanism belongs to phase boundary reaction Rn with integral form g(α)=1-(1-α)n and differential form f(α)=n(1-α)1-(1/n), where accommodation factor n=2.40-1.40.
Authors:Z. Lu, Y. Ding, Y. Xu, Z. Yao, Q. Liu, and J. Lang
Thermal analysis on two new heterometallic sulfide clusters, [PPh4]2[WS3(CuBr)3]2 and [PPh4]2[MoS3(CuBr)3]2 (where PPh4=tetraphenyl
phosphonium, =pentamethylcyclopenta- dienyl), was carried out using a simultaneous TG-DTA unit in an atmosphere of flowing
nitrogen and at various heating rates. Supplemented using EDS method, their thermal behavior and properties, together with
the composition of their intermediate product, were examined and discussed in connection with their distinctive molecular
structure as a dianion, which provided some theoretically and practically significant information. Both clusters decomposed
in a two-step mode, but without a stable new phase composed of Mo/W-Cu-S formed during their decomposition process as we expected.
Based on TG-DTG data, four methods, i.e. Achar-Brindley-Sharp, Coats-Redfern, Kissinger and Flynn- Wall-Ozawa equation, were
used to calculate the non-isothermal kinetic parameters and to determine the most probable mechanisms.
The complex of [Tb2(o-MBA)6(PHEN)2] (o-MBA: o-methylbenzoate and PHEN:1,10-phenanthroline) were synthesized and characterized by elemental analysis and IR spectroscopy.
The thermal behavior of [Tb2(o-MBA)6(PHEN)2] in dynamic nitrogen atmosphere was investigated by TG-DTG techniques. The thermal decomposition process of the [Tb2(o-MBA)6(PHEN)2] occurred in three consecutive stages at Tp 294, 427 and 512C. The kinetic parameters and mechanisms of first decomposition stage from analysis of the TG-DTG curves
were obtained by the Malek method.
Kinetics of exothermal decomposition of 2-nitrophenylhydrazine (2-NPH) and 4-nitrophenylhydrazine (4-NPH) was investigated
by differential scanning calorimetry. The isoconversional methods, Friedman and Flynn-Wall-Ozawa, were applied to determine
the activation parameters from the common analysis of multiple curves measured at different heating rates. For the processes
involving two-step reactions the multivariate non-linear regression was used. A good agreement between the experimental and
the fitted data was found.
Authors:A. Modestov, P. Poplaukhin, and N. Lyakhov
Some peculiar properties of lithium sulfate monohydrate dehydration kinetics are investigated. Experiments were carried out under both isothermal and non-isothermal conditions on the bulk single crystals (1 cm). Under both heating modes some new data were obtained. Uncommon high dehydration process rate under isothermal conditions and linear dependence of this rate under non-isothermal ones were discovered. Experiments over the water saturated porous ceramics drying and over the water vapors transmitting through the layer of preliminary dehydrated lithium sulfate were carried out. It is attempted to explain observed phenomena considering heat- and mass-transfer conditions.
Authors:Luciana Guinesi, C. Ribeiro, Marisa Crespi, A. Santos, and Marisa Capela
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.
The kinetics of dehydration and decomposition of VOSO4�2H2O, VOSO4 and VOSeO3�H2O was studied under non-isothermal heating on a derivatograph. The stages and products of the thermal decomposition were determined.
It was proved that VOSO4�2H2O decomposes to V2O5 while VOSeO3�H2O − to V2O4. A number of kinetic models and calculation procedures were used to determine the values of the kinetic parameters characterizing
the process. The parameters calculated were compared and analyzed. IR-spectra of the initial substances and the solid residue
after decomposition are presented.