E. Segal

CRITICAL ANALYSIS OF THE ISOCONVERSIONAL METHODS FOR EVALUATING THE ACTIVATION ENERGY I. Theoretical background

It is demonstrated that, if the activation energy depends on the degree of conversion, its values obtained by isoconversional differential and integral methods are different.

Critical Considerations on the Isoconversional Methods. III. On the evaluation of the activation energy from non-isothermal data

The differential and integral isoconversional methods for evaluation the activation energy, described in the first note of this series, were applied for:a) simulated data for two successive reactions;b) dehydration of calcium oxalate monohydrate.It was shown that for these systems the activation energy depends on the conversion degree as well as on the method of evaluation.

Some problems concerning the evaluation of non-isothermal kinetic parameters

The validity of isoconversional methods used to evaluate the activation energy is discussed. The authors have shown that the Flynn-Wall-Ozawa and Friedman methods give results that agree with each other only if the activation energy does not change with the degree of conversion. A criterion for the reaction mechanism as expressed by the differential conversion function is suggested too.

Thermal stability of some azo-derivatives and their complexes

Abstractthis paper deals with the first investigation concerning the thermal stability of two 1-(2-benzothiazolyl)-3-methyl-4-azo-pyrazil-5-one derivatives and their Cu(II) coordination compounds of type ((C4H9)4N)2[Cu(L)2]. The thermal decomposition steps were established.

THERMAL DECOMPOSITION KINETICS OF SOME AROMATIC AZOMONOEHTERS Part II. Non-isothermal study of three liquid crystals in dynamic air atmosphere

Thermal analysis of three azomonoether dyes, exhibiting liquid-crystalline properties, was performed in dynamic air atmosphere. Thermal stability studies and the evaluation of the kinetic parameters of each physical or chemical transformations are essential for a full characterization, before attempting accurate thin films’ depositions of such materials used in non-linear optical applications. New synthesized dyes with general formula: where R is a nematogenic group: CN, CF3 or a highly polarizable group: NO2 were investigated using TG, DTG, DTA and DSC techniques, under non-isothermal regime. The evolved gases were analyzed by FTIR spectroscopy. The activation energies of the first decomposition step were evaluated for each compound, the obtained results revealing complex mechanisms.

Basic versatile program for nonisothermal kinetics Part II

Abstract A program to evaluate nonisothermal kinetic parameters by means of nine methods selected from the literature, in addition to generating the thermogravimetric curves, is presented.

Iron, nickel and zinc malates coordination compounds cynthesis, characterization and thermal behaviour

The coordinations compounds (NH4)[Fe(C4H4O5)(OH)2]·0.5H2O, [Ni(C4H4O5)]·3H2O and [Zn(C4H4O5)]·5H2O were synthesized by a precipitation method and characterized by chemical analysis, spectral (IR, UV-VIS) and magnetical investigations. In the range 50-600°C stepped thermal decompositions occur with formation of anhydrous malates, malonates, oxoacetates (iron and nickel compounds) and hydroxocarbonate (Zn compound) as intermediates observed by FT-IR spectroscopy. α-Fe2O3, NiO and ZnO constitute the final decomposition products.

Non-isothermal kinetics of reactions whose activation energy depends on the degree of conversion

A procedure for evaluating the non-isothermal kinetic parameters of reactions for which the activation energy depends on the degree of conversion is suggested. The procedure has been applied to the dehydration of calcium oxalate monohydrate and to the thermal degradation of poly(vinyl chloride) (PVC) and polychloroprene rubber.

On the use of Diefallah's composite integral method for the non-isothermal kinetic analysis of heterogeneous solid-gas reactions

SummaryThe paper contains an analysis of the used of Diefallah’s composite integral method of kinetic parameters evaluation. It is shown that the application of this method should be preceded by the application of an isoconversional method through which the dependence of the activation energy, E, on the conversion degree, a, should be established. If E depends on a, Diefallah’s composite integral method leads to erroneous results. If E does not depend on a, the true kinetic model should be comprised in the pre-established set of kinetic models. These observations were checked for two sets of non-isothermal data, namely: (a) the TG curves corresponding to the dehydration of CaC2O4·H2O; (b) the TG curves corresponding to the thermal decomposition of polyvinyl chloride (PVC).

Some Polynuclear Coordination Compounds Precursors of Chromites Synthesis, Physicochemical Characterization and Thermal Stability

The polynuclear coordination compounds LnCr(tartrate)3·nH2O where Ln(III)=La-Er, obtained through a precipitation method, were characterized on the basis of elemental analysis, their electronic and vibrational spectra and magnetic susceptibility measurements. The possibility of obtaining chromites through the transformations of the polynuclear coordination compounds in the solid state was considered. The thermal decompositions of these compounds, studied by TG and DTA methods, were found to follow an almost uniform pattern. The decompositions occurred in six-eight steps. The first two steps involved dehydration, and the third the transformation of tartrate anions to oxalate, followed by conversion to carbonate and oxocarbonate intermediates. The final product in each case was LnCrO3. A non-isothermal kinetic analysis of the first decomposition steps was performed, the most probable decomposition mechanism being selected and the kinetic parameters evaluated. The final products of the transformations were characterized.