Alloys interstitial

Boron forms B—N compounds that are isoelectronic with graphite (see Boron compounds, refractoryboron compounds). The small size also has a significant role in the interstitial alloy-type metal borides boron forms. Boron forms borides with metals that are less electronegative than itself including titanium, zirconium, and hafnium. 

Extension to interstitial alloys can be accomplished without violating the one-to-one correspondence assumption. All atoms around the interstitial can be related to host lattice positions, see the lower defect in Fig. 1, while the host is treated as having no scatterer in the corresponding interstice. Nevertheless a rather serious problem arises, because the more complicated integral... 

Steel is an alloy of about 2% or less carbon in iron. Carbon atoms are much smaller than iron atoms, and so they cannot substitute for iron in the crystal lattice. Indeed, they are so small that they can fit into the interstices (the holes) in the iron lattice. The resulting material is called an interstitial alloy (Fig. 5.48). For two elements to form an interstitial alloy, the atomic radius of the solute element must be less than about 60% of the atomic radius of the host metal. The interstitial atoms interfere with electrical conductivity and with the movement of the atoms forming the lattice. This restricted motion makes the alloy harder and stronger than the pure host metal would be. 

Alloys of metals tend to be stronger and have lower electrical conductivity than pure metals. In substitutional alloys, atoms of the solute metal take the place of some atoms of a metal of similar atomic radius. In interstitial alloys, atoms of the solute element fit into the interstices in a lattice formed by atoms of a metal with a larger atomic radius. 

FIGURE 5.48 In an interstitial alloy, the atoms of one metal lie in the gaps between the atoms of another metal. The two elements need to have markedly different atomic radii. 

Beryllium is obtained by electrolytic reduction of molten beryllium chloride. The element s low density makes it useful for the construction of missiles and satellites. Beryllium is also used as windows for x-ray tubes because Be atoms have so few electrons, thin sheets of the metal are transparent to x-rays and allow the rays to escape. Beryllium is added in small amounts to copper the small Be atoms pin the Cu atoms together in an interstitial alloy that is more rigid than pure copper but still conducts electricity well. These hard, electrically conducting alloys are formed into nonsparking tools for use in oil refineries and grain elevators, where there is a risk of explosion. Beryllium-copper alloys are also used in the electronics industry to form tiny nonmagnetic parts and contacts that resist deformation and corrosion. 

A second way for a solid to accommodate a solute is interstitially, with solute atoms fitting in between solute atoms in the crystal stmcture. An important alloy of this type is carbon steel, a solid solution of carbon in iron, also shown in Figure 12-4. Steels actually are both substitutional and interstitial alloys. Iron is the solvent and carbon is present as an interstitial solute, but varying amounts of manganese, chromium, and nickel are also present and can be in substitutional positions. 

Jack, K. H. Binary and Ternary Interstitial Alloys. I. The Iron Nitrogen... 

Type of Interstitial Alloy formed during the Tempering of Nitrogen-Martensite. Proc. Roy. Soc. (London) A 208, 216 (1951)-... 

There are many metal alloys that contain interstitial atoms embedded in the metal structure. Traditionally, the interstitial alloys most studied are those of the transition metals with carbon and nitrogen, as the addition of these atoms to the crystal structure increases the hardness of the metal considerably. Steel remains the most important traditional interstitial alloy from a world perspective. It consists of carbon atoms distributed at random in interstitial sites within the face-centered cubic structure of iron to form the phase austenite, which exists over the composition range from pure iron to approximately 7 at % carbon. 

More recently, hydrogen storage has become important, and interstitial alloys formed by incorporation of hydrogen into metals are of considerable interest. Niobium is typical of these. This metal is able to incorporate interstitial hydrogen up to a limiting composition of approximately NbH0.i-... 

Gil, B. Group III Nilrule Semiconductor Compounds Physics and Applications, Oxford University Press, New York, NY, 1998 Goldschmidt. H. Interstitial Alloys. Biitterworths, London, 1967. 

Plate 1.1 shows examples of compounds of Groups 3-6, which typically have simple crystal structures and compositions. In these structures the large red spheres represent metal atoms and the small green spheres represent C or N atoms. The nonmetal atoms occupy interstitial positions, and for this reason the materials are known as interstitial alloys. 

H.T. Goldschmidt. Interstitial Alloys, (Plenum Press, New York, 1967). 

Alloys can also be formed when much smaller atoms are introduced into spaces between the metallic crystalline atoms. In steel, small carbon (C) atoms occupy spaces between larger iron (Fe) atoms. This type of alloy is called an interstitial alloy. The strength of the steel is much greater than the strength of the iron. Steel is used for posts in earrings because it is relatively nonreactive and very strong. For the same reasons, steel is used in the construction of decorative belt buckles. 

A. A. Smirnov, The Theory of Interstitial Alloys, Nauka, Moscow, 1979. 

Solute atoms, which are smaller than the solvent atoms in binary interstitial alloys, such as C, H, N, and O are usually incorporated as interstitials in the void sites of the lattice, for example, in octahedral and tetrahedral sites in the close-packed cubic and close-packed hexagonal lattices (see Figures 1.6, 1.7, and 2.12), and in the body-centered cubic lattices (Figure 5.9) [7],... 

The interstitial mechanism is fundamentally seen in solute atoms which, as was previously stated, are smaller than the solvent atoms in binary interstitial alloys. Then, in the present mechanism... 

Smirnov A.A. Theory of phase transformations and atoms distribution in interstitial alloys. K. Nauk. dumka. 1992. 280 p.(in Russian). 

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