Thermal analysis, activation energy

Procedure for DTA peak analysis of dioxouranium [UO, [VI]] complexes with cellulose acetate [CA], using the equation of Prout and Tompkins [Table 7.9] showed that the increase of DS of cellulose acetate [from 2.2 to 2.86] and its chelation with uranium [VI] ions increased the activation energies for degradation. The increase in the thermal stabilities [activation energy] of cellulose acetate complexes can be attributed to the coordination bonds between dioxouranium and acetyl of cellulose acetate, i.e., to the formation of five-membered rings [14,29]. 

Order of thermal stabiUty as determined by differential thermal analysis is sebacic (330°C) > a2elaic = pimelic (320°C) > suberic = adipic = glutaric (290°C) > succinic (255°C) > oxahc (200°C) > malonic (185°C) (19). This order is somewhat different than that in Table 2, and is the result of differences in test conditions. The energy of activation for decarboxylation has been estimated to be 251 kj/mol (60 kcal/mol) for higher members of the series and 126 kJ/mol (30 kcal/mol) for malonic acid (1). 

Crystallization kinetics have been studied by differential thermal analysis (92,94,95). The heat of fusion of the crystalline phase is approximately 96 kj/kg (23 kcal/mol), and the activation energy for crystallization is 104 kj/mol (25 kcal/mol). The extent of crystallinity may be calculated from the density of amorphous polymer (d = 1.23), and the crystalline density (d = 1.35). Using this method, polymer prepared at —40° C melts at 73°C and is 38% crystalline. Polymer made at +40° C melts at 45°C and is about 12% crystalline. 

Sharma et al. [153] have devised a gentle accelerated corrosion test using a kinetic rate equation to establish appropriate acceleration factors due to relative humidity and thermal effects. Using an estimate for the thermal activation energy of 0.6 eV and determining the amount of adsorbed water by a BET analysis on Au, Cu and Ni, they obtain an acceleration factor of 154 at 65°C/80% RH with respect to 25 °C/35-40% RH. 

The title compound (with 66.5% nitrogen content) is prepared by condensing formylhydrazine (2 mols, with elimination of 2H2O) by heating to 170°C. Dining a pilot production run in a 500 1 reactor, an explosion destroyed the vessel. The heat of decomposition of the compound was determined by thermal analysis as 1.5 kJ/g, with an energy of activation of 91 kJ/mol. 

As part of a multi-technique investigation (see also discussion under mid-infrared spectroscopy later), Corrales et al. [13] plotted the carbonyl index for films prepared from three grades of polyethylenes a high-density PE (HDPE), a linear low-density PE (LLDPE) and a metallocene PE (mPE) (see Figure 5). In this study, the data trend shown in Figure 5 correlated well with activation energies derived from the thermal analysis, which showed that the thermal-oxidative stability followed the order LLDPE > mPE > HDPE, whereas the trend... 

A comparative analysis of the kinetics of the reactions of atoms and radicals with paraffinic (R1 ), olefinic (R2H), and aromatic alkyl-substituted (R3H) hydrocarbons within the framework of the parabolic model permitted a new important conclusion. It was found that the tt-C—C bond occupying the a-position relative to the attacked C—H bond increases the activation energy for thermally neutral reaction [11]. The corresponding results are presented in Table 6.9. 

All these reactions are exothermic, and the AH values are negative. All these reactions should seemingly occur equally rapidly. The question to how easily the aminyl radicals react with the H—O and H—C bonds of the peroxyl radicals can be answered by analyzing these reactions in terms of the IPM model of free radical reaction (see Chapter 6). This model gives a tool to perform the calculation of the activation energy for a thermally neutral reaction of each class. Analysis of experimental data has shown (see Chapter 15) that, when aminyl... 

Table 13.5 Reaction rate constant0 and activation energy data for the thermal degradation of PET [29b, 29c, 39]. From Thermal degradation of PET. A kinetic analysis of gravimetric data , Covney, J. D., Day, M. and Wiles, D. M., J. Appl. Polym. Sci., 28, 2887 (1983), copyright (1983 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

In a similar fashion, o-phenylenecarbenonitrene (47) was generated by photolysis of the azido-diazo precursor 47-DN (Scheme 10) and identified by IR spectroscopy with the help of calculations. Further irradiation caused a ring opening of carbenonitrene 47 to its isomer 48, which was formed as a mixture of Z,Z and E,E isomers. The same isomerization can be achieved thermally, and from the kinetic analysis in the temperature range 40-50 K, the activation energy was found to be 5.1 kcal/mol [108]. 

Under thermal conditions, the Diels-Alder reaction is bimolecular with a 18 Kcal/mole activation energy. Analysis shows 98.5% 1, 3 dicarboxylate and 1.5% of the 1, -dicarboxylate product. 

Ldnnerdal, B., Stanislowski, A. G., Hurley, L. S. J. Inorg. Biochem. 12, 71 (1980) Woittierz, J. R. W. Elemental Analysis of Human Serum and Human Serum Protein Fractions by Thermal Neutron Activation, Netherlands Energy Research Foundation Report, ECN 147, January 1984... 

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