Authors:J. L. Martín, J. M. Salla, A. Cadenato, and X. Ramis
It is known that experimental parameters may affect peak characteristics in DSC studies. Kinetic parameters calculated from isothermal and dynamic runs, can also be affected by the choice of experimental conditions.
The kinetic parameters of dehydration were determined under non-isothermal conditions for different polystyrenedivinylbenzene
sulfonic acid type cationites (DVB) and their dependence on the degree of cross-linking granulation, porosity, specific surface,
content of SO3M groups (M=Li, Na, K, Rb), nature of the alkali metal in partially neutralized -SO3H groups and heating rate was investigated.
A consecutive model of surface reaction, consisting of two steps (desorption and diffusion) was applied. It was concluded that diffusion modifies the temperature programmed desorption spectra, although the single peak curves appear. The differential method for calculation of kinetic parameters based on thesTM shift give values close to predicted ones only in the cases when particular steps are rate limiting. Generally, the desorption process have to be considered as a complex reaction, with the overall kinetic parameters. As a consequence of diffusion influence, the overall kinetic parameters are smaller than those for desorption step was obtained.
Authors:M. Villetti, J. Crespo, M. Soldi, A. Pires, R. Borsali, and V. Soldi
The thermal degradation of sodium hyaluronate, xanthan and methylcellulose was evaluated by thermogravimetric and infrared
analysis. Kinetic parameters such as activation energy and pre-exponential factor were determined considering the Ozawa and
Freeman–Carroll methods. The results suggest changes in the degradation mechanism with the fraction of mass loss for both
the studied polysaccharides. The activation energy values determined by the Freeman–Carroll method are higher than those obtained
by the Ozawa method under the same conditions, probably because in the first method a first order reaction was assumed and
the thermal history effects were eliminated since only one TG curve was used to determine the kinetic parameters. Low thermal
stability was observed for polyanions e.g. sodium hyaluronate (Na-Hy) and xanthan(XT) in comparison with methylcellulose (MC)
which is a neutral polysaccharide. By infrared spectroscopy, it was observed that at low temperatures there occured only the
scission of the exocyclic groups for both polysaccharides and that the scission of strong links in the backbone occurred at
high temperatures, in agreement with the kinetic parameters determined for the degradation reaction.
In the present work, the Coats-Redfern method was used to determine the kinetic parameters and the possible reaction mechanism
of the thermal degradation of ultra-high molecular mass polyethene and its composites with fiber monocrystals in static air
at three different heating rates − 6, 10 and 16 K min−1. The analysis of the results obtained showed that the thermal degradation process of pure ultra-high molecular mass polyethene
corresponded to a diffusion controlled reaction (three-dimentional diffusion, mechanism D3), while its composites with fiber monocrystals degraded by two concurrent mechanisms (diffusion one D3 and A1,F1 mechanism). The fiber monocrystals used increased the thermal stability of the composite materials obtained. The values of
the activation energy, frequency factor, the changes of entropy, enthalpy and Gibbs energy for the active complex of the composites
Authors:L. Nagy, J. Zsakó, Cs. Novák, Cs. Várhelyi, Gy. Vankó, and G. Liptay
A number of 15 [Fe(Diox#x00B7;H)2L2] type chelates and [Fe(Diox)3(BOR)2] clathrochelates (Diox#x00B7;H2 — dimethylglyoxime, glyoxime, propoxime, nyoxime, furyl-dioxime; L-pyridine, alkyl-pyridine derivatives, diethyl-phenyl-phosphine, diethyl-p-tolyl-phosphine) were obtained and characterized by means of far and middle FTIR and Mössbauer spectroscopic methods. Some structural problems were discussed on the basis of the optical data.The DSC measurements show the higher thermal stability of the clathrochelates without O—HO intramolecular hydrogen bonds (with asymmetric octahedral structure), as compared to the [Fe(Diox#x00B7;H)2L2] trans, symmetric chelates containing O—HO bonds. The kinetic parameters of the thermal decomposition of the complexes have been derived using the nomogram method.
Authors:J. Rocco, J. Lima, A. Frutuoso, K. Iha, M. Ionashiro, J. Matos, and M. Suárez-Iha
Thermal decomposition kinetics of solid rocket propellants based on hydroxyl-terminated polybutadiene-HTPB binder was studied
by applying the Arrhenius and Flynn-Wall-Ozawa's methods. The thermal decomposition data of the propellant samples were analyzed
by thermogravimetric analysis (TG/DTG) at different heating rates in the temperature range of 300-1200 K. TG curves showed
that the thermal degradation occurred in three main stages regardless of the plasticizer (DOA) raw material, the partial HTPB/IPDI
binder and the total ammonium perchlorate decompositions. The kinetic parameters Ea (activation energy) and A (pre-exponential factor) and the compensation parameter (Sp) were determined. The apparent activation energies obtained from different methods showed a very good agreement.
Using DSC technique, the chemical interaction in Bi2O3+MO2 mixtures resulting the Bi12MO20 phase, (M=Ti, Ge and Si) was monitored. Kinetic parameters for the primary stage of interaction were yielded by the non-isothermal method of kinetic evaluation of experimental heat flux DSC curves. The model of three-dimensional diffusion according to Jander was fitted as the best in a statistical sense.
The kinetic parameters for the thermal degradation of high impact polystyrene (HIPS) in presence of some metal oxides exhibit
reaction rate compensation effect. In thermal degradation of HIPS in presence of transition metal oxides different active
centers act simultaneously as reaction sites and macroradicals are formed through random chain scission, disproportion or
cyclization. Some oxides retard the polymer degradation through crosslinking and cyclization by the interaction of macroradicals
with the double bond in butadiene.
The thermal dehydration and decomposition of Zn(BF4)2·6H2O have been studied by TG, DTA and DSC analyses. It is found that the dehydration occurs in two steps. Following the experimental
results a thermal decomposition scheme of the compound under investigation is proposed. The enthalpies of dehydration have
been determined as well as the formal kinetic parameters are presented.