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Multiple twinning

Vielling, m. Cryat.) multiple twin. Viellinienspektrum, n. many-line spectrum, viellinig, a. many-line, multilinear, viel-mal, adv. many times, -mehr, adv. much more, more. — conj. rather, -phasig, a. polyphase, multiphase, -polig, a. multipolar. [Pg.491]

The individual cubic crystals sometimes grow at equal rates, filling the spaces between them. Each assumes the shape of a trigonal pyramid, with the outer edges 5% longer than the radial edges. The multiple twin then has the macroscopic appearance of an icosahedron. [Pg.836]

It Is not necessarily to be concluded that. In general, the proportion of small metal particles having the multiplicity twinned form decreases as the size Is decreased. The evidence concerning particles formed in other ways shows a great deal of variability. [Pg.336]

The structure of these spherites is uncertain Bradford assumes that they consist of a regular crystalline growth formed by multiple twinning of minute crystals. Scherrer s examination of gold sols, however, has revealed the fact that the crystal interference lines are well developed when the particle contains as few as eighty molecules arranged in the cube lattice, a spherite of OTju. diameter would probably show crystalline properties even if excessive twinning has taken place. [Pg.304]

Since the discovery of Shechtman et al. (1984) that the rapidly quenched Al-14% Mn alloy is quasicrystalline with icosahedral symmetry, there has been intense activity to explore such alloys to find out whether there would be a conceptual revolution in crystallography. Pauling (1985) proposed that the icosahedral symmetry results from multiple twinning of cubic crystals, but many features of these unique alloys, especially their electron diffraction patterns, cannot be understood on the basis of twinning alone. [Pg.69]

Pauling, L. (1985) Apparent icosahedral symmetry is due to directed multiple twinning of cubic crystals, Nature 317, 512. [Pg.318]

HREM is particularly suitable for determining the nature and extent of twinning in faujasite crystals which are prone (8) to twinning by reflection across 111 planes as shown in Fig. 2. Multiple twinning (not necessarily on the same member of the family of 111 planes) is common and in Fig. 3 we show a crystal ( 110] zone-axis orientation) exhibiting the consequences of simultaneous twinning on (111) and (111) planes. In such a situation two further twin planes inclined to 010 are theoretically possible (i.e. (111) and (111)), but these twinned individual would be projected along a <1JM > type zone-axis. [Pg.182]

L. Pauling, Icosahedral and decagonal quasicrystals as multiple twins of cubic crystals, in Extended Icosahedral Structures (Aperiodidty and Order, Vol. 3), M. V. Jaric and D. Gratias, eds., Academic Press, New York, 1989, pp. 137-162. [Pg.745]

Figure 1.13. Dark-field TEM images of single-crystal calcite shocked to 85 GPa, displaying (a) the crossing of multiple twins, a large number of perfect dislocations and (b) numerous partial dislocations decorating the twin planes, (c) Secondary electron image of compacted calcite powder shocked to 85 GPa. The recovered specimen is composed of numerous foamy aggregates containing bubbles, voids, and crater-shaped objects. Figure 1.13. Dark-field TEM images of single-crystal calcite shocked to 85 GPa, displaying (a) the crossing of multiple twins, a large number of perfect dislocations and (b) numerous partial dislocations decorating the twin planes, (c) Secondary electron image of compacted calcite powder shocked to 85 GPa. The recovered specimen is composed of numerous foamy aggregates containing bubbles, voids, and crater-shaped objects.
K. Miyasaka, L. Han, S.N. Che, and O. Terasaki, A Lesson from the Unusual Morphology of Silica Mesoporous Crystals Growth and Close Packing of Spherical Micelles with Multiple Twinning. Angew. Chem. Int. Ed., 2006, 45, 6516-6519. [Pg.593]

The existence of these highly mobile quasi-isolated atoms (Fig. 10) could provide new possibilities for catalytic reactions, favoring, for instance, the occurrence of the nonselective cyclic mechanism. Although the potentials used in Hoare and Pal s calculations (Lennard-Jones and Morse-Mye) may be considered as unsuitable for metal clusters, recent calculations (181), made with more realistic potentials, indicate that below 15 A, the clusters with icosahedral symmetry are more stable than the fee cubooctahedra. Unfortunately, the size range in which the polyhedral metal clusters are supposed to be stable does not allow microdiffraction studies. Moreover, when platinum is deposited on an oriented rock-salt face, pseudocrystals with uncommon symmetry are present only in very small amounts, and in a particle size range of 80-120 A, where they obviously result from multiple twinning of fee tetrahedra (182). [Pg.78]

Figure 6.12 (a) Generation of twins by an ecliptic arrangement of C-atoms. Within the twinning plane the six-membered rings are boat-shaped, (b) Electron microscopic image and scheme of a multiple twin ( Taylor Francis 2001). [Pg.400]


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See also in sourсe #XX -- [ Pg.3 , Pg.4 , Pg.252 , Pg.253 ]




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