Metals crystalline structure

When a small amount of an element is added to a metal and the original metal crystalline structure remains the same, this alloy is called a metal solution. 

When new atoms are introduced into a metallic crystalline structure, the new atoms produce additional forces on surrounding atoms and cause some structural distortion due to their different size. The displaced atoms cannot slide along crystalline slip planes as easily as they did before. 

In ceramics, the heat flow is primarily due to phonon generation, and the thermal conductivity is generally lower than that of metals. Crystalline structures, such as alumina and beryllia, are more efficient heat conductors than amorphous structures such as glass. Organic materials used to fabricate printed circuit boards or epoxy attachment materials are highly amorphous electrical insulators, but tend to be very poor thermal conductors. 

Selenium exists in several allotropic forms. Three are generally recognized, but as many as that have been claimed. Selenium can be prepared with either an amorphous or crystalline structure. The color of amorphous selenium is either red, in powder form, or black, in vitreous form. Crystalline monoclinic selenium is a deep red crystalline hexagonal selenium, the most stable variety, is a metallic gray. 

Ordinary tin is composed of nine stable isotopes 18 unstable isotopes are also known. Ordinary tin is a silver-white metal, is malleable, somewhat ductile, and has a highly crystalline structure. Due to the breaking of these crystals, a "tin cry" is heard when a bar is bent. 

The metal has a silvery appearance and takes on a yellow tarnish when slightly oxidized. It is chemically reactive. A relatively large piece of plutonium is warm to the touch because of the energy given off in alpha decay. Larger pieces will produce enough heat to boil water. The metal readily dissolves in concentrated hydrochloric acid, hydroiodic acid, or perchloric acid. The metal exhibits six allotropic modifications having various crystalline structures. The densities of these vary from 16.00 to 19.86 g/cms. 

At the turn of the century it was still widely believed that, while a metal in its nalural slate is crystalline, after bending backwards and forwards (i.e., the process of fatigue damage), metal loctilly becomes amorphous (devoid of crystalline structure). Isolated observations (e.g., Percy 1864) showed that evidence of... 

Applicability Most hazardous waste slurried in water can be mixed directly with cement, and the suspended solids will be incorporated into the rigid matrices of the hardened concrete. This process is especially effective for waste with high levels of toxic metals since at the pH of the cement mixture, most multivalent cations are converted into insoluble hydroxides or carbonates. Metal ions also may be incorporated into the crystalline structure of the cement minerals that form. Materials in the waste (such as sulfides, asbestos, latex and solid plastic wastes) may actually increase the strength and stability of the waste concrete. It is also effective for high-volume, low-toxic, radioactive wastes. 

Corrosion also occurs where only one metal is involved. Here variations in oxidation potential caused by surface chemistry differences (such as irregularities in the metal s crystalline structure or stresses caused during the finishing stages of manufacture) create microanodes and microcathodes. 

The properties of alloys are affected by their composition and structure. Not only is the crystalline structure important, but the size and texture of the individual grains also contribute to the properties of an alloy. Some metal alloys are one-phase homogeneous solutions. Examples are brass, bronze, and the gold coinage alloys. Other alloys are heterogeneous mixtures of different crystalline phases, such as tin-lead solder and the mercury-silver amalgams used to fill teeth. 

The atomic and crystalline structure of the two non-metallic carbides, boron and silicon carbides, is less complex than that of the... 

Pure elemental silicon is a hard, dark gray solid with a metallic luster and with a crystalline structure the same as that of the diamond form of carbon. For this reason, silicon shows many chemical and physical similarities. There is also a brown, powdery form of silicon having a microcrystalline form. The element is prepared commercially by reducing the oxide by reacting it with carbon (as coke) in electric furnaces. On a small scale, silicon has been obtained from the oxide by reduction with aluminum meted. 

On metal electrodes having coarse-crystalline structure, the number of special crystal sites (vertices, edges) is small relative to the total number of all surface atoms, so that their (positive or negative) contribution to the overall rate must be quite small. At highly disperse, fine-crystalhne deposits, however, the situation is different. Here special effects are really observed they are considered in more detail in Section 28.5.4. 

For the spectra of Ni, peaks corresponding to Ni oxide and Ni metal are observed in the as-prepared sample [28-30]. After the etching with Ar, however, the peak of Ni metal is predominant. This implies that the state of Ni in the Ni-Zn nanoclusters is metallic, although their surface was oxidized under the atmospheric conditions. On the other hand, the identification of Zn state is difficult because the peak positions of Zn and ZnO in ESCA spectra are very close to each other. Furthermore, the B/Ni ratio determined by ESCA was increased with increasing Zn added e.g., Ni B = 73.3 26.7 and 60.6 39.4 for Zn/Ni = 0.0 and 1.0, respectively. Because no crystalline structure was found except for Ti02 from both electron and X-ray diffraction patterns of the respective samples, it can be concluded that formed nanoclusters were amorphous. Ni-Zn nanoclusters would be composed of amorphous intermetallic compounds through the... 

T ike metals minerals also exhibit typical crystalline structures. As an example, the structure of molybdenite is shown in Figure 1.17. It is hexagonal with six-pole symmetry and contains two molecules per unit cell. Each sulfur atom is equidistant from three molybdenum atoms and each molybdenum atom is surrounded by six sulfur atoms located at the comers of a trigonal prism. There are two types of bonds that can be established between the atoms which constitute the molybdenite crystal stmcture. They are the covalent bonds between sulfur and molybdenum atoms and the Van der Waals bonds between sulfur-sulfur atoms. The Van der Waals bond is considerably weaker than the covalent sulfur-molybdenum bond. This causes the bonds of sulfur-sulfur to cleave easily, imparting to molybdenite the property of being a dry lubricant. Molybdenite adheres to metallic surfaces with the development of a molecular bond and the friction between metallic surfaces is replaced by easy friction between two layers of sulfur atoms. 

The selection of materials for high-temperature applications is discussed by Day (1979). At low temperatures, less than 10°C, metals that are normally ductile can fail in a brittle manner. Serious disasters have occurred through the failure of welded carbon steel vessels at low temperatures. The phenomenon of brittle failure is associated with the crystalline structure of metals. Metals with a body-centred-cubic (bcc) lattice are more liable to brittle failure than those with a face-centred-cubic (fee) or hexagonal lattice. For low-temperature equipment, such as cryogenic plant and liquefied-gas storages, austenitic stainless steel (fee) or aluminium alloys (hex) should be specified see Wigley (1978). 

Solid metal electrodes with a crystalline structure are different. The crystal faces forming the surface of these electrodes are not ideal planes but always contain steps (Fig. 5.24). Although equilibrium thermal roughening corresponds to temperatures relatively close to the melting point, steps are a common phenomenon, even at room temperature. A kink half-crystal position—Fig. 5.24c) is formed at the point where one step ends and the... 

We and others have been involved in the study of such systems including Cu/Au(lll),85 86 Ag/Au(lll),87 Pb/Ag(lll),88 and Cu/Pt(lll).89 The first three systems involved the use of epitaxially deposited metal films on mica as electrodes.90 92 Such deposition gives rise to electrodes with well-defined single-crystalline structures. In the last case a bulk platinum single crystal was employed. Because of the single-crystalline nature of the electrodes, polarization dependence studies could be used to ascertain surface structure. 

The main considerations of mechanical properties of metals and alloys at low temperatures taken into account for safety reasons are the transition from ductile-to-brittle behavior, certain unconventional modes of plastic deformation, and mechanical and elastic properties changes due to phase transformations in the crystalline structure. 

M-M multiple bonding has long been known in metal oxide structures. The first Mo=Mo bond was seen in one crystalline form of Mo02 which has a distorted rutile structure wherein the Mo(4+) ions occupy adjacent octahedral holes throughout the lattice ( 4). The octahedra are distorted because of the short Mo-Mo distances 2.51 X. La. RejO has a fluorite type structure in which 02 is substituted for F and four of the five Ca2 sites are occupied by La3 ions. The remaining Ca2 site is occupied by an (Re=Re)8 unit with an Re-Re distance 2.259(1) A... 

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