Influence of Mechanical Stress

This chapter is concerned with the influence of mechanical stress upon the chemical processes in solids. The most important properties to consider are elasticity and plasticity. We wish, for example, to understand how reaction kinetics and transport in crystalline systems respond to homogeneous or inhomogeneous elastic and plastic deformations [A.P. Chupakhin, et al. (1987)]. An example of such a process influenced by stress is the photoisomerization of a [Co(NH3)5N02]C12 crystal set under a (uniaxial) chemical load [E.V. Boldyreva, A. A. Sidelnikov (1987)]. The kinetics of the isomerization of the N02 group is noticeably different when the crystal is not stressed. An example of the influence of an inhomogeneous stress field on transport is the redistribution of solute atoms or point defects around dislocations created by plastic deformation. 

The influence of plastic deformation on the reaction kinetics is twofold. 1) Plastic deformation occurs mainly through the formation and motion of dislocations. Since dislocations provide one dimensional paths (pipes) of enhanced mobility, they may alter the transport coefficients of the structure elements, with respect to both magnitude and direction. 2) They may thereby decisively affect the nucleation rate of supersaturated components and thus determine the sites of precipitation. However, there is a further influence which plastic deformations have on the kinetics of reactions. If moving dislocations intersect each other, they release point defects into the bulk crystal. The resulting increase in point defect concentration changes the atomic mobility of the components. Let us remember that supersaturated point defects may be annihilated by the climb of edge dislocations (see Section 3.4). By and large, one expects that plasticity will noticeably affect the reactivity of solids. 

If local stresses exceed the forces of cohesion between atoms or lattice molecules, the crystal cracks. Micro- and macrocracks have a pronounced influence on the course of chemical reactions. We mention three different examples of technical importance for illustration. 1) The spallation of metal oxide layers during the high temperature corrosion of metals, 2) hydrogen embrittlement of steel, and 3) transformation hardening of ceramic materials based on energy consuming phase transformations in the dilated zone of an advancing crack tip. 

So far, we have tacitly assumed that the stresses were applied externally. However, stresses which are induced by local changes in component concentrations and the corresponding changes in the lattice parameters during transport and reaction are equally important. These self-stresses can strongly influence the course of a solid state reaction. Similarly, coherent, semicoherent, and even incoherent interfaces during heterogeneous solid state reactions are sources of (local and nonlocal) stress. The 

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Ristic, R.L and Sherwood, J.N., 2001. The influence of mechanical stress on the growth and dissolution of crystals. Chemical Engineering Science, 56, 2267-2280. 

Influence of mechanical stresses on phase transitions of polydimethylsiloxane and diacetate cellulose solutions... 

Rheology details the behaviour of liquid-like materials under the influence of mechanical stresses and covers viscous and viscoelastic behaviour. 

FIGURE 18.5 Influence of mechanical stress on drying (A) API after filtration (B) API after drying in a paddle dryer. 

In the given study authors try to consider this problem from such poorly studied side as influencing of mechanical stress on conducting properties of material being a solid electrolyte. 

Let us consider the possible mechanisms of strengthening of epoxy polymers by rubbers. The failure of a polymeric material, as of any solid, proceeds through the development of cracks. In the failure of linear polymers the material structure can change under the influence of mechanical stresses in the tip of the growing crack, which in turn results in orientation and consequently in the strengthening of the polymer in the area of the crack tip. In network polymers (epoxy in particular) the possibility of plastic deformation in the crack tip is lower due to the additional limits on the chain mobility applied by the network chemical crosslinks. This is why one observes a low value of the effective failure surface energy compared with linear polymers. 

We begin with consideration of surface influence on resonance magnetic Adds for spherical nanoparticles. This influence defines the positions of corresponding spectral lines. As it was shown in the Sect. 3.1, the surface effect can be expressed via hydrostatic pressure p = 2 [l/R, where R is a particle radius and p, is a surface tension coefficient. It is known, that the influence of mechanical stress on resonant fields (frequencies) is defined by spin-phonon interaction coefficients. Therefore, the resonance frequency of some transition for nanoparticles can be expressed in the form ... 

VII. INFLUENCE OF MECHANICAL STRESSES ON THE AGING OF CURED RUBBERS... 

Reuss, M. (1988). Influence of mechanical stress on the growth of Rhizopus nigricans in stirred bioreactors, Chem. Eng. Technol, 11, 178-187. 

Do you intend to extend this program to include the added influence of mechanical stressing and deformation at low temperatures ... 

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