Activation energy of decomposition

The kinetic stability of pentazole has been estimated by the activation energy of decomposition or retro-[3 -i- 2]-cycloaddition reaction of 19.8 kcal moL [107] and 19.5 kcal mol- [108] with a half-life of only 14 s at 298 K [108]. 

The linear dependence between the activation energy of decomposition of the azocompounds RN2R and the BDE of the R—H bond (D(R—H)) was established [3], The rate constants of the decomposition of azo-compounds in the gas phase and hydrocarbon solvents have close values. The mean value of the rate constant of AIBN decomposition in hydrocarbon and aromatic solutions was recommended to bekd= 1015 x exp(— 127.5/RT) s-1 [2], The values of the activation energies and the rate constants of the decomposition of azo-compounds in the gas and liquid phases can be found in the Handbook of Radical Initiators [4],... 

Stability and decomposition kinetics of aspirin both as a solid and in solution continue to be studied. The topochemical decomposition pattern of aspirin tablets has been explored.175 The degradation of aspirin in the presence of sodium carbonate and high humidity was studied by x-ray diffraction.176 The activation energy of decomposition by water vapor in the solid state was found to be 30 kcal/mol.177 The effect of common tablet excipients on aspirin in aqueous suspension was also studied.178... 

The apparent activation energy of decomposition estimated from the Arrhenius plot for gave 120 kJ/mol. Conversely, Stander noticed that if the difference between the experimental dissociation pressures (e.g., 384 kPa) and the equilibrium (plateau) dissociation pressure corresponding to T = const (e.g., 404 kPa at T = 335°C for MgH ) is relatively small, then better fits were obtained with the model of random nucleation followed by one-dimensional growth or instantaneous nucleation followed by two-dimensional growth as given by the equation ... 

On the other hand, from the Kissinger analysis shown in Fig. 1.28 in Sect. 1.4.1, we calculated that the activation energy of decomposition for the reaction (Rib) from the liquid equals -122 kJ/mol. This is slightly higher than the value obtained by Andreasen. 

The rate and activation energy of decomposition depend to a great extent on the type of solvent used. 

The activation energy of decomposition, according to Hailes, is 46.7 kcal/mole, according to Tompkins and Young 33 kcal/mole and according to T. Urbanski and Kruszynska [41] 42.2 kcal/mole. 

According to Glasner and Makovky [13] the activation energy of decomposition of ammonium perchlorate is 31.0 kcal/mole in the temperature range 440-478°C. 

The activation energy of decomposition of both irradiated and unirradiated ammonium perchlorate in the orthorhombic form below 240°C is ca. 18.0 kcal/mole according to Freeman. This seems to indicate that irradiation of ammonium perchlorate does not change the decomposition mechanism but provides many more nucleation sites. 

The initial estimates of the parameters and k i are determined from the first stage data using Equations 5 and 6. Using the data obtained at different temperatures, the activation energy of decomposition is determined as 44 kcal/mole. This value is in good agreement with the values reported in literature (15, 16). 

FIG. 21.2 Relationships between (A) the activation energy of decomposition, act d and the characteristic decomposition temperature Td)/2 and (B) the characteristic decomposition temperature Td ]/2 and the temperature of initial decomposition Tdo. 

Figure 14. An Arrhenius plot of log ki against 1/T for the determination of the activation energy of decomposition of cobalt (III) acetylacetonate in aqueous and surfactant solutions...

The first estimate of kinetic parameters for the thermal decomposition of nitric oxide were made by Zeldovich and Frank-Kamenetsky . From a study of nitric oxide formation in H2-O2-N2 flames these workers proposed a value of 82+10 kcal. mole for the activation energy of decomposition. Vetter studied the reaction over the temperature range 1200-1900 K. He found a small rate increase on addition of oxygen and postulated a chain process involving the reactions... 

This commercial polymer is stable for a year at 275°C and can be used for 200 h at 358°C and 10 min at 377°C. At 600°C, volatiles are formed. They include CO, C02, H20 and H2 [288]. The activation energy of decomposition in vacuo in the range 585—632°C was estimated [289] to be 74 kcal mole-1. The purified polymer decomposes primarily by breaking of the amide group. Various other polyimides have been synthetized. 

Secondary radicals with free valence in the chain center ( CX ) participate as a rule in the reactions of macromolecular decomposition and the transfer of H atom. Decomposition is the inverse to the reaction of addition. That is why, the lower the polymerization heat, the lower the activation energy of decomposition and the stronger the probability of macromolecular destruction on free valence localization. Polymers characterized by low polymerization heat of their monomers (e.g. the polymerization heat of PMMA is about 55kJ/mole) are strongly decomposing, not only under mechanical effects, but also in other processes of radical formation. 

For radical polymerizations the activation energy of decomposition is of the order of 30 kcal/mol while (Ep - E(/2) is about 4 to 7 kcal/mol. Thus the temperature coefficients are, respectively. 

Table 20-1. Half-Lives and Activation Energies of Decomposition of Some Free Radical Initiators AI BN, Azobisisobutyronitrile BPO, Dibenzoyl Peroxide MEKP, Methyl Ethyl Ketone Peroxide IPP, Diisopropyl Peroxide Dicarbonate Dicup, Dicumyl Peroxide CuHP, Cumyl Hydroperoxide...

Polyarylates Activation energy of decomposition, kcal/mole Polyarylates Activation energy of decomposition, kcal/mole... 

Chapter 4 describes the behaviour of compostable polymer materials during degradation in different environments (inert and oxidative atmospheres). An overview concerning thermal stability and apparent activation energy of decomposition is presented. 

As an alternative reaction pathway to unimolecular decomposition in which the molecule rearranges or fissions by itself, one must also consider mechanisms in which the decomposition process is assisted by other molecular species formed during the decomposition. Such alternative reaction pathways can greatly reduce the effective activation energy of decomposition. In this section, we consider two possible decomposition pathways, radical assisted and water assisted. 

The viscoelastic and thermal properties of fully and partially cured DGEBA epoxy resin composites were smdied modified with montmorillonite nanoclay exposed to UV radiation. Samples were fabricated and cured to 80 % conversion (partially cured) based on isothermal cure kinetic smdies. Influence of 1-3 wt% loading of montmorillonite nanoclay on the cure behavior and development of physical properties of these composites were evaluated. Results of the smdy revealed that for optimization of modified epoxy composite properties, a different curing cycle was necessary due to interaction of different amounts of nanoclay and epoxy molecules. Addition of nanoclay increased the viscoelastic properties, storage modulus and activation energy of decomposition of partially cured samples evolved over exposure time, while fuUy cured samples degraded over the same period. 

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