Heterogeneous nucleation enhancement

Enhancement of Heterogeneous Nucleation by Specific Adsorption of Mineral Constituents... 

Increasing the temperature or lowering the pressure on a superheated liquid will increase the probability of nucleation. Also, the presence of solid surfaces enhances the probability because it is often easier to form a critical-sized embryo at a solid-liquid interface than in the bulk of the liquid. Nucleation in the bulk is referred to as homogeneous nucleation whereas if the critical-sized embryo forms at a solid-liquid (or liquid-liquid) interface, it is termed heterogeneous nucleation. Normal boiling processes wherein heat transfer occurs through the container wall to the liquid always occur by heterogeneous nucleation. 

Furthermore no nucleation was observed in the experimental time in any ampoules at any supersaturation levels if there was no stirrer in the ampoule. This implies that the heterogeneous nucleation was Induced by the presence of the stirrer, probably by enhancing the nucleation at the sites where fine scratches exist. This fact suggests that the solution is stable if there are no possible seed crystals in the system. The existence of the D-enantiomer in the seed crystals is therefore very likely to initiate the secondary nucleation after they grow to attain sufficient sizes, which results in the sudden purity decrease of the product crystals. 

In summary, compatibilization of PPE/SAN blends via SBM triblock terpolymers allows one to enhance significantly the homogeneity of the foam, while simultaneously reducing the cell size by heterogeneous nucleation activity of the... 

In some circumstances the rate of formation of nuclei is enhanced by the preliminary formation of an amorphous precipitate, which is usually more soluble than the crystal. With enolase, a significant portion of dissolved protein was in equilibrium with the precipitate, and crystals grew from this mixture [29]. However, frequently the outcome is not so happy. There are no general rules which favour crystal growth except that crystals grow best if supersaturation is approached slowly and there are no heterogeneous nucleation sites such as dust particles, impurities, etc. 

Nucleation rate is generally enhanced because (a) the effective value of ln/1 is larger (b) any heterogeneous nucleation at macroscopic surfaces will be enhanced and (c) secondary nucleation can be enhanced, be it due to contact nucleation, breaking off protrusions from crystals, or sweeping off clusters of oriented molecules from growing crystal faces. 

Heterogeneous Nucleation Primary nucleation in the presence of a foreign surface that enhances nucleation by reducing the critical size needed for crystal growth. 

In alloys and RPV steels with > 0.07wt%Cu, and irradiation temperatures > 200°C, Cu-enriched solute clusters form. At irradiation temperatures > 325 °C, these can grow to >4nm diameter, and probably transform to the equilibrium fee -Cu phase, but at the temperatures and fluence of interest most CECs in irradiated steels will be bcc." Radiation-induced point defects enhance the substitutional solute diffusion rate and enhance the rate of precipitation. In addition, nucleation of CECs appears to be easier in the presence of matrix defects. The nature of the matrix defects on which CECs nucleate is not clearThe relative importance of homogeneous and heterogeneous nucleation of CECs under irradiation is not agreed, although homogeneous nucleation will, naturally, become more likely as the Cu supersaturation increases. ... 

Since the details of these equations are explained elsewhere, only key ideas are briefly described here. One of these is to classify the solute atom clusters into irradiation-induced clusters and irradiation-enhanced clusters. Irradiation-induced clusters correspond to solute atom clusters with or without Cu atoms, whose formation mechanism is assumed to be the segregation of solute atoms based on point defect cluster or matrix damage (heterogeneous nucleation). On the other hand, the irradiation-enhanced clusters correspond to so-called CRPs (Cu-rich precipitates) or CELs (Cu-enriched clusters), and the formation mechanism is the clustering of Cu atoms above the solubility limit enhanced by the excess vacancies introduced by irradiation. This model also assumes that the formation of solute atom clusters and matrix damage is not independent to each other, which is a very different model from the conventional two-feature models as described in the previous sections. Another key idea is the introduction of a concept of a thermal vacancy contribution in the diffusivity model. This idea is essentially identical to that shown in Rg. 11.11. This is a direct modeling of the results of atomic-level computer simulations. ... 

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