Face-centered cubic crystalline structures

Niobium metal absorbs nitrogen, similar to hydrogen, forming interstitial solid solution. The absorption occurs at 300°C and the solubility of nitrogen in the metal is directly proportional to the square root of the partial pressure of nitrogen. The reaction is exothermic and the composition of such interstitial solid solution varies with the temperature. When the metal is heated with nitrogen at temperatures between 700 to 1,100°C, the product is niobium nitride, Nb2N or (NbNo.s) [12033-43-1]. When heated with ammonia at these temperatures, niobium forms this nitride. Another niobium nitride exists, NbN [24621-21-4], with a face-centered cubic crystalline structure. 

Silvery-white metal face-centered cubic crystalline structure density 12.02 g/cm Vickers hardness, annealed 37-39 melts at 1,554°C vaporizes at 2,970°C electrical resistivity 9.93 microhm-cm at 0°C Poisson s ratio 0.39 magnetic susceptibility 5.231x10 cm /g thermal neutron cross section 8... 

Similarly, charged solid particles (such as latex spheres) —kinetically stable lyophobic colloids —may exist in colloidal crystalline phases (with body-centered or face-centered cubic structures) as a consequence of thermodynamically favored reduction in free energies (see Chapter 13). Even neutrally charged spherical particles ( hard spheres ) undergo a phase transition from a liquidlike isotropic structure to face-centered cubic crystalline structures due to entropic reasons. In this sense, the stability or instability is of thermodynamic origin. 

When we determined the crystalline structure of solids in Chapter 4, we noted that most transitional metals form crystals with atoms in a close-packed hexagonal structure, face-centered cubic structure, or body-centered cubic arrangement. In the body-centered cubic structure, the spheres take up almost as much space as in the close-packed hexagonal structure. Many of the metals used to make alloys used for jewelry, such as nickel, copper, zinc, silver, gold, platinum, and lead, have face-centered cubic crystalline structures. Perhaps their similar crystalline structures promote an ease in forming alloys. In sterling silver, an atom of copper can fit nicely beside an atom of silver in the crystalline structure. 

The XRD for the sample of Ni-metallized on graphite (4.6wt%) is provided in Fig. 2c, however the strongest peaks of Ni metal are overlapping with those peak reflections from the MAG-10 graphite. But, the X-ray diffraction in Fig. 2a revealed the Ni particles were pure nickel crystalline with a face-centered cubic (fee) structure. 

According to Pearson (4), calcium exists in two crystalline modifications. The low temperature phase (a) has a face -centered - cubic (cF4) structure, as does o-Sr(cr). The high temperature phase ( B) has a body - centered - cubic (cI2) structure, as does B Sr(cr). In comparison, magnesium has a hexagonal - close - packed structure. The B-Ca(cr) region of stability is 716 3 K to 1115 2 K (5). 

Krypton is present in the air to the extent of about 1 ppm. The atmosphere of Mars has been found to contain 0.3 ppm of krypton. Solid krypton is a white crystalline substance with a face-centered cubic structure which is common to all the "rare gases."... 

Figure 4.3.2 The diamond crystalline lattice structure composed of two interpenetrating face-centered cubic lattices.

Colorless, odorless, and tasteless gas density 3.733 g/L at 0°C liquefies at -153.22°C sohdifies at -157.36°C to a white crystalline substance that has a face-centered cubic structure critical temperature -63.6°C critical pressure... 

The type of crystalline structure that is formed depends on the concentration of the particles as well as the magnitude of the Debye-Hiickel thickness. For large Debye-Hiickel thicknesses a body-centered cubic crystal is formed, whereas for smaller values a face-centered cubic crystal is preferred. An example of the latter observed experimentally in a dispersion of latex spheres is shown in Figure 13.3. Note that this crystallization phenomenon is analogous to crystallization of simple atomic fluids, as is evident from Figure 13.3a, which shows the coexistence of a crystal with a liquidlike structure. 

Multiple Melting Points A compound may have different crystal structures (i.e., solid phases). For example, carbon tetrachloride has three known solid phases at atmospheric pressure la (face-centered cubic), lb (rhombohedral), and II (monoclinic). Ia and lb melt at temperatures some 5K apart [3]. Multiple melting points have been reported for a large set of compounds, such as many of those listed in the Merck Index [4], Dearden and Rahman improved a structure-melting point correlation for substituted anilines by excluding two outliers on the ground that their Tm values were inadequate, due to different crystalline forms [5]. 

All silver crystals have the same geometric shape. Therefore, the crystalline shape of a metallic solid is a function of the size of the metal solid atoms and their electron configuration. Each metal has its own geometric crystalline shape. Aluminum atoms pack into a face-centered cubic cell. Iron s solid structure is body-centered cubic. 

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