Planar growth

For the sake of clarity, ten coordination sites are drawn a little further away from the surface of the particle in Fig. 15(a)-(c). These sites are real surface sites and the formal link is shown by a solid line. In this way the different C2 units are easily distinguished in the figure and the formation of six-membered rings is obvious. The planar tubule representations of Fig. 15(a )-(c ) are equivalent to those in Fig. 15(a)-(c), respectively. The former figures allow a better understanding of tubule growth. Arriving C, units are first coordinated to the catalyst coordination... 

Fig. 15. Growth of a (5ii,5n) tubule on the catalyst surface, illustrated by that of the (5,5) tubule. The central grey circle represents the catalyst particle with 10 coordination sites, and the small grey circles represent the other 10 catalyst coordination sites. The normal and bold lines represent single and double bonds, respectively, while coordinative bonds are represented by dotted lines [(a), (b) and (c)] (a ), (b ) and (c ) are the corresponding planar representations.

Growth mechanism of a (9n,0) tubule, over 24n coordination sites of the catalyst. The growth of a general (9 ,0) tubule on the catalyst surface is illustrated by that of the (9,0) tubule in Fig. 16 which shows the unsaturated end of a (9,0) tubule in a planar representation. At that end, the carbons bearing a vacant bond are coordinatively bonded to the catalyst (grey circles) or to a growing cis-polyacetylene chain (oblique bold lines in Fig. 16). Tlie vacant bonds of the six c/s-polyacetylene chains involved are taken to be coordinatively bonded to the catalyst [Fig. 16(b)]. These polyacetylene chains are continuously extruded from the catalyst particle where they are formed by polymerization of C2 units assisted by the catalyst coordination sites. Note that in order to reduce the number of representations of important steps, Fig. 16(b) includes nine new Cj units with respect to Fig. 16(a). 

Fig. 17. Growth mechanism of a (9/i,0)-(5n,5n) knee involving from 24 to 20 coordination sites of the catalyst, (a)-(g) Planar representation of the successive tubule growing steps (g ) Schlegel diagram representation of the whole knee with the Ci numbering corresponding to that of the individual steps (a)-(g).

Barium acetate decomposes [1050] with growth of planar product nuclei, E = 167 kJ mole-1 (720—750 K). Reactions of other Group II acetates are reported [1051] as being accompanied by at least partial melting. 

Sequence showing the temporal growth of instability on an initially planar lean propane-air flame. The flame speedis 11.5 cm/s. (FromQanet, C. and Searby, G., Phys. Rev. Lett., 80, 3867,1998. With permission.)... 

In the first step, lipid model membranes have been generated (Fig. 15) on the air/liquid interface, on a glass micropipette (see Section VIII.A.1), and on an aperture that separates two cells filled with subphase (see Section VIII.A.2). Further, amphiphilic lipid molecules have been self-assembled in an aqueous medium surrounding unilamellar vesicles (see Section VIII.A.3). Subsequently, the S-layer protein of B. coagulans E38/vl, B. stearother-mophilus PV72/p2, or B. sphaericus CCM 2177 have been injected into the aqueous subphase (Fig. 15). As on solid supports, crystal growth of S-layer lattices on planar or vesicular lipid films is initiated simultaneously at many randomly distributed nucleation... 

Similar to PbSe, the controlled growth of lead telluride, PbTe, on (111) InP was demonstrated from aqueous, acidic solutions of Pb(II) and Cd(II) nitrate salts and tellurite, at room temperature [13]. The poor epitaxy observed, due to the presence of polycrystalline material, was attributed to the existence of a large lattice mismatch between PbTe and InP (9%) compared to the PbSe/InP system (4.4%). The characterization techniques revealed the absence of planar defects in the PbTe structure, like stacking faults or microtwins, in contrast to II-VI chalcogenides like CdSe. This was related to electronic and structural anomalies. 

Convective diffusion to a growing sphere. In the polarographic method (see Section 5.5) a dropping mercury electrode is most often used. Transport to this electrode has the character of convective diffusion, which, however, does not proceed under steady-state conditions. Convection results from growth of the electrode, producing radial motion of the solution towards the electrode surface. It will be assumed that the thickness of the diffusion layer formed around the spherical surface is much smaller than the radius of the sphere (the drop is approximated as an ideal spherical surface). The spherical surface can then be replaced by a planar surface... 

Supported model catalysts are frequently prepared by thermally evaporating metal atoms onto a planar oxide surface in UHV. The morphology and growth of supported metal clusters depend on a number of factors such as substrate morphology, the deposition rate, and the surface temperature. For a controlled synthesis of supported model catalysts, it is necessary to monitor the growth kinetics of supported metal... 

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