Needle aggregate

If it is desired to observe the crystalline form of the osazone, draw up in a glass tube a few drops of the cold filtrate containing the fine crystals, and transfer to a microscope slide. Cover the drops with a slip and examine under the microscope unless the filtrate has been cooled very slowly and thus given moderately-sized crystals, the high power of the microscope will probably be required. Note the fine yellow needles aggregated in the form of sheaves. Compare with Fig. 63(A). 

Aragonitic precipitated calcium carbonate 95-98 0.75-2.5 Steep/ narrow 6-18 Clustered needle aggregates low aspect ratio... 

Amino-4,6-dichlorophenol. This compound (11) forms long white needles from carbon disulfide, and aggregate spheres from benzene. It sublimes at 70—80°C (8 Pa = 0.06 mm Hg) and decomposes above 109 °C. It is freely soluble in benzene and carbon disulfide, and is sparingly soluble in petroleum ether, water, and ethanol. The free base is unstable and the hydrochloride salt (mp 280—285°C, dec) is employed commercially. 

Two unnamed alkaloids have also been deseribed. One was obtained by Bredemann in work on the alkaloids of white hellebore it occurred in the mother liquors from protoveratrine crystallisation and formed spherical aggregates of needles, m.p. 239-241°. The other was isolated by. Jacobs and Craig during a chromatographic analysis of residual, benzene-soluble alkaloids of green hellebore. It is represented by the formula C27H41 (39)04N, crystallises in six-sided platelets or flat needles, sinters about 130°, effervesces at 170-5°, and on further heating solidifies and finally melts at 272-4° it has [a]n ° — 78° (MeOH). 

Many industrial semi-crystalline polymer materials like polypropylene, polyamides, or polyesters contain nucleating agents or clarifiers which form needle-shaped aggregates already in the polymer melt. "For this purpose the pattern is desmeared using the measured primary beam. For a less involved treatment it may be sufficient to know the integral width of the primary beam profile in fiber direction. 

An electron microscopy study by Mullen et al. (1989) showed that Cd2+, Cu2+ and La3+ accumulated on the cell surface of Bacillus cereus, B. subtilis, E. coli and Pseudomonas aeruginosa as needle-like, crystalline precipitates, while Ag+ precipitated as discrete colloidal aggregates at the cell surface and occasionally in the cytoplasm. The needle-like and hexagonal precipitates were also found for the biosorption of Ni2+ on the cell surface of P. fluorescens 4F39 at pH 9 and it was suggested as a microprecipitation process that followed on ion exchange (Lopez et al. 2000). 

ZnO particle morphologies are very complex and diversiform in comparison with Ti02. Thus, monodispersed ZnO particles with well-defined morphological characteristics, such as spherical, ellipsoidal, needle, prismatic, and rod-like shapes, have been obtained. Aggregates composed of these basic shape particles have also been achieved. The methods used for synthesis of these ZnO powders include alkali precipitation [214-216], thermal decomposition [217], hydrothermal synthesis [218], organo-zinc hydrolysis [219], spray pyrolysis [220], and other routes. 

Johannsenite, Ca(Mn,Fe )Si206, is a species in whieh p = 0. There is little additional trivalent ion (Al, Fe, or Cr ) substitution. The mineral is most commonly found as spherulitic aggregates of brittle fibers or prisms. Another pyroxene, acmite (NaFe Si206), has been found as large (100 X 35 X 20 cm) single crystals of prismatic shape, as needles, as felted aggregates of fine fibers, and as capillary crystals. 

When crystallized from an acetone-water mixture, benzoic acid is obtained as the crystalline needles shown in Figure 1 A. On the other hand, a mixture of needles and irregular crystalline solid is obtained from methanol-water mixtures (Figure IB). From pure water, aggregates of monoclinic crystals are obtained (Figure 1C). 

Crystals formed under small driving force conditions (see Section 3.2) in a dilute ambient phase, such as the vapor phase or solution phase, will generally exhibit polyhedral forms, irrespective of their size. Even crystals of micrometer size, such as clay minerals, show polyhedral forms. However, there are crystals that show elongated needle forms that resemble whiskers, coils, hollow tubes, and even ice cream cones (see Figs. 2.2 (a), (b)) others exhibit tree-like polycrystalline aggregates of dendrites (see Fig. 2.2 (c)). 

Complex crossed lamellar structure a layer consisting of aragonite needle crystals with orientations inclined at 45° to the inner portion of the cell. These needle crystals aggregate in a radial manner, forming a conical body, which is arranged nearly perpendicularly to the inner surface of the shell. 

Composite prismatic structure the c-axis of rhombic prisms align parallel to the shell. The rhombic prism is an aggregation of aragonite needle crystals aligned in conical form in its elongation direction. 

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