Prismatic structure layer

Prismatic structure layer the layer consisting of polygonal rhombic prismatic aragonite crystals perpendicular to the inner surface of the shell. 

At a larger order of size, enamel has a prismatic structure, the enamel prism or rod representing the most obvious histologically defined entity. In cross-section its dimensions are approximately the same as those of an ameloblast but it is extremely long and may extend from the amelodentinal junction to the enamel surface. Adjacent prisms are approximately parallel but show local changes of direction. The prisms are formed as the result of the activity of ameloblasts, and one ameloblast may contribute to several prisms, while each prism receives material from more than one cell. In the outermost layer of fully formed human enamel the prisms merge into each other and a thin surface layer is produced. This layer resembles reptile enamel which is less than 1 mm thick and is not prismatic but continuous. 

More recently, simulation studies focused on surface melting [198] and on the molecular-scale growth kinetics and its anisotropy at ice-water interfaces [199-204]. Essmann and Geiger [202] compared the simulated structure of vapor-deposited amorphous ice with neutron scattering data and found that the simulated structure is between the structures of high and low density amorphous ice. Nada and Furukawa [204] observed different growth mechanisms for different surfaces, namely layer-by-layer growth kinetics for the basal face and what the authors call a collected-molecule process for the prismatic system. 

All three metals form a wide variety of binary chalcogenides which frequently differ both in stoichiometry and in structure from the oxides. Many have complex structures which are not easily described, and detailed discussion is therefore inappropriate. The various sulfide phases are listed in Table 22.4 phases approximating to the stoichiometry MS have the NiAs-type structure (p. 556) whereas MS2 have layer lattices related to M0S2 (p. 1018), Cdl2, or CdCl2 (p. 1212). Sometimes complex layer-sequences occur in which the 6-coordinate metal atom is alternatively octahedral and trigonal prismatic. Most of the phases exhibit... 

Key Colour % indicates preparation but no report of colour) mp/°C (na indicates value not reported) coordination 9 ttp = tricapped trigonal prismatic 8 d = dodecahedral 8 sa = square antiprismatic 8 btp = bicapped trigonal prismatic 8,7 = mixed 8- and 7-coordination (SrBr2 structure) 7 cc = capped octahedral 7 pbp = pentagonal bipyramidal 6 o = octahedral 6 och = octahedral chain, 6 ol = octahedral layered. 

Structures of the lanthanide nitridoborates appear as layered structures with approximate hexagonal arrangements of metal atoms, and typical coordination preferences of anions. As in many metal nitrides, the nitride ion prefers an octahedral environment such as in lanthanum nitride (LaN). As a terminal constituent of a BNx anion, the nitrogen atom prefers a six-fold environment, such as B-N Lns, where Ln atoms form a square pyramid around N. Boron is typically surrounded by a trigonal prismatic arrangement of lanthanide atoms, as in many metal borides (Fig. 8.10). All known structures of lanthanide nitridoborates compromise these coordination patterns. 

The most important sulfides are MoSg and WSg, which possess a layered structure. The metal atoms occupy trigonal-prismatic holes in the plane between the hex-agonally arranged sulfur layers, as shown in Fig. 5.12. The layers are shifted with... 

It should be noted here, that not only the (chemical and morphological) composition of the protective layers at the basal plane surfaces and prismatic surfaces is different, but that these layers also have completely different functions. At the prismatic surfaces, lithium ion transport into/ffom the graphite structure takes place by intercalation/de-intercalation. Here the formed protective layers of electrolyte decomposition products have to act as SEI, i.e., as transport medium for lithium cations. Those protective layers, which have been formed on/at the basal plane surfaces, where no lithium ion transport into/from the graphite structure takes place, have no SEI function. However, these non-SEI layers still protect these anode sites from further reduction reactions with the electrolyte. 

Fig. 6. Examples of types of meshes developed to resolve laminar flow around particles (a) Chimera grid. Reprinted, with permission, from the Annual Review of Fluid Mechanics, Volume 31 1999 by Annual Reviews www.annualreviews.org (b) Unstructured grid with layers of prismatic cells on particle surfaces. Reprinted from Chemical Engineering Science, Vol. 56, Calis et al., CFD Modeling and Experimental Validation of Pressure Drop and Flow Profile in a Novel Structured Catalytic Reactor Packing, pp. 1713-1720, Copyright (2001), with permission from Elsevier.

This is a layer structure similar to the Cdl2 structure except that the pairs of S layers are directly superimposed upon each other, so that the central cation is in trigonal prismatic coordination, not octahedral or tetrahedral. In the structures derived from this S-Mo-S unit, these layers can be stacked like the simple layers in atomic close-packed sequences. The molybdenite ((3-MoS2) structure has these layers in... 

Figure 1. Schematic drawing showing the structure of the trigonal prismatic variety of the metal dichalcogenide structure. Note the structure is not drawn to scale but to emphasize the layered structure of the materials.

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