Body-centered cubic structure, and

Disordered alloys may form when two metals are mixed if both have body-centered cubic structures and if their atomic radii do not differ by much (e.g. K and Rb). The formation of ordered alloys, however, is usually favored at higher temperatures the tendency towards disordered structures increases. Such an arrangement can even be adopted if metals are combined which do not crystallize with body-centered cubic packings themselves, on condition of the appropriate composition. /J-Brass (CuZn) is an example below 300 °C it has a CsCl structure, but between 300 °C and 500 °C a A type transformation takes place resulting in a disordered alloy with a body-centered cubic structure. 

H3PW12O40 is one of the most common heteropoly compounds. A distinct X-ray diffraction pattern is seen for H3PWi2O40.6H2O, where the Keggin units are linked by H+(H20)2 bridges, resulting in a body-centered cubic structure and hence the X-ray diffraction pattern. The water molecules can be easily replaced by a number of polar molecules such as alcohols and amines (Misono, 1987). 

The characteristic parameters of both the body centered cubic structure and the inverse body centered cubic structure are the side a of the cell, the diameter 2R of the spheres, and the specific surface 2. 

It was a second-neighbor matrix element entering that table and it corresponded to an internuclear distance of the body-centered cubic cube edge a. Thus, writing 47cro/3 = for the body-centered cubic structure and expanding the sine for small /<, we may write... 

Sodium has the body-centered cubic structure, and its lattice parameter is 4.28 A. 

Solid chromium adopts a body-centered cubic structure and crystallizes in the space group Irnim with a = 288.46pm its density is 7.19gcm (at 293K). The metal melts at 2130 ( 20) K and boils at 2945 K the corresponding enthalpies are A//fusion = 15.3kJmoU and AT/vap = 348.78 kj mol Values of various thermodynamic functions are listed in Table 2. Some other values are thermal conductivity 93.7 W m (at 300 K), electrical resistivity 12.7 X 10 m (at 273 K), magnetic susceptibility 3.5 x... 

One way of producing the desired physical properties in steel is by controlling the chemical composition (see Table 21.21). Another method for tailoring the properties of steel involves heat treatment. Pure iron exists in two different crystalline forms, depending on the temperature. At any temperature below 912°C, iron has a body-centered cubic structure and is called a-iron. Between 912°C and 1394X, iron has a face-centered cubic structure called austentite, or y-iron. At 1394°C, iron changes to S-iron, a body-centered cubic structure identical to a-iron. 

The experimental evidence from diffraction indicates that solid TeFe has two solid phases, a low-temperature phase with an orientationally-ordered, base-centered monoclinic structure and C h symmetry, and a higher-temperature phase with a body-centered cubic structure and cubic Oh symmetry. The experiments with clusters of TeFs, done by electron diffraction, show both of these and at temperatures between the regions of stability of these phases, a monoclinic phase with only partial orientational order as well. Simulations of the clusters show that the transition from body-centered cubic to monoclinic involves both rotational and translational motion of the motion, while the lower-temperature transition, between monoclinic and base-centered monoclinic, requires only coupling of the molecular rotational motions.Furthermore the transition at higher temperature in clusters shows dynamic coexistence of two phases in equilibrium over a range of at least a few degrees of temperature, which immediately implies that this transition involves two local minima in the... 

Gschneidner (1990) selected 1610 K for the alpha-beta transformation from a hexagonal close-packed to a body-centered cubic structure and 1814 K for the melting point. 

Dankov et al. (1998) selected 294 1 K for the Curie temperature, while Gschneidner (1990) selected 1508 K for the transformation from the hexagonal close-packed structure to the body-centered cubic structure and 1586 K for the melting point. It is noted that the transition temperature, which was determined on the purest samples available at Iowa State University by both Beaudry and Daane (1964) and Beaudry and Spedding (1974), is notably lower than a consensus value of 1534 5 K obtained on materials of commercial purity (Konings and Benes, 2010). 

Jayasuriya et al. (1983) selected 221.45 K for the first-order Curie-like transformation from the alpha phase orthorhombic structure to the beta phase hex-agmial closed-packed structure, while Jayasuriya et al. (1984) selected 229.95 K for the second-order N l transformation. Gschneidner (1990) selected 1562 K for the transformation to the gamma phase body-centered cubic structure and 1629 K for the melting point. 

Experiments have shown that BPI has the body-centered cubic structure and EH has the simple cubic structure. The latter has a lower packing density than the body-centered cubic structure. Therefore the total length of the discUnations in the simple cubic packing is longer. From Equations (13.21) and (13.23), we know the elastic energy of the disclination is... 

The metal has a bright silvery metallic luster. Neodymium is one of the more reactive rare-earth metals and quickly tarnishes in air, forming an oxide that spalls off and exposes metal to oxidation. The metal, therefore, should be kept under light mineral oil or sealed in a plastic material. Neodymium exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at 863oC. 

As with other related rare-earth metals, gadolinium is silvery white, has a metallic luster, and is malleable and ductile. At room temperature, gadolinium crystallizes in the hexagonal, close-packed alpha form. Upon heating to 1235oG, alpha gadolinium transforms into the beta form, which has a body-centered cubic structure. 

Potassium. K aw 39.102 at no 19 valence 1 soft, silvery metal, rapidly oxidized in moist air body-centered cubic structure mp 63° bp 770° d 0.862g/cc. Sol in liq ammonia, aniline, Hg and Na... 

Self-Test 5.5B The atomic radius of iron is 124 pm and its density is 7.87 g-cm-3. Is this density consistent with a close-packed or a body-centered cubic structure ... 

Although the comer atoms must move apart to convert a simple cube into a body-centered cube, the extra atom in the center of the stracture makes the body-centered cubic lattice more compact than the simple cubic structure. All the alkali metals, as well as iron and the transition metals from Groups 5 and 6, form ciystals with body-centered cubic structures. 

An A-B diblock copolymer is a polymer consisting of a sequence of A-type monomers chemically joined to a sequence of B-type monomers. Even a small amount of incompatibility (difference in interactions) between monomers A and monomers B can induce phase transitions. However, A-homopolymer and B-homopolymer are chemically joined in a diblock therefore a system of diblocks cannot undergo a macroscopic phase separation. Instead a number of order-disorder phase transitions take place in the system between the isotropic phase and spatially ordered phases in which A-rich and B-rich domains, of the size of a diblock copolymer, are periodically arranged in lamellar, hexagonal, body-centered cubic (bcc), and the double gyroid structures. The covalent bond joining the blocks rests at the interface between A-rich and B-rich domains. 

Figure 5.8 Interstitial diffusion (a) interstitial diffusion involving the direct migration of an interstitial atom to an adjacent site in the crystal (b, c) some of the octahedral and tetrahedral interstitial sites in the body-centered cubic structure of metals such as iron and tungsten and (d) the total number of octahedral and tetrahedral sites in a unit cell of the body-centered cubic structure. Diffusion paths parallel to the unit cell edges can occur by a series of alternating octahedral and tetrahedral site jumps, dashed line.

Here, as in other branches of inorganic chemistry, interatomic distances show a considerable variation and, although some correlation with bond order is possible, attempts to do so should be regarded with caution.For metals with close-packed structures, the coordination number of any atom is 12 for cubic or hexagonal structures, and 14 (8 plus 6 more neighbors at about 15% further away) for body-centered cubic structures. In general, this number exceeds the number of electrons per atom available for metal-metal bond formation and precludes the formation of localized, two-electron bonds between metal atoms. Bond orders of less than 1 are therefore commonly recorded. For metal clusters, it is necessary to consider the variety of ways in which valence electrons may be utilized in chemical bonding within the Mm... 

Any study of colloidal crystals requires the preparation of monodisperse colloidal particles that are uniform in size, shape, composition, and surface properties. Monodisperse spherical colloids of various sizes, composition, and surface properties have been prepared via numerous synthetic strategies [67]. However, the direct preparation of crystal phases from spherical particles usually leads to a rather limited set of close-packed structures (hexagonal close packed, face-centered cubic, or body-centered cubic structures). Relatively few studies exist on the preparation of monodisperse nonspherical colloids. In general, direct synthetic methods are restricted to particles with simple shapes such as rods, spheroids, or plates [68]. An alternative route for the preparation of uniform particles with a more complex structure might consist of the formation of discrete uniform aggregates of self-organized spherical particles. The use of colloidal clusters with a given number of particles, with controlled shape and dimension, could lead to colloidal crystals with unusual symmetries [69]. 

Golden yellow, soft and ductile metal body-centered cubic structure density 1.93 g/cm melts at 28.44°C vaporizes at 671°C vapor pressure 1 torr at 280°C electrical resistivity 36.6 microhm-cm (at 30°C) reacts with water dissolves in liquid ammonia forming a blue solution. 

Silvery metal body-centered cubic structure imparts crimson-red color to flame density 0.862g/cm3 at 20°C melts at 63.25°C density of hquid potassium at 100°C is 0.819 g/cm and 0.771g/cm3 at 300°C vaporizes at 760°C vapor pressure 123 torr at 587°C electrical resistivity 6.1 microhm-cm at 0°C and 15.31 microhm-cm at 100°C viscosity 0.25 centipoise at 250°C surface tension 86 dynes/cm at 100°C thermal neutron absorption cross section 2.07 barns reacts violently with water and acids reacts with alcohol dissolves in liquid ammonia and mercury... 

Pale yellow metal attains a green oxide coating on exposure to air exhibits two crystalline modifications (1) an alpha form, that has a hexagonal close-packed structure, a density of 6.773 g/cm and a molar volume 20.82 cc/mol, and (2) a beta form that has an open body-centered cubic structure having a density of 6.64 g/cm and a molar volume of 21.20 cc/mol. The alpha form transforms to beta at 792°C. 

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