Stress induced chemical reactions

There are many other examples of chemical reactions being induced by shearing stresses. A mechanism involving metallization seems plausible. Areas of application include photochemistry, degradation of polymers, friction and wear, mechanical alloying and cutting processes. 

The constituent of a material predisposed to forming an unstable compound following a stress-induced chemical reaction (Wiederhom, 1968). 

These relations have been confirmed experimentally, this being evidence of a chemical reaction occurring at the crack tip, which following the action of stress a induces a displacement of the tip and a reduction in strength. 

The CEA decomposition loop operates at low pressures, near 5 bar. This is because the decomposition reaction is favoured at lower pressures. However, the GA flow sheet is conducted at 70 bar, near the expected operating pressure of the secondary helium loop. This is to minimise mechanical and thermal stress induced by a large pressure gradient between the helium and the chemical process at high temperatures. The GA design of the decomposition loop allows for more heat recovery, but does so with a more complex configuration. In practice, trade-offs between complexity and cost will be necessary to develop the most cost-efficient design. 

Plant use of iron depends on the plant s ability to respond chemically to iron stress. This response causes the roots to release H+ and deduct ants, to reduce Fe3+, and to accumulate citrate, making iron available to the plant. Reduction sites are principally in the young lateral roots. Azide, arsenate, zinc, copper, and chelating agents may interfere with use of iron. Chemical reactions induced by iron stress affect nitrate reductase activity, use of iron from Fe3+ phosphate and Fe3+ chelate, and tolerance of plants to heavy metals. The iron stress-response mechanism is adaptive and genetically controlled, making it possible to tailor plants to grow under conditions of iron stress. 

Iron-efficient and iron-inefficient plants can have several hundred /xgFe/g of root, but the iron-inefficient plant may die from lack of iron in its tops. In contrast, iron-efficient plants respond to iron stress, and the root makes iron available for transport and use in tops. In a similar way, iron may remain in the nutrient solution as Fe3+ chelate or Fe3+ phosphate and not be transported to the plant top until it is made available for transport through chemical reactions induced by iron stress. These observations stress the importance of a plant being able to respond to iron stress. Iron is usually used in plant tops once it is made available for transport by the roots. 

Nitrate Reductase Activity. There are similarities between induced nitrate reductase activity and induced iron stress response. In both, biochemical reactions are induced, and a substrate is reduced N03 to N02 by nitrate reductase and Fe3+ to Fe2+ by a reductant activated in response to iron stress. Chemical reactions induced by iron stress increased the use of iron, and simultaneously increased nitrate reductase activity in roots (Figure 5) and in tops of iron-efficient tomato. This induced nitrate reductase activity declined when iron was made available to the plants. 

How heavy metals, arsenate, and azide inhibit chemical reactions induced by iron stress. 

The above description stresses either chemical reactions in these combinations or physical interactions between components. In reality there is still additional effect which may induce changes to structure and thus properties. It is a commonly known effect of fillers on the nucleation of polymers. It can be perceived that filler does not affect nucleation of both polymers with the same intensity. In addition, the availability of polymers at the interface with fillers depends on various parameters such as viscosity, acid/base interaction, etc. If these two are included in the number of combinations, there is a theoretical abundance of possible combinations and thus... 

Mechanochemical processing has been used to conduct the esterification of poly(vinyl alcohol) (PVA) with maleic anhydride through stress-induced reaction by pan-milling (Scheme 8.5). In comparison with conventional methods for the esterification of PVA, this protocol is viable and environmentally friendly and can be an effective technique for the chemical modification of polymers. ... 

Shock wave compression cannot only induce deformation in the form of high density of defects such as dislocations and twins but can also result in phase transition, structural changes and chemical reaction. These changes in the material are controlled by different components of stress, the mean stress and the deviatoric stress. The mean stress causes pressure-induced changes such as phase transformations while the deviators control the generation and motion of dislocations. 

The instrumental aspects and applications of stress mass spectrometry (stress MS) to polymeric materials is reviewed critically from the inception of the technique to the present. Stress MS experiments are performed by mechanically deforming polymeric materials directly in the ion source housing of a time-of-flight mass spectrometer and mass analyzing the evolved volatile compounds. This technique has been applied to the study of stress-induced chemical reactions in polymeric materials, i.e., mechanochemistry, and to the characterization of residual volatile compounds in intractable polymer and composite matrices. Several polymeric systems ranging from polystyrene to fiber-epoxy composites have been studied by this technique. The significance of results achieved to date is assessed, and a systematic framework for further studies is developed. 

Although most stress MS studies to date have focused on stress-induced chemical reactions in polymeric materials, this analytical technique has proven utility in another important area of polymer research, namely characterization of volatile compounds indigenous to the polymeric matrix. It is possible that applications in this area could overwhelm mechanochemical applications. 

During fuel cell operation the membranes are stressed mainly by mechanical interference. Differences in the local gas and water distribution would lead to different processes in chemical reactions, shrinkage or expansion. The mechanical stress can induce changes in the distribution of the catalytic nanoparticles by e.g. agglomeration at fissures. 

The desired compatibilization can be obtained by different methods such as the addition of a third component (copolymer or functional polymer) or by inducing in situ chemical reactions (reactive blending) among blend components, leading to the modification of the polymer interfaces and tailoring the blend phase structure and the final properties. The final properties of a blend will be determined not only by the components properties but also by the phase morphology and the interface adhesion, both of which determine the stress transfer within the blend and its end-use applications. 

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