Cleavage planes

A direct measurement of surface tension is sometimes possible from the work of cleaving a crystal. Mica, in particular, has such a well-defined cleavage plane that it can be split into large sheets of fractional millimeter thickness. Orowan... 

Gilman [124] and Westwood and Hitch [135] have applied the cleavage technique to a variety of crystals. The salts studied (with cleavage plane and best surface tension value in parentheses) were LiF (100, 340), MgO (100, 1200), CaFa (111, 450), BaFj (111, 280), CaCOa (001, 230), Si (111, 1240), Zn (0001, 105), Fe (3% Si) (100, about 1360), and NaCl (100, 110). Both authors note that their values are in much better agreement with a very simple estimate of surface energy by Bom and Stem in 1919, which used only Coulomb terms and a hard-sphere repulsion. In more recent work, however, Becher and Freiman [126] have reported distinctly higher values of y, the critical fracture energy. ... 

Erlandsson R, Hadzioannou G, Mate M, McClelland G and Chiang S 1988 Atomic scale friction between the muscovite mica cleavage plane and a tungsten tip J. Chem. Phys. 89 5190... 

There are two basic types of cast iron white, and grey. The phases in white iron are a and FejC, and it is the large volume fraction of FejC that makes the metal brittle. The name comes from the silvery appearance of the fracture surface, due to light being reflected from cleavage planes in the FejC. In grey iron much of the carbon separates... 

Spaltebene, /. (Cryat.) cleavage plane, also cleavage face. 

Cleavage plane of high pressure stress annealed pyrol)dic graphite. 

Molybdenum trioxide has a layered structure with orthorhombic symetry [16] (a=3.963, b=ll855, c=3.696 A), this structure consists of double layer sheets parallel to the (010) cleavage plane. The building unit is a distorted M0O6 octahedron, with Mo-0 distances 1.67, 1.73, 1.95 (twice), 2.25 and 2.33 A (Fig.l)... 

A second product is the ICE Solid-State Model Kit, developed by L. A. Mayer and G. C. Lisensky, which makes it possible to build extended three-dimensional structures Using a base with holes, templates for some 60 different structures, rods, and four sizes of spheres in radius ratios, common crystal structures can be assembled in a matter of minutes (3). Furthermore, many structures can be assembled from different perspectives by teams of students For example, the cubic NaCl unit cell can be assembled with its orientation on the face of the cube or on the body diagonal. Natural cleavage planes can be found with the kit Lifting one sphere will separate atomic planes from one another. (Contact ICE for ordering information.)... 

Newport That would determine where the cleavage plane is going to occur. 

Break. In mining, a separation between strata or along a cleavage plane in coal or rock. 

Fig. 7 Form I unit cell packing of cocrystal 20 21 - possible cleavage planes are projected horizontally [50]...

A clear explanation for this observation was not offered. However, as a consequence of the space group symmetry, the crystals differ in their tertiary level of supramolecular architecture (see Fig. 13 and Fig. 14). The authors note that this difference affords a potential non-polar cleavage plane in form I but not in form II. As it is form I that preferentially formed in the presence of non-polar solvents, it is possible that this may play a role in the phenomenon. 

Fig. 13 Form I crystal packing of caffeine glutaric acid (35 36), as viewed down the length of the hydrogen-bonded combs, showing potential non-polar cleavage plane, projected vertically [59]...

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