Body center cubic structures

At 31OC, lanthanum changes from a hexagonal to a face-centered cubic structure, and at 865C it again transforms into a body-centered cubic structure. 

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. 

Allotropy in the solid state can also arise because of differences in crystal structure. For example, solid iron has a body-centered cubic structure (recall Figure 9.16, page 246) at room temperature. This changes to a face-centered structure upon heating to 910°C. 

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. 

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. 

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... 

Ordered body-centered cubic structures were observed by shearing aqueous gels made from anionic PtBS-PMANa block copolymer micelles [163]. The emergence of the ordered gel state could be accounted for similar building up of a polyelectrolyte-based fibrillar network that can be oriented under shear. 

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]. 

FIG. 11.8 (a) A section of the difference synthesis through the Cr nucleus, parallel to the (110) plane. Contours are drawn at intervals of 0.2 eA 3. (b) Theoretical contour map of valence electron distribution on the (110) plane for chromium metal. Contours are drawn at intervals of 0.5 eA-3. The lobes point towards the nearest neighbors in the body-centered cubic structure. Source Ohba et al. (1982). 

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. 

Soft, bright, silvery metal malleable, can be readily cut with a knife or extruded as wire liquid sodium in inert atmosphere appears like mercury blue vapor, appears brilliant green at high temperatures imparts golden-yellow color to flame body-centered cubic structure paramagnetic density 0.97... 

A bright white metal soft and ductile body-centered cubic structure index of refraction 3.03 density 5.96 g/cm melts at 1,910°C vaporizes at 3,407°C electrical resistivity, 18.1 microhm-cm at 0°C and 20.1 microhm-cm at 25°C magnetic susceptibility 1.4x10 cgs units modulus of elasticity 18-19x10 psi shear modulus 6.73xl0 psi Poisson s ratio 0.36 thermal neutron absorption cross section 5 barns/atom insoluble in water, dilute sulfuric acid, and hydrochloric acid at all concentrations soluble in nitric acid, aqua regia, and concentrated sulfuric acid insoluble in alkalies. 

White powder body-centered cubic structure density 5.03 g/cm melts at 2,436°C insoluble in water soluble in dilute acids. 

Silvery gray lustrous metal or bluish black amorphous powder close-packed hexagonal lattice transforms to a body-centered cubic structure at 865°C density 6.506 g/cm melts at about 1,852°C vaporizes at 4,377°C elec-... 

Jang et al. (2004) observed that ABA triblock copolymers composed of a docosyl chain, a rigid aromatic segment, and a flexible PEO dendrimer assemble into a hexagonal columnar or body-centered cubic structure in the solid state for the first- and second-generation dendrons, respectively (Fig. 11.27). 

The density of beryllium is 1.847 g/cm3 based upon average values of lattice parameters at 255C (a — 22.856 nm and c — 35.832 nm). Beryllium products generally have a density around 1.850 g/cm3 or higher because of impurities, such as aluminum and other metals, and beryllium oxide. The crystal structure is close-packed hexagonal. The alpha-form of beryllium transforms to a body-centered cubic structure at a temperature very close to the melung point. 

CALCIUM. CAS 7440-70-21. Chemical clement, symbol Ca. at. no. 20, at. in. 40.1)8. periodic table group 2 talkaline earths), nip X37-X4IU, bp 1.484 C, density 1.54 g/ent Isingle crystal). Elemental calcium has a luce-centered cubic crystal structure when at room tempcruturc. transforming to a body-centered cubic structure at 44X C... 

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