Unidirectional crystallization

Still stronger and stiffer forms of fibrous materials are the unidirectional crystals called whiskers.1 Under favorable conditions crystal-forming materials will crystallize as extremely fine filamentous single crystals a few microns in diameter and virtually free of the imperfections found in ordinary crystals. Whiskers are far stronger and stiffer than the same material in bulk form. 

Lu] X-ray diffraction, EPMA, FESEM unidirectional crystallization, 2.65-3.51 mass% C, 27.1-30.8 mass% Cr, 7/M7C3/M23C6... 

Gao F, El-Deab MS, Ohsaka T (2005) Electrodeposition of gold nanorods with a unidirectional crystal growth and lower Au(l 11) facets area. Indian J Chem A 44(5) 932—937... 

A base glass composed of Ca0 P205 = 0.85 (molar ratio) was used to produce these fibers. Crystallization took place at 600 C for 48 h. Unidirectional crystallization techniques were not conducted. Crystallization of P-Ca(P03)2 proceeded in needle form, with random orientation yielding an isotropic body. An ultraphosphate of the substantially lower chemical durability of the glass matrix and the ultraphosphate crystals compared with that of the P-Ca(P03)2, the matrix was easily extracted by aqueous leaching. These P-Ca(P03)2 fibers were subsequently used in a composite material with a very low modulus of elasticity (Kasuga 1996). 

Abe Y, Kasuga T, Hosono H., and de Groot K., "Preparation of High-Strength Calcium Phosphate Glass-Ceramic by Unidirectional Crystallization," /. Am. Ceram. Soc., 67, C-142-C-144 (1984). 

Abe, Y., Kasuga, T., Hosono, M. and de Groot, K., Preparation of High-Strength Calcium Phosphate Glass-Ceramics by Unidirectional Crystallization. J. Amer. Ceram. Soc. 67 C142-144 (1984). 

A crystal is suspended in fresh solvent and 5% of the crystal dissolves in 300 s. How long will it take before 10% of the crystal has dissolved Assume that the solvent can be regarded as infinite in extent, that the mass transfer in the solvent is governed by Fick s second law of diffusion and may be represented as a unidirectional process, and that changes in the surface area of the crystal may be neglected. Start your... 

The structural constraints imposed by the fused cyclic structure of the catenates and the ability to cleanly separate product mixtures greatly facilitates crystallization, and single crystal X-ray structures have been obtained for a number of ladder polysilanes.3 8 For the all-anti molecules, the non-planarity of the SI rings induces a unidirectional helical twist to the ladder structure, as is evident in Figure 63. 

Other square planar Pt(II) complexes able to form infinite unidirectional chains in the solid state are known, in particular the Magnus s green salt [Pt(NH3)4][PtCl4],u but also Pt(I) complexes such as [Pt(bipy)2](N03) 2FI20 (obtained by electrochemical reduction of [Pt(bipy)2](NC>3)2 H20) have recently shown linear chain crystals (Pt-Pt = 3.56 A).12... 

Figure 7.6. Morphological variation expected in twins of real crystals. The symbols indicate dislocations. Only similar forms or unidirectional growth are expected.

Coaxial intergrowth is a paragenetic relation that describes crystals of two different species growing with a common axis the misfit ratios between the two crystals in the direction of the common axis are small, without exception. The formation of coaxial intergrowth can be understood to be one crystal conjunct to the other in an epitaxial relation, where both continue to grow. If a liquid of eutectic A-B component is solidified from one side (unidirectional solidification), crystals of the two phases A and B precipitate in dotted, columnar or lamellar (with common axis) form, and show unique textures for unidirectional solidification. This is a well known phenomenon in metallurgy. 

Techniques and procedures of such thermoeleastic measurements under unidirectional or uniform (hydrostatic) deformation of solid and rubberlike polymers are described in 1 64 66). Similar methods have been used more often for recording the temperature changes resulting from the plastic deformation of solid polymers. Besides thermocouples, fluorescent substances, liquid crystals and IR-bolometers are used for such measurements. 

As mentioned in Section 13.5.1, the transient species [BO(OH)2]-has been stabilized by hydrogen-bonding interactions with the nearest urea molecules in the host framework of the inclusion compound [(CH3)4N]+[B0(0H)2]--2(NH2)2C0-H20. A perspective view of the crystal structure along the [010] direction is presented in Fig. 20.4.16. The host lattice consists of a parallel arrangement of unidirectional channels whose cross section has the shape of a peanut. The diameter of each spheroidal half is about 704 pm, and the separation between two opposite walls at the waist of the channel is about 585 pm. The well-ordered tetramethylammonium cations are accommodated in double columns within each channel. 

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