Paste preparation thermal effects during

The rise in temperature during paste preparation is a result of thermal effects of the chemical reactions that proceed and of the heat generated by the friction between particles caused by stirring. 

Three types of reactions take place during paste preparation (1) oxidation of lead, (2) formation of basic lead sulfates and (3) formation of hydrates. The thermal effects of the different reactions are calculated on the basis of thermodynamic data. The heat effects of the respective reactions of formation of basic lead sulfates and hydrates are given in Table 6.4. 

The thermal automerization and rearrangement reactions of PAHs have been widely investigated during the past two decades (for examples see refs. [31 e, g, 62-64]). The main objective was to understand the processes of formation of aromatic hydrocarbons in fuel rich flames and the mechanisms of transformation of the PAHs that have been observed at these elevated temperatures. In most cases, thermally initiated rearrangement reactions in the carbon skeletons of PAHs require high enthalpies of activation resulting in low product selectivities and poor overall yields. Because the expected products are often more effectively prepared by conventional routes, this approach has been used as a synthetic tool only in a few cases, e.g. the synthesis of azulenes [65] and the rearrangement of bifluorenylidenes to benzenoid hydrocarbons [38]. 

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