Phase Transitions and Topochemical Processes

Usually phase transition in a gas-solid system is described by the topochemical models [44,194]. Such models assuming chaotic or regular configurations of the islands or nuclei of the new phase - disks or squares for the two-dimensional and sphere for the three-dimensional reaction systems. The reaction rate depends on the duration of aggregation (on the initial distribution and configuration of the islands) and that of the reaction itself. Its value is much lower than that taking place in the chaotic distribution of the adspecies. 

A new phase formation inside solid connects with a creation of solid-solid interfaces. A total process is controlled by a diffusion transport of the absorbed species to these interfaces. At these interfaces similar Eq. (66) should be used 

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