Nonequilibrium structures in time and space

In the previous section we discussed a typical growth reaction (A+X— 2X). However, in realistic systems X will not only grow, it can also die out, e.g. according to the following decay mechanisms  

Whether X increases or decays, that is, whether W is positive or negative, clearly depends on the ratio k [A] /k.  

Even though the discussion of biological effects and specifically the immense importance of respective nonequilibrium defects (mutations) for our global history do form part of the subject matter of defect chemistry, it would take us much too far from our chosen theme. Let us now discuss some important implications for the inorganic field. 

Impact ionization is an autocatalytic process occurring in solids, that has already been mentioned, in which an excited electron in the conduction band drops down to a lower energy level generating another electron-hole pair. This can, with a pinch of salt, be described as 

The Liesegang phenomenon [521], which is a striking nonequilibrimn effect (not only) in laboratory chemistry, describes the formation of periodic precipitation bands of internal reaction products the effect can involve periodicity in time and space and depends on the interference of diffusion, supersaturation, nucleation and growth. The collapse and reformation of supersatnration is of importance, in the sense of an overshoot of a partial process. 

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