共查询到20条相似文献,搜索用时 15 毫秒
1.
P. Budrugeac 《Journal of Thermal Analysis and Calorimetry》2009,97(2):443-451
The thermo-oxidative degradation of a parchment recent manufactured from a goat skin has been investigated by TG/DTG, DSC
simultaneous analysis performed in static air atmosphere, at six heating rates in the range 3–15 K min−1. At the progressive heating in air atmosphere, the investigated material exhibits three main successive processes occurring
with formation of volatile products, namely the dehydration followed by two thermo-oxidative processes. The processing of
the non-isothermal data corresponding to the first process of thermo-oxidation was performed by using Netzsch Thermokinetics—a
Software Module for Kinetic Analysis. The dependence of activation energy, evaluated by isoconversional methods suggested
by Friedman, and Ozawa, Flynn and Wall, on the conversion degree and the relative high standard deviations of this quantity
show that the investigated process is a complex one. The mechanism and the corresponding kinetic parameters were determined
by Multivariate Non-linear Regression program. Three mechanisms, one consisting in four successive steps and two others in
five successive steps, exhibit the best F-test Fit Quality for TG curves. It was also used the previously suggested criterion, according to which the most probable
process mechanism correspond to the best agreement between E
FR
= E
FR
(α) (E
FR
is the activation energy evaluated by isoconversional method suggested by Friedman; α is the conversion degree) obtained
from non-isothermal experimental data and activation energy values, E
iso
, obtained by applying the differential method to isothermal data simulated using non-isothermal kinetic parameters. According
to this last criterion, the most probable mechanism of parchment oxidation consists in four successive steps. The contribution
of the thermo-oxidation process in the parchment damage by natural aging is discussed. 相似文献
2.
Y. Duan J. Li X. Yang X. -M. Cao L. Hu Z. -Y. Wang Y. -W. Liu C. -X. Wang 《Journal of Thermal Analysis and Calorimetry》2008,94(1):169-174
The thermal decomposition of strontium acetate hemihydrate has been studied by TG-DTA/DSC and TG coupled with Fourier transform
infrared spectroscopy (FTIR) under non-isothermal conditions in nitrogen gas from ambient temperature to 600°C. The TG-DTA/DSC
experiments indicate the decomposition goes mainly through two steps: the dehydration and the subsequent decomposition of
anhydrous strontium acetate into strontium carbonate. TG-FTIR analysis of the evolved products from the non-oxidative thermal
degradation indicates mainly the release of water, acetone and carbon dioxide. The model-free isoconversional methods are
employed to calculate the E
a of both steps at different conversion α from 0.1 to 0.9 with increment of 0.05. The relative constant apparent E
a values during dehydration (0.5<α<0.9) of strontium acetate hemihydrate and decomposition of anhydrous strontium acetate (0.5<α<0.9)
suggest that the simplex reactions involved in the corresponding thermal events. The most probable kinetic models during dehydration
and decomposition have been estimated by means of the master plots method. 相似文献
3.
B. Tiţa Eleonora Marian D. Tiţa Gabriela Vlase N. Doca T. Vlase 《Journal of Thermal Analysis and Calorimetry》2008,94(2):447-452
Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances.
TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability,
compatibility, polymorphism, kinetic analysis, phase transitions etc.).
The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process.
The results are further used to predict the system’s behaviour in various circumstances.
A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal
and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG
data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric
kinetics.
In the model-fitting methods the kinetic triplets (f(α), A and E
a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition.
The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation
energies on the extent of conversion.
It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous
work.
The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as
well as a different strategy of experimental data processing. 相似文献
4.
Abdollah Omrani Abbas Ali Rostami Fatemeh Ravari 《Journal of Thermal Analysis and Calorimetry》2013,111(1):677-683
The decomposition kinetics of glycerol diglycidyl ether (GDE)/3,3-dimethylglutaric anhydride/nanoalumina composite have been investigated by thermogravimetry analysis under nonisothermal mode. The activation energy, E a, of the solid-state decomposition process was evaluated using the advanced isoconversional method. From the experimental data, the dependence of conversion on temperature and activation energy was constructed allowing calculating the master plots. Our results showed that the decomposition mechanism at temperatures below 400 °C could be fitted by R2 kinetic model with E a = 143 kJ mol?1. The information about the kinetic parameters based only on thermal degradation data has been used for quick lifetime estimation at different temperatures. The Vyazovkin method was also employed to predict the times to reach α = 0.5 at isothermal mode using the activation energy calculated by the advanced isoconversional approaches. Scanning electron microscopy (SEM) analysis was carried out to investigate the fracture surface morphology. It was revealed from the SEM images that the presence of nanoalumina results in reinforcement of GDE matrix. 相似文献
5.
A. F. Santos L. Polese M. S. Crespi C. A. Ribeiro 《Journal of Thermal Analysis and Calorimetry》2009,96(1):287-291
The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent
kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably
managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(α)) could be calculated. Hence, the kinetic triplet (E±SD, logA±SD and f(α)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152±4 kJ mol−1, logA=14.1±0.2 s−1 for the kinetic model, and the autocatalytic model function was: f(α)=αm(1−α)n=α0.42(1−α)0.56. 相似文献
6.
The paper presents a non-isothermal kinetic study of the decomposition of Zn acetate-based gel precursors for ZnO thin films,
based on the thermogravimetric (TG) data. The evaluation of the dependence of the activation energy (E) on the mass loss (Δm) using the isoconversional methods (Friedman (FR), Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) has been presented
in a previous paper. It was obtained that the sample dried at 125°C for 8 h exhibits the activation energy independent on
the heating rate for the second decomposition step. In this paper the invariant kinetic parameter (IKP) method is used for
evaluating the invariant activation parameters, which were used for numerically evaluation of the function of conversion.
The value of the invariant activation energy is in a good agreement with those determined by isoconversional methods. In order
to determine the kinetic model, IKP method was associated with the criterion of coincidence of the kinetic parameters for
all heating rates. Finally, the following kinetic triplet was obtained: E=91.7 (±0.1) kJ mol−1, lnA(s−1)=16.174 (±0.020) and F1 kinetic model. 相似文献
7.
The thermal decomposition of three new reagent cyclohexylamine-p-tolylglyoxime (L1H2), tertiarybutyl amine-p-tolylglyoxime (L2H2) and secondary butylamine-p-tolylglyoxime (L3H2 and their Co-complexes were studied by both isothermal and nonisothermal methods. As expected, the complex structure of Co-complexes,
different steps with different activation energies were realized in decomposition process. Model-fitting and model-free kinetic
approaches were applied to nonisothermal and isothermal data. The kinetic triplet (f(α), A and E) related to nonisothermal model-fitting method can not be meaningfully compared with values obtained from isothermal method.
The complex nature of the multi-step process of the studied compounds was more easily revealed using a wider temperature range
in nonisothermal isoconversional method. 相似文献
8.
Arunjunai Raj Mahendran Günter Wuzella Andreas Kandelbauer Nicolai Aust 《Journal of Thermal Analysis and Calorimetry》2012,107(3):989-998
The thermal cure kinetics of an epoxidized linseed oil with methyl nadic anhydride as curing agent and 1-methyl imidazole
as catalyst was studied by differential scanning calorimetry (DSC). The curing process was evaluated by non-isothermal DSC
measurements; three iso-conversional methods for kinetic analysis of the original thermo-chemical data were applied to calculate
the changes in apparent activation energy in dependence of conversion during the cross-linking reaction. All three iso-conversional
methods provided consistent activation energy versus time profiles for the complex curing process. The accuracy and predictive
power of the kinetic methods were evaluated by isothermal DSC measurements performed at temperatures above the glass transition
temperature of the completely cured mixture (T
g∞
). It was found that the predictions obtained from the iso-conversional method by Vyazovkin yielded the best agreement with
the experimental values. The corresponding activation energy (E
a) regime showed an increase in E
a at the beginning of the curing which was followed by a continuous decrease as the cross-linking proceeded. This decrease
in E
a is explained by a diffusion controlled reaction kinetics which is caused by two phenomena, gelation and vitrification. Gelation
during curing of the epoxidized linseed/methyl nadic anhydride system was characterized by rheological measurements using
a plate/plate rheometer and vitrification of the system was confirmed experimentally by detecting a significant decrease in
complex heat capacity using alternating differential scanning calorimetry (ADSC) measurements. 相似文献
9.
Hernani S. Barud Clóvis A. Ribeiro Jorge M. V. Capela Marisa S. Crespi Sidney. J. L. Ribeiro Younes Messadeq 《Journal of Thermal Analysis and Calorimetry》2011,105(2):421-426
Cellulose can be obtained from innumerable sources such as cotton, trees, sugar cane bagasse, wood, bacteria, and others.
The bacterial cellulose (BC) produced by the Gram-negative acetic-acid bacterium Acetobacter xylinum has several unique properties. This BC is produced as highly hydrated membranes free of lignin and hemicelluloses and has
a higher molecular weight and higher crystallinity. Here, the thermal behavior of BC, was compared with those of microcrystalline
(MMC) and vegetal cellulose (VC). The kinetic parameters for the thermal decomposition step of the celluloses were determined
by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and at heating
rates of 5, 10, and 20 °C/min, the E
α
and B
α
terms could be determined and consequently the pre-exponential factor A
α as well as the kinetic model g(α). The pyrolysis of celluloses followed kinetic model
g(a) = [ - ln(1 - a)]1 \mathord