Prismatic plane

Beryllium is a light metal (s.g. 1 -85) with a hexagonal close-packed structure (axial ratio 1 568). The most notable of its mechanical properties is its low ductility at room temperature. Deformation at room temperature is restricted to slip on the basal plane, which takes place only to a very limited extent. Consequently, at room temperature beryllium is by normal standards a brittle metal, exhibiting only about 2 to 4% tensile elongation. Mechanical deformation increases this by the development of preferred orientation, but only in the direction of working and at the expense of ductility in other directions. Ductility also increases very markedly at temperatures above about 300°C with alternative slip on the 1010 prismatic planes. In consequence, all mechanical working of beryllium is carried out at elevated temperatures. It has not yet been resolved whether the brittleness of beryllium is fundamental or results from small amounts of impurities. Beryllium is a very poor solvent for other metals and, to date, it has not been possible to overcome the brittleness problem by alloying. 

Figure 2 Diffraction pattern on the prismatic plane for a specimen taken from a sample deformed at 2.69%. The long dimension is the height of the specimen, while the width corresponds to the size of the diffracted beam through 0.1mm slit. The intensity profile is taken along the black line.

Begining of the simulation (left), after deformation (right). Basal dislocations glide horizontally (horizontal lines), dislocations in the prismatic plane vertically (white vertical lines). The center of the cylinder is represented. 

Certain important crystal planes are often referred to by name without any mention of their Miller indices. Thus, planes of the form 111 in the cubic system are often called octahedral planes, since these are the bounding planes of an octahedron. In the hexagonal system, the (0001) plane is called the basal plane, planes of the form lOTO are called prismatic planes, and planes of the form lOTl are called pyramidal planes. 

Carbon nanofiber materials exhibit several advantages with respect to the conventional support materials (i) a high external surface area in a nanometric-scale size which significantly improves the mass transfer, especially in a liquid medium, (ii) a strong interaction generated by the exposed prismatic planes towards the active phase, which can induce peculiar catalytic activities and selectivities. However, to be used in an efficient way the carbon nanofibers should be able to be synthesized on a large scale with a uniform diameter and a low price. From the numerous reviews published on the subject its seems... 

The Pd/CNF catalyst displays a catalytic activity as high as that obtained on a commercial catalyst supported on activated charcoal despite the large difference between the two supports surface area, i.e. 100 m /g for the CNFs instead of 1000 m /g for the activated charcoal. The high hydrogenation activity observed on the CNF-based catalyst was attributed to the high external surface area of the support and to the peculiar interaction existing between the prismatic planes and the metallic particles. Recently, a significant improvement was introduced via a new synthesis route which allows the possibility for these nanoscopic materials, to be supported on a macroscopic host structure [17]. 

From the discussion above, we can conclude that further increases in the SiN deposition time will result in more effective dislocation reduction up to a point. Fiowever, much thicker GaN overlayers or modified growth conditions are needed for coalescence as the SiN deposition time is increased. When SiN was deposited more than 6.5 min, we could not get a coalesced surface even at 10 pm regrowth under the current growth conditions employed. The possible reasons might be the unoptimized lateral overgrowth rate when islands with (1101) prismatic planes were formed as well as the larger separation between nucleation sites. 

Zinc polar plane [0001] where zinc ions are more outwardly positioned than oxygen ions oxygen polar plane [0001], where ions are more outwardly positioned than zinc ions, and the non polar prismatic plane [1010], where both zinc and oxygen ions are on the same plane. They have reported that catalytic decomposition of propan-2-ol was highest on [0001] polar surface of zinc oxide. It is further reported that catalyst morphology and activity is influenced by zinc oxide precursors [8]. 

Figure 11. Growth rate of the basal plane (diffusion-controlled) and the prismatic planes (interface-controlled) as a function of oversaturation in the oxinitride liquid. The oversaturation after the a/P-transformation depends on the surface energy (a), the grain thickness (2D) and the length of the needle like grains (2L).

The thermal expansion coefficient of [3-Si3N4 depends on its crystallographic orientation, with values of 3.23 x 10 being determined for the basal plane and 3.72 X 10 for the prismatic plane, within a temperature range from 0 to 1000 °C [35]. Similar values were determined by Bruls et al. [44]. 

Slip Modes in the a-Phase. Various modes of slip can occur in a-Ti or in the a-phase of titanium alloys (see Table 4). In general, slip can occur on prismatic, pyramidal and basal planes by the movement of , [c] and -type dislocations. Since the <1120> slip directions are common to aU three planes, the -type dislocations can ghde on prism, pyramid, and basal planes. The -type slip can take place on prismatic and pyramidal planes. The [c]-type glide is restricted to only prismatic planes and generally does not occur. 

Interstitial and vacancy defects accumulate preferentially in the form of dislocation loops located respectively on basal and prismatic planes. 

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