Theoretical analysis thermal decomposition

Varhegyi G.P. et. al. (1994) Kinetics of the thermal decomposition of cellulose under the experimental conditions of thermal analysis. Theoretical extrapolations to higher heatinsTstes. Biomass and Bioenergy, Vo).7No. 1,69-74... 

Vyazovkin and Liimert [26] also regard the thermal decomposition of a solid as a multistep process. They report a quantitative analysis of the systematic variations of values of E with a using theoretically calculated data for two model processes (i) a simple reversible reaction and (ii) a reversible reaction followed by an irreversible step. It was shown that the dependence of E on a for measurements of the dehydrations of a number of crystalline hydrates was consistent with the latter model, (ii). 

This type of six-membered ring system with four heteroatoms does not occur in nature. Scarce spectroscopic data are available. The molecular structures of a 3,6-diaryl-l, 4,2,5-dithiadiazine1 and a 6-aryl-l,4,2,5-dithiadiazin-3-amine were examined.5 The crystal structure of 3,6-bis(4-methoxyphenyl)-l,4,2,5-dithiadiazine shows a boat conformation of the six-membered ring system.3 The structure was also determined by crystallographic analysis of 6-(4-chlorophenyl)-3-morpholino-l,4,2,5-dithiadiazine.5 Some theoretical studies on the thermal decomposition reactions of dithiadiazines have been performed.9... 

A theoretical study of the thermal decomposition kinetics of ethyl fluoride 1,1-difluoroethane 1,1,1-trifluoroethane and 1,1,2,2-tetrafluoroethane has been carried out at the B3LYP/6-31-H-G, B3PW91/6-31-H-G, and MP2/6-31-h-hG levels of theory. The calculated data demonstrate that in the HF elimination reaction of the compounds studied, the polarization of the C(l)-F(3) bond is rate determining. Analysis of bond order, charges, bond indexes, and synchronicity parameters suggests that HF elimination occurs through a concerted and asynchronous four-membered cyclic TS type of mechanism. 

The CVD of pyrolytic graphite can be optimized by experimentation. The carbon source (hydrocarbon gas), the method of activating the decomposition reaction (thermal, plasma, laser, etc.), and the deposition variables (temperature, pressure, gas flow, etc.) can be changed until a satisfeictory deposit is achieved. However, this empirical eipproach may be too cumbersome and, for more accurate results, it should be combined with a theoretical analysis. 

The kinetics of the thermal decomposition of solids are dominated by topochemical considerations. Thus the traditional concepts of order and mole-cularity, which play an important role in the kinetics of gas phase and liquid phase reactions, have little application in considerations of the kinetics of the thermal decomposition of solids. Experimental observations of the isothermal reaction are conveniently represented in the form of a plot of the fractional decomposition a against time t. The objective of a physicochemical study of the thermal decomposition of a solid is then the devising of a mechanism for the chemical reaction which can be formulated in mathematical terms leading to a theoretical representation of the a(f) curve which is in complete agreement with the experimental observations. Such an idealized procedure is seldom realized completely in practice and one often has to be content instead with an empirical analysis of the kinetics. 

A rational deduction of elemental abundance from solar and stellar spectra had to be based on quantum theory, and the necessary foundation was laid with the Indian physicist Meghnad Saha s theory of 1920. Saha, who as part of his postdoctoral work had stayed with Nernst in Berlin, combined Bohr s quantum theory of atoms with statistical thermodynamics and chemical equilibrium theory. Making an analogy between the thermal dissociation of molecules and the ionization of atoms, he carried the van t Hoff-Nernst theory of reaction-isochores over from the laboratory to the stars. Although his work clearly belonged to astrophysics, and not chemistry, it relied heavily on theoretical methods introduced by and associated with physical chemistry. This influence from physical chemistry, and probably from his stay with Nernst, is clear from his 1920 paper where he described ionization as a sort of chemical reaction, in which we have to substitute ionization for chemical decomposition. [81] The influence was even more evident in a second paper of 1922 where he extended his analysis. [82]... 

Some of dicarboxylic acids can also be distilled, without decomposition, under reduced pressures. This is at least a theoretical ground for the possibility of their direct GC analysis. Few successful attempts have been described, but these analytes require on-column injection of samples and extremely high inertness of chromatographic systems. Many types of polyfunctional carboxylic acids (hydroxy-, mercapto-, amino-, etc.) cannot be analyzed in free, underivatized form, owing to either non volatility and/or absence of thermal stability. These features are the principal reasons for the conversion of carboxylic adds, before their GC analysis, into less polar derivatives without active hydrogen atoms. 

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