Nucleation surface nudeation

Fig. 26 Deformation maps of a a non-nucleated PP/EPR with 15% EPR and b its /S-nudeated homologue for different temperatures and crack tip loading rates as deduced from the fracture surfaces of compact tension specimens. A rough indication of the test speed is provided by the upper scale...

The discussion in this paper appties to wide classes of phase transformations that occur by a nucleation and growth mechanism. Examples of such transformations indude many common transformations, such as boiling and freezing of a liquid and condensation of a vapor, as well as some much less well known transformations, such as oxidation of a metal surface and formation of voids in nudear reactor materials. There are some types of phase transformations, such as spinoidal decomposition, that occur as soon as they are thermodynamically allowed and do not require nudeation. 

Draft tube baffte DTB or draft tube, DT (either adiabatic cooling or evaporative type also called flash growth or Pachuca) MSMPR. Mother liquor is pumped up a vertical central draft tube liquor overflow and flows down the atmulus. Limits the amount of supersaturation created per pass past the heating surface to 1 °C and therefore limits the nucleation rate to very low values. Operates with a suspension of soUds that is 25-50% apparent settled volume. Used where solute solubility is temperature independent or moderately dependent and where excess nudeation makes it difficult to achieve crystals in the size 0.6-2 mm. Minimum crystallization buildup on walls no places with dose dearances (as in Oslo). 

The model used to describe the growth of crystals by It ers calls for a two-step process (1) formation of a two-dimensional nucleus on the surface and (2) spr ing of the solute from die two-dimen onal nucleus across the surface. The relative rates at which these two steps occur give rise to die mononurdear two-dimenskmal nucleation theory and the polynuclear two-dimensional nudeation theory. In the mononuclear two-dimensional nucleation theory, the surface nucleation step occurs id a finile rale ndiile die spreading across die surface occurs at an infinite rate. The reverse is true for the polynuclear two-dimensional nucleation theory. From the mononuclear two-dimensional nucleation thet, growth is related to supersaturation by the equation... 

It is usually considered that nudei are spread randomly over the sample, except for nuclei formed on outer surfaces, on surfaces allowing for transcrystallinity and on surfaces of the second dispersed component, e.g. short fibers. However, if the nudeation events occur not only at the very beginning of crystallization but also dining crystallization, then the volume occupied by already advanced spherulites is excluded from further nucleation. Such an exdusion always produces a kind of a distance correlation, if the nudeation process is prolonged in time. The close vicinity of an arbitrarily chosen nudeus is then poorer in other nuclei than more distant regions. 

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