Authors:B. Janković, B. Adnađević, and J. Jovanović
An isothermal dehydration of equilibrium swollen poly(acrylic acid) hydrogel in the temperature range from 306 to 361 K was
investigated. The specific parameters connected with shape of the conversion curves were defined. The activation parameters
(E, lnA) of the isothermal dehydration of equilibrium swollen poly(acrylic acid) hydrogel were calculated, using Johnson-Mehl-Avrami
(JMA), ‘initial rate’ and ’stationary point’ methods. The reaction models for the investigated dehydration are determined
using the ‘model-fitting’ method. It was established that both, the reaction model and activation parameters of the hydrogel
dehydration were completely different for the isothermal process than for the non-isothermal one. It was found that the increase
in dehydration temperature lead to the changes in isothermal kinetic model for the investigated hydrogel dehydration. It was
established that the apparent activation energy (E) of hydrogel dehydration is similar to the value of the molar enthalpy
of water evaporation.
In this research, the relationship between particle size and combustion kinetics and combustion properties of lignite samples
was examined by utilizing the thermogravimetric (TG/DTG) and differential thermal analysis (DTA) techniques. The lignite samples
separated into different size fractions were subjected to non-isothermal thermogravimetric analysis between ambient and 900�C
in the presence of 50 mL min−1 air flow rate. Activation energy (E) and Arrhenius constant (Ar) of combustion reaction of each size was evaluated by applying Arrhenius kinetic model to the resulting data. Combustion
properties of the samples were interpreted by careful examination of the curves. The apparent activation energies in major
combustion region were calculated as 41.03 and 53.11 kJ mol−1 for the largest size (−2360+2000 μm) and the finest size (−38 μm), respectively.
For the enhancement of thermal stability of poly(p-dioxanone) (PPDO), the isocyanate end-capping reagent was prepared by treatment of toluene-2,4-diisocyanate with an equivalent
of 1-hexyl alcohol. The end-capping reagent and the end-capping PPDO with an inherent viscosity of 0.26 dL g−1 were characterized by FTIR and 1H-NMR. Thermal stability of the end-capping PPDO with an inherent viscosity of 0.92 dL g−1 was investigated isothermally and non-isothermally under air atmosphere using thermogravimetry. It has been shown that the
addition of the prepared isocyanate can enhance significantly the thermal stability of PPDO. The activation energies for non-isothermal
degradation estimated by Kissinger method and Friedman method are 91, 81 kJ mol−1 for as-prepared PPDO, and 160, 149 kJ mol−1 for the end-capping PPDO, respectively. The activation energy increases by about 70 kJ mol−1 through the end-capping.
Authors:A. Małecki, B. Prochowska-Klisch, and R. Gajerski
It has been found that the modified Zhuravlev equation, [(1−α)−1/3−1]2=ktn, which describes the kinetics of oxidation of V2O4 and V6O13 in the temperature range 820–900 K and in the oxygen pressure range 1.0–20 kPa, can be derived via the assumption that the
changes in the observed activation energy result from the changing contributions of the two diffusion processes controlling
the reaction rate. The values of the observed activation energy are in the range 160–175 kJ mol−1 for V2O4 and 188–201 kJ mol−1 for V6O13 in the scope of the experimental oxygen pressures and temperatures and conversion degrees of 0.1–0.9.
Effects induced by γ -irradiation in the dose range of 0-10 Mrad on Tuffak polycarbonate track detector films have been studied
by thermogravimetry (TG). The samples were irradiated with 60Co γ -rays for doses of 3, 5 and 10 Mrad. The TG studies indicate that unirradiated and the γ -irradiated samples degrade
in two steps. The kinetics of the two steps of degradation was also evaluated from the TG curves. Irradiation enhances the
degradation rate and the effect increases further with increasing radiation dose. The activation energy values calculated
for all the steps decrease on irradiation. A linear relationship observed between the decrease in activation energy and the
dose received by the sample suggests the possibility of the use of Tuffak polycarbonate detector as γ dosimeter.
Authors:W. Lopes, Crislene Morais, A. Souza, V. Leite, and B. de A. Firmo
decomposition kinetic of three lanthanide mixed complexes with the general
formula of Ln(thd)3phen (where Ln=Nd3+,
Sm3+ or Er3+, thd=2,2,6,6-tetramethyl-3,5-heptanodione and phen=1,10-phenanthroline) has been studied in this
work. The powders were characterized by their melting point, elemental analysis,
FTIR spectroscopy and thermogravimetry. The isothermal TG curves have been
recorded under the same conditions at 265–285, 265–285 and 250–270°C
for Nd(thd)3phen, Sm(thd)3phen
and Er(thd)3phen, respectively.
parameters, i.e. activation energy, reaction order and frequency factor were
obtained through the technique of lineal regression using the relation g(α)=kt+g0. The analysis was done
at decomposed fractions between 0.10–0.90. The values of activation
energy were: 114.10, 114.24 and 115.04 kJ mol–1
for the Nd(thd)3phen, Sm(thd)3phen
and Er(thd)3phen complexes, respectively. The kinetic
models that best described the isothermal decomposition reaction the complexes
were R1 and R2. The values of activation energy suggests the following decreasing
order of stability: Nd(thd)3phen<Sm(thd)3phen<Er(thd)3phen.
The aim of this work is to highlight the importance of controlling the residual water vapour pressure above the sample as
well as the rate of the thermal decomposition during the thermal dehydration of cerium cyclotriphosphate trihydrate CeP3O9·3H2O.
For this reason, the dehydration of the titled compound was followed by both techniques: the constant rate thermal analysis
at PH2O = 5 hPa and the conventional TG-DTA in air.
It has been shown that the pathway of the thermal dehydration depends strongly on the nature of atmosphere above the sample.
However, in air atmosphere CeP3O9·3H2O decomposes in two well defined steps to give first an amorphous, phase in the temperature range 440–632 K, then the cerium
polyphosphate Ce(PO3)3 crystallizing in orthorhombic system (C2221) at T>632 K. Whereas decomposition carried out at 5 hPa water vapour pressure, also occurring in two steps, leads first to a crystallized
intermediate monohydrate at 259<T<343 K and second to a crystallized anhydrous cerium polyphosphate, at 343<T<791 K, with a structure different from those of all lanthanide polyphosphate known actually and particularly from that of
Ce(PO3)3 obtained in air.
The activation energy corresponding to the dehydration of the initial phosphate was also measured experimentally by means
of two CRTA curves and was found equal to 81±5 kJ mol−1.
Authors:W. Sułkowski, J. Borek, A. Danch, A. Radoń, A. Sułkowska, J. Ossowski, G. Toborowicz, and A. Bernatek
Spontaneous structural changes of a polymer that is its ageing due to thermal energy, radiation energy, chemical compounds
and micro-organisms lasting at least several season cycles change the characteristics of polymer products. Changes of polymer
characteristics found during ageing can be reversible or irreversible. The most substantial changes occur as the result of
UV radiation. Tests of selected aliphatic diamides of terephthalic acid as stabilisers of low density polyethylene (LD-PE)
used for the production of gardening films were performed. Accelerated ageing of films for a period of one year was done in
the Xenotest Alpha type apparatus. Studies were made for 0.1 mm thick commercial films. Studies of selected mechanical properties
of LD-PE films without stabilisers and of LD-PE sheeting containing an addition of one of the synthesised diamides of terephthalic
acid or the standard Tinuvin 783 stabiliser were performed before and after the ageing process. To determine the effect of
stabilisers on the ageing process of LD-PE films, thermogravimetric analysis was applied. This allowed us to determine the
decomposition activation energy of the investigated films before and after the ageing process and the influence of stabilisers
on the observed changes.
Reaction kinetics of the formation of TiC by calciothermic reduction of TiO2 in presence of carbon have been investigated using thermal analysis (TG-DTA) of a powder mixture of TiO2, Ca, and C in argon atmosphere at different heating rates. Both the reaction initiation and the peak temperatures are found
to increase with heating rates. The appearance of exothermic peaks in the DTA plots after Ca melting indicates the reduction
of TiO2 by liquid calcium and formation of TiC by in-situ reaction of Ti with C. The apparent activation energy of the process has
been found to be 170.80.5 kJ mol-1.
Authors:M. Gönen, D. Balköse, F. İnal, and S. Ülkü
In this research, the effects of zinc stearate addition on paraffin wax degradation were investigated by differential scanning
calorimetry (DSC) and thermogravimetry (TG). The apparent activation energies of wax decomposition in nitrogen and air atmospheres
were determined as 76 and 37 kJ mol−1, respectively applying Kissinger method to TG data. The degradation rate constants of paraffin containing zinc stearate (0.1–0.5%)
were found to be almost two times greater than that of paraffin only in air atmosphere. However, zinc stearate did not affect
the rate constants in nitrogen significantly.