Platelet textures

Fig. 6 Reflectance spectrum of Blue Phase I and polarizing optical micrograph of typical platelet texture...

Plate 6. The platelet texture of the TGBA phase of (S)-l-methylheptyl 4 -(4-n-tetradecyloxyphenylpropioloyloxy)biphenyl-4-carboxylate (xlOO)... 

It is apparent that while the grains maintain the unique platelet texture, so characteristic of M0O3, the microstructure lacks the uniformity that was obtained as a con-seqnence of identical treatment given to the M0O3 powder derived from foil oxidation (nearly monosized small platelets with narrow plate size distribution see Figure 2.5). 

Figure 14.3 BPLC platelet textures under a polarizing optical microscope with different chiral concentrations.

Between crossed polarizers, the phase transition into a columnar phase is often accompanied by a dendritic growth of the texture. If the director is oriented perpendicular to the viewing direction, pseudo-focal conic fan-shaped textures can be observed. If the viewing direction is parallel to the director, a platelet texture is formed. 

The blue phases BP I and BP II, which appear in a narrow temperature range between the cholesteric and isotropic phase, are not birefringent but optically active. In the transmitted light of a polarizing microscope they look like a blue isotropic liquid. Sometimes small single crystals of the blue phase with distinct habit are seen. The polycrystalline blue phase platelet texture resembles the mosaic texture of the smectic B phase. 

When smectic layers are mainly horizontal, the existence of walls often leads to mosaic textures, each domain extending over the entire thickness of the preparation. A platelet texture is observed when the do-... 

Planck constant, NMR 840 plastic crystals, definitions 23 platelet textures 440 plug flow 467... 

Fig. 6.1. Scanning electron micrographs showing the different surface textures of red (Er) and white blood cells. A Cells within a blood vessel. B,C A comparison of scanning electron micrographs with conventional light microscope images of the same field of stained cells. Enlarged pictures at the right emphasize the different surface textures of monocytes (Mo) and platelets (PI) in D, lymphocytes (Ly) in E, and neutrophils (Ne) in F. From Kessel RG and Kardon RH (1979). Tissues and Organs A Text Atlas of Scanning Electron Microscopy, WH Freeman, NY.

Figure 7.31 Templated grain growth process (a) templates (black platelets) are randomly oriented in powder (b) during consolidation, templates achieve a preferred orientation (c) larger templates grow at the expense of smaller particles during sintering (d) after sintering, the majority of the final part can be composed of grains with the preferred orientation or texture.

Insofar as small crystals of nonreducible oxides dispersed on the internal interfaces of the basic structural units (platelets) will stabilize the active catalyst surface Fe(lll), the paracrystallinity hypothesis will probably hold true. But the assumption that this will happen on a molecular level on each basic structural unit is not true. The unique texture and anisotropy of the ammonia catalyst is a thermodynamically metastable state. Impurity stabilization (structural promotion) kinetically prevents the transformation of platelet iron into isotropic crystals by Ostwald ripening [154]. Thus the primary function of alumina is to prevent sintering by acting as a spacer, and in part it may also contribute to stabilizing the Fe(lll) faces [155], [156], [298],... 

Its major asset is that it provides a very detailed textural description of the catalyst (size, shape and arrangement of the platelets constituting the support, size, shape and spatial distribution of the mesoporosity and macroporosity, relative distribution of phases, etc.) and can detect the local heterogeneities oflen at the origin of catalyst malfunctions. 

When powder particles have thin platelet-like shapes, they will tend to agglomerate, aligning their flat surfaces nearly parallel to one another Figure 3.20, left). As a result, the orientations of platelets are randomized via rotations about a common axis normal to their largest faces, and such samples are expected to have a uniaxial preferred orientation (or texture). 

Seiter et al. [80] found a correlation between the overpotential and growth forms of electrodeposited copper on copper sheet substrate with (100) texture, as shown in Fig. 31. Barnes etal. [81] observed similar results on copper single crystal surfaces near (100) face below 10-mV ridges, 40-70-mV platelets, 70-100-mV blocks and fine platelets and above 100-mV polycrystalline deposit. 

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