Authors:A. Rotaru, Anna Kropidłowska, Anca Moanţă, P. Rotaru, and E. Segal
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.
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.
Authors:N. Doca, Gabriela Vlase, T. Vlase, and G. Ilia
The thermal behavior of Cd2+ and Co2+ phenyl-vinyl-phosphonates was studied using two different experimental strategies: the coupled TG-EGA (FTIR) technique by
decomposition in nitrogen respectively air, and the kinetic analysis of TG data obtained in dynamic air atmosphere at four
heating rates. In nitrogen two decomposition steps were observed: the loss of crystallization water, respectively the decomposition
of the phenyl-vinyl radical. In air, the same dehydration was observed as the first step, but the second one is a thermooxidation
of the organic radical with formation of the pyrophosphoric anion.
The kinetic analysis of the TG non-isothermal data was performed by the isoconversional methods suggested by Friedman and
Flynn, Wall and Ozawa, as well as by the non-parametric (Sempere-Nomen) method. All processes put in evidence in TG curves
exhibit strong changes of the activation energy values with the conversion degree, which mean that these processes are complex
ones. Assuming that each of these processes consists in two steps, the application of non-parametric method leads to average
values of the activation energy close to the average values of this parameter obtained by isoconversional methods.
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 non-isothermal decomposition process of the powder sample of palladium acetylacetonate [Pd(acac)2] was investigated by thermogravimetric (TG) and the X-ray diffraction (XRD) techniques. Model-free isoconversional method
of Tang, applied to the investigated decomposition process, yield practically constant apparent activation energy in the range
of 0.05≤α≤0.95. It was established, that the Coats-Redfern (CR) method gives several statistically equivalent reaction models,
but only for the phase-boundary reaction models (R2 and R3), the calculated value of the apparent activation energy (E) is nearest to the values of E obtained by the Tang’s and Kissinger’s methods.
The apparent activation energy value obtained by the IKP method (132.4 kJ mol−1) displays a good agreement with the value of E obtained using the model-free analysis (130.3 kJ mol−1). The artificial isokinetic relationship (aIKR) was used for the numerical reconstruction of the experimental integral model
function, g(α). It was established that the numerically reconstructed experimental function follows R3 reaction model in the range of
α, taken from model-free analysis. Generally, decomposition process of Pd(acac)2 starts with initial nucleation which was characterized by rapid onset of an acceleratory reaction without presence of induction
A calculation technique based on the SVD algorithm is suggested for solving non-isothermal kinetics problems. The uncertainties in the sought parameter values are obtained by superimposing random (Gauss) noise on experimental dependences.