**2.3 "Growth of particles of phase-forming substance" stage**

Each nucleated particle, being in supersaturated media, attaches to itself the molecules of the medium more often than their separation from the particles. In order to join a particle, the molecule moves from the volume of the medium to the surface of the particle, is adsorbed on it, and then, migrating along the surface, takes the place where its connection with the particle becomes energetically favorable and in this sense strong enough to fix on its place. The probability of fixing a molecule depends on its size, shape, and electronic structure. In fact, controlled molecular selection occurs on the surface of the growing particle.

Considering the decrease in the free energy of the system, a phenomenon of *molecular selection*, which develops in it, results in the following process: nuclei become clusters of molecules containing only slightly different in structure and size of the molecule.

From a nanotechnological point of view, it is possible to keep in mind the tasks of changing the concentration conditions of crystallization as well as the use of nano-additives with a crystal-chemical structure similar to the germ of the phase and providing targeted acceleration of the particles' growth processes of the phase-forming substance [4–6] and their morphological structure—finification. In connection with the three global transitions indicated by us during the evolution of a solid substance, it is expedient to refine the classification of additives, dividing them according to the size attribute into nanoscale, ultrafine, and microdisperse (**Table 2**). In the general case, the structure-forming participation and the modifying influence of nanoscale modifiers can be the result of interrelated mechanisms.
