Thermal Decomposition Process

The acetylene black process relies on the exothermic decomposition of acetylene into carbon and hydrogen at elevated temperatures, the heat released sustaining the reaction. Acetylene blacks have average particles sizes in the 30-40 pm range, but the particle shape is more branched than the spherical shape of thermal blacks. 

The term carbonization is more correctly applied to the process for the production of char or coke when the coal is heated at temperatures in excess of ca. 500°C (ca. 930°F). The ancillary terms volatilization and distillation are also used from time to time but more correctly refer to the formation and ranoval of volatile products (gases and liquids) during the thermal decomposition process. 

The thermal decomposition process, while written as an orderly process, may be quite disordered. Nevertheless, it is proposed that as the coal particle temperature rises during thermal decomposition (which may also be the initial stages of the combustion process) (Chapters 14 and 15), the bonds between the aromatic clusters in the coal macromolecule break and create lower-molecular-weight fragments that are detached from the macromolecule—the larger fragments of this decomposition process are often (collectively) referred to as the metaplast. 

coal undergoes a large variety of physical and chemical changes when heated to temperatures where thermal decomposition occurs. However, some changes may be noted before the onset of what is often referred to as the thermal decomposition proper (i.e., carbon-carbon bond scission and the like) and may manifest themselves as the formation of low-molecular-weight species (Stein, 1981 Hessleyetal., 1986). 

For example, while the tanperature of the onset of thermal decomposition proper is generally recognized to be approximately 350°C (660°F the so-called cracking temperature), water will appear as a product of heating coal at temperatures below 100°C (120°F). In addition, when a coal is degassed at temperatures below 100°C, adsorbed methane and carbon dioxide will appear as products of the thermal treatment. On the other hand, a coal such as lignite, which contains many carboxylic functions as part of the coal structure, will evolve carbon dioxide by thermal decarboxylation  

Such changes are usually noted to occur at temperatures just in excess of 100°C (210°F) and more than 50% of the carboxylic acid functions can lose carbon dioxide over the temperature range 100°C-200°C (210°F-390°F). 

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Following the synthesis of the first methyl-palladium NHC complexes it was subsequently found that the complexes undergo a facile thermal decomposition process in which the NHC is lost as 2-methylimidazolium salt and the Pd is rednced to Pd(0) (Scheme 13.1) [15-17]. In ensuing studies investigating the reaction behavionr of a range of hydrocarbyl Pd and Ni carbene complexes, it was found that the decomposition reaction is ubiquitous. It occurs with varying ease, for mono-NHC, bis-NHC and donor functionalised-NHC complexes [16-23]. 

For technical purposes (as well as in the laboratory) RuOz and Ru based thin film electrodes are prepared by thermal decomposition techniques. Chlorides or other salts of the respective metals are dissolved in an aqueous or alcoholic solution, painted onto a valve metal substrate, dried and fired in the presence of air or oxygen. In order to achieve reasonable thicknesses the procedure has to be applied repetitively with a final firing for usually 1 hour at temperatures of around 450°C. A survey of the various processes can be found in Trasatti s book [44], For such thermal decomposition processes it is dangerous to assume that the bulk composition of the final sample is the same as the composition of the starting products. This is especially true for the surface composition. The knowledge of these parameters, however, is of vital importance for a better understanding of the electrochemical performance including stability of the electrode material. 

Also presented were data on carbon-coating of graphite powder using a propylene gas thermal decomposition processes. High weight percent amorphous carbon-coatings are possible with this method, and the process appears uniquely suited to materials that are reductively stable to 700°C. The coated materials work better in the 30% PC electrolyte solutions, thus showing better resistance to solvent co-intercalation problems versus uncoated types. 

Precursors obtained with various anions should be studied at comparable conditions, and the quality of target products should be compared in order to illuminate the role of anion in thermal decomposition processes. 

Kimura, J., and N. Kubota. 1980. Thermal decomposition process of HMX. Propellants Expolsives 5 1-8. 

Fig. 5.1 Thermal decomposition process of AP measured by thermal gravimetry (TG) and by differential thermal analysis (DTA).

As in the case of AN, the thermal decomposition process of HNF varies with the temperature of decomposition. Deflagatory decomposition of HNF produces ammonium nitroformate, which decomposes to hydrazine, nitroform, and am-monia.[2 l These products react to generate heat in the gas phase and the final combustion products are formed according to ... 

The thermal decomposition process of AP particles is altered significantly when 10% LiF is added, as shown in Fig. 7.25. The decomposition of AP particles without LiF commences at about 570 K and 50% mass loss occurs at 667 K, which corresponds to the exothermic peak. The TG curve consists of a two-stage mass-loss process. The first stage corresponds to the first exothermic reaction at 635 K, and the second stage corresponds to the second exothermic reaction in the high-temperature region between 723 K and 786 K observed in the DTA experi-... 

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