Small crystal grain

FIG. 3-6. A polished and etched surface of a piece of cold-drawn copper bar, showing the small crystal grains which compose the ordinary metal. Magnification 200 X (200-fold linearly). The small round spots are gas bubbles. (From Dr. S. Kyropoulos.)... 

In Figure 4-6 there is shown the atomic structure of the gold-copper alloy used in jewelry. This material consists of small crystal grains, held firmly together by the interatomic forces between them, each grain... 

Graining, flaking, and spraying have all been used to make soHd ammonium nitrate particles. Most plants have adopted various prilling or granulation processes. Crystallized ammonium nitrate has been produced occasionally in small quantities for use in specialty explosives. The Tennessee Valley Authority developed and operated a vacuum crystallization process (25), but the comparatively small crystals were not well received as a fertilizer. 

Fine-grain sugar, or fmit sugar, used because it is quick-dissolving, consists of small crystals obtained by screening. 

Klein-kohle, /. small-sized coal, buckwheat coal, pea coal small coal, slack, -koks, m. small-sized coke, nut coke, klein-komig, a. small-grained, fine-grained, -kristallinisch, a. finely crystalline, in small crystals. 

As remarked in the previous section, single crystals are not perfect but are built of domains of material that are slightly mismatched. The interfaces between these regions are called low-angle or small-angle grain boundaries. These boundaries consist of an array of dislocations arranged so as to remove the misfit between the... 

Most metals and ceramics in their normal states are polycrystalline. Polycrystalline solids are composed of many interlocking small crystals, often called grains (Fig. 3.33). The surfaces of the grains that make up the solid are often similar to the external surfaces found on large crystals. 

It has been observed by some experimenters, but not by the others, that the experimental lattice constant a in crystals of ordinary size was different from that, a + A a, found in extremely small crystals. A recent example72 refers to vacuum-deposited copper grains whose diameter D (they were, of course, not spherical) varied from 24 to 240 angstroms. The lattice constants calculated from the (111) reflexions increased from 3.577 to 3.6143 angstroms when the grain volume decreased, but the particle size had no definite effect on the reflexions from the 220 plane. 

Bubble Nucleation in a Liquid Phase The above classical nucleation theory can be easily extended to melt nucleation in another melt. It can also be extended to melt nucleation in a crystal but with one exception. Crystal grains are usually small with surfaces or grain boundaries. Melt nucleation in crystals most likely starts on the surface or grain boundaries, which is similar to heterogeneous nucleation discussed below. Homogeneous nucleation of bubbles in a melt can be treated similarly using the above procedures. Because of special property of gases, the equations are different from those for the nucleation of a condensed phase, and are hence summarized below for convenience. 

Ca- and Mg-oxides (lime, periclase [MgO]) may occur as small crystals embedded within the glass or they may be located on its surface depending on temperature and furnace conditions where the minerals formed. Low-temperature minerals such as anhydrite (CaS04) may form on the surface of the fly ash grains after they have left the high-temperature zones in the furnace (Linton et al. 1977 Soroczak et al 1987 Ainsworth et al. 1993 Fishman et al. 1999). 

At first, one can consider that the electrode is a single crystal. Thus, instead of consisting of small crystals separated by grain boundaries, there is one crystal with an uninterrupted network of atoms extending right through its bulk. The surface of such... 

In general, it is not desirable to obtain large crystals, since no two crops will look alike. The best preparation will consist of small crystals not larger than a grain of wheat, as uniform in size as possible, not too much matted together, but not necessarily of perfect form. 

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