Authors:H. Hoshi, E. Yonemochi, M. Takagi, Y. Yoshihashi, and K. Terada
Nedocromil sodium has a number of known hydrate states, a monohydrate, a trihydrate and a heptahemihydrate, including an amorphous
state. Effect of grinding on the hydration states of nedocromil sodium crystals was studied. After grinding the trihydrate,
heptahemihydrate was observed in the ground sample, even though, the water content in the ground sample was not sufficient
to cover the heptahemihydrate’s hydration level. On the other hand, in the ground heptahemihydrate, trihydrate was existed.
Apparent activation energies (ΔE) for hydrates, monohydrate→anhydrate, trihydrate→monohydrate and heptahemihydrate→amorphous(anhydrate), were calculated using
TG data. ΔE for the dehydration of heptahemihydrate was significantly lower than that of other hydrates. Obtained ΔE data
explained the inter-conversion behavior of nedocromil sodium induced by grinding.
Authors:B. Janković, B. Adnađević, and J. Jovanović
Kinetics of dehydration of equilibrium swollen poly(acrylic acid) hydrogel was investigated using methods of non-isothermal
thermal analysis. Methods of Kissinger, Coats-Redfern, Van Krevelen and Horowitz-Metzger were applied for determination the
kinetics parameters: activation energy (E), pre-exponent (lnA) as well as the kinetics model ƒ(69) for the process of hydrogel dehydration under different heating rates. An existence
of good agreement between determined values of kinetic parameters (Eand A), which were obtained applying different methods under the same heating rate. Functional relationship between changes of
kinetic parameters of dehydration and changes of heating rate was established. An existence of compensation effect is accepted
and explanation of compensation effect appearance during the hydrogel dehydration is suggested.
Authors:H. L. Anderson, R. Strey, A. Kemmler, and D. Haberland
For the calculation of kinetic parameters from thermal data files numeric optimization has been well introduced. But suitable starting values near the global minimum of the sum of deviation squares are needed for a successfully parameter estimation. Namely the search for starting values requires a lot of time and diminishes the effectiveness of the total procedure. Therefore we have developed an algorithm of the automatic search of starting values for the optimization of activation energy end frequency factor of a chemical reaction.
This search procedure uses the knowledge of the specific course of the correspondingSDS surface in the near of its global minimum. In this area theSDS describes two plateaus separated by a narrow valley. The search procedure avoids starting values at one of these plateaus. This PC program is part of the complex software package TA-kin v3.3 for kinetic evaluation of thermal measurements.
Authors:G. Chądzyński, J. Stępień-Damm, and Z. Damm
Thermogravimetric in situ measurements of oxygen loss from (RE)Ba2Cu3O6 samples (RE=Y, Nd, Er) heated isothermally in a relatively high dynamic vacuum were made with a Cahn RG electrobalance. Single-phase
orthorhombic samples of composition (RE)Ba2Cu3O7-x (highest oxygen content) were synthesized from stoichiometric (1:2:3) mixtures of high-purity (RE)2O3, BaCO3 and CuO. The original 1:2:3 mixture was prepared by the two-stage procedure described earlier. The crystal structure of the
sample in the original orthorhombic phase was controlled by the X-ray powder method (CuKα radiation) using a Stadi P Stoe
diffractometer with a position-sensitive detector. The decomposition curves are described by the sum of exponential terms
corresponding to rapid and slow first-order processes in which differently sized grains of the powder samples are involved.
The activation energies are estimated from appropriate Arrhenius plots.
The self-condensation reactions of 2- and 4-mono-methylol phenols (2-MMP and 4-MMP), in the presence of varying concentrations
of NaOH, have been studied by differential scanning calorimetry (DSC). The reaction exotherms were analysed to derive the
activation energy, Ea, and the heat of reaction, HT, for the condensation reactions. In the case of 2-MMP an increase in NaOH:2-MMP molar ratio caused an increased in Ea and a decrease in HT up to a molar ratio of 0.6:1. However, for 4-MMP, an increase in NaOH concentration caused an increase in Ea up to a molar ratio of 0.3:1 beyond which there appeared to be no further effect. The presence of NaOH had no effect on HT for this compound. The results suggest that in the range of NaOH concentration used the effect of NaOH was substantially
greater on 2-MMP compared to 4-MMP.
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.
Authors:S. Vyazovkin, J. Stone, and N. Sbirrazzuoli
Summary By applying an advanced isoconversional method to DSC data one can evaluate a dependence of the effective activation energy (the temperature coefficient of the growth rate) on the relative extent of melt crystallization. The conversion dependence can further be converted into a temperature dependence and parameterized in terms of the Hoffman-Lauritzen equation. For poly(ethylene terephthalate) (PET) we observe a transition from regime I to II. Poly(ethylene oxide) (PEO) crystallization appears to begin in regime II and then undergoes 2 consecutive changes that however cannot be clearly interpreted as regime III. The Kg and sse parameters obtained for regime I and II (PET) and regime II (PEO) are consistent with the respective parameters reported for isothermal crystallization.
Summary Simulation of thermal ageing is an important part of qualification of materials designed for the use in nuclear power plants (NPP). According to standards, the simulation of long-term service thermal ageing is performed isothermally at elevated temperature using Arrhenius methodology. The samples or equipment are aged in thermal chamber, to bring them to the same state as after long-term service time. To proceed a reliable simulation, the testing parameters should be taken very carefully and the accelerator factors should not be too high. The testing temperature and time and the activation energy are the most important parameters. Determination of these factors and the limitations of their use in practice are discussed.