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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.
Interstitial solid solutions form when the solute atom is small enough (radii up to 57% the radii of the parent atoms) [2] to fit at interstitial sites between the solvent atoms. 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 ).
In the case of an impurity, the atom is often incorporated at a regular atomic site in the crystal structure. This is neither a vacant site nor is the atom on an interstitial site and it is called a substitutional defect. The atom is not supposed to be anywhere in the crystal, and is thus an impurity.
Interstitial atoms (blue) occupy some of the spaces within a lattice of larger atoms (red) In materials science, an interstitial defect is a type of point crystallographic defect where an atom of the same or of a different type, occupies an interstitial site in the crystal structure.
In crystallography, interstitial sites, holes or voids are the empty space that exists between the packing of atoms (spheres) in the crystal structure. [ citation needed ] The holes are easy to see if you try to pack circles together; no matter how close you get them or how you arrange them, you will have empty space in between.
The IUPAC definition of a solid solution is a "solid in which components are compatible and form a unique phase". [3]The definition "crystal containing a second constituent which fits into and is distributed in the lattice of the host crystal" given in refs., [4] [5] is not general and, thus, is not recommended.
In the crystal solid state, diffusion within the crystal lattice occurs by either interstitial or substitutional mechanisms and is referred to as lattice diffusion. [1] In interstitial lattice diffusion, a diffusant (such as C in an iron alloy), will diffuse in between the lattice structure of another crystalline element.
Different atomic mechanisms of alloy formation, showing pure metal, substitutional, interstitial, and a combination of the two. When a molten metal is mixed with another substance, there are two mechanisms that can cause an alloy to form, called atom exchange and the interstitial mechanism. The relative size of each element in the mix plays a ...