Recrystallization of nanomaterials - recrystallization of nanomaterials - change in the size of grains in a polycrystalline solid due to the diffusion of matter between the grains of the same phase.
Description
Nanomaterials have very long grain boundaries and the resulting large excess of free energy, so the recrystallization of nanomaterials proceeds quite intensively; grain growth can occur even at room temperature. Spontaneous grain growth (collective recrystallization) occurs as a result of chemical diffusion, that is, a diffusion process in a chemical field, when there is no concentration gradient , but there is a non-zero gradient of chemical potential. The difference in chemical potential between grains of different sizes is due to the contribution of surface energy to the total energy of the grain. The relative size of this contribution is the larger, the smaller the grain size, therefore, ceteris paribus, small grains have excess energy compared to large ones. Since the thermodynamic cause of spontaneous grain growth in a homogeneous polycrystalline substance is a decrease in the total energy of the system, in the process of collective recrystallization the size of large grains grows due to the disappearance of a part of small grains. Recrystallization is a more complicated process than diffusion, and is not limited to the latter. Characteristic of collective recrystallization is the activation energy. The change in the average grain size during collective recrystallization in nanomaterials and its duration t are related by the relation, where n = 1–4. Taking into account the intensity of recrystallization processes, in order to preserve the small size of grains in nanomaterials, it is necessary to shorten the duration and lower the sintering temperature.
Sources
- Gusev A.I. Nanomaterials, nanostructures, nanotechnologies. - M .: Fizmatlit, 2007. - 416 p.
- Gusev AI, Rempel AA Nanocrystalline Materials. - Cambridge: Cambridge International Science Publishing, 2004. - 351 p.