Evidence of Homogeneous Nucleation

and these for e(L) as the size of the nano-crystal obtained by SAXS. This clarifies that with the increase oi ,d decreases slightly for e(S) and decreases discon-tinuously by as much as about 1(T times for e(L). We obtain the number density (v) of spherulites and nanocrystals against e by using the approximate equation, V = in Rgure 4.24. With the increase of e, the v increases slightly for e(S) and increases discontinuously by as much as about 10 times for e(L). 

It is well accepted that a spherulite forms from a nucleus therefore, the small v of the spherulite indicates that the number density of the nuclei should be small for quiescent conditions and e(S). On the other hand, the significant increase of the vfor e(L) indicates that the number density of nuclei should increase for e e. The discontinuous increase of v should be due to the change of nucleation mechanism at e from heterogeneous nucle-ation to homogeneous nucleation. 

In nature, only a small amount of heterogeneity is essentially included in the melt, and we know that most nucleation from the bulk melt is heterogeneous. The 

Therefore, we surmise that the electron density of the interface will be less than that of the NOCs because the entanglements need more free volume than the molecular packing within a crystal. 

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Lower, S. K., Maurice, P. A. Traina, S. J. 1998a. Simultaneous dissolution of hydroxylapatite and precipitation of hydroxypyromorphite direct evidence of homogeneous nucleation. Geochimica Cosmochimica Acta, 62, 1773-1780. 

Wang et al. [183] carried out hybrid mini emulsion polymerization of acrylates in the presence of polyurethane. The polyurethane was used as the costabilizer, and SLS as the surfactant. When MMA was used as the monomer, some homogenous nucleation was observed. This is in agreement with Tsavalas [179] who reported evidence of homogenous nucleation in the hybrid miniemulsion of MMA in the presence of alkyd. 

Extensive laboratory-scale studies have been conducted to investigate the triggering mechanism for RPTs when LNG, liquefied petroleum gas (LPG), and liquid refrigerants contact a hot liquid (usually water). These studies are covered in Sections III and VII. The evidence seems overwhelming that RPTs in these cases result from superheating of the cold, volatile liquid to its superheat-limit temperature where prompt homogeneous nucleation occurs in a time period of a few microseconds. (The properties of a superheated liquid and the concept of homogeneous nucleation are reviewed briefly in Section IX.)... 

Despite the reported agreement with the theory, the steady state parts of the transients as seen from Figure 13 lie in a range well below any of the theoretical curves. The most important fact, however, is that the first maximum of the experimental transients lies in a range around or below the maximum of the current-time curve for first layer formation as calculated from Jv obtained from the initial part of the same transient. This is obviously impossible within the model of homogeneous nucleation. One possible explanation is to assume that nucleation proceeds on nucleation centers. There is much evidence that active sites play a role in this believed-to-be very simple case of metal deposition. 

Although Eq. 27 appears to be the most likely initiation reaction, we cannot rule out a process in which water vapor and DMTC react, based on the ab initio results described in Sect. 4.6. If this does occur, however, it apparently does not lead to homogeneous nucleation of particles, since anecdotal evidence from the glass industry indicates that DMTC and water vapor can be premixed prior APCVD of tin oxide without substantial buildup of solids in delivery lines. Perhaps this is due to significant kinetic barriers to the decomposition of the tin-water complexes that initially form, so that further gas-phase reaction does not occur until the reactants enter the heated boundary layer above the substrate. 

The presence of HD in the resultant BA/VAc latex particles obtained by miniemulsion polymerization, in an amount far superior compared with that detected in the particles prepared in the absence of homogenization, provides strong evidence that particle nucleation occurs in the monomer droplets. When HD is... 

The emphasis of most studies on nucleation and growth of diamond has been placed on the heterogeneous formation of diamond particles and the crystallization and deposition of diamond films on substrate surfaces. Only a limited number of experiments have been conducted to achieve the homogeneous nucleation of diamond in the gas phase at atmospheric and subatmospheric pressures. However, there is evidence that, at least in some cases, diamond can be nucleated homogeneously in the nas phase.I2i H i]... 

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