Multiple nucleation

In contrast to chrysotile fibers, the atomic crystal stmcture of amphiboles does not inherentiy lead to fiber formation. The formation of asbestiform amphiboles must result from multiple nucleation and specific growth conditions. Also, whereas the difference between asbestiform and massive amphibole minerals is obvious on the macroscopic scale, the crystalline stmctures of the two varieties do not exhibit substantial differences. Nonfibrous amphiboles also exhibit preferential cleavage directions, yielding fiber-shaped fragments. 

It has been suggested [21,22] that the presence of Cu and K increases the rates and extent of Fe304 carburization during reaction and the FTS rates, by providing multiple nucleation sites that lead to the ultimate formation of smaller carbide crystallites with higher active surface area. In the present investigation, Cu- and K-promoted iron catalysts performed better than the unpromoted catalysts in terms of (1) a lower CH4 selectivity, (2) higher C5+ and alkene product selectivi-ties, and (3) an enhanced isomerization rate of 1-alkene. 

Using secondary nucleation analysis, Huang and Chang [51] found PTT to go through a transition in the multiple nucleation mechanisms from regimes II to III at around 194 °C. However, Lee et al. [50] found only regime II crystallization between 180 and 200 °C. 

In this regime the multiple nucleation of stems is so prohfic [Fig. 1.15(lateral spreading rate is irrelevant, i g. Now the growth rate is exactly of the same form as in regime 1... 

L-alanine deposited on a rhombohedral surface of quartz exhibits two preferential directions. A rough chain-folded surface is developed which is a result of multiple nucleations (Fig. 10). 

In order to explain this effect, two phenomena can be hypothesized (1) multiple nucleation of the PPE phases, and (2) break-up the PPE phase and, subsequently an increase of the particle density. Discussing the latter case first, it can be estimated that the time scale for dispersion is not sufficiently high [3, 83]. Therefore, multiple nucleation is likely to induce the higher nucleation densities, making SBM an ideal candidate for nucleation by interfacial effects. 

S(/) can be described by the well-known Avrami theorem [3.317], supposing multiple nucleation on a quasi-homogeneous substrate surface with a sufficient density of nuclei, statistically local distribution of nuclei, and overlapping of growing 2D islands ... 

Sharifker, B., and Hills, G. 1983. Theoretical and experimental studies of multiple nucleation. Electrochimica Acta 28, 879-889. 

Iron-Protein Interface Formation of the iron core appears to be initiated at an Fe-protein interface where Fe(ll)-0-Fe(III) dimers and small clusters of Fe(IIl) atoms have been detected attached to the protein and bridged to each other by oxo/hydroxo bridges. Evidence for multiple nucleation sites has been obtained... 

D16.4 The simple zipper model for the conversion of a polypeptide helical (h) chain to a random coil (c) begins with nucleation whereby an h residue makes an independent transition to a c residue with a probability that depends upon as where a < l and s is the stability parameter. After the nucleation conversion, only residues adjacent to a c undergo the h to c transition and they do so non-cooperatively with a probability that depends upon the stability parameter. The Zimm-Brag model allows for multiple nucleation sites. 

Fig. 2.19 A model of the growth of a polyethylene crystal through multiple nucleation on a growth face of dimensions L and i, showing a sketch of a dynamic reptation tube delivering molecules from the melt to the growth face (from Hoffman (1983) and Chang and Lotz (2005) courtesy of Elsevier).

Bieri and Fasel used the hexaiodo-substituted cyclohexa-m-phenylene 60 as monomer for polycondensation under UHV on Ag(lll) [132]. The polymer grew laterally from multiple nucleation sites, which gave rise to formation of fragments with different orientations (Figure 28.26b). The honeycomb-Uke network structure... 

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