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Interstitials modify the physical and chemical properties of materials. Interstitial carbon atoms have a crucial role for the properties and processing of steels, in particular carbon steels. Impurity interstitials can be used e.g. for storage of hydrogen in metals. The crystal lattice can expand with the concentration of impurity interstitials
For example, if a vacancy encounters an impurity, the two may bind together if the impurity is too large for the lattice. Interstitials can form 'split interstitial' or 'dumbbell' structures where two atoms effectively share an atomic site, resulting in neither atom actually occupying the site. [12] [13]
The atoms crowd into the interstitial sites, causing the bonds of the solvent atoms to compress and thus deform (this rationale can be explained with Pauling's rules). Elements commonly used to form interstitial solid solutions include H, Li, Na, N, C, and O. Carbon in iron (steel) is one example of interstitial solid solution.
Fundamentally, the Hume-Rothery rules are restricted to binary systems that form either substitutional or interstitial solid solutions. However, this approach limits assessing advanced alloys which are commonly multicomponent systems. Free energy diagrams (or phase diagrams) offer in-depth knowledge of equilibrium restraints in complex systems.
For example, the favorable properties of steel result from interstitial incorporation of carbon into the iron lattice. Brass , a binary alloy of copper and zinc , has superior mechanical properties compared to its constituent metals due to solution strengthening.
In crystallography, a Frenkel defect is a type of point defect in crystalline solids, named after its discoverer Yakov Frenkel. [1] The defect forms when an atom or smaller ion (usually cation) leaves its place in the structure, creating a vacancy and becomes an interstitial by lodging in a nearby location. [2]
interstitial compounds, and "intermediate" transition metal carbides. Examples include calcium carbide (CaC 2), silicon carbide (SiC), tungsten carbide (WC; often called, simply, carbide when referring to machine tooling), and cementite (Fe 3 C), [2] each used in key industrial applications. The naming of ionic carbides is not systematic.
Steel is an example of an interstitial alloy, because the very small carbon atoms fit into interstices of the iron matrix. Stainless steel is an example of a combination of interstitial and substitutional alloys, because the carbon atoms fit into the interstices, but some of the iron atoms are substituted by nickel and chromium atoms. [8]