Review of the phase transformation and synthesis of inorganic solids obtained by mechanical treatment (mechanochemical reactions)

Using Infrared Spectroscopy to Identify New Amorphous Phases - A Case Study of Carbonato Complex Formed by Mechanochemical Processing

“…Actually, during high-energy collisions the powder particles are subjected to a combination of hydrostatic and shear stress components, which further complicate the overall picture, even in apparently simple cases, such as polymorphic phase transitions. It was shown, for example, that conventional thermodynamic phase diagrams cannot be applied for polymorphic phase transitions realized during high-energy milling (Lin & Nadiv, 1979). In fact, the classical hydrostatic-pressure-temperature (p-T) phase diagram, e.g., in the case of a polymorphic transition between litharge and massicot forms of PbO, is considerably altered by introducing the shear component into the calculations; a twophase field region appears in the phase diagram, suggesting co-existence of the two polymorphs, rather than a sharp transition line characteristic for the conventional PbO p-T diagram.…”

“…In fact, the classical hydrostatic-pressure-temperature (p-T) phase diagram, e.g., in the case of a polymorphic transition between litharge and massicot forms of PbO, is considerably altered by introducing the shear component into the calculations; a twophase field region appears in the phase diagram, suggesting co-existence of the two polymorphs, rather than a sharp transition line characteristic for the conventional PbO p-T diagram. This might explain the often observed co-existence of two polymorphic modifications upon prolonged milling when "steady-state" milling conditions are reached (Lin & Nadiv, 1979;Iguchi & Senna, 1985). The influence of shear stress and local temperature rise on more complex mechanochemical reactions are still subject of intensive discussions.…”

Influencia de los tratamientos mecánicos y térmicos en materias primas que contienen pirofilita

“…Estas investigaciones han sido llevadas a cabo y se continuan en la actualidad en lo que respecta al estudio sobre la formación de mullita. Se pondrá de manifiesto que la reducción del tamaño de partícula de materias primas que contienen pirofilita se logra por medio del proceso de molienda, pero además se pueden producir varios efectos en la estructura y propiedades del sólido sometido a este tratamiento e inducir reacciones químicas debido al aumento de reactividad en el sistema, englobándose en lo que se ha denominado mecanoquímica (7,8). Un posterior tratamiento térmico acentúa aún más el aumento de reactividad que se ha producido.…”

“…It is remarked that the increase of surface area and particle size reduction is produced by grinding, but other effects are produced on the structure and properties of the solid submitted to grinding. In other words, mechanochemical reactions (7,8) are induced by dry grinding due to the increase of reactivity of the system. A subsequent thermal treatment enhances the increase of reactivity.…”

Specifics of thermodynamic description of nanocrystals

“…formation of the fcc phase in films and small particles of Co [8]), while, in the second case, crystal size reduction is accompanied by formation of phases that are not observed in bulk specimens (fcc phases in thin films of Nb, Ta, Mo and W [8]). New polymorphic modifications are usually observed in systems obtained by thin films deposition [8] or grinding of solids [15][16]. A similar size-induced effect takes place during amorphization of the matter in thin films (for reviews, see [7,8]).…”