Mechanochemical decomposition

Current explanations of tribochemical reactions state that the more obvious consequence of mechanical treatments, the increase of the surface area of a solid, is a minor factor, which contributes only to 10% of the reactivity increase. The more important effect is due to the accumulation of energy in lattice defects which can relax either physically by the emission of heat, or chemically by the ejection of atoms or electrons, formation of excited states on the surface, bond breakages, and other chemical transformations. Mechanical stress can be applied as single or periodic shocks, rapid loads, etc. An example is that of the mechanochemical decomposition of aluminum hydride, which increases with the frequency of the applied stress (Fig. 2).i ... 

Frequency of applied stress (per second) Figure 2 - Mechanochemical decomposition of aluminum hydride... 

Preparation of photoactive Ti02 has been achieved by mechanochemical decomposition of Ti0S04 H20 using NaQ diluents, reaction between TiCU and (NH4)2C03, or displacement reaction between Ti0S04-xH20 and Na2C03 [21]. 

Mechanical treatment alone may be sufficient to induce significant decomposition such processes are termed mechanochemical or tribo-chemical reactions and the topic has been reviewed [385,386]. In some brittle crystalline solids, for example sodium and lead azides [387], fracture can result in some chemical change of the substance. An extreme case of such behaviour is detonation by impact [232,388]. Fox [389] has provided evidence of a fracture initiation mechanism in the explosions of lead and thallium azide crystals, rather than the participation of a liquid or gas phase intermediate. The processes occurring in solids during the action of powerful shock waves have been reviewed by Dremin and Breusov [390]. 

E. Jeon, Y. Whan Cho, Mechanochemical synthesis and thermal decomposition of zinc borohydride, J. Alloys Compd. 422 (2006) 273-275. 

The activation of mixtures of calcium and aluminum hydroxides taken at different ratios was studied in [13], It was stated that 3Ca0-Al203 6H20 was the main product of mechanochemical synthesis within a wide range of component ratios (from 2 1 to 1 2). When a planetary mill AGO-2 is used, the synthesis completes within 10 min (Fig. 6.2). An increase of activation time brings to decrease of the intensity of reflections, which is an evidence of product amorphization or the beginning of hydroaluminate decomposition. 

Crystallization Decomposition Oxidation Synthesis Electrochemical Mechanochemical... 

The role of a peptizer is to enhance the mechanochemical degradation of a polymer, such as the mastication of natural mbber, and known peptizers are thiols and diarylsulfides. The mechanism of action is believed to be the redox decomposition of hydroperoxides (Scott, 1993b), as shown in Scheme 1.70(a) ... 

In-depth study of reaction mechanism limited to one system is often insufficient if fundamental characteristics governing certain type of mechanochemical reaction are to be determined. Following the results from the previous section, in which we identified an amorphous carbonato complex as a transitional stage of the reaction between Na2C03 and Nb20s, it is the next step to find out i) whether this mechanism is general for mechanochemical reactions involving COs - ions and ii) which parameters control the decomposition of the carbonato complex. The latter is particularly important as the decomposition of the complex is a necessary step for the formation of the final binary oxide. 

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