Кристалохiмія реакцій на поверхні твердої фази

• Дата: 2020
• Автор: Shablovsky, Ya. O.
• Формат: Стаття
• Мова: Російська
• Опубліковано: Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine 2020
• Теми: кристалічна поверхня; топохiмiчна реакція; тверда фаза
• Онлайн доступ: https://www.cpts.com.ua/index.php/cpts/article/view/552
• Назва журналу: Chemistry, Physics and Technology of Surface

If the reagent crystal has perfect cleavage, then its surface reactivity depends on its topochemical affinity with the reaction product. If the reagent cleavage is imperfect, then the surface reaction outcome is determined by crystallochemical barriers, i.e. the restrictions of positions for structural units that are imposed on those units by the lattice symmetry. In their turn, these restrictions determine "the structural preferences" of the crystallizing phase. The preferences of such kind can be characterized quantitatively by crystallochemical priorities of Fedorov groups, i.e. by relative frequencies of Fedorov groups in crystal structures. Respectively, there are primary and rare Fedorov groups of crystal structures. Paradoxal kinetic stability of thermodynamically unstable crystal phases is provided by their structure being of primary (i.e. most probable) type. On the other hand, forming a crystal structure of a rare (i.e. highly unlikely) type is possible only under condition of themodynamical stability of the structure because the rarity of a Fedorov group indicates a low "crystallochemical feasibility" of the corresponding structure.Dispersing a crystal phase induces forming a structure with a higher crystallochemical priority. Likewise, baric effect promotes forming a structure with a more probable crystallochemical type.Reproducibility a topochemical transformation is the evidence of regularity in the succession of crystal structures of the reagent and the reaction product. The symmetry of the crystal structure can lower not only as a result of topochemical recrystallization but also due to the crystal deformation. Hence, the deformational dissymmetrization can promote the topochemical process or suppress it.